nitroarginine and Hypoxia

In previous studies, upregulation of NOS during acclimatization of rats to sustained hypobaric hypoxia was associated to cardioprotection, evaluated as an increased tolerance of myocardium to hypoxia/reoxygenation. The objective of the present work was to investigate the effect of acute hypobaric hypoxia and the role of endogenous NO concerning cardiac tolerance to hypoxia/reoxygenation under β-adrenergic stimulation.. Rats were submitted to 58.7 kPa in a hypopressure chamber for 48 h whereas their normoxic controls remained at 101.3 kPa. By adding NOS substrate L-arg, or blocker L-NNA, isometric mechanical activity of papillary muscles isolated from left ventricle was evaluated at maximal or minimal production of NO, respectively, under β-adrenergic stimulation by isoproterenol, followed by 60/30 min of hypoxia/reoxygenation. Activities of NOS and cytochrome oxidase were evaluated by spectrophotometric methods and expression of HIF1-α and NOS isoforms by western blot. Eosin and hematoxiline staining were used for histological studies.. Cytosolic expression of HIF1-α, nNOS and eNOS, and NO production were higher in left ventricle of hypoxic rats. Mitochondrial cytochrome oxidase activity was decreased by hypobaric hypoxia and this effect was reversed by L-NNA. After H/R, recovery of developed tension in papillary muscles from normoxic rats was 51-60% (regardless NO modulation) while in hypobaric hypoxia was 70% ± 3 (L-arg) and 54% ± 1 (L-NNA). Other mechanical parameters showed similar results. Preserved histological architecture was observed only in L-arg papillary muscles of hypoxic rats.. Exposure of rats to hypobaric hypoxia for only 2 days increased NO synthesis leading to cardioprotection.

Topics: Altitude; Altitude Sickness; Animals; Blood Pressure; Cytosol; Electron Transport Complex IV; Heart Ventricles; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Papillary Muscles; Rats, Wistar

Augmented vasoconstrictor reactivity is thought to play an important role in the development of chronic hypoxia (CH)-induced neonatal pulmonary hypertension. However, whether this response to CH results from pulmonary endothelial dysfunction and reduced nitric oxide (NO)-mediated vasodilation is not well understood. We hypothesized that neonatal CH enhances basal tone and pulmonary vasoconstrictor sensitivity by limiting NO-dependent pulmonary vasodilation. To test this hypothesis, we assessed the effects of the NO synthase (NOS) inhibitor

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Animals, Newborn; Chronic Disease; Enzyme Inhibitors; Free Radical Scavengers; Hypoxia; Lung; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Tyrosine; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

Acute and sustained hypoxic pulmonary vasoconstriction (HPV), as well as chronic pulmonary hypertension (PH), is modulated by nitric oxide (NO). NO synthesis can be decreased by asymmetric dimethylarginine (ADMA), which is degraded by dimethylarginine dimethylaminohydrolase-1 (DDAH1). We investigated the effects of DDAH1 overexpression (DDAH1(tg)) on HPV and chronic hypoxia-induced PH. HPV was measured during acute (10 min) and sustained (3 h) hypoxia in isolated mouse lungs. Chronic PH was induced by the exposure of mice to 4 weeks of hypoxia. ADMA and cyclic 3',5'-guanosine monophosphate (cGMP) were determined by ELISA, and NO generation was determined by chemiluminescence. DDAH1 overexpression exerted no effects on acute HPV. However, DDAH1(tg) mice showed decreased sustained HPV compared with wild-type (WT) mice. Concomitantly, ADMA was decreased, and concentrations of NO and cGMP were significantly increased in DDAH1(tg). The administration of either Nω-nitro-l-arginine or 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one potentiated sustained HPV and partly abolished the differences in sustained HPV between WT and DDAH1(tg) mice. The overexpression of DDAH1 exerted no effect on the development of chronic hypoxia-induced PH. DDAH1 overexpression selectively decreased the sustained phase of HPV, partly via activation of the NO-cGMP pathway. Thus, increased ADMA concentrations modulate sustained HPV, but not acute HPV or chronic hypoxia-induced PH.

Topics: Amidohydrolases; Animals; Arginine; Blood Vessels; Cyclic GMP; Gene Expression; Hemodynamics; Hypertension, Pulmonary; Hypoxia; Lung; Mice; Nitric Oxide; Nitroarginine; Organ Culture Techniques; Oxadiazoles; Signal Transduction; Vasoconstriction

Many cancer research efforts focus on exploiting genetic-level features that may be targeted for therapy. Tissue-level features of the tumour microenvironment also represent useful therapeutic targets. Here we investigate the presence of low oxygen tension and sensitivity to NOS inhibition of tumour vasculature as potential tumour-specific features that may be targeted by hypoxic cytotoxins, a class of therapeutics currently under investigation. We have previously demonstrated that tirapazamine (TPZ) mediates central vascular dysfunction in tumours. TPZ is a hypoxic cytotoxin that is also a competitive inhibitor of NOS. Here we further investigated the vascular-targeting activity of TPZ by combining it with NOS inhibitor L-NNA, or with low oxygen content gas breathing. Tumours were analyzed via multiplex immunohistochemical staining that revealed irreversible loss of perfusion and enhanced tumour cell death when TPZ was combined with either low oxygen or a NOS inhibitor. Tumour growth rate was reduced by TPZ + NOS inhibition, and tumours previously resistant to TPZ-mediated vascular dysfunction were sensitized by low oxygen breathing. Additional mapping analysis suggests that tumours with reduced vascular-associated stroma may have greater sensitivity to these effects. These results indicate that poorly oxygenated tumour vessels, also being abnormally organized and with inadequate smooth muscle, may be successfully targeted for significant anti-cancer effects by inhibition of NOS and hypoxia-activated prodrug toxicity. This strategy illustrates a novel use of hypoxia-activated cytotoxic prodrugs as vascular targeting agents, and also represents a novel mechanism for targeting tumour vessels.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Cytotoxins; Female; HCT116 Cells; HT29 Cells; Humans; Hypoxia; Immunohistochemistry; Mice; Mice, Inbred C3H; Mice, Inbred NOD; Mice, SCID; Neoplasms; Neovascularization, Pathologic; Nitric Oxide Synthase; Nitroarginine; Tirapazamine; Treatment Outcome; Triazines; Tumor Burden; Xenograft Model Antitumor Assays

Acute respiratory disorders may lead to sustained alveolar hypoxia with hypercapnia resulting in impaired pulmonary gas exchange. Hypoxic pulmonary vasoconstriction (HPV) optimizes gas exchange during local acute (0-30 min), as well as sustained (> 30 min) hypoxia by matching blood perfusion to alveolar ventilation. Hypercapnia with acidosis improves pulmonary gas exchange in repetitive conditions of acute hypoxia by potentiating HPV and preventing pulmonary endothelial dysfunction. This study investigated, if the beneficial effects of hypercapnia with acidosis are preserved during sustained hypoxia as it occurs, e.g in permissive hypercapnic ventilation in intensive care units. Furthermore, the effects of NO synthase inhibitors under such conditions were examined.. We employed isolated perfused and ventilated rabbit lungs to determine the influence of hypercapnia with or without acidosis (pH corrected with sodium bicarbonate), and inhibitors of endothelial as well as inducible NO synthase on acute or sustained HPV (180 min) and endothelial permeability.. In hypercapnic acidosis, HPV was intensified in sustained hypoxia, in contrast to hypercapnia without acidosis when HPV was amplified during both phases. L-NG-Nitroarginine (L-NNA), a non-selective NO synthase inhibitor, enhanced acute as well as sustained HPV under all conditions, however, the amplification of sustained HPV induced by hypercapnia with or without acidosis compared to normocapnia disappeared. In contrast 1400 W, a selective inhibitor of inducible NO synthase (iNOS), decreased HPV in normocapnia and hypercapnia without acidosis at late time points of sustained HPV and selectively reversed the amplification of sustained HPV during hypercapnia without acidosis. Hypoxic hypercapnia without acidosis increased capillary filtration coefficient (Kfc). This increase disappeared after administration of 1400 W.. Hypercapnia with and without acidosis increased HPV during conditions of sustained hypoxia. The increase of sustained HPV and endothelial permeability in hypoxic hypercapnia without acidosis was iNOS dependent.

Topics: Acidosis; Animals; Enzyme Inhibitors; Hypercapnia; Hypoxia; Imines; Lung; Male; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Pulmonary Circulation; Rabbits; Sodium Bicarbonate; Vasoconstriction

The effects of chronic hypoxia (CH) on respiratory muscle are poorly understood. The aim of the present study was to examine the effects of CH on respiratory muscle structure and function, and to determine whether nitric oxide is implicated in respiratory muscle adaptation to CH. Male Wistar rats were exposed to CH for 1-6 weeks. Sternohyoid and diaphragm muscle contractile properties, muscle fibre type and size, the density of fibres expressing sarco/endoplasmic reticulum calcium-ATPase (SERCA) 2 and sodium-potassium ATPase (Na+,K+-ATPase) pump content were determined. Muscle succinate dehydrogenase (SDH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) dehydrogenase activities were also assessed. Acute and chronic blockade of nitric oxide synthase (NOS) was employed to determine whether or not NO is critically involved in functional remodelling in CH muscles. CH improved diaphragm, but not sternohyoid, fatigue tolerance in a time-dependent fashion. This adaptation was not attributable to increased SDH or NADPH dehydrogenase activities. The areal density of muscle fibres and relative area of fibres expressing SERCA2 were unchanged. Na+,K+-ATPase pump content was significantly increased in CH diaphragm. Chronic NOS inhibition decreased diaphragm Na+,K+-ATPase pump content and prevented CH-induced increase in muscle endurance. This study provides novel insight into the mechanisms involved in CH-induced muscle plasticity. The results may be of relevance to respiratory disorders characterised by CH, such as chronic obstructive pulmonary disease.

Topics: Adaptation, Physiological; Animals; Chronic Disease; Diaphragm; Enzyme Inhibitors; Hypoxia; Male; Muscle Fatigue; Muscle, Skeletal; NADPH Dehydrogenase; Nitric Oxide Synthase; Nitroarginine; Physical Endurance; Rats; Rats, Wistar; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Sodium-Potassium-Exchanging ATPase; Succinate Dehydrogenase

This study was designed to clarify whether nitric oxide (NO) participates in the regulation of local cerebral blood flow (CBF) during hypoxia (inhalation of 15% O(2) in N(2)). The CBF response to hind-paw stimulation (evoked CBF) of Sprague-Dawley (SD) rats was measured by laser-Doppler flowmetry. Physiological variables, such as heart rate, mean blood pressure, and PaCO(2) during hypoxia, were identical to those under normoxic conditions. Hypoxia increased the baseline CBF (17.5 ± 14.3%) and the normalized peak amplitude of evoked CBF (31.1 ± 18.5%) relative to those during normoxia. When an NOS inhibitor was infused intravenously, these differences were abolished in both the baseline CBF or evoked CBF between normoxic and hypoxic conditions, whereas the heart rate decreased and the mean blood pressure increased during hypoxia in comparison with these during normoxia. The field potential was constant under all experimental conditions. These results suggest that NO plays a major role in the regulation of baseline and evoked CBF during hypoxia.

Topics: Animals; Cerebrovascular Circulation; Hypoxia; Laser-Doppler Flowmetry; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley

Acute respiratory disorders and permissive hypercapnic strategy may lead to alveolar hypoxia and hypercapnic acidosis. However, the effects of hypercapnia with or without acidosis on hypoxic pulmonary vasoconstriction (HPV) and oxygen diffusion capacity of the lung are controversial. We investigated the effects of hypercapnic acidosis and hypercapnia with normal pH (pH corrected with sodium bicarbonate) on HPV, capillary permeability, gas exchange, and ventilation-perfusion matching in the isolated ventilated-perfused rabbit lung. No alteration in vascular tone was noted during normoxic hypercapnia with or without acidosis compared with normoxic normocapnia. Hypercapnia with normal pH resulted in a transient increase in HPV during the course of consecutive ventilation maneuvers, whereas hypercapnic acidosis increased HPV over time. Hypercapnic acidosis decreased exhaled NO during hypoxia more than hypercapnia with normal pH and normocapnia, whereas intravascular NO release was unchanged. However, inhibition of NO synthesis by nitro-L-arginine (L-NNA) resulted in a loss of the increased HPV caused by hypercapnic acidosis but not that caused by hypercapnia with normal pH. Furthermore, capillary permeability increased during hypoxic hypercapnia with normal pH but not hypoxic hypercapnic acidosis. This effect was NO-dependent because it disappeared during L-NNA administration. Ventilation-perfusion matching and arterial PO2 were improved according to the strength of HPV in hypercapnia compared with normocapnia during Tween nebulization-induced lung injury. In conclusion, the increased HPV during hypercapnic acidosis is beneficial to lung gas exchange by improving ventilation-perfusion matching and preserving the capillary barrier function. These effects seem to be linked to NO-mediated pathways.

Topics: Acidosis, Respiratory; Animals; Capillary Permeability; Endothelium, Vascular; Hydrogen-Ion Concentration; Hypercapnia; Hypoxia; In Vitro Techniques; Lung; Male; Metalloporphyrins; Nitric Oxide; Nitroarginine; Partial Pressure; Pulmonary Ventilation; Rabbits; Vasoconstriction

Addition of N-acetylcysteine induced relaxation of the coronary and basilar arteries thus indicating some basilar NO-stores in these vessels. The maximum capacity of the NO-stores was similar in the coronary and the basilar arteries. Following adaptation to hypoxia, however, the depot was much greater in the coronary artery wall. This seems to be connected with different degree of participation of the NO-dependent vasodiatation in implementation of the adaptive response to hypoxia in coronary and cerebral vascular systems.

Topics: Acetylcysteine; Adaptation, Physiological; Animals; Basilar Artery; Coronary Vessels; Hypoxia; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Organ Specificity; Rats; Rats, Wistar; Serotonin; Vasoconstriction

NO synthesis disturbances play an important role in the development of neurodegenerative damage in Alzheimer disease. We previously showed that adaptation to intermittent hypobaric hypoxia prevents cognitive disturbances in rats with experimental Alzheimer disease. Here we evaluated the role of NO in cognitive disorders and development of adaptive protection during experimental Alzheimer disease. Adaptation to hypoxia in rats was performed in a hypobaric pressure chamber at a simulated altitude of 4000 m (4 h per day for 14 days). Alzheimer disease was simulated by bilateral injections of a toxic fragment of beta-amyloid (25-35) into n. basalis magnocellularis. For evaluation of the role of NO in the development and prevention of memory disorders, the rats received intraperitoneally either NO-synthase inhibitor N omega-nitro-L-arginin (L-NNA, 20 mg/kg, every other day for 14 days) or NO-donor dinitrosyl iron complex (200 microg/kg daily for 14 days). NO-synthase inhibitor potentiated the damaging effect of beta-amyloid, abolished the protective effect of adaptation to hypoxia, and produced memory disorders in rats similar to those observed during experimental Alzheimer disease. In contrast, the increase in NO level in the body provided by injections of the NO-donor produced a protective effect against memory disorders caused by beta-amyloid similar to that induced by adaptation to hypoxia. We concluded that reduced NO production in the organism plays an important role in the development of cognitive disorders produced by injections of beta-amyloid, while prevention of NO deficit by administration of NO-donors or non-pharmacological stimulation of NO synthesis can provide a protective effect in experimental Alzheimer disease.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Cognition Disorders; Hypoxia; Iron; Male; Nerve Degeneration; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Peptide Fragments; Rats; Rats, Wistar

Hypoxia in the fetus and/or newborn is associated with an increased risk of pulmonary hypertension. The present study tested the hypothesis that long-term high-altitude hypoxemia differentially regulates contractility of fetal pulmonary arteries (PA) and veins (PV) mediated by differences in endothelial NO synthase (eNOS). PA and PV were isolated from near-term fetuses of pregnant ewes maintained at sea level (300 m) or high altitude of 3,801 m for 110 days (arterial Po(2) of 60 Torr). Hypoxia had no effect on the medial wall thickness of pulmonary vessels and did not alter KCl-induced contractions. In PA, hypoxia significantly increased norepinephrine (NE)-induced contractions, which were not affected by eNOS inhibitor N(G)-nitro-l-arginine (l-NNA). In PV, hypoxia had no effect on NE-induced contractions in the absence of l-NNA. l-NNA significantly increased NE-induced contractions in both control and hypoxic PV. In the presence of l-NNA, NE-induced contractions of PV were significantly decreased in hypoxic lambs compared with normoxic animals. Acetylcholine caused relaxations of PV but not PA, and hypoxia significantly decreased both pD(2) and the maximal response of acetylcholine-induced relaxation in PV. Additionally, hypoxia significantly decreased the maximal response of sodium nitroprusside-induced relaxations of both PA and PV. eNOS was detected in the endothelium of both PA and PV, and eNOS protein levels were significantly higher in PV than in PA in normoxic lambs. Hypoxia had no significant effect on eNOS levels in either PA or PV. The results demonstrate heterogeneity of fetal pulmonary arteries and veins in response to long-term high-altitude hypoxia and suggest a likely common mechanism downstream of NO in fetal pulmonary vessel response to chronic hypoxia in utero.

Topics: Acetylcholine; Altitude; Animals; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Hypoxia; Nitric Oxide; Nitric Oxide Synthase Type III; Nitroarginine; Nitroprusside; Norepinephrine; Potassium Chloride; Pregnancy; Pulmonary Artery; Pulmonary Veins; Sheep; Time Factors; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

To identify a possible role for nitric oxide (NO) in acute hypoxic tolerance (HT) we measured hypoxic survival time (HST), effect of hypoxic conditioning (HC), and survival following hypoxic conditioning while blocking or mimicking the action of nitric oxide synthase (NOS). To inhibit NOS, CD-1 mice were given supplemental endogenous NOS inhibitor asymmetrical dimethylarginine (ADMA) or a synthetic NOS inhibitor N(omega)-nitro-L-arginine (L-NNA), both of which nonselectively inhibit three of the isoforms of NOS [inducible (iNOS), neuronal (nNOS), and endothelial NOS (eNOS)]. ADMA (10 mg/kg i.p.) or saline vehicle was given 5 min before HST testing. L-NNA was given orally at 1 g/l in drinking water with tap water as the control for 48 h before testing. Both ADMA and L-NNA significantly increased HST and augmented the HC effect on HST. Neither the nNOS selective inhibitor 7-nitroindazole (7-NI) nor the iNOS selective inhibitor N-{[3-(aminomethyl)phenyl]methyl}-enthanimidamide (1400W) had a statistically significant effect on HST or HT. The NO donor, 3-morpholinosydnoeimine, when given alone did not significantly decrease HT, but it did mitigate the increased HT effect of L-NNA. These data confirm that acute hypoxic conditioning increases HT and that NOS inhibition by endogenous (ADMA) and a synthetic NOS inhibitor (L-NNA) further increases HT, whereas iNOS and nNOS inhibition does not, suggesting that it is the inhibition of eNOS that mediates enhancement of HT.

Topics: Acute Disease; Animals; Arginine; Endothelium, Vascular; Enzyme Inhibitors; Hypoxia; Imines; Indazoles; Male; Mice; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Time Factors

Hypoxia impairs neuromuscular transmission in the rat diaphragm. In previous studies, we have shown that nitric oxide (NO) plays a role in force modulation of the diaphragm under hypoxic conditions. The role of NO, a neurotransmitter, on neurotransmission in skeletal muscle under hypoxic conditions is unknown. The effects of the NO synthase (NOS) inhibitor nomega-nitro-L-arginine (L-NNA, 1 mM) and the NO donor spermine NONOate (Sp-NO, 1 mM) were evaluated on neurotransmission failure during nonfatiguing and fatiguing contractions of the rat diaphragm under hypoxic (PO2 approximately 5.8 kPa) and hyperoxic conditions (PO2 approximately 64.0 kPa). Hypoxia impaired force generated by both muscle stimulation at 40 HZ (P40M) and by nerve stimulation at 40 HZ (P40N). The effect of hypoxia in the latter was more pronounced. L-NNA increased P40N whereas Sp-NO decreased P40N during hypoxia. In contrast, neither L-NNA nor Sp-NO affected P40N during hyperoxia. L-NNA only slightly reduced neurotransmission failure during fatiguing contractions under hyperoxic conditions. Consequently, neurotransmission failure assessed by comparing force loss during repetitive nerve simulation and superimposed direct muscle stimulation was more pronounced in hypoxia, which was alleviated by L-NNA and aggravated by Sp-NO. These data provide insight in the underlying mechanisms of hypoxia-induced neurotransmission failure. This is important as respiratory muscle failure may result from hypoxia in vivo.

Topics: Animals; Diaphragm; Enzyme Inhibitors; Hypoxia; Male; Muscle Contraction; Muscle Fatigue; Neuromuscular Junction Diseases; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitrogen Oxides; Rats; Rats, Wistar; Spermine

Endothelins (ET) have opposite vascular effects mediated through different receptors: ET(A) receptors mediating vasoconstriction and ET(B) receptors mediating vasoconstriction as well as vasodilation. The role of ET in acute hypoxic pulmonary vasoconstriction (HPV) was studied after dual ET receptor blockade with bosentan and nitric oxide (NO) synthase inhibition with nitro-L-arginine (L-NA). We started from the hypothesis that ET antagonism may inhibit HPV but, if not, would do so after NO synthase inhibition. HPV was evaluated in anesthetized lambs, with an intact pulmonary circulation, by the increase in the mean pulmonary artery pressure (Ppa) minus occluded Ppa (Ppao) gradient in response to hypoxia (inspiratory oxygen fraction of 0.1) at different levels of pulmonary flow (multipoint pressure/flow relationships). ET receptor antagonism decreased pulmonary and systemic vascular tone both in hyperoxia and hypoxia. ET antagonism had no effect on HPV. NO synthase inhibition increased pulmonary vascular tone more in hypoxia than in hyperoxia so that HPV was enhanced. After L-NA, bosentan still decreased pulmonary vascular tone in hypoxia but did not affect the magnitude of HPV. The present results suggest that ET and NO are involved in the regulation of basal pulmonary vascular tone. Furthermore, the vasodilator effect of bosentan persisted in the presence of NO synthase inhibition, suggesting a non NO-dependent vasodilator mechanism. The results from these experiments are in agreement with the idea that ET do not play a major role in HPV in the perinatal lamb, even when it is enhanced by NO synthase inhibition.

Topics: Animals; Animals, Newborn; Blood Pressure; Bosentan; Constriction, Pathologic; Dilatation, Pathologic; Endothelin Receptor Antagonists; Endothelins; Hyperoxia; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Artery; Pulmonary Circulation; Sheep, Domestic; Sulfonamides; Vascular Resistance

Hypoxia relaxes endothelium-denuded bovine coronary arteries (BCA) through mechanisms that do not appear to involve reactive oxygen species, prostaglandins, or nitric oxide. Because of similarities in the relaxation of BCA to hypoxia (Po(2) = 8-10 Torr) and inhibitors of the pentose phosphate pathway (PPP) including 6-aminonicotinamide and epiandrosterone, we measured NADPH and NADP and found that hypoxia caused NADPH oxidation (decreased NADPH/NADP). The relaxation to hypoxia was similar to previously reported properties of relaxation to PPP inhibitors in that both responses were associated with glutathione oxidation and depressed intracellular calcium release and calcium influx-mediated contractile responses. Inhibitors of potassium channels had minimal effects on these relaxation responses. Relaxation to hypoxia and PPP inhibitors were attenuated by a thiol reductant (3 mM dithiothreitol) and by eliciting contraction with an activator of protein kinase C (phorbol 12,13-dibutyrate). In the presence of contraction to U-46619, relaxation to hypoxia and PPP inhibitors were attenuated by the sarco(endo)plasmic reticulum Ca(2+)-ATPase pump inhibitor 200 microM cyclopiazonic acid and by 10 mM pyruvate. Hypoxia decreased BCA levels of glucose-6-phosphate but not ATP. Pyruvate prevented the hypoxia-elicited decrease in glucose-6-phosphate and glutathione oxidation, and it increased NADPH levels under hypoxia to levels observed under normoxia. Thus hypoxia causes a metabolic stress on the PPP that promotes BCA relaxation through processes controlled by lowering the levels of cytosolic NADPH.

Topics: Adenosine Triphosphate; Animals; Anti-Inflammatory Agents, Non-Steroidal; Calcium; Calcium Signaling; Cattle; Coronary Vessels; Cytosol; Dithiothreitol; Endothelium, Vascular; Glucosephosphates; Glutathione; Hypoxia; In Vitro Techniques; Indomethacin; Muscle Contraction; NADP; Nitroarginine; Oxidation-Reduction; Phosphofructokinases; Potassium Channel Blockers; Pyruvic Acid; Sarcoplasmic Reticulum; Vasodilation

As arterial partial pressure of O(2) (Pa(O(2))) is reduced during systemic hypoxia, right ventricular (RV) work and myocardial O(2) consumption (MVo(2)) increase. Mechanisms responsible for maintaining RV O(2) demand/supply balance during hypoxia have not been delineated. To address this problem, right coronary (RC) blood flow and RV O(2) extraction were measured in nine conscious, instrumented dogs exposed to normobaric hypoxia. Catheters were implanted in the right ventricle for measuring pressure, in the ascending aorta for measuring arterial pressure and for sampling arterial blood, and in an RC vein. A flow transducer was placed around the RC artery. After recovery from surgery, dogs were exposed to hypoxia in a chamber ventilated with N(2), and blood samples and hemodynamic data were collected as chamber O(2) was reduced progressively to approximately 8%. After control measurements were made, the chamber was opened and the dog was allowed to recover. N(omega)-nitro-L-arginine (L-NNA) was then administered (35 mg/kg, via RV catheter) to inhibit nitric oxide (NO) production, and the hypoxia protocol was repeated. RC blood flow increased during hypoxia due to coronary vasodilation, because RC conductance increased from 0.65 +/- 0.05 to 1.32 +/- 0.12 ml x min(-1) x 100 g(-1) x L-NNA blunted the hypoxia-induced increase in RC conductance. RV O(2) extraction remained constant at 64 +/- 4% as Pa(O(2)) was decreased, but after L-NNA, extraction increased to 70 +/- 3% during normoxia and then to 78 +/- 3% during hypoxia. RV MVo(2) increased during hypoxia, but after L-NNA, MVo(2) was lower at any respective Pa(O(2)). The relationship between heart rate times RV systolic pressure (rate-pressure product) and RV MVo(2) was not altered by l-NNA. To account for L-NNA-mediated decreases in RV MVo(2), O(2) demand/supply variables were plotted as functions of MVo(2). Slope of the conductance-MVo(2) relationship was depressed by L-NNA (P = 0.03), whereas the slope of the extraction-MVo(2) relationship increased (P = 0.003). In summary, increases in RV MVo(2) during hypoxia are met normally by increasing RC blood flow. When NO synthesis is blocked, the large RV O(2) extraction reserve is mobilized to maintain RV O(2) demand/supply balance. We conclude that NO contributes to RC vasodilation during systemic hypoxia.

Topics: Animals; Coronary Circulation; Dogs; Enzyme Inhibitors; Female; Hypoxia; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen Consumption; Vasodilation

Nitric oxide (NO) plays an important role for the pulmonary circulation in normal and chronic hypoxia. We examined effects of endogenous nitric oxide synthase (NOS) inhibition on pulmonary and systemic vascular resistance in unanesthetized pigs living at three levels of altitude to evaluate the role of NO in adaptation to a hypoxic environment. Unanesthetized male adult pigs in three areas [Matsumoto, Japan (680 m above sea level, n = 5); Xing, China (2,300 m, n = 5); and Maxin, China (3,750 m, n = 5)] were prepared for vascular monitoring. Pulmonary (P(pa)), and systemic artery pressure (P(sa)) were monitored, and pulmonary artery wedge pressure (P(cwp)) and cardiac output (CO) were measured before and after treatment with a non-selective NOS inhibitor, N(w)-nitro-L-argine (NLA; 20 mg/kg). Pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) were (P(pa)-P(cwp))/CO and P(sa)/CO, respectively. Related to altitude baseline P(pa) was elevated. After NLA administration, P(pa) and P(sa) increased and CO decreased in all animals, resulting in increases in PVR and SVR. However, there were no significant differences in the increase in PVR and SVR in the three groups of pigs. Thus, endogenous NO production contributes to regulate the basal pulmonary vascular tone, but the development of hypoxic pulmonary hypertension appears to be independent of the NO pathway in adult pigs.

Topics: Acclimatization; Altitude; Animals; Blood Pressure; Hypertension, Pulmonary; Hypoxia; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Swine; Vascular Resistance

The effect of ZD6126 on tumor oxygen tension and tumor growth delay in combination with ionizing radiation was examined in the human U87 glioblastoma tumor model. Resistance to ZD6126 treatment was investigated with the nitric oxide synthase inhibitor, l-N(G)-nitroarginine methyl ester (hydrochloride; l-NAME/active form, l-NNA).. U87 human xenografts were grown in athymic nude mice. ZD6126 was given with or without l-NNA. Tumor oxygen tension was measured using the Oxford Oxylite (Oxford, England) fiberoptic probe system. Tumor volume was determined by direct measurement with calipers and calculated by the formula [(smallest diameter(2) x widest diameter)/2].. Multiple doses of ZD6126 treatment (three doses) had a significant effect on tumor growth delay, reducing the average daily tumor growth rate from 29% to 16%. When given 1 hour before radiation, ZD6126 caused an acute increase in hypoxia in U87 tumors, and reduced tumor growth delay compared with that of radiation alone. The combination of ZD6126 given after radiation, either as a single dose or in multiple doses, had greater or similar antitumor activity compared with radiation alone. Twenty-four hours after administration, a single dose of ZD6126 induced little (10 +/- 8%) necrosis in U87 xenografts. l-NNA, when given in combination with ZD6126, significantly enhanced the effectiveness of ZD6126 in inducing tumor necrosis.. Our observation that ZD6126-induced tumor hypoxia can decrease radiation response when ZD6126 is given prior to radiation indicates the importance of scheduling. Our findings suggest that the optimal therapeutic benefit of ZD6126 plus radiation in human glioblastoma may require multiple dosing in combination with a nitric oxide synthase inhibitor, to be scheduled following radiotherapy.

Topics: Angiogenesis Inhibitors; Animals; Blood Vessels; Brain Neoplasms; Combined Modality Therapy; Drug Therapy, Combination; Enzyme Inhibitors; Glioblastoma; Humans; Hypoxia; Mice; Mice, Nude; Necrosis; Neovascularization, Pathologic; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Organophosphorus Compounds; Oxygen; Radiation Tolerance; Radiation, Ionizing; Transplantation, Heterologous; Tumor Cells, Cultured; Vascular Endothelial Growth Factor A

The present study investigated whether activation of vasodilatory mechanisms masks the involvement of endothelin in hypoxic pulmonary vasoconstriction. Rat intrapulmonary arteries were mounted in microvascular myographs. In arteries with endothelium and contracted with phenylephrine, hypoxia, evoked by exchanging 5% CO2 in air for CO2 in N2, caused a transient contraction followed by a sustained contraction. Hypoxia evoked relaxation in preparations without endothelium. An inhibitor of ATP-sensitive K+ channels (KATP), glibenclamide (10 microM), blunted hypoxic relaxation in arteries without endothelium and enhanced the sustained hypoxic vasoconstriction in arteries with endothelium. Hypoxic contraction was more pronounced in endothelin compared with phenylephrine-contracted preparations in the absence, but not in the presence of glibenclamide. Antagonism of the endothelin ETA and ETB receptors with SB217242 or the combination of BQ123 and BQ788 inhibited endothelin and hypoxic contraction, but the latter only in the presence of glibenclamide. An inhibitor of nitric oxide (NO) synthase, N-nitro-L-arginine (100 microM), evoked contractions, which were left unaltered by SB217242 in hypoxic conditions. In conclusion, hypoxic contraction is mediated in part by an unknown endothelium-derived contractile factor and incubation with glibenclamide shows endothelin enhances hypoxic contraction in part through inhibition of KATP channels. Moreover, inhibition of NO formation in pulmonary arteries does not change endothelin receptor activation in severe hypoxia.

Topics: Animals; Anti-Arrhythmia Agents; Carboxylic Acids; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Enzyme Inhibitors; Glyburide; Hypoxia; In Vitro Techniques; Indans; Male; Nitric Oxide Synthase; Nitroarginine; Oligopeptides; Oxyhemoglobins; Peptides, Cyclic; Phenylephrine; Pinacidil; Piperidines; Pulmonary Artery; Rats; Rats, Wistar; Receptors, Endothelin; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

We reported previously that 17-beta estradiol (E2-beta) attenuates hypoxic induction of erythropoietin (EPO) synthesis in rats. We hypothesized this attenuation is mediated by increased nitric oxide (NO) bio-availability. To investigate this hypothesis, ovariectomized estrogen-depleted rats were instrumented with arterial and venous catheters and treated with either E2-beta (20 microg/24 hrs) or vehicle (polypropylene glycol) for 7 days. Rats were placed in Plexiglas boxes and administered a bolus of either the NO synthase inhibitor, Nomega-nitro-L-arginine (l-NNA, 15 mg/kg) or saline. Following this bolus, saline or l-NNA was continuously infused (15 mg/kg/h) throughout the 8 hours of hypoxic exposure (12% O2). Hypoxia increased plasma NO metabolites (NOx) in both saline groups but more in E2-beta-treated rats. l-NNA prevented this increase in both groups. Renal endothelial NO synthase (NOS) expression was unaltered by hypoxia, l-NNA, or E2-beta. Despite preventing increases in plasma NOx during hypoxia, l-NNA did not affect E2-beta attenuation of EPO synthesis. We conclude that E2-beta independently attenuates hypoxic induction of EPO and augments hypoxic increases in NO synthesis.

Topics: Animals; Blood Pressure; Erythropoietin; Estradiol; Female; Heart Rate; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Ovariectomy; Rats; Rats, Sprague-Dawley

We tested the hypotheses that pregnancy increases the uterine artery (UA) vasodilator response to flow and that this increase is impaired under conditions of chronic hypoxia (30 days, simulated elevation 3,960 m). UA were isolated from 24 normoxic or chronically hypoxic midpregnant guinea pigs and studied with the use of pressure myography. Normoxic pregnancy increased UA flow vasodilator response and protected against a rise in wall shear stress (WSS). Chronic hypoxia opposed these effects, prompting vasoconstriction at high flow and increasing WSS above levels seen in normoxic pregnant UA. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA) eliminated the pregnancy-associated increase in flow vasodilation in normoxic UA, suggesting that increased nitric oxide production was responsible. The considerable residual vasodilation after nitric oxide synthase and cyclooxygenase inhibition implicated endothelial-derived hyperpolarizing factor (EDHF) as an additional contributor to flow vasodilation. l-NNA increased flow vasodilation in UA from chronically hypoxic animals, suggesting that chronic hypoxia may have lowered EDHF or elevated peroxynitrite production. In conclusion, flow is an important physiological vasodilator for the acute and more chronic UA dimensional changes required to increase uteroplacental blood flow during normal pregnancy. Chronic hypoxia may be a mechanism that opposes the pregnancy-associated rise in UA flow vasodilation, thereby increasing the incidence of preeclampsia and intrauterine growth restriction at a high altitude.

Topics: Altitude; Animals; Arteries; Atmosphere Exposure Chambers; Blood Flow Velocity; Chronic Disease; Enzyme Inhibitors; Female; Guinea Pigs; Hypoxia; In Vitro Techniques; Meclofenamic Acid; Nitric Oxide Synthase; Nitroarginine; Pregnancy; Stress, Mechanical; Uterus; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

We previously found that nitric oxide synthase (NOS) inhibition fully blocked alkalosis-induced relaxation of piglet pulmonary artery and vein rings. In contrast, NOS inhibition alone had no effect on alkalosis-induced pulmonary vasodilation in isolated piglet lungs. This study sought to identify factors contributing to the discordance between isolated and in situ pulmonary vessels. The roles of pressor stimulus (hypoxia vs. the thromboxane mimetic U-46619), perfusate composition (blood vs. physiological salt solution), and flow were assessed. Effects of NOS inhibition on alkalosis-induced dilation were also directly compared in 150-350-microm-diameter cannulated arteries and 150-900-microm-diameter, angiographically visualized, in situ arteries. Finally, effects of NOS inhibition on alkalosis-induced vasodilation were measured in intact piglets. NOS inhibition with N(omega)-nitro-L-arginine fully abolished alkalosis-induced vasodilation in all cannulated arteries but failed to alter alkalosis-induced vasodilation in intact lungs. The results indicate that investigation of other factors, such as perivascular tissue (e.g., adventitia and parenchyma) and remote signaling pathways, will need to be carried out to reconcile this discordance between isolated and in situ arteries.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Alkalosis; Animals; Animals, Newborn; Blood Flow Velocity; Catheterization; Enzyme Inhibitors; Hypoxia; Nitroarginine; Perfusion; Pulmonary Artery; Pulmonary Circulation; Swine; Vasoconstrictor Agents; Vasodilation

The effects of endothelin receptor blockade on the pulmonary circulation have been reported variably, possibly in relation to a more or less important associated release of endogenous nitric oxide (NO). The aim of this study was to test whether endothelin antagonism would inhibit hypoxic pulmonary vasoconstriction, and if it would not, then would it do so after NO synthase inhibition. Hypoxic pulmonary vasoconstriction (HPV) was evaluated in anesthetised dogs by the increase in the mean pulmonary artery pressure (Ppa) minus occluded Ppa (Ppao) gradient in response to hypoxia (inspiratory oxygen fraction of 0.1) at constant pulmonary blood flow. Bosentan, an endothelin A and B receptor antagonist, did not affect baseline Ppa, Ppao or systemic arterial pressure (Psa) and did not alter HPV (n=8). The NO synthase inhibitor N(G)-nitro-L-arginine (L-NA) did not affect baseline Ppa and Ppao, but increased Psa and enhanced HPV (n=12). The addition of bosentan in these dogs did not affect baseline Ppa or Ppao, but decreased Psa and inhibited HPV. Exhaled NO was decreased by L-NA and by bosentan and abolished by L-NA+bosentan (n=9). The authors conclude that endogenous nitric oxide is released by, and opposes the vasoconstricting effects of, endothelins in vivo, reducing systemic blood pressure and limiting hypoxic pulmonary vasoconstriction.

Topics: Animals; Antihypertensive Agents; Bosentan; Dogs; Endothelin Receptor Antagonists; Endothelins; Hypoxia; Lung; Nitric Oxide; Nitroarginine; Sulfonamides; Vascular Resistance; Vasoconstriction

Ischaemic stroke is characterised by reduction of blood flow, tissue hypoxia, energy depletion and neuronal death. Drugs causing vasodilatation of cerebral arteries may potentially enhance blood supply to the ischaemic area and improve clinical outcome. However, vasodilators could also reduce cerebral blood flow in the ischaemic region by acting on blood vessels in non-ischaemic tissue, a phenomenon known as blood flow steal. To explore whether these drugs could act selectively on cerebral blood vessels in a hypoxic environment, we examined the effect of hypoxia on vasodilator responses to the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and the ATP-dependent potassium channel (K(ATP)) opener levcromakalim in guinea-pig basilar arteries contracted by endothelin-1. Hypoxia considerably enhanced the vasodilator responses to SNAP, while those to levcromakalim were unaffected. In the presence of the NO synthase inhibitor N(G)-nitro-L-arginine, hypoxia no longer enhanced the vasodilator response to SNAP and suppressed responses to levcromakalim. The results show that the NO donor SNAP, but not the K(ATP) opener levcromakalim, is a more effective vasodilator of cerebral arteries contracted by endothelin-1 during hypoxia than under control conditions. Hypoxia-induced inhibition of basal NO synthesis could explain this enhancement of the vasodilator response to SNAP. Thus, NO donors may have a selective effect on blood vessels in ischaemic brain areas and therefore warrant further evaluation as therapeutic agents in cerebral ischaemia.

Topics: Acetylcholine; Animals; Basilar Artery; Biological Factors; Cromakalim; Endothelium, Vascular; Guinea Pigs; Hypoxia; Male; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; S-Nitroso-N-Acetylpenicillamine; Vasodilation

Although in tissue injury following hypoxia/reoxygenation (H/R) an increased endothelial formation of superoxide anions (O(2)(-)) plays an important role, it is still not fully understood which of the potential enzymatic sources of endothelial O(2)(-) are crucially involved. In this study, we particularly examined the activities of NAD(P)H oxidase and xanthine oxidase (XO) after 8 h of exposure to mild hypoxia. We further studied whether enzyme activities can be modified by NO and adenosine during hypoxic treatment.. In human umbilical vein endothelial cells O(2)(-) production was measured immediately after exposure to hypoxia ('early reoxygenation') or after 2 h of reoxygenation at normoxic conditions ('late reoxygenation'). In the early reoxygenation phase the O(2)(-) production was attenuated by 28.5% while it was enhanced by 58.2% after late reoxygenation. Using specific inhibitors of NAD(P)H oxidase and XO, gp91ds-tat and oxypurinol, respectively, we show that the constitutively active NAD(P)H oxidase was blocked following hypoxia while XO was activated. The presence of NO during hypoxia had no effect on NAD(P)H oxidase activity but it significantly inhibited the activation of XO. Inhibition of XO activation was, at least in part, caused by the release of adenosine from endothelial cells which induces an increased formation of NO by its A1 and A2 receptors.. Our results indicate that during exposure to mild hypoxia for 8 h, a change in the enzymatic source of endothelial O(2)(-) occurs: a prolonged inhibition of NAD(P)H oxidase was found while an enhanced activity of XO occurs in the reoxygenation phase. These results suggest that different strategies of antioxidant therapy should be taken into consideration in oxidative stress related to chronic hypoxia when compared to normoxic atherosclerotic tissues with an activated vascular NAD(P)H oxidase as the main source of O(2)(-).

Topics: Adenosine; Anti-Arrhythmia Agents; Cells, Cultured; Chromans; Cytochromes c; Endothelium, Vascular; Humans; Hypoxia; NADPH Oxidases; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Oxygen; Potassium Channels; Pyrrolidines; Reactive Oxygen Species; Superoxide Dismutase; Xanthine Oxidase

Nitric oxide (NO) inhibition with NG-nitro-l-arginine methyl ester (l-NAME) in the last trimester of pregnancy caused intrauterine growth retardation and hind-limb disruptions in rats. In the present study, the effect of maternal NO inhibition with NG-nitro-l-arginine (l-NNA) on hypoxic newborn rats was investigated.. Timed-pregnant rats were obtained on gestational day 17. Four groups of rats were used: control, hypoxic, l-NNA and l-NNA + hypoxic groups. In the last two groups, l-NNA (2 mg/kg bolus, i.p.) was administered to the mothers of pups antenatally on 3 consecutive days. Hypoxia was induced in newborn rats by breathing of a mixture of 8% oxygen and 92% nitrogen for 3 h. Pups were then allowed to inhale normal atmospheric air for 30 min. All newborn rats were decapitated on the first day of life after hypoxia and reoxygenation. Brain, heart, lung, liver, kidney and intestinal tissues were studied biochemically. Hypoxia-induced biochemical changes were determined by measuring lipid peroxidation. Histopathologic examination of lung tissue was performed.. Nitric oxide synthase inhibition in pregnancy did not cause fetal growth retardation. Hypoxia increased lipid peroxidation in all tissues except the heart; this increase was decreased by maternal l-NNA administration in brain, lung, liver and kidney tissues. However, lipid peroxidation was increased by NO synthase inhibition in the intestines. In the lungs, pulmonary hemorrhage was observed in the hypoxic group. Minimal pulmonary hemorrhage was detected in the l-NNA and l-NNA + hypoxic groups.. These data suggest that antenatal administration of an NO synthase inhibitor acts as both a destructive and protective agent in hypoxic newborn rats.

Topics: Animals; Animals, Newborn; Embryonic and Fetal Development; Enzyme Inhibitors; Hypoxia; Nitroarginine; Rats; Rats, Wistar

It has previously been shown that both hypoxemia and nitric oxide (NO) synthase blockade depress the activation of group IV muscle afferents after muscle stimulation (MS). In the present study, we questioned whether hypoxemia exerts a specific inhibitory influence, independently from its effects on endogenous NO formation. This hypothesis was tested in two groups of anesthetized rabbits in which we examined the effects of hypoxemia, and then of subsequent NO synthase blockade by N(G)-nitro-L-arginine methyl ester (L-NAME), and vice versa. In each protocol, group IV afferent activity was recorded from the resting tibialis anterior muscle and after 3-min periods of MS that elicited a significant decrease in muscle force. NO synthase blockade in normoxemia suppressed the group IV afferent response to MS, and hypoxemia alone significantly reduced the post-MS activation of these nerve afferents (+18% vs. +28% in normoxemia). In hypoxemic rabbits, further NO synthase blockade abolished the post-MS activation of group IV afferents. Moreover, when hypoxemia followed the NO synthase blockade, MS significantly reduced the discharge of group IV afferents (-28%). Thus, while these muscle afferents are activated after fatiguing muscle contractions when the endogenous NO production is present, they are deactivated by hypoxemia when NO production is blocked. We conclude that endogenous NO production and hypoxemia exert opposite effects on the activation of the group IV afferents. Our data anticipate the neuromuscular side effects of treatments using exogenous NO or drugs acting on endogenous NO production.

Topics: Animals; Enzyme Inhibitors; Hypoxia; Muscle Fatigue; Muscle, Skeletal; Neurons, Afferent; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rabbits

To investigate whether the retina of the rat exerts a vasodilatory influence by the release of a relaxing factor and to characterize the retinal relaxing factor (RRF).. The relaxing influence of the rat retina was investigated by placing the retina in close proximity with a precontracted isolated rat carotid artery ring segment, mounted for isometric tension measurements.. Application of rat retina relaxed the artery in a reliable and reproducible way. The nitric oxide (NO)-synthase inhibitor N(omega)-nitro-L-arginine (L-NA), the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and the removal of the endothelium of the artery all failed to affect the RRF response. The RRF response was not decreased; in contrast, it increased after treatment with a cyclooxygenase (COX) inhibitor (indomethacin or sodium diclofenac). Acute hypoxia largely enhanced retina-induced relaxation. Several potential mediators of hypoxia-induced vasodilation were excluded as candidates for the RRF or for mediating the enhanced response to RRF in hypoxia. Inhibition of the plasma membrane Ca(2+)-adenosine triphosphatase (ATPase) with vanadate significantly affected the RRF response.. The release of an as yet unidentified relaxing factor(s) from the rat retina was demonstrated. Acute hypoxia profoundly enhances the RRF response. None of the known mediators of hypoxia-induced vasodilation nor NO, prostanoids, or endothelial factors mediate the RRF response. Activation of the plasma membrane Ca(2+)-ATPase seems to be involved in the RRF response.

Topics: Acute Disease; Animals; Calcium-Transporting ATPases; Carotid Arteries; Cyclooxygenase Inhibitors; Diclofenac; Endothelium, Vascular; Enzyme Inhibitors; Female; Guanylate Cyclase; Hypoxia; In Vitro Techniques; Indomethacin; Isometric Contraction; Nitroarginine; Oxadiazoles; Quinoxalines; Rats; Rats, Wistar; Retina; Sarcoplasmic Reticulum; Thapsigargin; Vasodilation; Vasodilator Agents

It is known that protective effects of adaptation to intermittent hypoxia are mediated partly by stimulating of some mitochondrial and microsomal enzymes activity. Our objective was to investigate whether exogenous NO (L-arginine) or NO blocker (L-NNA) modulate mitochondrial and microsomal oxidation during acute hypoxia (AH) and intermittent hypoxic training (IHT). In control rats AH (inhalation of 7% O2, 30 min) provoked a decrease of ADP-stimulated liver mitochondrial respiration. However, the pattern of oxidation substrates was different from normoxic controls. In the presence of succinate, an increase of the Chance respiratory coefficient and the phosphorylation rate and a decrease of O2 uptake efficacy with simultaneous activation of aspartate aminotransferase activity were observed. Simultaneously, oxidation of a-ketoglutarate, an NAD-dependent substrate, was inhibited. IHT caused reorganization of mitochondrial energy metabolism favoring NAD-dependent oxidation and improving the protection against acute hypoxia. After 14 days of normobaric IHT (10% O2, 15-min sessions with 15 min rest intervals, 5 times daily), in comparison to controls acute hypoxic challenge in the presence of succinate resulted in an increase of the Chance respiratory coefficient, the ADP/O ratio and the phosphorylation rate, in activation of both aspartate and alanine aminotranferases, and in less lipid peroxidation. The microsomal oxidation was not changed under AH per se but significantly decreased (by 37%) during acute hypoxic test after ITH. These findings indicated a more efficient use of oxygen under hypoxic conditions after IHT pre-conditioning. The combination of IHT with L-arginine treatment (600 mg/kg intraperitoneally, daily before IHT sessions) provoked more pronounced decrease of tissue oxygen consumption and microsomal oxidative processes in comparison with IHT animals. L-arginine effects were abolished by the NO-synthase blocker L-NNA. We conclude that the combination of IHT with NO-donor treatment provokes a decrease in aerobic link of energy regulation thereby increasing the tolerance to episodes of acute hypoxia.

Topics: Adaptation, Physiological; Animals; Arginine; Energy Metabolism; Enzyme Inhibitors; Hypoxia; Lipid Peroxidation; Male; Microsomes, Liver; Mitochondria, Liver; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar

Chronic hypoxia (CH) is associated with a persistent reduction in systemic vasoconstrictor reactivity. Experiments on aortic ring segments isolated from CH rats suggest that enhanced vascular expression of heme oxygenase (HO) and resultant production of the vasodilator carbon monoxide (CO) may underlie this attenuated vasoreactivity after hypoxia. Similar to the aorta, small arteries from CH rats exhibit blunted reactivity; however, the regulatory role of CO in the resistance vasculature has not been established. Therefore, we examined the significance of HO activity on responsiveness to phenylephrine (PE) in the mesenteric circulation of control and CH rats. To document that the mesenteric bed demonstrates reduced reactivity after CH, we determined the vasoconstrictor responses of conscious, chronically instrumented male Sprague-Dawley rats to PE under control conditions and then immediately after exposure to 48 h CH (0.5 atm). All rats showed reduced mesenteric vasoconstriction to PE after CH. To examine the role of CO in reduced reactivity, small mesenteric arteries (100-200 microm intraluminal diameter) from control and 48-h CH rats were isolated and mounted on glass cannulas, pressurized to 60 mmHg and superfused with increasing concentrations of PE under normoxic conditions. Similar to the intact circulation, vessels from CH rats exhibited reduced vasoconstrictor sensitivity to PE compared with controls that persisted in the presence of nitric oxide synthase inhibition. The HO inhibitor, zinc protoporphyrin IX (5 microM) enhanced reactivity only in CH vessels. Additionally, a range of concentrations of the HO substrate heme-L-lysinate caused vasodilation in CH vessels but not in controls. Thus we conclude that CO contributes a significant vasodilator influence in resistance vessels after CH that may account for diminished vasoconstrictor responsiveness under these conditions.

Topics: Animals; Blood Pressure; Carbon Monoxide; Heme; Hypoxia; Lysine; Male; Mesenteric Arteries; Nitric Oxide; Nitroarginine; Phenylephrine; Rats; Rats, Sprague-Dawley; Reference Values; Vascular Resistance; Vasoconstriction; Vasodilator Agents

Studies of thapsigargin, cyclopiazonic acid, and ryanodine in isolated pulmonary arteries and smooth muscle cells suggest that release of Ca(2+) from inositol 1,4,5-trisphosphate (IP(3))- and/or ryanodine-sensitive sarcoplasmic reticulum Ca(2+) stores is a component of the mechanism of acute hypoxic pulmonary vasoconstriction (HPV). However, the actions of these agents on HPV in perfused lungs have not been reported. Thus we tested effects of thapsigargin and cyclopiazonic acid, inhibitors of sarcoplasmic reticulum Ca(2+)-ATPase, and of ryanodine, an agent that either locks the ryanodine receptor open or blocks it, on HPV in salt solution-perfused rat lungs. After inhibition of cyclooxygenase and nitric oxide synthase, thapsigargin (10 nM) and cyclopiazonic acid (5 microM) augmented the vasoconstriction to 0% but not to 3% inspired O(2). Relatively high concentrations of ryanodine (100 and 300 microM) blunted HPV in nitric oxide synthase-inhibited lungs. The results indicate that release of Ca(2+) from the ryanodine-sensitive, but not the IP(3)-sensitive, store, contributes to the mechanism of HPV in perfused rat lungs and that Ca(2+)-ATPase-dependent Ca(2+) buffering moderates the response to severe hypoxia.

Topics: Animals; Calcium; Enzyme Inhibitors; Hypoxia; Indoles; Male; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Ryanodine; Thapsigargin; Vasoconstriction

Hypoxia triggers a mechanism that induces vasodilation in the whole heart but not necessarily in isolated coronary arteries. We therefore studied the role of cardiomyocytes (CM), smooth muscle cells (SMC), and endothelial cells (EC) in coronary responses to hypoxia (PO(2) of 5-10 mmHg). In an attempt to determine the factor(s) released in response to hypoxia, we inhibited the contribution of adenosine, ATP-sensitive K(+) channels, prostaglandins, and nitric oxide. Isolated rat septal artery segments without (-T) and with a layer of cardiac tissue (+T) were mounted in a double wire myograph, and constriction was induced. Hypoxia induced a decrease in isometric force of 21% and 61% in -T and +T segments, respectively (P < 0.05). EC removal increased the relaxation to hypoxia in -T segments to 33% but had the same effect in +T segments (61%). Only one of the inhibitors, the adenosine antagonist in +T segments, partially affected the relaxation due to hypoxia. The role of adenosine is thus limited and other mechanisms have to contribute. We conclude that hypoxia induces a relaxation of SMC that is augmented by the presence of CM and blunted by the endothelium. A single mediator does not induce those effects.

Topics: Acetylcholine; Animals; Arachidonic Acid; Coronary Vessels; Endothelium, Vascular; Glyburide; Heart; Hypoxia; In Vitro Techniques; Indomethacin; Male; Muscle, Smooth, Vascular; Nitroarginine; Rats; Rats, Wistar; Temperature; Vasoconstriction

Chronic hypoxia (CH) augments endothelium-derived nitric oxide (NO)-dependent pulmonary vasodilation; however, responses to exogenous NO are reduced following CH in female rats. We hypothesized that CH-induced attenuation of NO-dependent pulmonary vasodilation is mediated by downregulation of vascular smooth muscle (VSM) soluble guanylyl cyclase (sGC) expression and/or activity, increased cGMP degradation by phosphodiesterase type 5 (PDE5), or decreased VSM sensitivity to cGMP. Experiments demonstrated attenuated vasodilatory responsiveness to the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate and to arterial boluses of dissolved NO solutions in isolated, saline-perfused lungs from CH vs. normoxic female rats. In additional experiments, the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, blocked vasodilation to NO donors in lungs from each group. However, CH was not associated with decreased pulmonary sGC expression or activity as assessed by Western blotting and cGMP radioimmunoassay, respectively. Consistent with our hypothesis, the selective PDE5 inhibitors dipyridamole and T-1032 augmented NO-dependent reactivity in lungs from CH rats, while having little effect in lungs from normoxic rats. However, the attenuated vasodilatory response to NO in CH lungs persisted after PDE5 inhibition. Furthermore, CH similarly inhibited vasodilatory responses to 8-bromoguanosine 3'5'-cyclic monophosphate. We conclude that attenuated NO-dependent pulmonary vasodilation after CH is not likely mediated by decreased sGC expression, but rather by increased cGMP degradation by PDE5 and decreased pulmonary VSM reactivity to cGMP.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Blotting, Western; Chronic Disease; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Enzyme Inhibitors; Female; Guanylate Cyclase; Hypertrophy, Right Ventricular; Hypoxia; In Vitro Techniques; Lung; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Donors; Nitroarginine; Polycythemia; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Receptors, Cytoplasmic and Nuclear; Soluble Guanylyl Cyclase; Vasodilation

Chronic hypoxia (CH) results in reduced sensitivity to vasoconstrictors in conscious rats that persists upon restoration of normoxia. We hypothesized that this effect is due to endothelium-dependent hyperpolarization of vascular smooth muscle (VSM) cells after CH. VSM cell resting membrane potential was determined for superior mesenteric artery strips isolated from CH rats (PB = 380 Torr for 48 h) and normoxic controls. VSM cells from CH rats studied under normoxia were hyperpolarized compared with controls. Resting vessel wall intracellular Ca(2+) concentration ([Ca(2+)](i)) and pressure-induced vasoconstriction were reduced in vessels isolated from CH rats compared with controls. Vasoconstriction and increases in vessel wall [Ca(2+)](i) in response to the alpha(1)-adrenergic agonist phenylephrine (PE) were also blunted in resistance arteries from CH rats. Removal of the endothelium normalized resting membrane potential, resting vessel wall [Ca(2+)](i), pressure-induced vasoconstrictor responses, and PE-induced constrictor and Ca(2+) responses between groups. Whereas VSM cell hyperpolarization persisted in the presence of nitric oxide synthase inhibition, heme oxygenase inhibition restored VSM cell resting membrane potential in vessels from CH rats to control levels. We conclude that endothelial derived CO accounts for persistent VSM cell hyperpolarization and vasoconstrictor hyporeactivity after CH.

Topics: Animals; Electrophysiology; Endothelium, Vascular; Enzyme Inhibitors; Heme Oxygenase (Decyclizing); Hypoxia; In Vitro Techniques; Male; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Protoporphyrins; Rats; Rats, Sprague-Dawley; Time Factors

The present study tested the hypothesis that nitration is a mechanism of hypoxia-induced modification of the N-methyl-D-aspartate (NMDA) receptor. To test this hypothesis the effect of hypoxia on the nitration of the NR1, NR2A and NR2B subunits of the NMDA receptor was determined. Furthermore, the effect of administration of a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine (NNLA) on the hypoxia-induced nitration of the NMDA receptor subunits as well as the NMDA receptor-mediated Ca2+ influx, an index of NMDA receptor-ion channel function, were determined in cortical synaptosomes. Studies were performed in newborn piglets divided into normoxic, hypoxic and hypoxic-NNLA groups. Hypoxia was induced by decreasing the FiO(2) to 0.07-0.09 for 60 min. Cerebral tissue hypoxia was confirmed by determining the levels of high energy phosphates ATP and phosphocreatine. Nitration of the NMDA receptor subunits was determined by immunoprecipitation using specific antibodies and western blot analysis. NMDA receptor-ion channel-mediated Ca2+ influx was determined using 45Ca2+. There was a significant increase in the nitrated NR1, NR2A and NR2B subunits following hypoxia: 104+/-11 vs. 275+/-18 optical density (OD)xmm(2) for NR1 (P<0.05), 212+/-36 vs. 421+/-16 ODxmm(2) for NR2A (P<0.05) and 246+/-44 vs. 360+/-26 ODxmm(2) for NR2B (P<0.05). This increase in nitrated NR1, NR2A and NR2B subunits of the NMDA receptor was prevented by the administration of NNLA prior to hypoxia (NR1 160+/-19, P=NS, NNLA vs. normoxic; NR2A 304+/-49, P=NS, NNLA vs. normoxic, and NR2B 274+/-19, P=NS, NNLA vs. normoxic). The increase in nitration of the NR1, NR2A and NR2B subunits of the NMDA receptor increased as a function of decreased cerebral high-energy phosphates, ATP and phosphocreatine, during hypoxia. Furthermore, NOS blockade prior to hypoxia resulted in prevention of the hypoxia-induced increase in NMDA receptor-mediated Ca2+ influx. Our results demonstrate that hypoxia results in increased nitration of the NMDA receptor subunits and that administration of an NOS inhibitor prior to hypoxia prevents the hypoxia-induced nitration of the NMDA receptor subunits as well as the hypoxia-induced increase in NMDA receptor-mediated Ca2+ influx. We conclude that nitration is a mechanism of modification of the NMDA receptor function during hypoxia in the newborn piglet brain.

Topics: Animals; Animals, Newborn; Blotting, Western; Calcium; Cerebral Cortex; Enzyme Inhibitors; Hypoxia; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitroarginine; Precipitin Tests; Receptors, N-Methyl-D-Aspartate; Swine; Synaptosomes

Female rats develop less severe pulmonary hypertension (PH) in response to chronic hypoxia compared with males, thus implicating a potential role for ovarian hormones in mediating this gender difference. Considering that estrogen upregulates endothelial nitric oxide (NO) synthase (eNOS) in systemic vascular tissue, we hypothesized that estrogen inhibits hypoxic PH by increasing eNOS expression and activity. To test this hypothesis, we examined responses to the endothelium-derived NO-dependent dilator ionomycin and the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate in U-46619-constricted, isolated, saline-perfused lungs from the following groups: 1) normoxic rats with intact ovaries, 2) chronic hypoxic (CH) rats with intact ovaries, 3) CH ovariectomized rats given 17 beta-estradiol (E(2)beta), and 4) CH ovariectomized rats given vehicle. Additional experiments assessed pulmonary eNOS levels in each group by Western blotting. Our findings indicate that E(2)beta attenuated chronic hypoxia-induced right ventricular hypertrophy, pulmonary arterial remodeling, and polycythemia. Furthermore, although CH augmented vasodilatory responsiveness to ionomycin and increased pulmonary eNOS expression, these responses were not potentiated by E(2)beta. Finally, responses to S-nitroso-N-acetylpenicillamine and spermine NONOate were similarly attenuated in all CH groups compared with normoxic control groups. We conclude that the inhibitory influence of E(2)beta on chronic hypoxia-induced PH is not associated with increased eNOS expression or activity.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Chronic Disease; Endothelium, Vascular; Enzyme Inhibitors; Estradiol; Female; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; Ionomycin; Ionophores; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Nitrogen Oxides; Ovariectomy; Penicillamine; Polycythemia; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Spermine; Vascular Resistance; Vasoconstrictor Agents; Vasodilation

We tested the hypothesis that carbon monoxide might participate in the modulation of hypoxic pulmonary vasoconstriction (HPV) by prostacyclin (PGI2) and nitric oxide.. Prospective, interventional study.. University laboratory.. Nineteen intact anesthetized mongrel dogs.. Right heart catheterization for the measurements of mean pulmonary artery pressure (Ppa), left atrial pressure estimated from occluded Ppa (Ppao), pulmonary capillary pressure (Pcp) calculated from the Ppa decay curve after balloon occlusion, and cardiac output (Q); inferior vena cava balloon for the control of Q by manipulation of venous return; ventilation in hyperoxia (fraction of inspired O2, 0.4) or in hypoxia (Fio2, 0.1); inhibition of cyclooxygenase by indomethacin (Indo); inhibition of nitric oxide synthase by NG-nitro-l-arginine (L-NA); inhibition of heme oxygenase by mesoporphyrin IX (SnMP); inhalation of nitric oxide (20 ppm); and inhalation of carbon monoxide (100 ppm).. The first seven dogs were weak responders to hypoxia as assessed by a hypoxia-induced increase in the gradient between Ppa and Ppao, measured at one level of Q kept constant, by an average of only 2 mm Hg (p = NS). This HPV was markedly increased by the combined administration of Indo and L-NA. A further enhancement of HPV was observed after the addition of SnMP, leading to severe pulmonary hypertension with an average increase in Ppa to 39 mm Hg. Inhaled nitric oxide inhibited HPV only after the combined administration of Indo, L-NA, and SnMP. Inhaled carbon monoxide had no effect. The next 12 dogs were stronger responders to hypoxia, as assessed by a hypoxia-induced increase in the gradient between Ppa and Ppao, measured at several levels of Q, by an average of 3 mm Hg (p <.05). This HPV was of the same magnitude after administration of placebo (n = 6) or SnMP (n = 6). Addition of Indo enhanced HPV to the same extent in the placebo and in the SnMP groups. Addition of L-NA induced a further enhancement of HPV, which was, however, greater in the SnMP group. There was a slight increase in the capillary-venous segment relative to the arterial segment in hypoxic conditions, but the partitioning of pulmonary vascular resistance was otherwise unaffected by nitric oxide, carbon monoxide, or PGI2.. Endogenous carbon monoxide modulates canine HPV only in the absence of nitric oxide. The vasodilation mediated by nitric oxide, PGI2, or carbon monoxide is essentially distributed between proximal and distal sites proportionally to the degree of constriction produced during hypoxia.

Topics: Administration, Inhalation; Animals; Carbon Monoxide; Cyclooxygenase Inhibitors; Disease Models, Animal; Dogs; Drug Evaluation, Preclinical; Epoprostenol; Hemodynamics; Hypoxia; Indomethacin; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Prostaglandin-Endoperoxide Synthases; Pulmonary Circulation; Vasoconstriction

The main components of antioxidant enzyme system (AOS) are superoxide dismutase (SOD) and glutathione reductase (GR) catalyses the conversion of the superoxide anion. The important role in AOS belongs to catalase and glutathione peroxidase which perform H2O2 to nontoxic products. Simultaneous determination of AOS activity and malonic dialdehide (MDA) concentration (the index of lipid peroxidation in tissues and blood) characterize cells complex resistance to damage factor. The effect of L-arginine, as a precursor of nitric oxide synthesis and blocator NO-synthase (Nw-nitro-L-arginine) on AOS of rats with different resistance to hypoxia under stress condition is unknown and were subject of our investigation. Experiments were done on liver and blood tissues of white laboratory rats. The experimental animals were divided on two groups depending on hypoxia factor: high resistance (HR) and low resistance (LR). The type of resistance was determined by the time of ability to respire in barocamera with oxygen deficient equal to 12.000 meters over sea level. The animals adaptation to laboratory conditions continue during 14 days after in barocamera presence. All animals were divided dependent on experiment conditions on fourth groups. The first group: intact (HR and LR) animals parentherally injected by 1 ml of 0.9% NaCl solution. The second group was subject of stress condition. The third group: HR and LR animals injected parentherally by 1 ml L-arginine (Sigma, USA) dose (600 mg/kg body weight). The fourth one: rats injected by 1 ml Nw-nitro-L-arginine (L-NNA, Sigma, USA)--the blocator of NO-synthase. The animals were decapitated 30 min after injection and stress condition under ethereal anesthesia. Activity of antioxidant system enzymes superoxide dismutase (SOD), catalase (CAT); glutathione reductase (GR), glutathione peroxidase (GP) were measured spectrophotometrically. Also was investigated the concentration of serum antioxidant ceruloplasmin (CP). Level of lipid peroxidation was estimate by examination of concentration of lipids of hydroperoxides (LHP) and malonic dialdehyde (MDA). Our data confirm suggesting that nitric oxide (NO) is a major regulator in the AOS enzymes activity and limit damage influence of AOF. Action precursor NO L-arginine might be capable of protective role in various disorders which are connected with hypoxia factor. Following thing can be interred the investigation of influence of nitric oxide adaptive answers in stress condition mo

Topics: Animals; Antioxidants; Arginine; Catalase; Enzyme Inhibitors; Glutathione Peroxidase; Glutathione Reductase; Hypoxia; Lipid Peroxidation; Liver; Male; Nitric Oxide Synthase; Nitroarginine; Oxidative Stress; Rats; Superoxide Dismutase

After birth, the full-term ductus arteriosus actively constricts and undergoes extensive histologic changes that prevent subsequent reopening. These changes are thought to occur only if a region of intense hypoxia develops within the ductus wall after the initial active constriction. In preterm infants, indomethacin-induced constriction of the ductus is often transient and is followed by reopening. Prostaglandins and nitric oxide both play a role in inhibiting ductus closure in vitro. We hypothesized that combined inhibition of both prostaglandin and nitric oxide production (with indomethacin and N-nitro-L-arginine (L-NA), respectively) may be required to produce the degree of functional closure that is needed to cause intense hypoxia. We used preterm (0.67 gestation) newborn baboons that were mechanically ventilated for 6 d: 6 received indomethacin alone, 7 received indomethacin plus L-NA, and 16 received no treatment (control). Just before necropsy, only 25% of control ductus and 33% of indomethacin-treated ductus were closed on Doppler examination; in contrast, 100% of the indomethacin-plus-L-NA-treated ductus were closed. Control and indomethacin-treated baboons developed negligible-to-mild ductus hypoxia (EF5 technique). Similarly, there was minimal evidence of ductus remodeling. In contrast, indomethacin-plus-L-NA-treated baboons developed intense hypoxia in regions where the ductus was most constricted. The hypoxic muscle strongly expressed vascular endothelial growth factor, and proliferating luminal endothelial cells filled and occluded the lumen. In addition, cells in the most hypoxic regions were undergoing DNA fragmentation. In conclusion, preterm newborns are capable of remodeling their ductus, just like the full-term newborn, if they can reduce their luminal blood flow to a point that produces intense ductus wall hypoxia. Combined prostaglandin and nitric oxide inhibition may be necessary to produce permanent closure of the ductus and prevent reopening in preterm infants.

Topics: Animals; Animals, Newborn; Bisbenzimidazole; Blood Pressure; Cardiovascular Agents; DNA Fragmentation; Ductus Arteriosus; Endothelial Growth Factors; Enzyme Inhibitors; Etanidazole; Fetus; Fluorescent Dyes; Hydrocarbons, Fluorinated; Hypoxia; Immunohistochemistry; In Situ Nick-End Labeling; Indicators and Reagents; Indomethacin; Lymphokines; Nitric Oxide; Nitroarginine; Papio; Prostaglandins; Respiratory Physiological Phenomena; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors

The implication of endogenous nitric oxide in the effect of hypoxia on the neurotransmission in the enteric nervous system of guinea-pig ileum was studied in vitro. Three methodological approaches have been used: (i) Stretch-induced phases of peristaltic reflex in ileal segments; (ii) twitch contractions of longitudinal segments, evoked by electrical field stimulation; and (iii) release of [3H]acetylcholine from longitudinal muscle-myenteric plexus preparations, measured by liquid spectrophotometry. The effect of nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA, 100 microM) was studied under normoxic conditions. L-NNA did not change significantly the ascending contraction phase of peristaltic reflex and the amplitude of twitch contractions. However, the same concentration of L-NNA increased the stimulation-evoked acetylcholine release. The descending relaxation phase decreased in the presence of L-NNA. In another set of experiments, hypoxia was mimicked by replacement of oxygen from the perfusion medium with nitrogen for a period of 30 min. Hypoxia significantly decreased the ascending contraction phase, the twitch contractions, and the release of acetylcholine from the myenteric plexus. Under hypoxic conditions, pretreatment with L-NNA did not change either the contractile responses, nor the release of acetylcholine. Our results suggest that under conditions of oxygen deprivation, endogenous nitric oxide seems to be inefficient in modulating the cholinergic neurotransmission in guinea-pig ileum.

Topics: Acetylcholine; Animals; Cholinergic Fibers; Electric Stimulation; Enteric Nervous System; Enzyme Inhibitors; Female; Guinea Pigs; Hypoxia; Ileum; In Vitro Techniques; Male; Nitric Oxide; Nitroarginine; Peristalsis; Reflex; Synaptic Transmission; Tritium

August rats are more resistant to stress-induced gastric damages than Wistar rats. These interstrain differences were abolished after blockade of nitric oxide (NO) synthesis with NO-synthase inhibitor L-NNA, which indicates that NO contributes to genetically determined resistance to stress-induced injuries. Repeated treatment with L-NNA caused gastric ulceration in Wistar, but not in August rats. This is probably related to higher basal production and more intensive accumulation of NO in August rats compared to Wistar rats. Administration of L-NNA during adaptation to hypoxia suppressed its protective effects on the stomach in stress, which indicates that NO acts as the factor of adaptive protection.

Topics: Animals; Digestive System; Enzyme Inhibitors; Hypoxia; Male; Nitric Oxide; Nitroarginine; Oxidative Stress; Rats; Rats, Wistar; Species Specificity; Stress, Physiological; Time Factors

This study tests the hypothesis that brain tissue hypoxia results in modification of spermine-dependent activation of the cerebral N-methyl-D-aspartate (NMDA) receptor ion-channel in newborn piglet brains and that pretreatment with N(omega)-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthase, will reduce the hypoxia-induced modification of the spermine-dependent activation of the receptor. Piglets were assigned to one of four groups; normoxia or hypoxia with or without NNLA. The infusion of NNLA or vehicle lasted for 60 min while the animals were ventilated under either hypoxic or normoxic conditions. Cerebral tissue hypoxia was confirmed by measuring ATP and phosphocreatine (PCr) levels. P2 membranes were isolated and 3H-MK-801 binding was measured in the presence of spermine. Steady state 3H-MK-801 binding in the presence of spermine, showed an increase in receptor affinity in both normoxic (47% of control) and hypoxic (42% of control) animals without change in receptor density. During hypoxia, the spermine-dependent increase in the maximal response of the 3H-MK-801 binding correlated inversely with the ATP concentrations. NNLA pretreatment prior to hypoxia, resulted in a decrease in the slope of the regression line describing the relationship between cellular energy state (ATP) and percent change in maximal response to spermine compared with vehicle treated animals indicating attenuation of the response to hypoxia. We conclude that the spermine-dependent modification of the affinity of the NMDA receptor ion-channel as assessed by 3H-MK-801 binding is similar in hypoxic and normoxic cortical tissue. NNLA administration reduces the hypoxia-induced spermine-dependent activation of the receptor indicating that nitric oxide mediates modification of the spermine site activation of the NMDA receptor ion-channel complex.

Topics: Adenosine Triphosphate; Animals; Animals, Newborn; Cerebral Cortex; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hypoxia; Nitric Oxide Synthase; Nitroarginine; Receptors, N-Methyl-D-Aspartate; Reference Values; Spermine; Swine

Red blood cells (RBCs) augment hypoxic pulmonary vasoconstriction (HPV) in part by scavenging of nitric oxide (NO) by Hb (Deem S, Swenson ER, Alberts MK, Hedges RG, and Bishop MJ, Am J Respir Crit Care Med 157: 1181-1186, 1998). We studied the contribution of the RBC compartmentalization of Hb to augmentation of HPV and scavenging of NO in isolated perfused rabbit lungs. Lungs were initially perfused with buffer; HPV was provoked by a 5-min challenge with hypoxic gas (inspired O(2) fraction 0.05). Expired NO was measured continuously. Addition of free Hb to the perfusate (0.25 mg/ml) resulted in augmentation of HPV and a fall in expired NO that were similar in magnitude to those associated with a hematocrit of 30% (intracellular Hb of 100 mg/ml). Addition of dextran resulted in a blunting of HPV after free Hb but no change in expired NO. Blunting of HPV by dextran was not prevented by NO synthase inhibition with N(omega)-nitro-L-arginine and/or cyclooxygenase inhibition. RBC ghosts had a mild inhibitory effect on HPV but caused a small reduction in expired NO. In conclusion, the RBC membrane provides a barrier to NO scavenging and augmentation of HPV by Hb. Increased perfusate viscosity inhibits HPV by an undetermined mechanism.

Topics: Animals; Cyclooxygenase Inhibitors; Dextrans; Erythrocyte Membrane; Hemoglobins; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Perfusion; Pulmonary Circulation; Rabbits; Respiration; Vasoconstriction; Viscosity

To investigate the mechanisms involved in hypoxic vasodilation using an in vitro setup.. Retinal arteries with and without retinal tissue were mounted on a wire myograph. The segments were contracted with prostaglandin (PG)F(2alpha) (30 microM) or 120 mM K(+). Hypoxia was induced by replacement of O(2) by N(2) in the gas used to bubble the Krebs-Ringer bicarbonate organ bath solution.. Hypoxia induced complete relaxation of preparations with adherent retinal tissue contracted with PGF(2alpha). Preparations without retinal tissue were not affected by the change in oxygenation. When the retinal arteries were contracted with 120 mM K(+), hypoxia no longer induced relaxation of the preparation with adherent retinal tissue. The presence of an NO-synthase inhibitor (L-NA, 0.1 mM), a cyclooxygenase inhibitor (indomethacin, 50 microM), or an adenosine receptor antagonist (8-sulfophenyltheophylline, 1 mM) did not affect hypoxic vasodilation. Excitatory amino acids and lactate had no or only a limited effect on the PGF(2alpha)-induced contraction and are therefore unlikely mediators of hypoxic vasodilation. HCl (10 mM) reduced the pH to 6.1 +/- 0.08 (n = 4) and induced a pronounced but transient relaxation of the retinal artery contracted with PGF(2alpha) or 120 mM K(+), whereas hypoxia induced relaxation of the retinal artery contracted with PGF(2alpha) only in the presence of adherent retinal tissue.. Adherent retinal tissue mediates the hypoxic vasodilatation of bovine retinal arteries in vitro. Neither NO, prostanoids, adenosine, excitatory amino acids lactate or changes in pH seem to be involved in this hypoxic response.

Topics: Animals; Cattle; Cyclooxygenase Inhibitors; Dinoprost; Electromyography; Eye Proteins; Hydrogen-Ion Concentration; Hypoxia; Indomethacin; Muscle Proteins; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Purinergic P1 Receptor Antagonists; Retina; Retinal Artery; Theophylline; Vasodilation

In order to investigate the role of nitric oxide (NO) in hypoxic tissue damage in newborns, we studied the effects of systemic administration of an inhibitor of NO synthase, N(G)-nitro-L-arginine (L-NNA), and the precursor for the synthesis of NO, L-arginine (L-ARG), on the biochemical and histological changes in brain, heart, lung, liver, kidney, intestine, and skeletal muscle tissues. Four groups of 1-day-old Wistar rat pups were used: control, hypoxic, L-ARG, and L-NNA groups. L-ARG 100 mg/kg or L-NNA 2 mg/kg was administered as a bolus intraperitoneally 1.5 h before hypoxia. Hypoxia increased lipid peroxidation in all tissues except muscle; this increase was prevented by L-NNA and L-ARG in brain, heart, lung, kidney, and liver tissues. L-NNA in intestine and L-ARG in muscle tissue increased lipid peroxidation. The tissue-associated myeloperoxidase activity was decreased in the liver by L-NNA and L-ARG. Histopathological changes in intestines were villous epithelial separation and hyperemia in hypoxic and L-NNA groups which were not observed in control and L-ARG groups. In lungs, pulmonary hemorrhage was observed only in the hypoxic group. These data suggest that NO acts both as a destructive and a protective agent in the pathogenesis of hypoxia-reoxygenation injuries.

Topics: Animals; Animals, Newborn; Arginine; Enzyme Inhibitors; Hypoxia; Intestinal Mucosa; Intestines; Lipid Peroxides; Liver; Lung; Muscle, Skeletal; Nitric Oxide; Nitroarginine; Peroxidase; Rats; Rats, Wistar; Thiobarbituric Acid Reactive Substances

Previous studies suggest that inducible (i) nitric oxide synthase (NOS) expression within the pulmonary vasculature is increased in rats with chronic hypoxia (CH)-induced pulmonary hypertension. We therefore hypothesized that enhanced iNOS expression associated with CH causes attenuated pulmonary vasoconstrictor responsiveness. To test this hypothesis, we examined the effect of selective iNOS blockade with L-N6-(1-iminoethyl)lysine dihydrochloride (L-NIL) and nonselective NOS inhibition with Nomega-nitro-L-arginine (L-NNA) on vasoconstrictor responses to U-46619 in isolated saline-perfused lungs from both control and CH (4 wk at 380 mmHg) rats. We additionally measured pulmonary hemodynamic responses to L-NIL in conscious CH rats (fraction of inspired O2 = 0.12). Finally, iNOS mRNA levels were assessed in lungs from each group of rats using ribonuclease protection assays. Despite a significant increase in iNOS mRNA expression after exposure to CH, responses to U-46619 were unaltered by L-NIL but augmented by L-NNA in lungs from both control and CH rats. Pulmonary hemodynamics were similarly unaltered by L-NIL in conscious CH rats. We conclude that iNOS does not modulate pulmonary vasoconstrictor responsiveness after long-term hypoxic exposure.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Chronic Disease; Enzyme Inhibitors; Hemodynamics; Hypoxia; In Vitro Techniques; Lipopolysaccharides; Lung; Lysine; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents

Endothelial nitric oxide (NO) synthase (eNOS) mRNA and protein and NO production are increased in hypoxia-induced hypertensive rat lungs, but it is uncertain whether eNOS gene expression and activity are increased in other forms of rat pulmonary hypertension. To investigate these questions, we measured eNOS mRNA and protein, eNOS immunohistochemical localization, perfusate NO product levels, and NO-mediated suppression of resting vascular tone in chronically hypoxic (3-4 wk at barometric pressure of 410 mmHg), monocrotaline-treated (4 wk after 60 mg/kg), and fawn-hooded (6-9 mo old) rats. eNOS mRNA levels (Northern blot) were greater in hypoxic and monocrotaline-treated lungs (130 and 125% of control lungs, respectively; P < 0.05) but not in fawn-hooded lungs. Western blotting indicated that eNOS protein levels increased to 300 +/- 46% of control levels in hypoxic lungs (P < 0.05) but were decreased by 50 +/- 5 and 60 +/- 11%, respectively, in monocrotaline-treated and fawn-hooded lungs (P < 0.05). Immunostaining showed prominent eNOS expression in small neomuscularized arterioles in all groups, whereas perfusate NO product levels increased in chronically hypoxic lungs (3.4 +/- 1.4 microM; P < 0.05) but not in either monocrotaline-treated (0.7 +/- 0.3 microM) or fawn-hooded (0.45 +/- 0.1 microM) lungs vs. normotensive lungs (0.12 +/- 0.07 microM). All hypertensive lungs had increased baseline perfusion pressure in response to nitro-L-arginine but not to the inducible NOS inhibitor aminoguanidine. These results indicate that even though NO activity suppresses resting vascular tone in pulmonary hypertension, there are differences among the groups regarding eNOS gene expression and NO production. A better understanding of eNOS gene expression and activity in these models may provide insights into the regulation of this vasodilator system in various forms of human pulmonary hypertension.

Topics: Animals; Enzyme Inhibitors; Guanidines; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; In Vitro Techniques; Male; Monocrotaline; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Pulmonary Circulation; Rats; Rats, Mutant Strains; Rats, Sprague-Dawley; RNA, Messenger; Tissue Distribution; Vasomotor System

Neuroprotection against cerebral ischemia can be realized if the brain is preconditioned by previous exposure to a brief period of sublethal ischemia. The present study was undertaken to test the hypothesis that nitric oxide (NO) produced from the neuronal isoform of NO synthase (NOS) serves as a necessary signal for establishing an ischemia-tolerant state in brain. A newborn rat model of hypoxic preconditioning was used, wherein exposure to sublethal hypoxia (8% oxygen) for 3 hours renders postnatal day (PND) 6 animals completely resistant to a cerebral hypoxic-ischemic insult imposed 24 hours later. Postnatal day 6 animals were treated 0.5 hour before preconditioning hypoxia with the nonselective NOS inhibitor L-nitroarginine (2 mg/kg intraperitoneally). This treatment, which resulted in a 67 to 81% inhibition of calcium-dependent constitutive NOS activity 0.5 to 3.5 hours after its administration, completely blocked preconditioning-induced protection. However, administration of the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg intraperitoneally) before preconditioning hypoxia, which decreased constitutive brain NOS activity by 58 to 81%, was without effect on preconditioning-induced cerebroprotection, as was pretreatment with the inducible NOS inhibitor aminoguanidine (400 mg/kg intraperitoneally). The protective effects of preconditioning were also not blocked by treating animals with competitive [3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate; 5 mg/kg intraperitoneally] or noncompetitive (MK-801; 1 mg/kg intraperitoneally) N-methyl-D-aspartate receptor antagonists prior to preconditioning hypoxia. These findings indicate that NO production and activity are critical to the induction of ischemic tolerance in this model. However, the results argue against the involvement of the neuronal NOS isoform, activated secondary to a hypoxia-induced stimulation of N-methyl-D-aspartate receptors, and against the involvement of the inducible NOS isoform, but rather suggest that NO produced by the endothelial NOS isoform is required to mediate this profound protective effect.

Topics: Animals; Animals, Newborn; Brain Ischemia; Calcium; Dizocilpine Maleate; Enzyme Inhibitors; Guanidines; Hypoxia; Indazoles; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Nitroarginine; Oxygen; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

An enhanced peripheral chemoreflex has been documented in patients with chronic heart failure (CHF). This study aimed to examine the characteristics of carotid body (CB) chemoreceptors in response to isocapnic hypoxia in a rabbit model of pacing-induced CHF and to evaluate the possible role that nitric oxide (NO) plays in the altered characteristics. The chemosensitive characteristics of the CB were evaluated by recording single-unit activity from the carotid sinus nerve in both an intact and a vascularly isolated preparation. It was found that the baseline discharge under normoxia (intact preparation: arterial PO2 90-95 Torr; isolated preparation: PO2 100-110 Torr) and the chemosensitivity in response to graded hypoxia (PO2 40-70 Torr) were enhanced in CHF vs. sham rabbits. These alterations were independent of the CB preparations (intact vs. isolated). NO synthase inhibition by Nomega-nitro-L-arginine increased the baseline discharge and the chemosensitivity in the intact preparation, whereas L-arginine (10(-5) M) inhibited the baseline discharge and the chemosensitivity in the isolated preparation in sham but not in CHF rabbits. S-nitroso-N-acetylpenicillamine, an NO donor, inhibited the baseline discharge and the chemosensitivity in both CB preparations in CHF rabbits but only in the isolated preparation in sham rabbits. The amount of NO produced in vitro by the CB under normoxia was less in CHF rabbits than in sham rabbits (P < 0.05). NO synthase-positive varicosities of nerve fibers within the CB were less in CHF rabbits than in sham rabbits (P < 0.05). These data indicate that an enhanced input from CB occurs in the rabbit model of pacing-induced CHF and that an impairment of NO production may contribute to this alteration.

Topics: Animals; Arginine; Carbon Dioxide; Cardiac Pacing, Artificial; Carotid Body; Chemoreceptor Cells; Disease Models, Animal; Heart Failure; Hypoxia; Male; Nitric Oxide Synthase; Nitroarginine; Oxygen; Partial Pressure; Rabbits

Since recent studies show that pial artery dilation during a 20 or 40 min hypoxic exposure was less than that observed during a 5 or 10 min exposure, stimulus duration determines the nature of the vascular response to hypoxia. Decremented hypoxic pial dilation during longer exposure periods results, at least in part, from decreased release of methionine enkephalin (Met), an opioid known to contribute to dilation during hypoxia. Nitric oxide and cGMP contribute to both release and the vascular response to this opioid. The present study was designed to determine if the stimulus duration modulates the interaction between opioids and NO in hypoxic pial dilation using newborn pigs equipped with a closed cranial window. Elevation of CSF cGMP during hypoxia (Po2 approximately 35 mmHg) was dependent on stimulus duration (435+/-31, 934+/-46, 747+/-25, and 623+/-17 fmol/ml cGMP during normoxia and after 10, 20, and 40 min of hypoxia). Met-induced pial dilation during hypoxia was also stimulus duration dependent (7+/-1, 10+/-1, and 15+/-1, vs. 4+/-1, 6+/-1, and 8+/-2 vs. 2+/-1, 3+/-1, and 5+/-1% for 10(-10), 10(-8), 10(-6) M Met during normox and after 20, and 40 min of hypoxia). Additionally, the release of cGMP by Met during hypoxia was also stimulus duration dependent (1.8+/-0.1 vs. 1.6+/-0.1 vs. 1.3+/-0.1 fold change in CSF cGMP for 10(-8) M Met during normoxia and after 20 and 40 min of hypoxia). These data indicate that the diminished role of Met in pial dilation during longer hypoxic exposure periods results from a diminished capacity of this opioid to elicit dilation. Such impaired dilation is correlated with diminished stimulated cGMP release. These data also suggest that diminished CSF cGMP release during prolonged hypoxia contributes to decreased release of Met during longer hypoxic periods. Therefore, stimulus duration modulates the interaction between opioids and NO in hypoxic pial artery dilation.

Topics: Animals; Animals, Newborn; Blood Gas Analysis; Blood Pressure; Cerebral Arteries; Cyclic GMP; Enkephalin, Methionine; Female; Hydrogen-Ion Concentration; Hypoxia; Hypoxia, Brain; Male; Nitric Oxide; Nitroarginine; Pia Mater; Swine; Vasodilation

Cyclooxygenase (COX) products and nitric oxide (NO) inhibit hypoxic pulmonary vasoconstriction (HPV), and their release could contribute to alterations in gas exchange in lung injury. We tested the hypothesis that combined blockade of COX and NO synthase (NOS) could further increase HPV and better protect gas exchange in lung injury than could blockade of either COX or NOS alone. We determined pulmonary vascular pressure-flow relationships in pentobarbital-anesthetized and ventilated dogs submitted to hypoxic challenges before and after administration of solvent (n = 4), indomethacin alone (2 mg/kg intravenously, n = 8), Nomega-nitro-L-arginine (L-NA) alone (10 mg/kg intravenoulsy, n = 8), indomethacin followed by L-NA (n = 8), and L-NA followed by indomethacin (n = 8). All of the dogs so treated then received oleic acid (0.06 ml/kg intravenously) to induce lung injury. Blood flow was manipulated by establishing a femoral arteriovenous bypass or by inflating an inferior vena caval balloon. Gas exchange was evaluated by measuring arterial PO2 and intrapulmonary shunt (using the inert gas sulfur hexafluoride) at identical cardiac outputs. The magnitude of HPV was not affected by solvent. Indomethacin and L-NA given separately enhanced HPV. L-NA added to indomethacin further enhanced HPV, as did indomethacin added to L-NA. After oleic acid-induced lung injury, gas exchange deteriorated less in dogs pretreated with indomethacin than in dogs pretreated with solvent or with L-NA alone. These results suggest that in pentobarbital-anesthetized dogs: (1) the magnitude of HPV is limited by the corelease of COX metabolites and of NO; and (2) inhibition of COX, but not of NOS, attenuates the deterioration of gas exchange in oleic acid-induced lung injury.

Topics: Animals; Blood Pressure; Cyclooxygenase Inhibitors; Dogs; Enzyme Inhibitors; Hypoxia; Indomethacin; Lung Diseases; Nitric Oxide Synthase; Nitroarginine; Oleic Acid; Pulmonary Circulation; Vasoconstriction

The in vitro responses to ACh, flow, and hypoxia were studied in arterioles isolated from the diaphragms of rats. The endothelium was removed in some vessels by low-pressure air perfusion. In endothelium-intact arterioles, pressurized to 70 mmHg in the absence of luminal flow, ACh (10(-5) M) elicited dilation (from 103 +/- 10 to 156 +/- 13 microm). The response to ACh was eliminated by endothelial ablation and by the nitric oxide synthase antagonists NG-nitro-L-arginine (L-NNA; 10(-5) M) and NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) but not by indomethacin (10(-5) M). Increases in luminal flow (5-35 microl/min in 5 microl/min steps) at constant distending pressure (70 mmHg) elicited dilation (from 98 +/- 8 to 159 +/- 12 microm) in endothelium-intact arterioles. The response to flow was partially inhibited by L-NNA, L-NAME, and indomethacin and eliminated by endothelial ablation and by concurrent treatment with L-NAME and indomethacin. The response to hypoxia was determined by reducing the periarteriolar PO2 from 100 to 25-30 Torr by changing the composition of the gas used to bubble the superfusing solution. Hypoxia elicited dilation (from 110 +/- 9 to 165 +/- 12 microm) in endothelium-intact arterioles but not in arterioles from which the endothelium had been removed. Hypoxic vasodilation was eliminated by treatment with indomethacin and was not affected by L-NAME or L-NNA. In rat diaphragmatic arterioles, the response to ACh is dependent on endothelial nitric oxide release, whereas the response to hypoxia is mediated by endothelium-derived prostaglandins. Flow-dilation requires that both nitric oxide and cyclooxygenase pathways be intact.

Topics: Acetylcholine; Animals; Anti-Inflammatory Agents, Non-Steroidal; Arterioles; Diaphragm; Enzyme Inhibitors; Hypoxia; Indomethacin; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Oxygen Consumption; Prostaglandins; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Vasodilation

Excess neuronal nitric oxide (NO) production might cause adenosine triphosphate loss and cellular damage in hypoxic brain parenchyma. 31P nuclear magnetic resonance spectroscopy was used to study hypoxic intracellular responses in perfused respiring cerebrocortical slices, in which NO scavenging by hemoglobin is absent, during NO synthase blockade and NO augmentation.. Adenosine triphosphate concentrations were monitored at 4.7 Tesla in respiring slices before, during, and after 60 min of hypoxia (oxygen tension < 5 mmHg). Slices were not treated or were pretreated with 27 microM L-nitroarginine methyl ester (L-NAME), 27 microM 7-nitroindozole (7-NI), or 27 microM L-nitroarginine. Nitrotyrosine:tyrosine ratios of slice extracts were measured using high-performance liquid chromatography. Cresyl violet-stained sections (2 microm) from random slices were examined histologically.. After 60 min of hypoxia, adenosine triphosphate decreased to < or = 3, < or = 3, 65 +/- 6, and 25 +/- 4% of control in slices that were untreated or treated with L-nitroarginine, L-NAME, and 7-NI, respectively. After 120 min of hyperoxic recovery, adenosine triphosphate levels returned to control values in slices pretreated with L-NAME and 7-NI, but to only 30% of control in untreated or L-nitroarginine-treated slices. Nitric oxide donors administered during posthypoxic recovery partially antagonized the adenosine triphosphate recovery found with L-NAME and 7-NI. Nitric oxide synthase activity in slice homogenates, assayed via conversion of L-arginine to citrulline, was < or = 2% of control after all inhibitory treatments. The nitrotyrosine:tyrosine ratio increased by 52% in slices treated with 7-NI and by 200-300% in all other groups. Pretreatment with L-NAME and 7-NI reduced histologic evidence of cell swelling.. Neuronal NO is associated with rapid adenosine triphosphate reductions and peroxynitrite formation in acutely hypoxic cerebrocortical slices.

Topics: Adenosine Triphosphate; Animals; Cerebral Cortex; Enzyme Inhibitors; Hypoxia; Indazoles; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley

To evaluate whether nitric oxide (NO) plays a role in the mechanism of generation of cochlear dysfunction induced by anoxia and reperfusion, the effects of a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine, were examined using 71 albino guinea pigs. Transient cochlear anoxia of different duration (15, 30 or 60 min) was induced by pressing the labyrinthine artery and compound action potential (CAP) was measured before and 4 h after anoxia. N-nitro-L-arginine (1-30 mg/kg) administered intraperitoneally 1 h before the onset of anoxia alleviated the cochlear dysfunction when the anoxic period was 15 or 30 min. No beneficial effect was observed, however, in the 60-min anoxia. These results indicate that NO contributes to the generation of anoxia-induced cochlear dysfunction and that NOS inhibitor has a protective effect on the cochlear injury induced by anoxia of moderate duration.

Topics: Action Potentials; Animals; Cochlea; Enzyme Inhibitors; Guinea Pigs; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Time Factors

In lungs from chronically hypoxic (CH, 3 weeks at 10% inspired O2) rats, oxygenation (20% O2, 5% CO2, 75% N2; PO2 121 mmHg) of the perfusate increases pulmonary perfusion pressure (PPP) and lung weight (LW). Hypoxic perfusate (95% N2, 5% CO2; PO2 5.5 mmHg) had no effect on PPP in lungs from CH rats. Indomethacin and nitro-L-arginine (L-NOARG) augmented the oxygen-induced increase in PPP. In contrast, the free radical scavengers superoxide dismutase (SOD) plus catalase delayed the onset of oxygen-induced vasoconstriction, while the endothelin (ET)B receptor antagonist BQ788 inhibited it. The ET(A) receptor antagonist BQ123 did not affect the PPP changes. This suggests a role for endogenous endothelins and ET(B) receptors in mediating the oxygenation-induced pulmonary vasoconstriction. Indomethacin had no effect on oxygen-induced lung weight (LW) changes while BQ788 and L-NOARG reduced the LW increase. This evidence shows that ET(B) receptor activation and NO generation are involved in the LW changes. In conclusion, oxygenation of the perfusate in isolated lungs from CH rats leads to pulmonary vasoconstriction which involves endothelins and activation of ET(B) receptors. In addition, increased NO production associated with ET(B) receptor activation is the prime stimulus for observed LW increase.

Topics: Adrenergic alpha-Antagonists; Animals; Chronic Disease; Cyclooxygenase Inhibitors; Endothelin Receptor Antagonists; Endothelins; Free Radical Scavengers; Hypoxia; In Vitro Techniques; Indomethacin; Lung; Male; Nitroarginine; Oxygen; Perfusion; Pressure; Pulmonary Artery; Rats; Rats, Wistar; Vasoconstriction

Intact Madison (M) rats have greater pulmonary pressor responses to acute hypoxia than Hilltop (H) rats. We tested the hypothesis that the difference in pressor response is intrinsic to pulmonary arteries and that endothelium contributes to the difference. Pulmonary arteries precontracted with phenylephrine (10(-7) M) from M rats had greater constrictor responses [hypoxic pulmonary vasoconstriction (HPV)] to acute hypoxia (0% O(2)) than those from H rats: 473 +/- 30 vs. 394 +/- 29 mg (P < 0.05). Removal of the endothelium or inhibition of nitric oxide (NO) synthase by N(omega)-nitro-L-arginine (L-NA, 10(-3) M) significantly blunted HPV in both strains. Inhibition of cyclooxygenase by meclofenamate (10(-5) M) or blockade of endothelin type A and B receptors by BQ-610 (10(-5) M) + BQ-788 (10(-5) M), respectively, had no effect on HPV. Constrictor responses to phenylephrine, endothelin-1, and prostaglandin F(2alpha) were similar in pulmonary arteries from both strains. The relaxation response to ACh, an NO synthase stimulator, was significantly greater in M than in H rats (80 +/- 3 vs. 62 +/- 4%, P < 0.01), but there was no difference in response to sodium nitroprusside, an NO donor. L-NA potentiated phenylephrine-induced contraction to a greater extent in pulmonary arteries from M than from H rats. These findings indicate that at least part of the strain-related difference in acute HPV is attributable to differences in endothelial function, possibly related to differences in NO production.

Topics: Animals; Blood Pressure; Cyclooxygenase Inhibitors; Endothelin Receptor Antagonists; Endothelium, Vascular; Enzyme Inhibitors; Hypoxia; In Vitro Techniques; Male; Meclofenamic Acid; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oligopeptides; Piperidines; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Species Specificity; Vasoconstriction

Hypoxia causes a regulated decrease in body temperature (T(b)), and nitric oxide (NO) is now known to participate in hypoxia-induced hypothermia. Hypoxia also inhibits lipopolysaccharide (LPS)-induced fever. We tested the hypothesis that NO may participate in the hypoxia inhibition of fever. The rectal temperature of awake, unrestrained rats was measured before and after injection of LPS, with or without concomitant exposure to hypoxia, in an experimental group treated with N(omega)-nitro-L-arginine (L-NNA) for 4 consecutive days before the experiment and in a saline-treated group (control). L-NNA is a nonspecific NO synthase inhibitor that blocks NO production. LPS caused a dose-dependent typical biphasic rise in T(b) that was completely prevented by hypoxia (7% inspired oxygen). L-NNA caused a significant drop in T(b) during days 2-4 of treatment. When LPS was injected into L-NNA-treated rats, inhibition of fever was observed. Moreover, the effect of hypoxia during fever was significantly reduced. The data indicate that the NO pathway plays a role in hypoxia inhibition of fever.

Topics: Animals; Body Temperature; Enzyme Inhibitors; Fever; Hypoxia; Lipopolysaccharides; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar

Red blood cells (RBCs) are known to augment hypoxic pulmonary vasoconstriction (HPV). To determine whether this phenomenon is hematocrit (Hct) dependent and related to alterations of either nitric oxide (NO) or adenosine metabolism, we studied mechanically ventilated, pump-perfused lungs from euthanized New Zealand White rabbits. Lungs were perfused in situ in a recirculating manner at constant flow; perfusates consisted of Krebs-Henseleit buffer or buffer plus washed RBCs at a Hct of 10% or 30%. HPV was quantitated as the increase in pulmonary artery pressure (Ppa) from baseline after 5 min of hypoxia. In three experimental sets, we studied the effects of Hct on HPV and expired NO, the effects of nitric oxide synthase (NOS) inhibition, and the effects of adenosine receptor blockade. HPV was greater at a higher Hct, and expired NO varied inversely with Hct and decreased with hypoxia. NOS inhibition eliminated RBC-dependence of HPV. Adenosine-receptor blockade did not affect the RBC-dependence of HPV. We conclude that HPV is dependent on Hct, and that this phenomenon may be related to scavenging of NO but not adenosine by RBCs.

Topics: Adenosine; Animals; Erythrocytes; Hematocrit; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Purinergic P1 Receptor Antagonists; Rabbits; Vasoconstriction

The effects of agents which affect the action of nitric oxide (NO) were studied intracellularly on the ischemia-induced changes in membrane potential of single CA1 pyramidal neurons of the rat hippocampal slice preparations. The N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 250 microM) or Co2 (2 mM) restored the membrane potential in more than 80% of the neurons. In about 60% of the neurons, the membrane potential was partially recovered as a result of exposure to the NO synthase inhibitor, NG-nitro-L-arginine (100 microM). The NO scavengers, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO, 300 microM) and hemoglobin (10 microM) restored the membrane potential in all neurons examined. Superoxide dismutase (50 U/ml) protected about 75% of the neurons from irreversible membrane dysfunction. It is concluded that the release of NO induced by experimental ischemia may result in the irreversible membrane dysfunction, and that a NO scavenger, carboxy-PTIO, prevents the ischemic changes in membrane potential. With respect to ischemic brain damage, the neuroprotection provided by carboxy-PTIO may have clinical relevance in the management of a variety of neurological conditions.

Topics: 2-Amino-5-phosphonovalerate; Animals; Benzoates; Cell Membrane; Cobalt; Glucose; Hemoglobins; Hippocampus; Hypoxia; Imidazoles; In Vitro Techniques; Ischemic Attack, Transient; Male; Membrane Potentials; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pyramidal Cells; Rats; Rats, Wistar; Reaction Time; Receptors, N-Methyl-D-Aspartate; Superoxide Dismutase

This study was designed to investigate the potential role of endogenous peroxynitrite (ONOO-) formation in the inhibition of cardiac muscle contractility and mitochondrial respiration during posthypoxic reoxygenation. Isometric contraction of isolated rat left ventricular posterior papillary muscle was virtually eliminated at the end of an exposure to 15 minutes of hypoxia and remained 40+/-5% depressed an hour after the reintroduction of O2. O2 uptake by rat left ventricular cardiac muscle, measured by a Clark-type O2 electrode, was also inhibited by 24+/-2% at 10 minutes after reoxygenation. The inhibition of contractility and respiration during posthypoxic reoxygenation was markedly attenuated by the NO synthase inhibitor nitro-L-arginine, exogenous superoxide dismutase, and the ONOO- scavenger urate but not by the hydroxyl radical scavenger mannitol. Generation of ONOO- with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) plus the superoxide-releasing agent pyrogallol caused an irreversible inhibition of cardiac contractile and respiratory function. Unlike ONOO-, exogenous (SNAP) and endogenous (bradykinin) sources of NO inhibited contractility in a reversible manner. Under conditions of comparable amounts of respiratory inhibition in unstimulated incubated muscle, the NO-dependent agents and the mitochondrial antagonist NaCN produced a smaller degree of suppression of contractility compared with ONOO- and posthypoxic reoxygenation. These results are consistent with a contributing role for endogenous ONOO- formation in the inhibition of cardiac muscle contractility and mitochondrial respiration during posthypoxic reoxygenation.

Topics: Animals; Bradykinin; Cyclic GMP; Free Radical Scavengers; Hydroxyl Radical; Hypoxia; In Vitro Techniques; Kinetics; Mannitol; Mitochondria, Heart; Myocardial Contraction; Nitrates; Nitric Oxide; Nitroarginine; Oxidants; Oxygen Consumption; Penicillamine; Rats; S-Nitroso-N-Acetylpenicillamine; Sodium Cyanide; Superoxide Dismutase

Greater release of endothelium-derived nitric oxide is implicated in the superior patency of the internal mammary artery (IMA) used in coronary artery bypass grafting. This study compared the release of endothelium-derived nitric oxide into the lumen of the IMA and the saphenous vein under normoxic versus hypoxic conditions.. Segments of canine IMA and saphenous vein were perfused in vitro. Vasorelaxant activity was measured as vasodilatation of coronary artery smooth muscle induced by the effluent.. Effluents from the IMA and saphenous vein caused comparable vasodilation of coronary artery smooth muscle. The vasodilatation reversed when perfusion was switched to a prosthetic conduit. Vasodilator activity from the IMA and saphenous vein was attenuated by removing the intima of the grafts or by adding N(G)-monomethyl-L-arginine (10(-4) mol/L) or N(G)-nitro-L-arginine (10(-4) mol/L), two inhibitors of nitric oxide synthesis. Indomethacin attenuated vasorelaxant activity from saphenous vein grafts but not IMA grafts (n = 10). Vasodilator release from the IMA and saphenous vein was augmented by hypoxia. This augmentation was inhibited by indomethacin (n = 10, p < 0.05). Hypoxic augmentation reversed with return to normoxia.. The release of endothelium-derived nitric oxide and prostacyclin from bypass grafts into the lumen, particularly during hypoxemia, could promote the vasodilation of distal coronary arterial beds, enhancing myocardial perfusion.

Topics: Animals; Coronary Artery Bypass; Coronary Circulation; Cyclooxygenase Inhibitors; Dogs; Endothelium, Vascular; Enzyme Inhibitors; Epoprostenol; Hypoxia; Indomethacin; Mammary Arteries; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; omega-N-Methylarginine; Platelet Aggregation Inhibitors; Saphenous Vein; Tunica Intima; Vascular Patency; Vasodilation

We studied the role of nitric oxide (NO) on the regulation of blood flow in the immature kidney during hypoxia, resuscitation and the recovery period using the NO inhibitor N(omega)-nitro-L-arginine (L-NNA) in a newborn piglet model, and the possibility of urinary cGMP as an index of renal function. After administration of L-NNA, the blood flow in both the cortex and medulla significantly decreased, indicating that NO is constantly released to maintain renal circulation. During hypoxia, the renal blood flow fell remarkably, and there were no differences between the control and L-NNA groups. During the post-resuscitation period, the recovery of renal blood flow was significantly suppressed in L-NNA administration, and it was speculated that NO might be an important factor for recovery of circulation from vasoconstriction due to hypoxemia. Urinary cGMP/cr was significantly increased on recovery from hypoxemia and was suppressed by L-NNA administration. This result suggested that the change in cGMP/cr represents renal blood flow change. We conclude that NO may play an important role in maintaining basal hemodynamics, and may also be a crucial factor for recovery from post-hypoxic vasoconstriction in premature kidneys. Urinary cGMP/cr might serve as one of the indices for assessment of premature renal circulation.

Topics: Animals; Animals, Newborn; Cyclic GMP; Enzyme Inhibitors; Hypoxia; Nitric Oxide; Nitroarginine; Reference Values; Renal Circulation; Swine

Elevated levels of the potent vasoactive peptide endothelin (ET), have been found in pathophysiological conditions associated with pulmonary hypertension. In this study, we have investigated the effects of the ETA receptor antagonist, BMS-182874, on hypoxic pulmonary hypertension in pigs.. Pigs were subjected to acute, intermittent 15-min periods of hypoxia (FiO2 0.1). Following a first hypoxia establishing hypoxic baseline values, vehicle or BMS-182874 (10 or 30 mg/kg) was administered i.v. before a second hypoxic period. In separate groups of animals, the effects of the nitric oxide synthase inhibitor N omega-nitro-L-arginine (L-NNA) in combination with BMS-182874 (10 mg) during repeated hypoxia were investigated. The ET-1-blocking properties of BMS-182874 were studied in vivo by infusion of ET-1 during normoxia and in vitro using isolated porcine pulmonary arteries.. The hypoxia-evoked increase in mean pulmonary artery pressure was reduced by administration of BMS-182874 (10 mg/kg i.v.; from 42 +/- 8 to 34 +/- 4 mmHg, P < 0.05 and 30 mg/kg i.v.; from 38 +/- 4 to 30 +/- 5 mmHg, P < 0.05). In addition, BMS-182874 at 30 mg/kg reduced the pulmonary vascular resistance during hypoxia (from 7.4 +/- 1.5 to 5.3 +/- 1.1 mmHg.min.l-1 P < 0.05). The hemodynamic response to repeated hypoxia was reproducible in control animals and unaffected by the cyclo-oxygenase inhibitor diclophenac (3 mg/kg). Infusion of L-NNA alone resulted in an augmented pulmonary vasoconstriction during hypoxia; pulmonary arterial pressure from 35 +/- 6 to 43 +/- 9 mmHg; P < 0.05 and vascular resistance from 7.2 +/- 1.1 to 9.9 +/- 1.8 mmHg.min.l-1; P < 0.05. L-NNA in combination with BMS-182874 (10 mg/kg) resulted in a hypoxic pulmonary vasoconstriction of similar magnitude as hypoxic baseline. In addition, BMS-182874 reduced the hemodynamic response to ET-1 in normoxic pigs and competitively antagonized the vasoconstrictor effect of ET-1 in isolated porcine pulmonary arteries.. The non-peptide, selective ETA receptor antagonist, BMS-182874, reduces hypoxic pulmonary vasoconstriction in pigs. The reduction in pulmonary vascular response to hypoxia following BMS-182874 is at least partly independent of nitric oxide.

Topics: Animals; Antihypertensive Agents; Dansyl Compounds; Drug Synergism; Endothelin Receptor Antagonists; Endothelin-1; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Nitric Oxide Synthase; Nitroarginine; Pulmonary Artery; Swine

This study was designed to clarify the dependency of hypoxic coronary vasodilation (HCD) on the endothelium and the role of the K+ channels on HCD in the rabbit coronary artery. HCD was investigated in an isolated left circumflex coronary artery precontracted with prostaglandin F2 alpha. Vascular rings were suspended for isometric tension recording in an organ chamber filled with Krebs-Henseleit (KH) solution. Hypoxia was induced by gassing the chamber with 95% N2 + 5% CO2 and was maintained for 15 approximately 25 min. Hypoxia elicited a vasodilation in the precontracted coronary artery with and without endothelium. There was no difference between the amplitude of the HCD induced by two consecutive hypoxic challenges and the effects of 20% O2 + 5% CO2 + 75% N2 and 95% O2 + 5% CO2 control K-H solution of subsequent responses to hypoxia. Inhibition of the cyclooxygenase pathway by treatment with indomethacin had no effect on HCD. Blockades of the tetraethylammonium chloride-sensitive K+ channel abolished HCD. Apamin, a blocker of the small conductance Ca(2+)-activated K+ (KCa) channel, and iberiotoxin, a blocker of the large conductance KCa channel had no effect on HCD, respectively. Glibenclamide, a blocker of the ATP-sensitive K+ (K+ATP) channel, reduced HCD. Cromakalim, an opener of the K+ATP channel, relaxed the coronary artery precontracted with prostaglandin F2 alpha. The degree of relaxation by cromakalim was similar to that by hypoxia while glibenclamide reduced both hypoxia- and cromakalim-induced vasodilatations. In conclusion, these results suggest that HCD is independent on endothelium and HCD is considered to be induced by activation of K+ATP channel.

Topics: Animals; Coronary Vessels; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Female; Hypoxia; Indomethacin; Male; Nitroarginine; Rabbits; Tetraethylammonium; Vasodilation

Although hypoxic pulmonary vasoconstriction (HPV) has been recognized by many researchers, the precise mechanism remains unknown. As isolated pulmonary arteries will constrict in vitro in the response to hypoxia, the oxygen sensor/transduction mechanism must reside in the pulmonary arterial smooth muscle or in the endothelium, or in both. Unfortunately, much of the current evidence is conflicting, especially as to the dependency of HPV on the endothelium and the role of a K+ channel. Therefore, this experiment was attempted to clarify the dependency of HPV on the endothelium and the role of a K+ channel on HPV in rat pulmonary artery. The effects of hypoxia were investigated in isolated main pulmonary arteries precontracted with norepinephrine. Vascular rings were suspended for isometric tension recording in an organ chamber filled with a Krebs-Henseleit solution. Hypoxia was induced by gassing the chamber with 95% N2 + 5% CO2 and this was maintained for 20 min. Hypoxia elicited a vasoconstriction in arteries with endothelium. Mechanical disruption of the endothelium abolished HPV. There was no difference between the amplitude of the HPV induced by two consecutive hypoxic challenges and the effect of normoxic and hyperoxic control Krebs-Henseleit solution on a subsequent response to hypoxia. Inhibition of NO synthesis by treatment with N(omega)-nitro-L-arginine reduced HPV, but inhibition of a cyclooxygenase pathway by treatment with indomethacin had no effect on HPV. Blockades of a tetraetylammonium chloride-sensitive K+ channel abolished HPV. Verapamil, a Ca2+ entry blocker reduced HPV. In conclusion, these results suggest that HPV was dependent on the endothelium and that HPV can be considered to be induced by inhibition of the mechanisms of NO-dependent vasodilation such as the opening of a K+ channels.

Topics: Animals; Blood Vessels; Calcium Channel Blockers; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Hypoxia; Indomethacin; Nitroarginine; Pulmonary Circulation; Rats; Tetraethylammonium; Vasoconstriction; Verapamil

Although nitric oxide (NO) and calcium sensitive K+ channel (Kca) activation contribute to hypoxic pial artery dilation in the piglet, responses to the NO releasers SNP and SNAP are unchanged by the Kca channel antagonist iberiotoxin. These data suggest that NO does not elicit dilation via Kca channel activation. The present study was designed to determine if dilation by Kca channel activation is mediated by NO in newborn pigs equipped with a closed cranial window. NS1619 (10(-8), 10(-6) M), a Kca agonist, produced dilation that was unchanged by the NO synthase inhibitor, L-NNA (10(-6) or 10(-3) M) (11+/-1 and 20+/-1 vs. 11+/-1 and 18+/-1% before and after L-NNA 10(-3) M). NS1619 dilation also was not associated with increased CSF cGMP and was unchanged by Rp 8-Bromo cGMPs, a cGMP antagonist (9+/-1 and 17+/-1 vs. 9+/-1 and 16+/-2% before and after Rp 8-Bromo cGMPs 10(-5) M). Iberiotoxin (10(-7) M) attenuated hypoxic dilation but hypoxia associated CSF cGMP release was unchanged (418+/-11 and 897+/-31 vs. 419+/-10 and 896+/-25 fmol/ml for control and moderate hypoxia before and after iberiotoxin). Coadministration of L-NNA with iberiotoxin further decremented hypoxic pial dilation and blocked the hypoxia-associated rise in CSF cGMP. These data show that pial artery dilation by Kca channel activation is not mediated by NO/cGMP. Further, these data suggest that NO and the Kca channel act at different sites in their contributions to hypoxic pial artery dilation.

Topics: Animals; Arteries; Benzimidazoles; Cerebrovascular Circulation; Cyclic GMP; Endorphins; Enzyme Inhibitors; Female; Hypoxia; Intermediate-Conductance Calcium-Activated Potassium Channels; Male; Nitric Oxide; Nitroarginine; Pia Mater; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Calcium-Activated; Swine; Vasodilation

The role of nitric oxide (NO) in the regulation of sympathetic activity during hypoxia was studied in anesthetized pigs (n = 21). Hypoxia (fractional concentration of O2 in inspired air = 0.1) increased pulmonary arterial pressure and decreased arterial blood pressure and peripheral vascular resistance. Renal sympathetic nerve activity (RSNA) was moderately increased during hypoxia but decreased instantaneously on reoxygenation. Blockade of NO synthesis by NG-nitro-L-arginine (L-NNA, 0.3 mmol/l) administered to the ventral surface of the medulla oblongata (VLM) significantly enhanced RSNA increases induced by hypoxia and abolished the RSNA response to reoxygenation. Furthermore, L-NNA significantly reduced peripheral hypoxic vasodilation but did not affect pulmonary vasoconstriction. The inactive enantiomer D-NNA had no measurable effects at the same concentration. Actions of L-NNA were effectively counteracted by the NO donor S-nitroso-N-acetyl-penicillamine (0.1 mmol/l). Deafferentiation (carotid sinus and vagal nerves cut) abolished sympathetic responses to hypoxia and their modulation by NO. The results suggest that activation of peripheral chemoreceptors induces NO release in the VLM that buffers sympathoexcitation during hypoxia and contributes to sympathoinhibition during reoxygenation.

Topics: Animals; Blood Pressure; Cardiac Output; Heart Rate; Hemodynamics; Hypoxia; Infusions, Parenteral; Kidney; Medulla Oblongata; Nitric Oxide; Nitroarginine; Penicillamine; Pulmonary Artery; S-Nitroso-N-Acetylpenicillamine; Stereotaxic Techniques; Swine; Sympathetic Nervous System; Vascular Resistance

1. The aims of this study were to investigate the effects of potassium (K+) channel blockers and the nitric oxide (NO) synthase inhibitor, L-nitroarginine (L-NOARG), on the response produced by acute hypoxia in rat intrapulmonary artery rings in vitro. 2. In rat phenylephrine-precontracted pulmonary artery rings, hypoxia (pO2 = 7 mmHg) induced a response which consisted of a rapidly developing initial contraction (phase 1), a transient relaxation (phase 2) and a slowly developing sustained contraction (phase 3) over 30 min. The NOS inhibitor, L-NOARG (300 microM), attenuated phase 1 and 3, and amplified phase 2 of the response to hypoxia. The voltage-gated K+ channel blocker 4-aminopyridine (4-AP) (10 mM) also abolished phase 3 and magnified phase 2 of the response to hypoxia. 3. The hypoxic response was not modified by the calcium-activated K+ channel (KCa) blockers, tetraethylammonium (TEA) (20 mM) or charybdotoxin (50 or 200 nM), nor by the ATP-dependent K+ channel (KATP), blocker, glibenclamide (10 microM). 4. L-NOARG (300 microM) and 4-AP (10 mM) also abolished carbachol-induced endothelium-dependent NO-mediated relaxation. Relaxation produced by the NO releasing agent 3-morpholino sydnonimine (SIN-1) was reduced by 4-AP (10 mM) and TEA (20 mM). 5. The data suggest that NO production is reduced during severe hypoxia in rat intrapulmonary artery rings and that this underlies the sustained phase of the hypoxic contraction. The data also suggests that 4-AP-sensitive K+ channels play an important role in the release and or action of NO, and therefore, in the response to hypoxia.

Topics: Animals; Cell Hypoxia; Endothelium, Vascular; Enzyme Inhibitors; Hypoxia; In Vitro Techniques; Male; Molsidomine; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Potassium Channel Blockers; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Vasoconstriction; Vasodilation

Chronic hypoxic exposure has been previously demonstrated to attenuate systemic vasoconstrictor activity to a variety of agents. This attenuated responsiveness is observed not only in conscious animals but in isolated vascular preparations as well. Because hypoxia has been documented to increase heme oxygenase (HO) levels and the subsequent production of the vasodilator CO in vitro, we hypothesized that the blunted reactivity observed with chronic hypoxia (CH) may be in part due to increased HO activity. In thoracic aortic rings from CH rats, cumulative dose-response curves to phenylephrine (PE) in the presence of the nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine (L-NNA) and the HO inhibitor zinc protoporphyrin 9 (ZnPPIX) elicited increased contractility compared with CH rings treated with only L-NNA. Similar results were observed in rings incubated overnight with the HO-inducing agent sodium m-arsenite. In contrast, contractile responses in rings from control rats were unaffected by the HO inhibitor. Furthermore, endothelium-denuded rings from either control or CH rats did not exhibit an increase in reactivity to PE following ZnPPIX incubation. ZnPPIX had no effect on relaxant responses to the NO donor S-nitroso-N-penicillamine, suggesting that its actions were specific to HO inhibition. Finally, aortic rings exhibited dose-dependent relaxant responses to exogenous CO that were endothelium independent and blocked by an inhibitor of soluble guanylyl cyclase. The other products of HO enzyme activity, iron and biliverdin, were without effect on vasoreactivity. Thus we conclude that the attenuated vasoreactivity to PE following CH is likely to involve the induction of endothelial HO and the subsequent enhanced production of CO.

Topics: Animals; Aorta, Thoracic; Arsenites; Carbon Monoxide; Endothelium, Vascular; Enzyme Inhibitors; Guanylate Cyclase; Heme Oxygenase (Decyclizing); Hypoxia; In Vitro Techniques; Kinetics; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitroarginine; Oxadiazoles; Penicillamine; Phenylephrine; Protoporphyrins; Quinoxalines; Rats; Rats, Sprague-Dawley; Reference Values; S-Nitroso-N-Acetylpenicillamine; Sodium Compounds

Decreased contractile response to vasoconstrictors in uterine and nonuterine vessels contributes to increased blood flow to the uterine circulation during normal pregnancy. Pregnancies complicated by preeclampsia and/or chronic hypoxia show a reversal or diminution of these pregnancy-associated changes. We sought to determine whether chronic hypoxia opposes the reduction in contractile response in uterine and nonuterine vessels during normal pregnancy and, if so, whether decreased basal nitric oxide (NO) activity was involved. We examined the contractile response to phenylephrine (PE) in guinea pig uterine artery (UA), mesenteric artery (MA), and thoracic aorta (TA) rings isolated from nonpregnant or pregnant guinea pigs that had been exposed throughout gestation to either low (1,600 m, n = 47) or high (3,962 m, n = 43) altitude. In the UA, pregnancy reduced contractile sensitivity to PE and did so similarly at low and high altitude (EC50: 4.0 x 10(-8) nonpregnant, 9.3 x 10(-8) pregnant at low altitude; 4.8 x 10(-8) nonpregnant, 1.0 x10(-8) pregnant at high altitude; both P < 0.05). Addition of the NO synthase inhibitor nitro-L-arginine (NLA; 200 mM) to the vessel bath increased contractile sensitivity in the pregnant UA (P < 0.05) and eliminated the effect of pregnancy at both altitutes. NLA also raised contractile sensitivity in the nonpregnant high-altitude UA, but contractile response without NLA did not differ in the high- and low-altitude animals. In the MA, pregnancy decreased contractile sensitivity to PE at high altitude only, and this shift was reversed by NO inhibition. In the TA, neither pregnancy nor altitude affected contractile response, but NO inhibition raised contractile response in nonpregnant and pregnant TA at both altitudes. We concluded that pregnancy diminished contractile response to PE in the UA, likely as a result of increased NO activity, and that these changes were similar at low and high altitude. Counter to our hypothesis, chronic hypoxia did not diminish the pregnancy-associated reduction in contractile sensitivity to PE or inhibit basal NO activity in the UA; rather it enhanced, not diminished, basal NO activity in the nonpregnant UA and the pregnant MA.

Topics: Adrenergic alpha-Agonists; Altitude; Animals; Aorta, Thoracic; Enzyme Inhibitors; Female; Guinea Pigs; Humans; Hypoxia; In Vitro Techniques; Mesenteric Arteries; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylephrine; Pregnancy; Pregnancy Complications; Receptors, Adrenergic, alpha-1; Uterus; Vasoconstriction

Nitric oxide concentrations in the exhaled gas (NOe) increases during various inflammatory conditions in humans and animals. Little is known about the sources and factors that influence NOe. NOe at end expiration was measured by chemiluminescence in an isolated, blood-perfused rabbit lung. The average end-expiratory concentration over 10 breaths was used. The effect of positive end-expiratory pressure (PEEP), flow rate, pH, hypoxia, venous pressure, and flow pulsatility on NOe were determined. At constant blood flow, increasing PEEP from 1 to 5 cm H2O elicited a reproducible increase in NOe from 49 +/- 7 to 53 +/- 8 parts per billion (ppb) (p < 0.05). When blood pH was increased from 7.40 to 7.74 by breathing low CO2 gas, NOe rose from 45 +/- 7 to 55 +/- 7 ppb (p < 0.001). Hypoxia caused a dose-dependent decrease in NOe from 37 +/- 3 during baseline to 23 +/- 2 during ventilation with 0% O2 (p < 0.01). Venous pressure elevation from 0 to 5 and 10 mm Hg decreased NOe from 32 +/- 5, to 26 +/- 5 and 24 +/- 5 ppb, respectively (p < 0.05). Switching from steady to pulsatile flow (same man flow) resulted in a small, albeit significant reduction in NOe; 30 +/- 4 to 28 +/- 4 ppb (p < 0.05). Changes in flow rate between 200 and 20 ml/min were associated with small changes in NOe; however, when flow was stopped, NOe rose substantially to 56 +/- 6 ppb (p < 0.05). The changes in NOe were rapid (1 to 2 min) and reversible. The results suggest that NOe is influenced by ventilatory and hemodynamic variables, pH, and hypoxia. We suggest that caution must be taken when interpreting changes in exhaled NO in humans or experimental animals. Changes in total and regional blood flow, capillary blood volume, ventilation, hypoxia, and pH should not be overlooked.

Topics: Animals; Blood Pressure; Breath Tests; Enzyme Inhibitors; Hydrogen-Ion Concentration; Hypoxia; Luminescent Measurements; Lung; Nitric Oxide; Nitroarginine; Perfusion; Positive-Pressure Respiration; Pulsatile Flow; Rabbits; Regional Blood Flow; Respiration

We investigated the relationship between sensitivity to hypoxia and culture age in in vitro hippocampal neurons. Hypoxia was induced by 24 hr incubation in an oxygen-free environment. Up to 6 days in vitro (DIV) mortality was very low or negligible, with few exceptions. Starting at 7 DIV, significant mortality began to be observed; in the age range 7 10 DIV, mortality of 50% or more was observed in five out of 11 experiments (45%) and average mortality was 51 +/- 15% (mean +/- standard deviation, N = 11). In older (12 18 DIV) cultures, mortality of 50% or more was the rule (13 out of 13 experiments) and average mortality was 83 +/- 16% (mean +/- standard deviation, N = 13). The data could be fitted by a sigmoid line (r = 0.87, P < 10(-6) in which 50% mortality corresponds to 8.6 DIV. The N-methyl-D-aspartate antagonist amino-phosphono-valerate and the nitric oxide synthase inhibitor nitroarginine both provided protection. Degree of protection was comparable for the two compounds, but was not observed in cultures younger than approximately 7 DIV. By contrast exogenous creatine was not protective, at variance with findings from other models. The data represent the first description of how sensitivity to hypoxic damage varies during the lifetime of an in vitro neuronal hippocampal culture. Moreover, they suggest the hypothesis that some maturational changes occurring at 79 days in vitro may make previously resistant in vitro neurons significantly sensitive to hypoxic damage, and that at least some of these changes may reflect the development of N-methyl-D-aspartate-mediated glutamatergic transmission.

Topics: 2-Amino-5-phosphonovalerate; Animals; Disease Susceptibility; Embryo, Mammalian; Embryonic and Fetal Development; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Hypoxia; Neurons; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine; Rats; Time Factors

The ability of nitric oxide to enhance vesicular glutamate release during anoxia was examined in the present study. Whole-cell patch clamp recordings were obtained from CA1 pyramidal neurons in rat hippocampal slices perfused in media containing tetrodotoxin. These cells exhibit spontaneous inward currents previously identified as glutamatergic miniature excitatory postsynaptic currents (mEPSCs). The frequency of these mEPSCs increases during exposure to anoxia. The anoxia-induced increase in frequency is reduced when experiments are performed in the presence of the competitive nitric oxide (NO)-synthase inhibitors N(G)-nitro-L-arginine methyl ester and N(G)-nitro-L-arginine, as well as reduced hemoglobin. Arginine reversed the suppression by the NO-synthase inhibitors. The N-methyl-D-aspartate (NMDA) receptor antagonists 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid and MK-801 also suppressed the anoxia-induced increase in mEPSC frequency. These data indicate that NMDA receptor-activated NO production may enhance vesicular synaptic glutamate release, which would in turn contribute to excitotoxicity during hypometabolic states.

Topics: Animals; Electric Conductivity; Enzyme Inhibitors; Glutamic Acid; Hippocampus; Hypoxia; In Vitro Techniques; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Patch-Clamp Techniques; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Synapses

Perfusate levels of nitric oxide (NO)-containing compounds and guanosine 3',5'-cyclic monophosphate (cGMP) are increased in hypoxia-induced hypertensive rat lungs. To test if increased cGMP was due to NO stimulation of soluble guanylate cyclase (sGC), we examined effects of inhibition of NO synthase with N omega-nitro-L-arginine (L-NNA) on perfusate accumulation of cGMP in physiological salt solution (PSS)-perfused hypertensive lungs isolated from rats exposed for 3-4 wk to hypobaric hypoxia. Because 200 microM L-NNA did not reduce cGMP, we next examined inhibitors of other pathways of stimulation of either sGC or particulate GC (pGC). Neither 5 microM Zn-protophorphyrin, an inhibitor of CO production by heme oxygenase, nor 10 mM aminotriazole, an inhibitor of H2O2 metabolism by catalase, reduced perfusate cGMP. However, an antiserum to atrial natriuretic peptide (ANP; 100 microliters antiserum/30 ml PSS), to inhibit ANP activation of pGC, completely prevented accumulation of the nucleotide. ANP antiserum was also more effective than L-NNA in reducing lung tissue cGMP. In contrast, L-NNA but not ANP antiserum increased resting vascular tone. These results suggested that whereas ANP determined perfusate and tissue levels of cGMP, NO regulated vascular tone. To test if perfusate cGMP reflected ANP stimulation of pGC in endothelial rather than smooth muscle cells, we examined effects of 10 microM Zaprinast, an inhibitor of cGMP hydrolysis in smooth muscle but not endothelial cells, and found no increase of cGMP in hypertensive lungs. ANP levels were not elevated in hypertensive lungs, and it is unclear by what mechanism the ANP-stimulated activity of pGC is increased in hypertensive pulmonary vascular endothelial cells.

Topics: Altitude; Amitrole; Animals; Atrial Natriuretic Factor; Catalase; Cyclic GMP; Enzyme Inhibitors; Guanylate Cyclase; Heme Oxygenase (Decyclizing); Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; Immune Sera; Kinetics; Lung; Male; Nitroarginine; Protoporphyrins; Purinones; Rats; Rats, Sprague-Dawley; Reference Values

We have recently reported in normal isolated-perfused rat lungs that low basal tone appears to be regulated by nitric oxide (NO)-dependent and -independent mechanisms of soluble guanylate cyclase activation. In this study, we examined the role of NO in the regulation of pulmonary artery (PA) tone from rats with renin-dependent hypertension. Rats were made hypertensive by ligating the abdominal aorta above the left and below the right renal artery (aortic coarctation, AC). Mean arterial pressure significantly increased from 119 +/- 8.4 mmHg in control animals to 156 +/- 15 mmHg 7-14 days after AC surgery. PA pressures, however, remained unchanged (8.5 +/- 3.4 mmHg in control animals vs. 11 +/- 3.3 mmHg in AC animals). Hypoxic contractions in U-46619 precontracted isolated small PA (160-260 microns diameter) were significantly increased from 51 +/- 13 mg in the control group to 142 +/- 38 mg (P < or = 0.05) in AC animals. Nitro-L-arginine (NLA; 100 microM) contractions were also enhanced in the AC animal. The enhanced NLA response may correlate with an increase in endothelial cell NO synthase (NOS) as detected by Western blotting (132 +/- 28% of control; P < 0.05). These data suggest that, in this renin-dependent model of systemic hypertension, there is increased endothelial cell NOS activity that maintains low PA tone, preventing the lung from developing increased pressures.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Aorta, Abdominal; Aortic Coarctation; Blood Pressure; Endothelium, Vascular; Guanylate Cyclase; Hypertension; Hypoxia; In Vitro Techniques; Male; Muscle Contraction; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Regression Analysis; Renin; Thromboxane A2; Vasoconstrictor Agents

Hypoxia activates erythropoietin-producing cells, chemoreceptor cells of the carotid body and pulmonary artery smooth muscle cells (PSMC) with a comparable arterial PO2 threshold of some 70 mmHg. The inhibition by CO of the hypoxic responses in the two former cell types has led to the proposal that a haemoprotein is involved in the detection of the PO2 levels. Here, we report the effect of CO on the hypoxic pulmonary vasoconstriction (HPV). Pulmonary arterial pressure (PAP) was measured in an in situ, blood-perfused lung preparation. PAP in normoxia (20% O2, 5% CO2) was 15.2+/-1.8 mmHg, and hypoxia (2% O2, 5% CO2) produced a DeltaPAP of 6.3+/-0.4 mmHg. Addition of 8% or 15% CO to the hypoxic gas mixture reduced the DeltaPAP by 88.3+/-2.7% and 78.2+/-6.1% respectively. The same levels of CO did not affect normoxic PAP nor reduced the DeltaPAP produced by angiotensin II. The effect of CO was studied after inhibition of the NO-cyclic guanosine monophosphate (cGMP) cascade with N-methyl-l-arginine (5.10(-5) M) or methylene blue (1.4.10(-4) M). It was found that both inhibitors more than doubled the hypoxic DeltaPAP without altering the effectiveness of CO to inhibit the HPV. In in vitro experiments we verified the inhibition of guanylate cyclase by measuring the levels of cGMP in segments of the pulmonary artery. Cyclic GMP levels were 1.4+/-0.2 (normoxia), 2.5+/-0.3 (hypoxia) and 3.3+/-0.5 pmole/mg tissue (hypoxia plus 8% CO); sodium nitroprusside increased normoxic cGMP levels about fourfold. Methylene blue reduced cGMP levels to less than 10% in all cases, and abolished the differences among normoxic, hypoxic and hypoxic plus CO groups. It is concluded that CO inhibits HPV by a NO-cGMP independent mechanism and it is proposed that a haemoprotein could be involved in O2-sensing in PSMC.

Topics: Animals; Carbon Monoxide; Cyclic GMP; Enzyme Inhibitors; Female; Guanylate Cyclase; Hypoxia; In Vitro Techniques; Methylene Blue; Nitric Oxide Synthase; Nitroarginine; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Wistar; Solubility; Vasoconstriction

Nitric oxide (NO) is reported to cause neuronal damage through various mechanisms. The present study tests the hypothesis that NO synthase inhibition by N(omega)-nitro-L-arginine (NNLA) will result in decreased oxygen-derived free radical production leading to the preservation of cell membrane structure and function during cerebral hypoxia. Ten newborn piglets were pretreated with NNLA (40 mg/kg); five were subjected to hypoxia, whereas the other five were maintained with normoxia. An additional 10 piglets without NNLA treatment underwent the same conditions. Hypoxia was induced with a lowered FiO2 and documented biochemically by decreased cerebral ATP and phosphocreatine levels. Free radicals were detected by using electron spin resonance spectroscopy with a spin trapping technique. Results demonstrated that free radicals, corresponding to alkoxyl radicals, were induced by hypoxia but were inhibited by pretreatment with NNLA before inducing hypoxia. NNLA also inhibited hypoxia-induced generation of conjugated dienes, products of lipid peroxidation. Na+,K+-ATPase activity, an index of cellular membrane function, decreased following hypoxia but was preserved by pretreatment with NNLA. These data demonstrate that during hypoxia NO generates free radicals via peroxynitrite production, presumably causing lipid peroxidation and membrane dysfunction. These results suggest that NO is a potentially limiting factor in the peroxynitrite-mediated lipid peroxidation resulting in membrane injury.

Topics: Animals; Animals, Newborn; Brain; Brain Diseases; Cell Membrane; Electron Spin Resonance Spectroscopy; Enzyme Inhibitors; Free Radicals; Hypoxia; Lipids; Nitric Oxide Synthase; Nitroarginine; Phosphates; Sodium-Potassium-Exchanging ATPase; Swine

The involvement of nitric oxide in anoxia-induced long-term potentiation (anoxic LTP) of synaptic transmission was investigated in CA1 neurons of rat hippocampal slices using intracellular recording techniques in vitro. In response to superfusion of an anoxic artificial cerebral spinal fluid saturated with 95% N2-5% CO2, the excitatory postsynaptic potential (EPSP) generated in hippocampal CA1 neurons by stimulation of the Schaffer collateral/commissural afferent pathway was completely abolished within 10 min of anoxia. On return to reoxygenated medium, the EPSP returned to the control value within 10 min and was subsequently and progressively potentiated to reach a plateau 15-20 min after return to oxygen. This anoxia-induced persistent increase in synaptic transmission lasted for more than 1 h. Application of the nitric oxide synthase inhibitors 7-nitroindazole (7-NI) or L-N(G)-nitroarginine (NOARG) produced no effects on the baseline EPSP amplitude, but effectively attenuated the anoxic LTP. The inhibitory effects of both 7-NI and NOARG on the anoxic LTP were blocked by L-arginine, a substrate for nitric oxide synthase. These results suggest that nitric oxide is required for the generation of anoxia-induced LTP of glutamatergic synaptic transmission in the CA1 region of the rat hippocampus.

Topics: Animals; Arginine; Enzyme Inhibitors; Excitatory Postsynaptic Potentials; Hippocampus; Hypoxia; In Vitro Techniques; Indazoles; Long-Term Potentiation; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Reaction Time; Signal Transduction; Synaptic Transmission

We investigated the distribution and regulation of the optic nerve head (ONH) tissue partial pressure of oxygen (PO2) under various stimuli and the role of the nitric oxide in the ONH circulation. Tissue PO2 was measured using double-barreled recess microelectrodes in the intact eyes of miniature pigs during normoxia, hyperoxia, hypoxia, variations of systemic blood pressure, and after inhibition of the endothelial nitric oxide synthesis by the administration of nitro-L-arginine. Measurements were performed in front of the ONH at intervascular and juxta-arteriolar areas and at a depth of 50 and 200 microm within the ONH at the center and the rim. During normoxia, PO2 was heterogeneously distributed in the ONH, higher close to the arterioles than in intervascular areas. Hyperoxia induced a significant increase of juxta-arteriolar tissue PO2, while in intervascular areas no change was noticed. Hypoxia did not modify intervascular tissue PO2 at 200 microm depth within the ONH. Variations of the systemic blood pressure did not induce any significant change in ONH tissue PO2. Similarly, no modification was noticed after the administration of nitro-L-arginine. There is a remarkable autoregulatory capacity of the ONH circulation that may compensate for parameters such as hyperoxia, hypoxia, and variations of the systemic blood pressure. Endothelially derived nitric oxide inhibition does not modify the ONH tissue PO2, probably because the tissue PO2 is stabilized by compensatory regulation.

Topics: Animals; Blood Pressure; Endothelium, Vascular; Homeostasis; Hyperoxia; Hypoxia; Microelectrodes; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Optic Disk; Oxygen; Oxygen Consumption; Perfusion; Regional Blood Flow; Swine; Swine, Miniature

This experiment in rats was designed to investigate the effect and mechanism of nitric oxide (NO) in the induction of hypoxic pulmonary hypertension. The plasma concentrations of NO in normal controls and in the 1-, 2- and 3-week hyporemic ventilation groups were measured. The hemodynamic and pathological changes were observed in rats of the 2-week group after bolus injection of L-Arginine and NG-nitro-L-arginine. The results showed that NO concentrations of the 1-2- and 3-week groups were 5 +/- 2.67 mumol/L 2.1 +/- 0.41 mumol/L and 0.5 +/- 0.16 mumol/L respectively, which were significantly lower than the control group's 6.73 +/- 1.83 mumol/L (P < 0.05). Bolus injection of L-Arginine 100 mg.kg-1.d-1 could relieve chronic hypoxic pulmonary hypertension and decrease the thickening of pulmonary arteries, but L-NNA could antagonize the effect of L-Arginine. This experiment demonstrates that chronic hypoxemia may decrease the release of NO and result in pulmonary hypertension. L-Arginine may be used to relieve pulmonary hypertension, but L-NNA may antagonize the effect of L-Arginine.

Topics: Animals; Arginine; Hemodynamics; Hypertension, Pulmonary; Hypoxia; Male; Nitric Oxide; Nitroarginine; Pulmonary Artery; Rats; Rats, Sprague-Dawley

The effect of endogenous nitric oxide (NO) on the pulmonary hypoxic vasoconstriction was studied in isolated and blood perfused rat lungs. By applying the occlusion technique we partitioned the total pulmonary vascular resistance (PVR) into four segments: (1) large arteries (Ra), (2) small arteries (Ra'), (3) small veins (Rv'), and (4) large veins (Rv). The resistances were evaluated under baseline (BL) conditions and during; hypoxic vasoconstriction and acetylcholine (Ach) which was injected during hypoxic vasoconstriction. After recovery from hypoxia and Ach, Nomega-nitro-L-arginine (L-NA) was added to the reservoir and the responses to hypoxia and Ach were reevaluated. Before L-NA, hypoxia caused significant increase in the resistances of all segments (P < 0.05), with the largest being in Ra and Ra'. Ach-induced relaxation during hypoxia occurred in Ra, Ra' and Rv' (P < 0.05). L-NA did not change the basal tone of the pulmonary vasculature significantly. However, after L-NA, hypoxic vasoconstriction was markedly enhanced in Ra, Ra', and Rv' (P < 0.01) compared with the hypoxic response before L-NA. Ach-induced relaxation was abolished after L-NA. We conclude that, in rat lungs, inhibition of NO production during hypoxia enhances the response in the small arteries and veins as well as in the large arteries. The results suggest that hypoxic vasoconstriction in the large pulmonary arteries and small vessels is attenuated by NO release.

Topics: Acetylcholine; Animals; Arginine; Blood Pressure; Enzyme Inhibitors; Hypoxia; In Vitro Techniques; Lung; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Vascular Resistance; Vasoconstriction

The aim of this study was to characterise the response to acute hypoxia in pulmonary artery rings isolated from rats exposed to chronic hypoxia for 2 weeks (CH) and following recovery in room air for 24 h (post hypoxic, PH). Large intrapulmonary artery (IPA) rings (internal diameter = 1.5 +/- 0.11 mm; n = 13) from CH and PH rats and age-matched controls were studied. These were precontracted with phenylephrine using standard organ bath procedures at an oxygen tension of 152 mmHg and subjected to an acute hypoxia stimulus (bubbling with 0% O2 giving Po2 = 7 mmHg or 2% O2 giving PO2 = 20 mmHg). Acute hypoxia-induced pulmonary vasoconstriction (HPV) consisted of a transient contraction, a relaxation and a sustained contraction over 30 min. Pulmonary vasoconstriction induced by 0% O2 was significantly reduced in IPA rings from the CH but not PH group compared with the response obtained from the control group. HPV induced by 2% O2 in IPA rings from CH and PH rats was not significantly different from that in control rats not subjected to chronic hypoxia. Mechanical removal of the endothelium or inhibition of nitric oxide (NO) synthase by L-NOARG (300 microM) reduced the contractile phases of HPV in IPA rings from control and CH rats. Carbachol-induced endothelium-dependent relaxation in phenylephrine precontracted IPA rings was significantly attenuated in the CH but not PH group. In conclusion, the present study demonstrates that HPV induced by 0% O2 in rat IPA rings was blunted in CH rats and restored following 24 h in room air, in parallel with changes in endothelium function.

Topics: Animals; Body Weight; Carbachol; Endothelium, Vascular; Enzyme Inhibitors; Hypoxia; Male; Muscle Contraction; Nitroarginine; Oxygen; Partial Pressure; Phenylephrine; Pulmonary Artery; Rats; Rats, Wistar; Vasoconstriction

The purpose of this study was to determine the effect of inhibition of nitric oxide (NO) release on the diaphragmatic microvascular responses to hypoxia. In alpha-chloralose-anesthetized mongrel dogs, the microcirculation of the vascularly isolated ex vivo left hemidiaphragm was studied by intravital microscopy. The diaphragm was pump perfused with blood diverted from the femoral artery through a series of membrane oxygenators. The responses to supramaximal concentrations of sodium nitroprusside, moderate hypoxia (phrenic venous PO2 27 Torr), and severe hypoxia (phrenic venous PO2 15 Torr) were recorded before and after an infusion of NG-nitro-L-arginine (L-NNA; 6 x 10(-4) M) into the phrenic circulation for 20 min. Under control conditions, diaphragmatic blood flow was 12.4 +/- 1.1 ml.min-1.100g-1. Diaphragmatic blood flows recorded during moderate and severe hypoxia were 15.6 +/- 1.2 and 24.3 +/- 1.5 ml.min-1. 100 g-1, respectively (P < 0.05 for both compared with control values). Treatment with L-NNA reduced diaphragmatic blood flow to 9.6 +/- 0.8 ml.min-1.100 g-1 under control conditions (P < 0.05) and caused arteriolar vasoconstriction to a degree that was dependent on vessel size (i.e., larger vessels constricted more than smaller vessels). L-NNA eliminated the increase in blood flow during moderate hypoxia and inhibited arteriolar dilation by an amount that was related to vessel size (i.e., dilation of larger vessels was inhibited more than that of smaller vessels). Inhibition of NO synthesis had no effect on the increase in diaphragmatic blood flow (23.6 +/- 1.9 ml.min-1.100 g-1; P > 0.05 compared with that during severe hypoxia before treatment with L-NNA) or arteriolar diameters during severe hypoxia. NO release plays a role in the diaphragmatic vascular response to hypoxia, but this role is limited to dilation of larger arterioles during hypoxia of moderate severity.

Topics: Animals; Arterioles; Blood Gas Analysis; Capillaries; Diaphragm; Dogs; Enzyme Inhibitors; Hypoxia; Microcirculation; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Oxygen Consumption

Making use of nitric oxide synthesase (NOS) inhibitor Nw-nitric-oxide-L-arginine (L-NNA), the effect of NO and the pressence of endothelial cell on hypoxia-induced vascular dilatation was studied with new-born calve basilar artery. The experimental results show that L-NNA can attenuate the hypoxia-induced vascular dilatation, but the magnitude of attenuation is smaller than that of constriction caused by L-NNA on normoxic calve basilar artery. Under hypoxia, the vascular dilatation of endothelial cell denuded artery is smaller than that of endothelial cell intact artery; the difference between them is approximate by the same as the change caused by L-NNA on endothelial call intact artery. After destroying the endothelial cell, L-NNA has no obvious effect on the vascular tension. These results suggest that NO and endothelial cell are involved in hypoxia-induced vascular dilaxation.

Topics: Animals; Animals, Newborn; Basilar Artery; Cattle; Endothelium, Vascular; Hypoxia; In Vitro Techniques; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Vasodilation

The present study was designed to investigate the contribution of opioids and nitric oxide (NO) to hypoxia-induced pial vasodilation. Newborn pigs equipped with a closed cranial window were used to measure pial arteriolar diameter and to collect cortical periarachnoid cerebrospinal fluid (CSF) for assay of opioids and guanosine 3',5'-cyclic monophosphate (cGMP). Hypoxia-induced pial dilation was potentiated by norbinaltorphimine, 10(-6) M, a kappa-opioid antagonist (25 +/- 2 vs. 33 +/- 3%, n = 5), but was blunted by beta-funaltrexamine, 10(-8) M, a mu-opioid antagonist (28 +/- 2 vs. 19 +/- 1%, n = 5). Hypoxia-induced vasodilation was associated with increased CSF methionine enkephalin, a mu-opioid agonist (884 +/- 29 vs. 2,638 +/- 387 pg/ml, n = 5). N omega-nitro-L-arginine (L-NNA), an NO synthase inhibitor (10(-6) M), also blunted hypoxia-induced vasodilation that was further diminished by coadministration of L-NNA and beta-funaltrexamine (26 +/- 2, 14 +/- 1, and 9 +/- 1%, respectively, n = 5). Reversal of the above order of antagonist administration resulted in similar inhibition of hypoxia-induced pial dilation. Hypoxia-induced vasodilation was also associated with an increase in CSF cGMP that was attenuated by L-NNA (2.1 +/- 0.1- vs. 1.1 +/- 0.2-fold change in CSF cGMP, n = 5). Sodium nitroprusside (10(-6) M) increased CSF cGMP and methionine enkephalin concentration similar to hypoxia. These data suggest that hypoxia-induced pial arterial vasodilation, in part, is due to NO and/or cGMP-induced methionine enkephalin release as well as the direct action of NO.

Topics: Amino Acid Oxidoreductases; Analysis of Variance; Animals; Animals, Newborn; Arginine; Arterioles; Cerebral Arteries; Cyclic GMP; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Methionine; Enkephalins; Female; Hypoxia; Male; Muscle, Smooth, Vascular; Naltrexone; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Receptors, Opioid, kappa; Receptors, Opioid, mu; Swine; Vasodilation

Acute anoxia or severe hypoxia causes an initial transient contraction followed by marked relaxation of vascular tissues. We observed a spontaneous gradual sustained contraction of rat aortic rings following relaxation when hypoxia was prolonged. Deendothelialization as well as treatment of the endothelium-intact rings with nitric oxide synthase inhibitors or oxyhemoglobin abolished the late hypoxic contraction despite prolonged hypoxia. The prolonged hypoxia-induced sustained contraction was not affected by adenosine receptor blockade, cyclooxygenase inhibition, free radical scavengers, or the endothelin receptor antagonists. The ATP-sensitive K+ channel blocker glibenclamide abbreviated the duration of hypoxic relaxation and potentiated the magnitude of late hypoxic contraction. These data suggest that the late-sustained hypoxic contraction of arterial tissues is dependent on the presence of intact functional endothelium. Activation of ATP-sensitive K+ channels may participate in the genesis of hypoxic relaxation. However, cyclooxygenase products, free oxygen radicals, adenosine, and endothelin are not involved in the regulation of hypoxia-mediated events in rat aortic rings.

Topics: Adenosine Triphosphate; Amino Acid Oxidoreductases; Animals; Aorta, Thoracic; Arginine; Endothelium, Vascular; Glyburide; Hypoxia; In Vitro Techniques; Indomethacin; Nitric Oxide Synthase; Nitroarginine; omega-N-Methylarginine; Oxyhemoglobins; Potassium Channel Blockers; Potassium Channels; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Vasoconstriction; Vasodilation

We designed experiments to determine in vitro the influence of hypoxia on endothelium function in porcine pulmonary artery and vein. Rings of large isolated intralobar pulmonary arteries and veins were mounted in organ chambers for isometric tension recording. In veins and arteries with endothelium (precontracted with histamine and U 46619, respectively), hypoxia induced a transient contractile response that was significantly greater in veins. These contractile responses were fully blocked by L-nitro arginine (LNA) in arteries but only partially in veins. In pulmonary vessels without endothelium, only venous rings produced a contractile response to hypoxia; this contraction was blocked by indomethacin. In precontracted pulmonary arterial and venous rings, bradykinin (BK) induced endothelium-dependent relaxations unaffected by indomethacin. Venous relaxations were fully blocked by LNA, but arterial relaxations were only partially inhibited by the nitric oxide (NO) synthase inhibitor. In KCl (30 mM)-precontracted vessels, the endothelium-dependent relaxations were minimally affected in veins but significantly inhibited in arteries. Identical results were obtained in tissue contracted with histamine or U 46619 in presence of tetraethyl ammonium (TEA 10 mM). Hypoxia (30 mm Hg) abolished the venous relaxation but did not significantly influence the arterial relaxation. In arterial rings, the effects of KCl and LNA (or hypoxia) were additive. These results suggest that in isolated porcine pulmonary veins, endothelium-dependent relaxation to BK is exclusively dependent on NO formation. In arteries, however, NO production is partially involved. Another mechanism, possibly endothelium-dependent hyperpolarization, exists. These differences in endothelial responsiveness lead to different patterns of response to hypoxia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arginine; Bradykinin; Endothelium, Vascular; Female; Hypoxia; In Vitro Techniques; Indomethacin; Male; Nitric Oxide; Nitroarginine; Potassium Channels; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Veins; Swine; Tetraethylammonium Compounds; Thromboxane A2; Vasoconstrictor Agents; Vasodilation

To study the effects of ketamine on structurally remodeled pulmonary arteries from rats with hypoxic pulmonary hypertension (PH) and the effects of ketamine on endothelium-dependent and -independent relaxation, rats were exposed to hypobaric hypoxia (air at 380 mm Hg for 10 days). We measured the responses to ketamine, acetylcholine, and sodium nitroprusside (SNP) in prostaglandin F2 alpha-precontracted ring segments from a left extrapulmonary artery (EPA, 1.4-1.6 mm in outside diameter [OD] and an intrapulmonary artery (IPA, 0.7-1.1 mm OD) obtained from control and PH rats. The effects of acetylcholine and SNP were decreased in EPA and IPA rings from PH rats compared with control rings. In contrast, ketamine produced a greater relaxation response in rings from PH rats at 3 x 10(-5) -3 x 10(-4) in the EPA and at 10(-4) -10(-3) M in the IPA compared to control rings. A nitric oxide synthase inhibitor, nitro-L-arginine (10(-4) M), inhibited the relaxation in response to acetylcholine in both control and PH rats. Pretreatment with ketamine (10(-4) M) had no effect on the relaxation response to any concentration of acetylcholine or SNP in either control or PH rats. We conclude that nitric-oxide-mediated relaxation, but not ketamine-induced relaxation, was impaired in structurally remodeled hypertensive pulmonary arteries. Ketamine had no effects on nitric oxide-mediated relaxation in either normal or PH rats.

Topics: Acetylcholine; Animals; Arginine; Dinoprost; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Ketamine; Male; Nitric Oxide; Nitroarginine; Nitroprusside; Pulmonary Artery; Rats; Rats, Wistar; Vasodilation

The influence of nitric oxide (NO) blockade on resting tone and on hypoxia-induced vasodilatation of the cerebral vascular bed was examined in chronically instrumented lamb fetuses. Total (Qbrain-tot) and regional brain blood flow were measured using radioactive microspheres. NO blockade was achieved by N omega-nitro-L-arginine (NNLA) infusion into the carotid artery via a lingual artery. Fetal cerebral blood flow and cerebral vascular resistance (Rcer) were determined during normoxemia and hypoxemia and before and during infusion of L-arginine. During normoxemia, the brain blood flow decreased, and the resistance increased significantly after NNLA infusion (Qbrain-tot from 129 +/- 25 to 89 +/- 26 ml/100 g/min, p < 0.05; Rcer from 0.46 +/- 0.03 to 0.80 +/- 0.09 mm Hg/ml/100 g/min, p < 0.05). During hypoxemia before NNLA infusion, Qbrain-tot increased (from 129 +/- 25 to 187 +/- 56 ml/100 g/min, p < 0.05), and Rcer decreased (from 0.46 +/- 0.03 to 0.39 +/- 0.07 mm Hg/ml/100 g/min, p < 0.05). This vasodilatory response was largely blocked after NNLA (Qbrain-tot 143 +/- 45 ml/100 g/min; Rcer 0.58 +/- 0.07 mm Hg/ml/100 g/min). The response to hypoxemia was restored after infusion of L-arginine (Qbrain-tot 180 +/- 47 ml/100 g/min). The resting tone of the cerebral vascular bed of the lamb fetus is under NO control, and NO mediates the cerebral vasodilatory response to hypoxia in the lamb fetus.

Topics: Animals; Arginine; Cerebrovascular Circulation; Fetus; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Reference Values; Sheep; Vasodilation; Vasomotor System

Fourteen fetal lambs were instrumented with atrial, coronary sinus, and arterial catheters and a proximal left circumflex coronary artery Doppler probe and were studied at a mean gestational age of 130 +/- 3 (SD) days, 7 +/- 2 days after surgery. Myocardial blood flow was assessed using 15-microns microspheres and Doppler flow velocities. In 11 fetuses, the maximal myocardial flow response to left atrial adenosine infusion was 802 +/- 215 ml.min-1 x 100 g-1, 3.5-fold greater than baseline flow. Acute fetal hypoxemia in six fetuses to an arterial PO2 of 8.8 +/- 0.8 mmHg and an arterial O2 content (CaO2) of 1.7 +/- 0.2 ml/dl was not associated with significant change in coronary perfusion pressure; yet left ventricular myocardial flow increased to 1,020 +/- 198 ml.min-1 x 100 g-1, a value significantly greater than that seen with adenosine (P < 0.05). Left atrial N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of nitric oxide synthase (NOS), was infused at a dosage of approximately 1 mg.kg-1.min-1 for 60 min in 10 fetuses. Although L-NNA was associated with a significant increase in arterial pressure, left ventricular myocardial flow decreased (162 +/- 79 ml.min-1 x 100 g-1) as did myocardial O2 consumption (P < 0.05). Acute hypoxemia in five fetuses that received L-NNA was associated with significant further increases in systemic arterial pressure; however, left ventricular myocardial flow was only 771 +/- 237 ml.min-1 x 100 g-1, a value similar to that seen with adenosine and approximately 75% of that seen with acute hypoxemia alone. We conclude that nitric oxide plays an important role in the regulation of fetal myocardial flow during basal conditions as well as in the exuberant vasodilatory response associated with acute hypoxemic stress.

Topics: Adenosine; Animals; Arginine; Blood Flow Velocity; Coronary Circulation; Coronary Vessels; Fetus; Hypoxia; Microspheres; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rest; Sheep; Stress, Physiological; Ultrasonography

It is believed that hypoxia results in the release of neurotransmitters in the central nervous system, which can excite or inhibit breathing. Recent evidence indicates that nitric oxide (NO) is a physiological messenger molecule that may serve as a neurotransmitter in the CNS. In this study we examined (1) the localization of nitric oxide synthase (NOS) within the nucleus tractus solitarius, and (2) the role of the NO-cGMP pathway in the respiratory response to oxygen deprivation. Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry was used to determine the distribution of neurons that express NOS, an enzyme involved in NO formation. The NOS inhibitor N omega-nitro-L-arginine was used as tool to assess the NOS activity in the medulla, and to define the role of NO in the respiratory response to acute oxygen deprivation. In the rat and the cat brainstem, histochemical studies showed the presence of NADPH-diaphorase reactive neurons within subnuclei of the nucleus tractus solitarius which receive peripheral chemoreceptor inputs. Chronic pretreatment of rats with N omega-nitro-L-arginine (75 mg/kg, ip, twice daily for 7 days) caused a significant decrease in cGMP, and attenuated the ventilatory response to hypoxia. In anesthetized, paralyzed, vagotomized and artificially ventilated cats with intact carotid sinus nerves (n = 8), administration of N omega-nitro-L-arginine (30-100 mg/kg) attenuated the response to hypoxia, and caused the hypoxia induced roll-off of phrenic nerve activity to occur significantly earlier than when NOS activity was not inhibited. In sinoaortic denervated cats (n=9) blockage of NOS potentiated the decline of the phrenic nerve output. The data suggest that oxygen deprivation leads to activation of NO-cGMP pathway in the central nervous system, which contributes to the induction and maintenance of hypoxia-induced increase in respiratory output. In addition, these findings indicate that NO may inhibit inhibitory synaptic transmission that is triggered by CNS hypoxia, and this is not directly related to peripheral chemoreceptor inputs.

Topics: Animals; Arginine; Blood Pressure; Carotid Body; Cats; Cyclic GMP; Enzyme Inhibitors; Heart Rate; Hypoxia; Medulla Oblongata; NADPH Dehydrogenase; Neurons; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Partial Pressure; Rats; Rats, Sprague-Dawley; Respiration; Solitary Nucleus

This study investigated the effects of in vivo inhibition of cerebral nitric oxide synthase by intravenous administration of NG-nitro-L-arginine (NNLA) on the cell membrane Na+,K(+)-ATPase activity in the cerebral cortex of newborn piglets. NNLA was administered intravenously to 22 piglets at doses of 5 mg/kg (n = 3), 25 (n = 3), 50 (n = 4), 75 (n = 4), and 100 mg/kg (n = 2). Control animals (n = 6) received normal saline only. 90 min after infusion the cerebrum was obtained. The cerebral nitric oxide synthase activity, determined by measuring the conversion of [3H]-L-arginine into [3H]-L-citrulline in the brain homogenate, decreased from 9.1 +/- 2.0 pmol/mg protein/min in controls to 1.7 +/- 0.6 pmol/mg protein/min after the administration of 75 and 100 mg/kg NNLA. The Na+,K(+)-ATPase activity was measured in the P2 fraction of cortical tissue homogenate. The Na+,K(+)-ATPase activity was within the normal range (48.3 +/- 4.9 mumol/mg protein/h) up to 75 mg/kg of NNLA. At a dose of NNLA of 100 mg/kg, the Na+,K(+)-ATPase activity decreased to 31.5 +/- 0.7 mumol/mg protein/h (p < 0.05). Four animals developed hypoxemia and lactic acidosis. The results demonstrate that inhibition of the cerebral nitric oxide synthase activity in vivo in newborn piglets by intravenous administration of NNLA did not affect the cortical cell membrane Na+,K(+)-ATPase activity up to a dose of 75 mg/kg. Doses of 100 mg/kg decreased the Na+,K(+)-ATPase activity, probably by inducing cerebral hypoxia-ischemia.

Topics: Acidosis, Lactic; Animals; Animals, Newborn; Arginine; Cell Membrane; Cerebral Cortex; Enzyme Inhibitors; Hemodynamics; Hypoxia; Injections, Intravenous; Nitric Oxide Synthase; Nitroarginine; Sodium-Potassium-Exchanging ATPase; Swine

Nitric oxide (NO) is a potent endogenous vasodilator. Its role in the normal and stressed pulmonary circulation is unclear. To better understand the importance of endogenous NO in normal physiological responses, we studied the effects of altered NO availability on the change in pulmonary vascular tone that accompanies exercise. In paired studies we measured blood flow and pressures in the pulmonary circulation at rest and during treadmill exercise at a speed of 4 mph with and without (a) N omega-nitro-L-arginine, 20 mg/kg intravenously, a selective inhibitor of NO synthase; (b) L-arginine, 200 mg/kg intravenously, substrate for NO synthase; (c) combination of the inhibitor and substrate; and (d) inhalation of NO > 30 ppm, to determine if endogenous release of NO elicits maximal vasodilation. In addition, we sought to determine the site of NO effect in the pulmonary circulation by preconstriction with either U-44619 or hypoxia (fraction of inspired O2 = 0.12) using a distal wedged pulmonary catheter technique. NO synthase inhibition raised pulmonary vascular tone equally at rest and exercise. L-Arginine reversed the effects of NO synthase inhibition but had no independent effect. NO inhalation did not reduce pulmonary vascular tone at rest or enhance the usual reduction in pulmonary vascular resistance with exercise. The effect of NO synthase inhibition was in pulmonary vessels upstream from small veins, suggesting that endogenous NO dilates primarily small arteries and veins at rest. We conclude that, in sheep, endogenous NO has a basal vasodilator function that persists during, but is not enhanced by, exercise.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Hemodynamics; Hypoxia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Physical Conditioning, Animal; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Sheep; Thromboxane A2; Vascular Resistance; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Carotid Body; Chemoreceptor Cells; Heart Rate; Hypoxia; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar

The interaction between inspiratory fraction of O2 (FIO2) and endogenous nitric oxide (NO) regulation of pulmonary vascular tone was examined in intact anesthetized dogs. Stimulus (FIO2 of 1, 0.4, 0.21, 0.12, and 0.1)-response (changes in pulmonary artery pressure minus pulmonary artery occlusion pressure) curves were constructed with cardiac output kept constant (by opening a femoral arteriovenous bypass or inflating an inferior vena cava balloon catheter), before and after administration of compounds acting at different levels of the L-arginine-NO pathway, NG-nitro-L-arginine (L-NNA, 10 mg/kg iv, n = 16), a NO synthase inhibitor, and methylene blue (8 mg/kg iv, n = 16), a guanylate cyclase inhibitor. L-NNA and methylene blue did not influence pulmonary vascular tone in hyperoxic and in normoxic conditions, but they increased it during hypoxia, thus enhancing the vasopressor response to hypoxia (from 4.5 +/- 0.9 to 10.4 +/- 1.2 mmHg and from 4.2 +/- 0.8 to 9 +/- 1.5 mmHg, respectively, both P < 0.01). Hypoxic pulmonary vasoconstriction was augmented in dogs with a baseline hypoxic response ("responders") and restored in dogs without hypoxic response ("nonresponders"). These results suggest that endogenous NO does not influence hyperoxic and normoxic pulmonary vascular tone, but that it inhibits hypoxic pulmonary vasoconstriction in intact anesthetized dogs.

Topics: Animals; Arginine; Dogs; Hemodynamics; Hypoxia; Methylene Blue; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Oxygen; Pulmonary Circulation; Reference Values; Respiration

Pulsatile flow is thought to lower pulmonary vascular resistance by passive recruitment of capillaries and by active vasodilation. This study was undertaken to investigate the role of endothelium-derived relaxing factor (EDRF) during pulsatile flow in isolated canine left lower lobes pretreated with indomethacin. The lobes were perfused in situ with autologous blood (approximately 500 ml/min) using a nonpulsatile pump (Masterflex) or a pulsatile pump (Harvard). With the occlusion techniques, vascular resistance was partitioned into four segments: arterial (Ra), small arterial (R'a), small venous, and venous (Rv). Pulsatile flow (frequency = 70 min-1) did not lower total vascular resistance during baseline or during vasoconstriction. Distribution of vascular resistance among the four segments was not altered significantly by pulsatile flow during normoxia and angiotensin. In contrast, switching to pulsatile flow during hypoxia was associated with an increase in Ra and a decrease in R'a and Rv. N omega-nitro-L-arginine (L-NNA) had no effect on total or segmental resistance during baseline conditions but potentiated the hypoxic pressor response and prevented its recovery by 50%. In addition, the reduction in R'a by pulsatile flow was attenuated by L-NNA, suggesting that EDRF is released by pulsatile flow in this segment. We conclude that a shear stress-induced EDRF release from the small arteries is present in canine lungs and is experimentally demonstrable during pulsatile flow and hypoxia.

Topics: Angiotensin II; Animals; Arginine; Blood Vessels; Dogs; Female; Hypoxia; In Vitro Techniques; Indomethacin; Male; Nitric Oxide; Nitroarginine; Pulmonary Circulation; Pulsatile Flow; Stress, Mechanical; Vascular Resistance

Hypoxic vasoconstriction was investigated in isolated pulmonary and mesenteric arteries of the rat. Experiments were performed on large (approximately 2 mm pulmonary, approximately 0.8 mm mesenteric) and small (100-350 microns) arteries. Hypoxia [oxygen partial pressure (PO2) approximately 33 mmHg] elicited a biphasic response in arteries precontracted with prostaglandin F2 alpha (10 microM). A transient contraction reaching a peak within 2-3 min was observed in both large and small pulmonary and mesenteric arteries (phase 1). In pulmonary arteries, this was followed by a slowly developing contraction over 45 min (phase 2). In mesenteric arteries, there was no phase 2 but instead a profound relaxation. Mechanical disruption of the endothelium had no significant effect on phase 1 in preconstricted large pulmonary arteries but reduced phase 1 in small arteries by 40%. Phase 2 was abolished in both large and small arteries. Inhibition of endothelium-derived relaxing factor synthesis or cyclooxygenase pathways had no effect on either phase. Verapamil substantially reduced phase 1 but abolished phase 2. In conclusion, we have found a clear biphasic response to hypoxia in pulmonary arteries of the rat, but, in contrast to some previous reports, phase 1 was only partially dependent on the endothelium, whereas phase 2 was entirely dependent on the endothelium. Small and large arteries had qualitatively similar responses. These results are consistent with the involvement of at least two mechanisms for hypoxic vasoconstriction, one of which may involve release of an as yet unidentified endothelium-derived constrictor factor.

Topics: Animals; Arginine; Calcium; Cyclooxygenase Inhibitors; Endothelium, Vascular; Extracellular Space; Hypoxia; In Vitro Techniques; Male; Mesenteric Arteries; Nitric Oxide; Nitroarginine; Pulmonary Artery; Rats; Rats, Wistar; Sympatholytics; Vasoconstriction

The vascular endothelium mediates, in part, pulmonary vascular tone. Because endothelin-1 (ET-1), a paracrine hormone produced by vascular endothelial cells, has vasoactive properties, we investigated the hemodynamic effects of intrapulmonary injections of ET-1 in eight intact newborn lambs at rest and during pulmonary hypertension. At rest, ET-1 (50-1,000 ng/kg) did not change pulmonary arterial pressure. During pulmonary hypertension induced by the infusion of U46619 (a thromboxane A2 mimic), ET-1 (50-1,000 ng/kg) produced a selective dose-dependent decrease in pulmonary arterial pressure (5.8 +/- 3.9 to 32.9 +/- 6.9%; P < 0.05). Similarly, during pulmonary hypertension induced by alveolar hypoxia, ET-1 (50-500 ng/kg) produced a selective dose-dependent decrease in pulmonary arterial pressure (7.2 +/- 3.6 to 26.1 +/- 3.3%; P < 0.05). The decrease in pulmonary arterial pressure produced by ET-1 (250 ng/kg) was attenuated by N omega-nitro-L-arginine (an inhibitor of endothelium-derived nitric oxide synthesis, 23.7 +/- 3.4 vs. 12.5 +/- 4.7%; P < 0.05) and by glibenclamide (an ATP-gated potassium-channel blocker, 25.2 +/- 5.0 vs. 9.6 +/- 5.3%; P < 0.05) but not by meclofenamic acid (an inhibitor of prostaglandin synthesis). ET-1 is a pulmonary vasodilator during pulmonary hypertension in the intact newborn lamb. The vasodilating properties are mediated, in part, by release of endothelium-derived nitric oxide, and by activation of ATP-gated potassium channels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Animals, Newborn; Arginine; Endothelins; Glyburide; Hypertension, Pulmonary; Hypoxia; Injections, Intra-Arterial; Meclofenamic Acid; Nitroarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Circulation; Rest; Sheep; Vasodilation

The changes in pulmonary artery (PA) tone that develop during hypoxia are complex and appear to involve multiple vasoregulatory pathways. This study was designed to identify the phases of the response to severe hypoxia in isolated segments of rat PA and to evaluate the mechanisms involved. Exposure of preconstricted PA segments to severe hypoxia (i.e., PO2 < 3 Torr) resulted in transient relaxation followed by vigorous hypoxic vasoconstriction (HVC), which averaged 0.26 +/- 0.02 g (or 43.9 +/- 3.7% of the maximal force developed in response to phenylephrine). HVC was followed by sustained and nearly complete inhibition of existing tone. The first two phases of the response were endothelium dependent and could be blocked by nonspecific inhibitors of endothelium-derived relaxing factor (EDRF) activity and by 500 microM N omega-nitro-L-arginine, a specific inhibitor of nitric oxide (NO) formation. The transient early relaxation could also be inhibited by superoxide dismutase (50 U/ml). In contrast, the late relaxation phase was neither endothelium dependent nor could it be blocked by inhibitors of EDRF/NO activity. Rat PA segments were relaxed by pinacidil and lemakalim, both of which activate ATP-sensitive potassium channels. Preincubation with glibenclamide, a selective inhibitor of these channels, blocked this response and also reduced late hypoxic vasodilation by nearly 40% (P < 0.001). These findings demonstrate that the response of rat PA to hypoxia involves both endothelium-dependent and endothelium-independent components. The initial relaxation results from enhanced EDRF/NO activity, which is likely due to diminished breakdown by superoxide radicals.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetylcholine; Animals; Arginine; Endothelium, Vascular; Glyburide; Hemoglobins; Hypoxia; In Vitro Techniques; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Oxygen; Partial Pressure; Propranolol; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Superoxide Dismutase; Vasoconstriction; Vasodilation

To investigate dilator effects of endothelins (ETs) on the pulmonary circulation and possible changes induced by chronic hypoxia, we examined vascular responses to ET-1 and ET-3 as well as ET binding to receptor subtypes ETA and ETB in the lungs from rats exposed to either room air (controls), hypoxia (10% O2) for 3 wk (3 WH), or 3 WH followed by recovery to room air (3 WH+R). In controls, both ETA and ETB receptor binding was present in smooth muscle of airways and vessels. Infusion of ET-1 or ET-3 (3-100 pM) to isolated perfused lungs preconstricted by U-46619 produced dose-dependent vasodilation with a greater potency of ET-3 (P < 0.01). The vasodilator responses to ET-1 and ET-3 were potentiated by the cyclooxygenase blocker meclofenamate (3 x 10(-6) M) or by the thromboxane synthetase inhibitor R-68070. In meclofenamate-treated lungs, the vasodilator responses to ET-1 and ET-3 remained unaffected by the inhibitor of nitric oxide synthesis, NG-monomethyl-L-arginine (5 x 10(-4) M) or by the guanylate cyclase inhibitor, methylene blue (10(-4) M). Conversely, the K+ channel blockers glibenclamide (10(-4) M) and tetraethylammonium (10(-4) M) attenuated the vasodilator responses to both ET-1 and ET-3. The selective ETA receptor antagonist BQ-123 did not alter ET-induced vasodilation, whereas it attenuated ET-induced vasoconstriction. Vasodilation to both ET-1 and ET-3 was abolished in lungs from 3 WH rats (P < 0.01) but was fully restored in lungs from 3 WH+R rats. Pulmonary vasodilation induced by the K+ channel opener pinacidil, which was suppressed by glibenclamide, did not differ between controls and 3 WH rat lungs. We found no change in ETA and ETB receptor binding from pulmonary vessels in H rat lungs compared with controls. In conclusion, endothelin-induced pulmonary vasodilation which may involve activation of K+ channels is abolished during chronic hypoxia. This abolition does not appear to be related to alterations in ET-receptor subtypes or to unresponsiveness of K+ channels in the pulmonary circulation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arginine; Autoradiography; Dose-Response Relationship, Drug; Endothelins; Glyburide; Guanidines; Hypoxia; In Vitro Techniques; Iodine Radioisotopes; Lung; Male; Meclofenamic Acid; Nitroarginine; Pentanoic Acids; Pinacidil; Potassium Channel Blockers; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Pyridines; Rats; Rats, Wistar; Receptors, Endothelin; Tetraethylammonium; Tetraethylammonium Compounds; Thromboxane A2; Thromboxane-A Synthase; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

Topics: Acute Disease; Animals; Arginine; Cerebrovascular Circulation; Disease Models, Animal; Endothelium, Vascular; Hemodynamics; Homeostasis; Hypoxia; Infusions, Intravenous; Nitric Oxide; Nitroarginine; Oxygen Consumption; Pulmonary Circulation; Streptococcal Infections; Streptococcus agalactiae; Swine

To determine whether endothelium-derived nitic oxide (EDNO), like dilator prostaglandins, attenuates pulmonary vasomotor tone more in younger than in older newborns, we examined the effects of a nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NA), on total and segmental pulmonary vascular resistance (PVR) in isolated blood-perfused cyclooxygenase-inhibited lungs of < 2-day-old (2D) and 1-mo-old (1M) lambs. Total PVR was determined both from steady-state pressure-flow curves and total pressure gradients (delta PT) measured at constant flow (100 ml.kg-1 x min-1). Pressure gradients across arterial (delta Pa), middle (delta Pm), and venous (delta Pv) segments were determined by inflow-outflow occlusion. In 1M lungs (n = 6), L-NA increased delta PT, delta Pa, and delta Pv during normoxia and hypoxia. However, delta Pm increased only during hypoxia, suggesting that EDNO attenuates resistance of small vessels more when tone is high. The response to L-NA in 2D lungs was variable. In four "responders" (2D"R"), normoxic and hypoxic delta PT and all segmental resistances increased markedly after L-NA, but in five "nonresponders" (2D"NR"), L-NA had an insignificant effect on delta PT. Moreover, control delta PT values were higher in 2D"NR" than in 2D"R" lungs, suggesting that basal EDNO activity was minimal in some young newborns. Nonetheless, EDNO appears to attenuate venous resistance in newborns, because L-NA increased delta Pv in all groups. The significance of and mechanism(s) responsible for lesser modulation of PVR by EDNO in some young newborns remain to be determined.

Topics: Acetylcholine; Animals; Arginine; Blood Pressure; Endothelium, Vascular; Hypoxia; In Vitro Techniques; Lung; Muscle Tonus; Nitroarginine; Norepinephrine; Perfusion; Pulmonary Circulation; Sheep; Vascular Resistance; Vasodilation

To investigate the hypothesis that pulmonary vascular tone and endothelium-dependent pulmonary vasodilation are mediated by changes in the vascular smooth muscle cell concentration of cGMP, we studied the hemodynamic effects of M&B 22948, a selective guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase inhibitor, in eight intact newborn lambs. At rest, M&B 22948 (1.0-2.5 mg/kg) selectively decreased pulmonary arterial pressure (by 8.5 +/- 6.6 to 10.3 +/- 4.5%, P < 0.05). Similarly, M&B 22948 (0.5-5.0 mg/kg) produced selective dose-dependent decreases in pulmonary arterial pressure during pulmonary hypertension induced either by U46619 (by 7.7 +/- 4.2 to 44.2 +/- 4.4%, P < 0.05) or by alveolar hypoxia (by 9.5 +/- 6.2 to 29.0 +/- 11.0%, P < 0.05). In addition, M&B 22948 augmented the pulmonary vasodilating effects of acetylcholine and ATP (both endothelium- and cGMP-dependent vasodilators) but not isoproterenol (an endothelium-independent and cAMP-dependent vasodilator). Because M&B 22948 inhibits the breakdown of cGMP, this study supports the in vitro data that changes in the vascular smooth muscle cell concentration of cGMP, in part, may regulate pulmonary vascular tone and mediate endothelium-dependent vasodilator responses in the pulmonary circulation. In addition, N omega-nitro-L-arginine (an inhibitor of endothelium-derived relaxing factor synthesis) blocked the vasodilating effects of M&B 22948, suggesting that the majority of endogenous cGMP is generated by the release of endothelium-derived relaxing factor.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Animals, Newborn; Arginine; Hypertension, Pulmonary; Hypoxia; Infusions, Intravenous; Nitroarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Purinones; Sheep; Vasodilator Agents

We have previously demonstrated that arginine vasopressin (AVP) dilates the preconstricted pulmonary vasculature via the release of nitric oxide (NO). However, recent evidence suggests that NO release in response to other agents may be suppressed in lungs from animals that have been chronically exposed to hypoxia. The purpose of the present experiment was to determine whether vasopressinergic pulmonary vasodilation is similarly affected by chronic exposure to hypoxia (barometric pressure = 380 Torr for 4 wk). Inhibition of NO synthesis with N omega-nitro-L-arginine (L-NNA) had no effect on baseline perfusion pressure in isolated salt-perfused lungs from either control or chronically hypoxic rats. Similarly, pulmonary vasodilatory responses to AVP and the calcium ionophore A23187 were unaffected by chronic hypoxic exposure. Pretreatment with the cyclooxygenase inhibitor meclofenamate did not alter vasopressinergic pulmonary vasodilation in lungs from either control or chronically hypoxic animals, ruling out involvement of vasodilator prostaglandins in the response to AVP. In contrast, vasodilatory responses to both AVP and A23187 were inhibited by L-NNA pretreatment not only in lungs from control animals but also in lungs from chronically hypoxic rats, suggesting the involvement of NO in the vasodilatory response. The inhibition by L-NNA was reversible by prior addition of excess L-arginine but not by D-arginine. In addition, vasodilatory responses to the endothelium-independent vasodilators sodium nitroprusside and isoproterenol were unaffected by chronic hypoxic exposure. We conclude that endothelium-dependent vasodilation remains intact in male Sprague-Dawley rats after chronic hypoxic exposure.

Topics: Air Pressure; Animals; Arginine; Arginine Vasopressin; Calcimycin; Chronic Disease; Endothelium, Vascular; Hypoxia; In Vitro Techniques; Isoproterenol; Male; Meclofenamic Acid; Nitroarginine; Nitroprusside; Prostaglandins; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Vasodilation; Vasodilator Agents

Endotoxin decreases pulmonary vascular reactivity. Because tumor necrosis factor-alpha (TNF-alpha) is a primary mediator of endotoxemia, we tested whether TNF-alpha altered pulmonary vascular reactivity in conscious adult female rats. Osmotic pumps were implanted intraperitoneally, and low-dose TNF-alpha (62 micrograms, TNF62; n = 7), high-dose TNF-alpha (> or = 250 micrograms, TNF250; n = 5), or saline (n = 5) was administered for 2 wk. Pulmonary pressor responses to 14% O2 and angiotensin II (ANG II, 0.0206 micrograms/min for 10 min) were measured without (day 13) or after (day 14) administration of nitro-L-arginine (4.4 mg/kg iv), an inhibitor of endothelium-derived relaxing factor (EDRF). TNF-alpha administration slightly decreased (P < or = 0.08) baseline pulmonary arterial pressure in TNF250 rats and decreased (P < or = 0.05) hypoxia- and ANG II-induced constrictions in TNF62 and TNF250 rats. Whereas nitro-L-arginine potentiated (P < or = 0.05) pressure responses in control rats, it had no effect on hypoxic responses in TNF-alpha-treated rats. Nitro-L-arginine increased (P < or = 0.05) ANG II-induced vasoconstriction in TNF-alpha-treated rats, but the pulmonary arterial pressure response was still lower (P < or = 0.05) in TNF250 than in control and TNF62 rats. These results suggest that chronic TNF-alpha decreases 1) pulmonary vascular reactivity in the intact rat, 2) hypoxic pulmonary vasoconstriction by a mechanism that is independent of EDRF, and 3) ANG II-induced constriction by a mechanism that is partly EDRF dependent.

Topics: Angiotensin II; Animals; Arginine; Female; Hemodynamics; Hypoxia; Nitric Oxide; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Tumor Necrosis Factor-alpha; Vascular Resistance; Vasoconstriction

Our laboratory has previously described in isolated 1- to 4-mm calf pulmonary arteries, an endothelium-independent contraction to hypoxia that appears to involve the removal of a H2O2-elicited guanosine 3',5'-cyclic monophosphate (cGMP)-mediated relaxation. In this study, we examined the effects of changes in O2 tension (PO2) on isolated endothelium-intact and endothelium-denuded calf pulmonary resistance arteries of approximately 200 microns in diameter. Resistance arteries precontracted with U46619 were found to undergo a contraction when exposed to a PO2 of 24-27 Torr (hypoxia) from a Po2 of 150 Torr (O2 atmosphere). This contraction was significantly larger in endothelium-intact than endothelium-removed arteries. In the intact artery, 30 microM nitro-L-arginine (NLA), an inhibitor of the biosynthesis of nitric oxide-like activators of guanylate cyclase, increased tone under O2 atmosphere and reduced the contraction to hypoxia to the level observed in the endothelium-removed artery. Reoxygenation caused a relaxation, which was not dependent on the endothelium or inhibited by NLA. The inhibitor of guanylate cyclase activation, LY83583 (10 microM), increased tone under O2 atmosphere, eliminated the contraction to hypoxia, and inhibited the relaxation to reoxygenation, whereas indomethacin (10 microM) did not alter these responses. Thus modulation of a cGMP mechanism, not involving the endothelium or metabolism of arginine, is a primary mediator of responses to changes in O2 tension, and the endothelium appears to cause an enhancement of the contraction to hypoxia via suppression by hypoxia of the tonic generation of an arginine-derived relaxing factor.

Topics: Acetylcholine; Aminoquinolines; Animals; Arginine; Cattle; Cyclic GMP; Endothelium, Vascular; Hypoxia; Indomethacin; Nitroarginine; Oxygen; Partial Pressure; Prostaglandin Antagonists; Pulmonary Artery; Vascular Resistance; Vasoconstriction; Vasodilation

We have demonstrated previously that in response to hypoxia, isolated rat pulmonary arteries show an initial endothelium-dependent relaxation followed by an endothelium-independent transient contraction. In the presence of increased extracellular Ca2+, both of these responses were enhanced in endothelium-intact arteries. Nitro-L-arginine, a blocker of the biosynthesis of endothelium-derived relaxing factor (EDRF), abolished the initial endothelium-dependent relaxation and Ca(2+)-induced enhancement of hypoxic contraction in endothelium-intact arteries but did not alter responses in endothelium-denuded vessels. Inhibition of prostaglandin formation with indomethacin had no effect on the hypoxia-elicited responses. Preincubation with LY 83583, an inhibitor of guanylate cyclase activation, abolished the initial hypoxia-elicited relaxation and subsequent contraction. M & B 22948, a guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase inhibitor, decreased tone under O2 but not under N2, causing an apparent enhancement of the contraction to hypoxia. Thus the modulation of hypoxic responses by the endothelium is dependent on changes in EDRF production, and a decrease in smooth muscle cGMP not involving an EDRF mechanism appears to mediate the endothelium-independent hypoxic contraction observed in the isolated rat pulmonary artery.

Topics: Aminoquinolines; Animals; Arginine; Cyclic GMP; Hypoxia; In Vitro Techniques; Indomethacin; Male; Nitroarginine; Pulmonary Artery; Purinones; Rats; Rats, Inbred Strains

There is increasing evidence that resting pulmonary vascular tone is mediated by the release of endothelium-derived relaxing factors (EDRF). However, the importance of EDRF release during pulmonary hypertension is unknown. Therefore, in eight newborn lambs we studied the effects of both N omega-nitro-L-arginine (an inhibitor of EDRF synthesis) and L-arginine (a precursor of EDRF synthesis) during pulmonary hypertension induced either by the intravenous infusion of U-46619 (a thromboxane A2 mimic) or by hypoxia. After pretreatment with N omega-nitro-L-arginine, the increases in pulmonary arterial pressure produced by U-46619 (102.0 +/- 34.9% vs. 144.8 +/- 28.6%, P less than 0.05) and by hypoxia (35.6 +/- 17.3% vs. 91.4 +/- 24.8%, P less than 0.05) were significantly augmented. However, after pretreatment with L-arginine, the increases in pulmonary arterial pressure produced by U-46619 (107.0 +/- 21.4% vs. 62.6 +/- 22.6%, P less than 0.05) and hypoxia (44.3 +/- 18.3% vs. 9.2 +/- 11.7%, P less than 0.05) were significantly attenuated. These results suggest that during pulmonary hypertension, EDRF is released to limit the increase in pulmonary arterial pressure and that L-arginine availability becomes rate limiting for further EDRF synthesis and release.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Animals, Newborn; Arginine; Blood Pressure; Cardiac Output; Heart Rate; Hypertension, Pulmonary; Hypoxia; Nitric Oxide; Nitroarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Sheep; Vascular Resistance; Vasoconstrictor Agents

Systemic hypoxia, produced in deeply anesthetized, paralyzed rats in which arterial chemoreceptors were denervated, elicited a decrease in arterial pressure (AP) averaging -47 mmHg. Systemic administration of NG-nitro-L-arginine (L-NO2Arg), an inhibitor of nitric oxide (NO) synthase, attenuated the hypoxic depressor response by 79% and elevated AP by 21 mmHg. The effects of L-NO2Arg on the hypoxic depressor response and arterial pressure were reversed by systemic administration of L- but not D-arginine. Elevation of AP with arginine-vasopressin or reduction of AP with nitroprusside to the pre-L-NO2Arg levels did not modify the fall of AP to hypoxia. Endogenous NO synthesized in vivo from L-arginine, mediates most of the hypoxic depressor response.

Topics: Anesthesia, General; Animals; Arginine; Arginine Vasopressin; Blood Pressure; Carotid Sinus; Denervation; Hypoxia; Male; Nitric Oxide; Nitroarginine; Nitroprusside; Rats; Rats, Inbred Strains

The effect of severe hypoxia in quiescent or contracted (prostaglandin F2 alpha) canine coronary artery rings with and without endothelium was studied. Hypoxia induced an initial transient relaxation followed by a sustained contraction. The hypoxic contraction in quiescent rings was comparable in rings with and without endothelium. The facilitation of the contraction to prostaglandin F2 alpha was more pronounced in rings with endothelium. Increasing the level of contractions by augmenting the contraction of prostaglandin F2 alpha potentiated the hypoxic contraction in rings with endothelium only. Methylene blue, LY 83583, and nitro-L-arginine reversed the hypoxic facilitation in contracted rings into relaxation, whereas M&B 22948 augmented it. In quiescent coronary preparations, methylene blue reversed the hypoxic contraction into relaxation in preparations with and without endothelium, whereas nitro-L-arginine had the same effect in vessels with endothelium only. SIN-1, nitroglycerin, and dibutyryl guanosine 3',5'-cyclic monophosphate (cGMP) unmasked hypoxic facilitation in rings without endothelium. This was not observed with isoproterenol. The measurement of the level of cGMP revealed an increased level in rings with endothelium compared with those without endothelium under control oxygenation. This difference disappeared during hypoxia due to a decrease of cGMP content in vessels with endothelium. The results suggest that a moderate increase of the cGMP level in vascular smooth muscle is a prerequisite for the occurrence of hypoxia-induced facilitation in contracted canine coronary arteries.

Topics: Animals; Arginine; Coronary Vessels; Cyclic GMP; Dinoprost; Dogs; Endothelium, Vascular; Female; Hypoxia; In Vitro Techniques; Male; Methylene Blue; Muscle Contraction; Muscle, Smooth, Vascular; Nitric Oxide; Nitroarginine; Oxygen

1. The mechanisms underlying hypoxic dilatation of coronary arteries were studied in isolated guinea-pig hearts perfused with physiological salt solution at 37 degrees C. The hearts were perfused at a constant rate of 3-10 ml min-1; coronary perfusion pressure (CPP) and isovolumetric left ventricular pressure (LVP) were measured with piezoresistive transducers. 2. Addition of the K+ channel opener cromakalim (500 nM) to the perfusate caused a maximal vasodilatation in beating hearts, i.e. a decrease in CPP of about 50%. Switching from normal perfusate (partial pressure of O2 (PO2), 650-700 mmHg) to hypoxic perfusate (PO2, 9-10 mmHg) caused a similar vasodilatation. Both of these effects were prevented by 2 microM-glibenclamide, a blocker of ATP-sensitive potassium channels. Hypoxic vasodilatation was accompanied by a marked decrease in LVP, which was reduced by 56 +/- 22% (mean +/- S.D.) in the presence of glibenclamide. 3. In hearts arrested by increasing the K+ concentration of the perfusate to 15 mM, the addition of the adenosine-uptake inhibitor dipyridamole evoked a maximal vasodilatation and this was inhibited by 76 +/- 7% in the presence of glibenclamide. 4. The adenosine antagonist 8-phenyltheophylline (8-PT; 5 microM) inhibited the vasodilatation induced by dipyridamole by 88 +/- 10%. In contrast, hypoxic vasodilatation was unaffected by 5 microM 8-PT. This suggests that hypoxic dilatation of coronary arteries is not mediated by release of adenosine from cardiomyocytes. 5. In order to test whether release of endothelium-derived relaxing factor (EDRF) contributed to hypoxic vasodilatation we blocked EDRF synthesis with N omega-nitro-L-arginine (NNA). When applied at a perfusion rate of 10 ml min-1 to arrested hearts, 10 microM-NNA increased CPP by 35% and prolonged the delay between application of hypoxic solution and half-maximal vasodilatation from 52 +/- 9 to 129 +/- 29 s. 6. Under control conditions the relation between perfusion rate and the CPP measured in the steady state was linear. In the presence of 10 microM-NNA coronary resistance was increased more than twofold at low perfusion rates; at perfusion rates between 4 and 10 ml min-1 coronary resistance decreased progressively. This change in the pressure-flow relationship may be responsible for the alterations in the time course of hypoxic vasodilatation induced by NNA. 7. In order to test whether changes in energy metabolism in coronary smooth muscle cells were responsible for hypoxic va

Topics: Adenosine; Animals; Arginine; Coronary Vessels; Deoxyglucose; Glycolysis; Guinea Pigs; Hypoxia; Nitric Oxide; Nitroarginine; Perfusion; Potassium Channels; Receptors, Purinergic; Theophylline; Vascular Resistance; Vasodilation

1. The effects of endothelin-1 on perfusion pressure and on arterial and venous diameters were examined simultaneously in a rabbit isolated ear preparation perfused with physiological buffer. The effects of hypoxia and inhibition of endothelium-derived relaxant factor (EDRF) activity on vascular responses to endothelin-1 were also investigated. 2. Endothelin-1 was potent at increasing perfusion pressure (ED50 = 46.7 +/- 11.0 pmol; Rmax = 85.3 +/- 5.3 mmHg). The potency and maximum reactivity were not significantly affected by hypoxia, inhibition of EDRF activity with 50 microns N-nitro-L-arginine methyl ester (NAME) or a combination of hypoxia and NAME. 3. Endothelin-1 caused equipotent dose-dependent constrictions of the first four generations of arterial branch vessels (G1-G4) but did not influence the diameter of the central ear artery except at high doses of the peptide when paradoxical dilatation' was observed. The peptide was also equipotent at causing constriction of the smaller venous vessels (V1-V4) but did not affect the large veins (V0). 4. Under conditions of hypoxia the potency of endothelin-1 was reduced in G2 and G3, was unaffected in G4 and the peptide did not significantly constrict either G0 or G1. Hypoxia reduced the potency of endothelin-1 in the smaller venous vessels (V1-V4), but conversely unmasked a marked constriction of the large veins (V0), which was not observed under normoxic conditions. 5. NAME 50 micron abolished the vasodilator effects of acetylcholine in this preparation. Inhibition of EDRF activity with NAME under normoxic conditions did not influence the constrictor activity of endothelin-1 on the arterial or venous branch vessels. However, inhibition of EDRF activity under hypoxic conditions prevented the reduction of potency of endothelin-1 as a constrictor of arterial and venous branch vessels which occurred in hypoxia. In the presence of NAME endothelin-1 constricted VO in both normoxia and hypoxia with equipotency but the maximum effect was greatest in hypoxia. 6. In conclusion, endothelin-1 is a powerful vasoconstrictor which acts with greater potency in veins than arteries in the rabbit isolated ear. Although hypoxia does not influence pressor responses it nevertheless alters the spatial pattern of vasoconstriction. In particular hypoxia unmasks constriction of the large veins by endothelin-1. Constriction of these veins was also observed in the absence of EDRF in normoxia, but to a much lesser degree so that the

Topics: Angiography; Animals; Arginine; Ear, External; Endothelins; Hypoxia; In Vitro Techniques; Male; Microcirculation; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroarginine; Perfusion; Rabbits