nitroarginine and Hypertension--Pulmonary

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

Mechanisms that impair angiogenesis in neonatal persistent pulmonary hypertension (PPHN) are poorly understood.. To determine if PPHN alters fetal pulmonary artery endothelial cell (PAEC) phenotype and impairs growth and angiogenesis in vitro, and if altered vascular endothelial growth factor-nitric oxide (VEGF-NO) signaling contributes to this abnormal phenotype.. Proximal PAECs were harvested from fetal sheep that had undergone partial ligation of the ductus arteriosus in utero (PPHN) and age-matched control animals. Growth and tube formation +/- VEGF and NO stimulation and inhibition were studied in normal and PPHN PAECs. Western blot analysis was performed for VEGF, VEGF receptor-2 (VEGF-R2), and endothelial NO synthase (eNOS) protein content. NO production with VEGF administration was measured in normal and PPHN PAECs.. PPHN PAECs demonstrate decreased growth and tube formation in vitro. VEGF and eNOS protein expression were decreased in PPHN PAECs, whereas VEGF-R2 protein expression was not different. VEGF and NO increased PPHN PAEC growth and tube formation to values achieved in normal PAECs. VEGF inhibition decreased growth and tube formation in normal and PPHN PAECs. NOS inhibition decreased growth in normal and PPHN PAECs, but tube formation was only reduced in normal PAECs. NO reversed the inhibitory effects of VEGF-R2 inhibition on tube formation in normal and PPHN PAECs. VEGF increased NO production in normal and PPHN PAECs.. PPHN in utero causes sustained impairment of PAEC phenotype in vitro, with reduced PAEC growth and tube formation and down-regulation of VEGF and eNOS protein. VEGF and NO enhanced growth and tube formation of PPHN PAECs.

Topics: Animals; Cell Division; Cells, Cultured; Endothelial Cells; Endothelium, Vascular; Enzyme Inhibitors; Fetal Development; Fetal Diseases; Hypertension, Pulmonary; Neovascularization, Physiologic; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenotype; Pulmonary Artery; Sheep; Signal Transduction; Vascular Endothelial Growth Factor A

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

Nitric oxide (NO) is an important mediator of pulmonary vascular reactivity, and decreased NO synthase expression has been demonstrated in children with advanced pulmonary hypertension secondary to congenital heart disease and increased pulmonary blood flow. Using aortopulmonary vascular graft placement in the fetal lamb, we have established a unique animal model of pulmonary hypertension with increased pulmonary blood flow. At 4 wk of age, these lambs display an early, selective impairment in agonist-induced NO responses, but an up-regulation of basal NO activity and gene expression. We hypothesized that further exposure to increased flow and/or pressure results in progressive endothelial dysfunction and a subsequent decrease in basal NO production. The objective of this study was to characterize potential later alterations in agonist-induced NO responses and basal NO activity and gene expression induced by 8 wk of increased pulmonary blood flow and pulmonary hypertension. Twenty-two fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt), and were studied 8 wk after delivery. Both in vivo and in isolated pulmonary arteries, the pulmonary vasodilating response to endothelium-dependent agents was attenuated in shunted lambs (p < 0.05), whereas the response to endothelium-independent agents was unchanged. The pulmonary vasoconstricting responses to Nomega-nitro-L-arginine, and lung tissue endothelial NO synthase mRNA, endothelial NO synthase protein, NO synthase activity, and NO(X) levels were all unchanged. These data suggest that the increase in basal NO activity demonstrated after 4 wk of increased pulmonary blood flow is lost by 8 wk of age, whereas the attenuation of agonist-induced responses persists. We speculate that the progressive decrease in basal NO activity participates in the development of pulmonary hypertension secondary to increased pulmonary blood flow.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Anastomosis, Surgical; Animals; Aorta; Caveolin 1; Caveolins; Enzyme Inhibitors; Female; HSP90 Heat-Shock Proteins; Hypertension, Pulmonary; Lung; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Pregnancy; Pulmonary Artery; Pulmonary Circulation; RNA, Messenger; Sheep; Vasoconstrictor Agents; Vasodilation

This study investigated the role of nitric oxide (NO) in the control of right coronary (RC) blood flow at rest and during acute pulmonary hypertension. Experiments were performed in seven chronically instrumented, conscious dogs. NO synthesis was inhibited by systemic administration of N(omega)-nitro-L-arginine (LNA, 35 mg/kg). Inflation of a balloon in the main pulmonary artery raised right ventricular (RV) peak systolic pressure from 34 +/- 2 to 47 +/- 3 mmHg before LNA and from 37 +/- 2 to 47 +/- 3 mmHg after LNA, but did not affect mean systemic arterial pressure. RV O(2) consumption (MVO(2)) increased from 4.4 +/- 0.7 to 6.1 +/- 0.7 ml/min/100 g. 82 % of the elevated RV MVO(2) was provided by RC blood flow, which increased from 46 +/- 7 to 61 +/- 8 ml/min/100 g. After LNA, resting RV MVO(2) and RC flow fell. RC venous PO(2) fell, but RV lactate uptake was not altered. During pulmonary hypertension, the increase in RC blood flow was blunted by LNA, so that only 66 % of the elevated RV MVO(2) was supplied by increased RC flow. Analysis of O(2) supply variables as functions of RV MVO(2) further demonstrated a significant role of NO in regulating RC flow at rest and during moderate pulmonary hypertension. Conclusions NO is required for the RC hyperemic response to acute pulmonary hypertension as well as for normal resting RC blood flow. After blockade of NO synthesis, RV O(2) supply at rest and during pulmonary hypertension was sustained by increased RV O(2) extraction.

Topics: Animals; Blood Pressure; Coronary Circulation; Coronary Vessels; Disease Models, Animal; Dogs; Female; Hypertension, Pulmonary; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen Consumption; Regional Blood Flow

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

To determine the effects of chronic nitric oxide (NO) blockade on the pulmonary vasculature, 58-day-old spontaneously hypertensive rats of the stroke-prone substrain (SHRSP) and Wistar-Kyoto rats (WKY) received N(omega)-nitro-L-arginine (L-NNA; 15 mg. kg(-1). day(-1) orally for 8 days). Relaxation to acetylcholine (ACh) in hilar pulmonary arteries (PAs), the ratio of right ventricular (RV) to body weight (RV/BW) to assess RV hypertrophy (RVH), and the percent medial wall thickness (WT) of resistance PAs were examined. L-NNA did not alter the PA relaxation, RV/BW, or WT in WKY. Although the PA relaxation and RV/BW in control SHRSP were comparable to those in WKY, the WT was increased (31 +/- 2 vs. 19 +/- 1%). L-NNA-treated SHRSP showed two patterns: in one group, the relaxation, RV/BW, and WT were comparable to those in the control SHRSP; in the other, impaired relaxation (36 +/- 7 vs. 88 +/- 4% for WKY) was associated with an increase in WT (37 +/- 1%) and RV/BW (0. 76 +/- 0.05). Thus the abnormal pulmonary vasculature in SHRSP at <10 wk of age is not accompanied by impaired relaxation in PAs or RVH; however, impaired relaxation is associated with increased WT and RVH.

Topics: Animals; Blood Pressure; Blood Vessels; Cyclic AMP; Cyclic GMP; Endothelium, Vascular; Enzyme Inhibitors; Genetic Predisposition to Disease; Hypertension, Pulmonary; Hypertrophy, Left Ventricular; Hypertrophy, Right Ventricular; Lung; Nitric Oxide Synthase; Nitroarginine; Pulmonary Circulation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Stroke; Vasodilation

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

To determine whether acute pulmonary hypertension in utero alters fetal pulmonary vascular reactivity, we compared pulmonary vasodilation with an endothelium-dependent agonist, acetylcholine, with that of an endothelium-independent agonist, 8-bromo-guanosine 3',5'-cylic monophosphate. Acute pulmonary hypertension was produced in chronically prepared, late-gestation fetal lambs by 3 repeated 30-minute partial occlusions of the ductus arteriosus (DA). The first DA compression increased LPA blood flow from 80 +/- 10 to 180 +/- 21 mL/min (p < 0.01) and decreased pulmonary vascular resistance. In contrast, LPA blood flow did not change and pulmonary vascular resistance increased by 25% during the third period of DA compression. Pulmonary vasodilation during acetylcholine infusion after serial DA compressions was decreased in comparison with the acetylcholine-induced vasodilator response achieved during the baseline period (fall in pulmonary vascular resistance = -49 +/- 7% (baseline) versus -25 +/- 5% after repeated DA compressions; p < 0.05). In contrast, the vasodilator response to 8-bromo-guanosine 3',5'-cylic monophosphate remained intact. To determine whether decreased nitric oxide (NO) production may contribute to altered vasoreactivity after acute pulmonary hypertension, repeated DA compressions were performed after treatment with a nonspecific NO synthase inhibitor (nitro-L-arginine). NO synthase inhibition blocked the pulmonary vasodilation during the first DA compression period, and repeated DA compressions after NO synthase inhibition did not further alter the hemodynamic response to DA compression. These findings support the hypothesis that brief hypertension due to DA compression impairs endothelium-dependent pulmonary vasodilation in the fetus, and that this may be due to decreased NO production.

Topics: Acetylcholine; Animals; Carbon Dioxide; Cyclic GMP; Ductus Arteriosus; Endothelium, Vascular; Female; Gestational Age; Heart Rate, Fetal; Hemodynamics; Hypertension, Pulmonary; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Pregnancy; Pulmonary Circulation; Sheep; Vasodilation

Platelet-activating factor (PAF), a lipid mediator released during endotoxin shock, induces pulmonary hypertension, systemic hypotension and cardiac dysfunction. In this study, we compared the effect of inhaled nitric oxide (NO) on PAF-induced pulmonary hypertension and NO metabolism with that on pulmonary hypertension induced by a stable thromboxane A2 mimetic, U46619. Since PAF-induced hypotension might be mediated by NO, the effect of inhaled NO combined with an intravenously administered NO synthase inhibitor, NG-nitro-L-arginine (L-NNA), on PAF-induced hemodynamic change was also investigated.. In a total of 28 beagles anesthetized with pentobarbital the following substances were intravenously administered: PAF 0.56 +/- 0.30 microgram.kg-1.min-1 (group PAF), L-NNA 10 mg.kg-1 + PAF 0.04 +/- 0.03 microgram.kg-1.min-1 (group L-NNA + PAF), U46619 0.60 +/- 0.11 microgram.kg-1.min-1 (group U46619) or L-NNA 10 mg.kg-1 + U46619 0.61 +/- 0.23 microgram.kg-1.min-1 (group L-NNA + U46619) to obtain a mean pulmonary arterial pressure (MPAP) of 25 mmHg. Nitric oxide was then inhaled at 5, 10, 20 and 40 ppm for 15 min at 15-min intervals in the order of increasing concentration. An additional 7 dogs (control group) inhaled NO at normal MPAP (17 mmHg). Hemodynamic and respiratory parameters, NOHb, NO2- + NO3-, and MetHb levels in blood were measured before and during NO administration.. In the control group, hemodynamic and respiratory values did not change significantly during NO administration. In group PAF, NO significantly reversed the PAF-induced pulmonary hypertension. PAF induced a marked systemic hypotension and cardiac output reduction, but these changes were not affected by inhalation of NO. L-NNA pretreatment markedly decreased the dose of PAF required to maintain a MPAP of 25 mmHg, and abolished the PAF-induced hypotension. In group L-NNA + PAF, the diminishing effect of inhaled NO on pulmonary vascular resistance (PVR) was significantly greater than that in group PAF. U46619 induced pulmonary hypertension and increases in blood pressure, intrapulmonary shunt and peak airway pressure. L-NNA pretreatment did not change the dose of U46619 required to maintain a MPAP of 25 mmHg. The effects of inhaled NO on PVR decrease were similar in groups U46619 and L-NNA + U46619. No NOHb was detected in any group. NO2- + NO3- concentration increased during NO administrations. There were no significant differences in NO2- + NO3- concentration among groups.. Inhaled NO at the dose of 5-40 ppm effectively reversed PAF-induced pulmonary hypertension, especially following pretreatment with L-NNA. Inhaled NO did not affect PAF-induced hypotension or cardiac dysfunction. These findings indicate that low concentrations of inhaled NO may be useful in reversing pulmonary hypertension in the endotoxemia where PAF may be one mediator.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Administration, Inhalation; Animals; Dogs; Dose-Response Relationship, Drug; Hemodynamics; Hemoglobins; Hypertension, Pulmonary; Injections, Intravenous; Methemoglobin; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Platelet Activating Factor; Pulmonary Circulation; Vasoconstrictor Agents

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

Inhibition of endothelium-derived nitric oxide (NO) synthesis by L-arginine analogs such as nitro-L-arginine (L-NNA) elicits marked precapillary vasoconstriction in lungs from rats with chronic hypoxia-induced pulmonary hypertension. To investigate the role of endogenous endothelin (ET)-1 in L-NNA-induced vasoconstriction, we tested, in salt solution-perfused hypertensive lungs isolated from chronically hypoxic (3-4 wk at barometric pressure = 410 mmHg) adult male rats, if the pressor responses to L-NNA and exogenous ET-1 were inhibited by either separate or combined ETA and ETB receptor blockade. Whereas only combined pretreatment with 5 microM BQ-123 (selective ETA receptor blocker) and 5 microM BQ-788 (selective ETB receptor blocker) inhibited the response to 100 microM L-NNA, the response to 10 nM ET-1 was reduced by both BQ-123 alone and the combined blockers. Because exogenous ET-1 causes postcapillary vasoconstriction in salt solution-but not blood-perfused normotensive rat lungs, we next compared effects of ETA and ETB receptor blockade on L-NNA and ET-1 vasoconstrictions in blood-perfused hypertensive lungs. In this case, the combined but not the separate effects of BQ-123 and BQ-788 inhibited the responses to both L-NNA and ET-1. The last experiment showed that the use of BQ-788 to inhibit ETB receptor-mediated clearance of circulating ET-1 resulted in greater accumulation of endogenous ET-1 in the perfusate of hypertensive than of normotensive lungs. There was no difference between L-NNA-treated and vehicle control hypertensive lungs in accumulation of ET-1. These results suggest that increased endogenous levels of ET-1 acting through stimulation of both ETA and ETB receptors contribute to the vasoconstriction unmasked by inhibition of NO synthesis in hypertensive rat lungs. The increased ET-1 is apparently not due to the inhibition of NO synthesis, but, instead, its underlying stimulation of smooth muscle cell contraction is counteracted by NO activity.

Topics: Animals; Blood; Endothelin Receptor Antagonists; Endothelin-1; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; In Vitro Techniques; Lung; Male; Nitroarginine; Perfusion; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Sodium Chloride; Vasoconstriction

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

Acute inhibition of endothelium-derived nitric oxide (NO) synthesis by L-arginine analogs such as N omega-nitro-L-arginine (L-NNA) has little effect on basal vascular tone in normal rat lungs but elicits marked vasoconstriction in hypertensive lungs. The NO-suppressible vasoconstriction is dependent on extracellular Ca2+ but is not mediated by L-type Ca2+ channels. This study tested whether the response was mediated by Ca2+ influx through receptor-operated channels, reverse Na+/Ca2+ exchange, or low-threshold voltage-gated (T-type) Ca2+ channels. We first examined whether SKF-96365, a blocker of receptor-operated Ca2+ channels, inhibited L-NNA-induced vasoconstriction in salt solution-perfused hypertensive lungs isolated from chronically hypoxic male rats (exposed to hypobaria of 410 mmHg for 3-5 wk). Whereas 50 microM SKF-96365 inhibited pressor responses to angiotensin II and acute hypoxia, it did not reduce vasoconstriction in response to 100 microM L-NNA. We next examined effects of pretreatment with Na+/Ca2+ exchange blockers and observed that L-NNA vasoconstriction was reduced by both 100 microM amiloride and 50 microM ethylisopropyl amiloride (EIPA). The third experiment showed that each of two different blockers of T-type Ca2+ channels, 10 microM Ro-40-5967 and 300 microM nordihydroguariaretic acid, inhibited L-NNA vasoconstriction and that the combination of EIPA and Ro-40-5967 did not cause more inhibition than did Ro-40-5967 alone. These results suggest that, whereas receptor-operated Ca2+ channels are not significantly involved in the mechanism of NO-suppressible vasoconstriction in hypertensive rat lungs, Ca2+ influx through reverse Na+/Ca2+ exchange and/or T-type Ca2+ channels may play a role. Because both amiloride and EIPA also inhibit T-type Ca2+ channels, we speculate that Ca2+ influx through these channels rather than through reverse Na+/Ca2+ exchange is an important mediator of the vasoconstriction.

Topics: Animals; Calcium Channels; Carrier Proteins; Enzyme Inhibitors; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Male; Nitroarginine; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Ryanodine; Sodium-Calcium Exchanger; Vasoconstriction

In the fetal lamb, oxygen-induced pulmonary vasodilation is attenuated by the combined use of purinergic receptor P1 and P2y antagonists, which block the effect of adenosine and adenosine triphosphate (ATP), respectively, and by N(omega)-nitro-L-arginine [an inhibitor of endothelium-derived nitric oxide (EDNO) synthesis]. In the newborn lamb, oxygen-induced pulmonary vasodilation is not blocked by N(omega)-nitro-L-arginine. We investigated the role of ATP and adenosine in oxygen-induced pulmonary vasodilation in eight newborn lambs with pulmonary hypertension induced by the thromboxane mimic, U46619. The hemodynamic effects of hyperoxia, ATP, adenosine, sodium nitroprusside (SNP), and acetylcholine (ACh) were compared before and after purinergic receptor blockade with Cibacron blue (CB, a P2y-receptor antagonist) and 8-phenyltheophylline (8PT, a P1-receptor antagonist) individually, together, and on a separate day, after infusion of N(omega)-nitro-L-arginine. During pulmonary hypertension, combined pretreatment with 8PT and CB attenuated the decrease in pulmonary arterial pressure caused by hyperoxia (11.3 vs. 35.2%), ATP (10.6 vs. 32.2%), and adenosine (1.9 vs. 33.7%) without change in the effect of ACh or SNP (p < 0.05). N(omega)-Nitro-L-arginine attenuated the pulmonary vasodilation caused by ATP and ACh but not by hyperoxia, adenosine, or SNP. In the newborn lamb, the pulmonary vasodilating effect of both oxygen and ATP are attenuated by combined P1 and P2y purinergic-receptor antagonists. Postnatally, oxygen-induced pulmonary vasodilation appears to be mediated by ATP through purinergic receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenosine; Adenosine Triphosphate; Animals; Animals, Newborn; Endothelium, Vascular; Enzyme Inhibitors; Hemodynamics; Hypertension, Pulmonary; Nitric Oxide; Nitroarginine; Oxygen; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Purinergic Antagonists; Sheep; Theophylline; Thromboxane A2; Triazines; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

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

To investigate early endothelial function associated with increased pulmonary blood flow, vascular shunts were placed between the ascending aorta and main pulmonary artery in 18 late-gestation fetal sheep. Four weeks after delivery, the lambs were instrumented to measure vascular pressures and blood flows, and blood was collected to measure plasma concentrations of guanosine 3',5'-cyclic monophosphate [cGMP, the second messenger to nitric oxide (NO)-mediated vasodilation] and L-arginine (the precursor for NO synthesis). The responses to the endothelium-dependent vasodilators acetylcholine (ACh, 1.0 microgram/kg) and ATP (0.1 mg.kg-1.min-1), the endothelium-independent vasodilators M & B-22948 (a cGMP-specific phosphodiesterase inhibitor, 2.5 mg/kg) and inhaled NO (40 ppm), and N omega-nitro-L-arginine (an inhibitor of NO synthase, 5 mg/kg) were then compared with responses in 12 age-matched controls. Vasodilator responses in control lambs were determined during pulmonary hypertension induced by U-46619 (a thromboxane A2 mimic). Shunted lambs displayed a selective impairment of endothelium-dependent pulmonary vasodilation, an augmented pulmonary vasoconstricting response to NO synthase inhibition, increased plasma cGMP concentrations, and decreased L-arginine concentrations. Taken together, these data suggest that lambs with pulmonary hypertension and increased pulmonary blood flow have early aberrations in endothelial function, as manifested by increased basal NO activity, that cannot be further increased by agonist-induced endothelium-dependent vasodilators.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Adenosine Triphosphate; Animals; Animals, Newborn; Arginine; Cyclic GMP; Endothelium, Vascular; Hemodynamics; Hypertension, Pulmonary; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phosphodiesterase Inhibitors; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Purinones; Sheep; Thromboxane A2; Vasoconstrictor Agents

To determine whether altered NO production contributes to attenuated distensibility (alpha), vasoreactivity, and acetylcholine (ACh) dilation in pulmonary arteries from monocrotaline (MCT)-treated rats (J.A. Madden, P.A. Keller, R. M. Effrosa, C. Sequitte, J.S. Choy, and A.D. Hacker. J. Appl. Physiol. 76: 1589-1593, 1994), intralobar and sidebranch arteries from rats 21 days after MCT treatment were cannulated and pressurized and their diameter changes in response to KCl, norepinephrine, angiotensin II, and pressure were measured in the presence of N omega-nitro-L-arginine (NLA) and L-arginine. NLA treatment decreased MCT artery diameters more than normal arteries (P < 0.05) and abolished ACh dilation in both. Agonist responses were greater in normal but not MCT arteries. The alpha increased in NLA-treated normal (P < 0.05) but not MCT arteries. After L-arginine, normal and MCT arteries returned to control diameters and dilated to ACh. Agonist responses returned to control in normal but not MCT arteries. Normal but not MCT arteries dilated in calcium-free solution (P < 0.05). These results suggest that pulmonary arteries from rats with MCT-induced pulmonary hypertension produce more NO than do pulmonary arteries; inhibiting NO does not increase contractility; and decreased vasoreactivity and alpha values are not due to smooth muscle cell tone but may be due to abnormal vascular remodeling.

Topics: Air Pressure; Animals; Arginine; Calcium; Enzyme Inhibitors; Hypertension, Pulmonary; Male; Monocrotaline; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pulmonary Artery; Rats; Rats, Sprague-Dawley

Reversal of heparin anticoagulation with protamine may be associated with acute pulmonary vasoconstriction. The specific site of pulmonary vasoconstriction has not been determined. This study was designed to determine the site of protamine-induced pulmonary vasoconstriction and the role of nitric oxide (NO) after protamine injection. Pigs were anesthetized and instrumented with catheters for monitoring pulmonary arterial, systemic arterial, and central venous pressures. Pulmonary capillary pressure was estimated using the arterial occlusion concept, while left atrial pressure was estimated from the equilibrium wedge pressure. Hemodynamic measurements were made during baseline, before and after heparin (200 U/kg), at peak pressure response after protamine injection (2 mg/kg), and 10 and 30 min thereafter. In the control group, pulmonary vascular resistance (PVR) values during baseline and after heparin were identical (2.7 +/- 0.4 mm Hg.L-1.min-1). At peak protamine response (1-2 min) PVR increased to 8.0 +/- 1.6, but returned to baseline value after 10 min (2.8 +/- 0.3) and remained stable for 30 min (2.2 +/- 0.3). The increase in PVR after protamine was primarily due to an increase in venous resistance from 1.0 +/- 0.2 to 4.9 +/- 1.4 mm Hg.L-1.min-1, and a much smaller increase in arterial resistance from 1.7 +/- 0.3 to 3.4 +/- 0.6 mm Hg.L-1.min-1. A second group was treated with nitrow-L-arginine (LNA, 20 mg/kg) to inhibit NO release, and then heparin and protamine were administered as in the first group. Heparin had no effect on pressures, but protamine increased PVR by the same magnitude as in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Blood Pressure; Cardiac Output; Central Venous Pressure; Disease Models, Animal; Female; Heparin; Hypertension, Pulmonary; Male; Nitric Oxide; Nitroarginine; Protamines; Pulmonary Artery; Pulmonary Veins; Pulmonary Wedge Pressure; Swine; Vascular Resistance; Vasoconstrictor Agents

The hemodynamic effects of endothelin-1 (ET-1) are mediated by at least two distinct receptors: ETa and ETb receptors. Recently, ETb receptor agonists (4 Ala ET-1 and IRL 1620) were developed. To investigate the role of ETb receptor activation on the pulmonary and systemic circulations, we studied the hemodynamic effects of intrapulmonary arterial injections of these receptor agonists in 10 intact newborn lambs. At rest, 4 Ala ET-1 (290-1,725 ng/kg) changed no hemodynamic variables. IRL 1620 (180-1,095 ng/kg) decreased mean pulmonary arterial pressure (PAP, 16.8% +/- 15.0 and 17.8% +/- 8.5, p < 0.05) and left pulmonary artery blood flow (21.6% +/- 22.1 and 33.4% +/- 27.7, p < 0.05) at the two highest doses only. During U46619-induced pulmonary hypertension, both 4 Ala ET-1 (3.2% +/- 8.0 to 15.9% +/- 6.4, p < 0.05) and IRL 1620 (8.7% +/- 6.3 to 21.9% +/- 4.1, p < 0.05) produced selective dose-dependent decreases in PAP. The decrease in mean PAP induced by 4 Ala ET-1 and IRL 1620 was attenuated by N omega-nitro-L-arginine [an inhibitor of endothelium-derived nitric oxide (EDNO) synthesis] (16.6% +/- 3.5 vs. 5.9% +/- 2.3 and 16.2% +/- 3.4 vs. 6.6% +/- 2.8, p < 0.05) and by glybenclamide (a blocker of ATP-dependent potassium channels) (18.2% +/- 7.9 vs. 7.5% +/- 8.3 and 14.7% +/- 3.6 vs. 6.3% +/- 3.2, p < 0.05). ETb receptor activation produces selective pulmonary vasodilation during pulmonary hypertension in intact newborn lambs. The vasodilating properties are mediated in part by release of ENDO and by potassium channel activation.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Animals, Newborn; Arginine; Blood Pressure; Disease Models, Animal; Endothelins; Endothelium, Vascular; Glyburide; Hypertension, Pulmonary; Injections, Intra-Arterial; Nitroarginine; Peptide Fragments; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Circulation; Regional Blood Flow; Sheep; Thromboxane A2; Vascular Resistance; 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

1. The effect of the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NOARG), on endothelium-dependent relaxation to a receptor-independent agent, ionomycin, was examined in isolated pulmonary arteries and veins from control, short-term and chronic pulmonary hypertensive sheep. All vessel segments were contracted to optimal levels of active force with endothelin-1 to record endothelium-dependent relaxation. 2. Pulmonary hypertension was induced by continuous pulmonary artery air embolization for 1 day (short-term) and 14 days (chronic) and was associated with a 2 and 3 fold increase in pulmonary vascular resistance respectively. 3. L-NOARG (0.1 mM) reduced the maximum relaxation (Rmax) to ionomycin in large and medium-sized pulmonary arteries from control sheep by approximately 70%. By contrast, L-NOARG (0.1 mM) did not inhibit the Rmax to ionomycin in matched vessels from short-term and chronic pulmonary hypertensive sheep. 4. Resistance of ionomycin-induced relaxations to inhibition by L-NOARG, was confined to the arterial vasculature in chronic pulmonary hypertensive animals, as relaxations to ionomycin in large and medium-sized chronic pulmonary hypertensive veins were, like those in control veins, abolished by L-NOARG. Both large and medium-sized pulmonary veins from short-term pulmonary hypertensive sheep, however, were resistant to block by L-NOARG. 5. Neither sensitivity (pEC50) nor Rmax to ionomycin in large, short-term pulmonary hypertensive arteries was affected when the extracellular concentration of K+ was increased isotonically to 30 mM. Nifedipine (0.3 microM) was present throughout to prevent high K(+)-induced smooth muscle contraction. In the presence of this high extracellular K+, however, L-NOARG (0.1 mM) caused complete inhibition of the relaxation to ionomycin, whereas in normal extracellular K+ (4.7 mM), L-NOARG only weakly inhibited ionomycin relaxations. 6. In conclusion, the onset of pulmonary hypertension in sheep following air embolization, is associated with the development of resistance of endothelium-dependent relaxations to block by L-NOARG. The mechanism of L-NOARG resistance appears to be due to the up-regulation of a K+ channel-mediated backup vasodilator mechanism which can compensate for the loss of nitric oxide (NO)-mediated relaxation. Although this mechanism remains functionally 'silent' in the presence of NO it is able to maintain adequate endothelium-dependent vasodilatation during pulmonary hypertension if

Topics: Animals; Arginine; Blood Gas Analysis; Endothelium, Vascular; Enzyme Inhibitors; Female; Hemodynamics; Hypertension, Pulmonary; In Vitro Techniques; Ionomycin; Ionophores; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Potassium Channels; Potassium Chloride; Pulmonary Artery; Pulmonary Veins; Sheep; Up-Regulation; Vasodilator Agents

Endothelin-1 (ET-1) is a polypeptide that has potent hemodynamic effects on the pulmonary circulation. To determine whether there are changes in these effects with increasing postnatal age, we investigated the effects of ET-1 (250 ng/kg) at rest and during pulmonary hypertension in eight lambs (< 1 wk old) and 11 juvenile sheep (6-12 mo old). At rest, ET-1 did not change pulmonary arterial pressure in lambs, but increased pulmonary arterial pressure by 64.0 +/- 37.5% (p < 0.05) in sheep. During pulmonary hypertension, ET-1 produced greater decreases in pulmonary arterial pressure in lambs than in sheep (26.6 +/- 3.4% versus 18.7 +/- 8.3%, p < 0.05). In juvenile sheep, the increase in resting pulmonary arterial pressure produced by ET-1 was inhibited by meclofenamic acid, an inhibitor of prostaglandin synthesis (40.3 +/- 9.9% versus 2.3 +/- 4.7%, p < 0.05); during pulmonary hypertension, the decrease in pulmonary arterial pressure produced by ET-1 was inhibited by N omega-nitro-L-arginine, an inhibitor of endothelium-derived nitric oxide synthesis (21.4 +/- 10.7% versus 8.0 +/- 3.6%, p < 0.05) and by glybenclamide, an ATP-dependent potassium-channel blocker (18.8 +/- 8.4% versus 4.0 +/- 4.4%, p < 0.05). The hemodynamic effects of ET-1 on the pulmonary circulation are dependent on postnatal age. Pulmonary vasoconstriction is mediated by prostaglandin production, and pulmonary vasodilation is mediated, in part, by release of endothelium-derived nitric oxide and activation of ATP-dependent potassium channels.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Aging; Animals; Arginine; Endothelins; Glyburide; Hemodynamics; Hypertension, Pulmonary; Meclofenamic Acid; Nitric Oxide; Nitroarginine; Potassium Channel Blockers; Prostaglandin Endoperoxides, Synthetic; Prostaglandins; Pulmonary Circulation; Sheep; Thromboxane A2; Vasoconstrictor Agents

To determine the potential contribution of endothelin (ET) to modulation of high pulmonary vascular resistance in the normal fetus, we studied the effects of BQ 123, a selective ET-A receptor antagonist, and sarafoxotoxin S6c (SFX), a selective ET-B receptor agonist, in 31 chronically prepared late gestation fetal lambs. Brief intrapulmonary infusions of BQ 123 (0.1-1.0 mcg/min for 10 min) caused sustained increases in left pulmonary artery flow (Qp) without changing main pulmonary artery (MPA) and aortic (Ao) pressures. In contrast, BQ 123 did not change vascular resistance in a regional systemic circulation (the fetal hindlimb). To determine whether big-endothelin-1 (big-ET-1)-induced pulmonary vasoconstriction is mediated by ET-A receptor stimulation, we studied the effects of big-ET-1 with or without pretreatment with BQ 123. BQ 123 (0.5 mcg/min for 10 min) blocked the rise in total pulmonary resistance caused by big-ET-1. CGS 27830 (100 mcg/min for 10 min), an ET-A and -B receptor antagonist, did not change basal tone but blocked big-ET-1-induced pulmonary vasoconstriction. Brief and prolonged intrapulmonary infusion of SFX (0.1 mcg/min for 10 min) increased Qp twofold without changing MPA or Ao pressures. Nitro-L-arginine (L-NA), a selective endothelium-derived nitric oxide (EDNO) antagonist, blocked vasodilation caused by BQ 123 and SFX. We conclude that: (a) BQ 123 causes sustained fetal pulmonary vasodilation, but did not change vascular resistance in the fetal hindlimb; (b) Big-ET-1-induced pulmonary vasoconstriction may be mediated through ET-A receptor stimulation; and (c) ET-B receptor stimulation causes pulmonary vasodilation through EDNO release. These findings support the hypothesis that endothelin may play a role in modulation of high basal pulmonary vascular resistance in the normal fetus.

Topics: Animals; Arginine; Blood Pressure; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Fetus; Hypertension, Pulmonary; Muscle Tonus; Nitric Oxide; Nitroarginine; Peptides, Cyclic; Perfusion; Protein Precursors; Pulmonary Circulation; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Sheep; Vascular Resistance; Viper Venoms

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

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

Nitric oxide (10 ppm) inhaled by pigs before or during endotoxin shock induced by an infusion of E. coli lipopolysaccharide. Nitric oxide inhalation selectively attenuated pulmonary hypertension during endotoxin infusion without influencing mean arterial blood pressure and cardiac output. Upon cessation of nitric oxide inhalation, pulmonary artery pressure rapidly increased to levels seen in endotoxin-treated controls. The oxygenation and pH of arterial blood were significantly higher in the animals receiving nitric oxide. A marked increase in arterial plasma noradrenaline and neuropeptide Y was seen in endotoxin-treated control pigs while in the nitric oxide-treated pigs this increase was markedly reduced. The increase in arterial plasma endothelin-1 was not influenced by nitric oxide inhalation. Infusion of L-arginine (substrate for nitric oxide synthesis) also attenuated the pulmonary hypertension but was not selective for the pulmonary vasculature. L-Nitro-arginine (a nitric oxide synthesis inhibitor) initiated a rapid but brief elevation of arterial blood pressure and of pulmonary artery pressure as well as a reduction in cardiac output. Nitric oxide inhalation selectively reduces pulmonary hypertension in porcine endotoxin shock and improves arterial oxygenation and pH with a marked attenuation of sympathetic activation.

Topics: Administration, Inhalation; Animals; Arginine; Blood Gas Analysis; Blood Pressure; Endothelins; Female; Hemodynamics; Hypertension, Pulmonary; Male; Neuropeptide Y; Nitric Oxide; Nitroarginine; Norepinephrine; Pulmonary Circulation; Pulmonary Gas Exchange; Shock, Septic; Swine; Vascular Resistance

Supplemental oxygen and alkalosis are the most effective treatments used to lower pulmonary arterial pressure in children with pulmonary hypertensive disorders. However, their mechanisms of action are unknown. Endothelium-derived nitric oxide (EDNO) is an important mediator of pulmonary vascular tone and produces potent pulmonary vasodilation during pulmonary hypertension. In vitro evidence suggests that EDNO may mediate the vasodilating effects of oxygen. To investigate whether EDNO synthesis mediates the pulmonary vasodilation produced by hyperoxia [normocarbic ventilation with 100% oxygen, arterial oxygen tension > 450 torr (60 kPa)] or alkalosis (hyperventilation with 21% oxygen, pH > 7.55) in vivo, eight intact newborn lambs were studied during similar degrees of pulmonary hypertension induced either by the infusion of U46619 (a thromboxane A2 mimic) or N omega-nitro-L-arginine (an inhibitor of EDNO synthesis). The lambs were sedated, paralyzed, and mechanically ventilated. Meclofenamic acid was infused to inhibit prostaglandin synthesis. During pulmonary hypertension induced by U46619, pulmonary arterial pressure and pulmonary vascular resistance were significantly decreased by acetylcholine (an EDNO-dependent vasodilator) (23.1 +/- 3.4% and 43.3 +/- 14.5%, respectively), hyperoxia (26.8 +/- 7.8% and 32.9 +/- 10.6%), and alkalosis (32.1 +/- 10.3% and 36.1 +/- 17.0%) (p < 0.05). During pulmonary hypertension induced by N omega-nitro-L-arginine, the decreases in pulmonary arterial pressure and pulmonary vascular resistance produced by acetylcholine (9.6 +/- 6.4% and 23.9 +/- 14.1%, respectively) were significantly attenuated (p < 0.05), but the decreases produced by hyperoxia or alkalosis were unchanged. Therefore, hyperoxia and alkalosis can produce pulmonary vasodilation independent of EDNO synthesis in the intact newborn lamb.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Alkalosis; Animals; Animals, Newborn; Arginine; Hypertension, Pulmonary; Nitric Oxide; Nitroarginine; Oxygen; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Sheep; Vasodilation

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

To investigate the role of endothelium-derived relaxing factor (EDRF) in the regulation of resting pulmonary vascular tone and endothelium-dependent pulmonary vasodilation, we studied the hemodynamic effects of N omega-nitro-L-arginine (a new stereospecific EDRF inhibitor) in 10 spontaneously breathing lambs and then compared the hemodynamic responses to five vasodilators during pulmonary hypertension induced by the infusion of U-46619 (a thromboxane A2 mimetic) or N omega-nitro-L-arginine. N omega-nitro-L-arginine caused a significant dose-dependent increase in pulmonary arterial pressure. Pretreatment with L-arginine blocked this increase, but pretreatment with D-arginine did not, suggesting that N omega-nitro-L-arginine is a competitive inhibitor of L-arginine for EDRF production. During U-46619 infusions, acetylcholine, ATP-MgCl2, isoproterenol, sodium nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-bromo-cGMP) decreased pulmonary arterial pressure. During N omega-nitro-L-arginine infusions, the decrease in pulmonary arterial pressure caused by acetylcholine and ATP-MgCl2 (endothelium-dependent vasodilators) was significantly attenuated, but the decrease caused by isoproterenol, sodium nitroprusside, and 8-bromo-cGMP (endothelium-independent vasodilators) was unchanged. This study supports the hypothesis that EDRF in part mediates resting pulmonary vascular tone and endothelium-dependent pulmonary vasodilation. N omega-nitro-L-arginine is useful for studying EDRF inhibition in intact animals.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Adenosine Triphosphate; Animals; Arginine; Binding, Competitive; Blood Pressure; Cyclic GMP; Endothelium, Vascular; Hemodynamics; Hypertension, Pulmonary; Isoproterenol; Lung; Nitric Oxide; Nitroarginine; Nitroprusside; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Sheep; Vasodilation