nitroarginine and Hyperemia

We previously reported that combined blockade of adenosine receptors and ATP-sensitive K+ channels (K+(ATP) channels) blunted but did not abolish the response of coronary blood flow to exercise. This study tested the hypothesis that the residual increase in coronary flow in response to exercise after adenosine receptor and K+(ATP) channel blockade is dependent on endogenous NO. Dogs were studied at rest and during a four-stage treadmill exercise protocol under control conditions, during K+(ATP) channel blockade with glibenclamide (50 microg x kg(-1) x min(-1) i.c.) in the presence of adenosine receptor blockade with 8-phenyltheophylline (8-PT, 5 mg/kg i.v.), and after the addition of the NO synthase inhibitor N(G)-nitro-L-arginine (LNNA, 1.5 mg/kg i.c.). During control conditions, coronary blood flow was 49 +/- 3 mL/min at rest and increased to 92 +/- 8 mL/min at peak exercise. LNNA alone or in combination with 8-PT did not alter resting coronary flow and did not impair the normal increase in flow during exercise, indicating that when K+(ATP) channels are intact, neither NO nor adenosine-dependent mechanisms are obligatory for maintaining coronary blood flow. Combined K+(ATP) channel and adenosine blockade decreased resting coronary flow to 27 +/- 3 mL/min (P<.05), but exercise still increased flow to 45 +/- 5 mL/min (P<.05). The subsequent addition of LNNA further decreased resting coronary flow to 20 +/- 2 mL/min and markedly blunted exercise-induced coronary vasodilation (coronary vascular conductance, 0.20 +/- 0.03 mL x min(-1) x mm Hg(-1) at rest versus 0.24 +/- 0.04 mL x min(-1) x mm Hg(-1) during the heaviest level of exercise; P=.22), so that coronary flow both at rest and during exercise was below the control resting level. The findings suggest that K+(ATP) channels are critical for maintaining coronary vasodilation at rest and during exercise but that when K+(ATP) channels are blocked, both adenosine and NO act to increase coronary blood flow during exercise. In the presence of combined K+(ATP) channel blockade and adenosine receptor blockade, NO was able to produce approximately one quarter of the coronary vasodilation that occurred in response to exercise when all vasodilator systems were intact.

Topics: Adenosine; Adenosine Triphosphate; Animals; Coronary Disease; Coronary Vessels; Dogs; Enzyme Inhibitors; Glyburide; Hemodynamics; Hyperemia; Nitric Oxide; Nitroarginine; Physical Exertion; Potassium Channels; Purinergic P1 Receptor Antagonists; Theophylline; Vasodilation

Sustained inhibition of NO synthesis (N omega-nitro-L-arginine [L-NNA], 20 mg.kg-1.d-1, 7 days) was investigated at rest and during exercise in conscious dogs. At rest, L-NNA did not alter mean arterial blood pressure but markedly increased total peripheral resistance (+73 +/- 14%, P < .01). Exaggerated hypertension was observed during exercise (+132 +/- 5 mm Hg after L-NNA versus +113 +/- 5 mm Hg before L-NNA, P < .01). L-NNA decreased the resting coronary artery diameter by 6 +/- 1% and suppressed its exercise-induced dilation but had no effect on coronary blood flow and resistance. L-NNA decreased flow repayment volumes during reactive hyperemia, but corresponding flow debt volumes remained unchanged. The cyclooxygenase inhibitor diclofenac (10 mg/kg) had no effect on reactive hyperemia parameters before L-NNA but reduced flow repayment volumes, durations, and corresponding debt-to-repayment ratios in L-NNA-treated dogs (all P < .05). In vitro, indomethacin blunted the residual relaxation to bradykinin of large coronary arteries taken from L-NNA-treated, but not from control, dogs. Bradykinin-induced increase in 6-ketoprostaglandin F1 alpha production was greater in coronary arteries taken from L-NNA-treated dogs (+ 179 +/- 41 pg/mm2) than from control dogs (+ 66 +/- 18 pg/mm2) (P < .05). These results indicate that (1) NO is of major importance in the control of systemic but not coronary resistance vessels at rest and during exercise, and (2) after L-NNA, the cyclooxygenase pathway is involved in myocardial reactive hyperemia and in the residual relaxation to bradykinin of isolated coronary arteries. Thus, in conscious dogs, the cyclooxygenase pathway might act as a protective mechanism of the coronary circulation when endothelial nitric oxide synthesis is altered.

Topics: Acetylcholine; Animals; Bradykinin; Coronary Circulation; Coronary Vessels; Diclofenac; Dogs; Epoprostenol; Femoral Artery; Hemodynamics; Hyperemia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Physical Exertion; Prostaglandin-Endoperoxide Synthases

1. In the present study the highly potent nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) was intravenously infused and examined for its efficacy in inhibiting NOS activity and in altering blood flow and oxygen uptake in human skeletal muscle. 2. The plasma concentrations of L-NAME and its active metabolite NG-nitro-L-arginine (L-NA), and the activity of NOS in skeletal muscle were measured in healthy male subjects (n = 6) before (control) and after 60 min of intravenous infusion of L-NAME (4 mg kg(-1)). In another group of healthy males (n = 8), the physiological effects of L-NAME were studied at rest, and during submaximal and exhaustive knee extensor exercise before (control) and 30 min after L-NAME infusion (4 mg kg(-1)). 3. The plasma concentrations of L-NAME and L-NA were highest (8.4 +/- 1.6 and 8.3 +/- 0.8 micromol l(-1)) after 60 min of L-NAME infusion. Ninety minutes later mainly L-NA remained in plasma (5.1 +/- 0.4 micromol l(-1)). Thirty minutes after L-NAME infusion, the muscle L-NA content was 38 +/- 4 micromol (kg dry wt)-1 and muscle NOS activity was reduced by 67 +/- 8 % (P < 0.05). 4. Leg blood flow and leg oxygen uptake during submaximal and exhaustive exercise were similar (P > 0.05) following L-NAME infusion and in control. Blood flow during recovery was lower in the L-NAME condition (P < 0.05). 5. In conclusion, the present study shows for the first time that systemic infusion of L-NAME in humans causes a marked reduction in skeletal muscle NOS activity. Despite this attenuated NOS activity, exercise-induced hyperaemia and oxygen uptake were unaltered. Thus, the data strongly suggest that NO is not essential for the regulation of blood flow or oxygen uptake in contracting human skeletal muscle.

Topics: Adult; Blood Pressure; Enzyme Inhibitors; Exercise; Hemodynamics; Humans; Hyperemia; Leg; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitroarginine; Oxygen Consumption; Regional Blood Flow

The aim of this study was to evaluate the role of nitric oxide (NO) in the mechanisms of arterial distensibility and intravascular pressure stability in normotensive and spontaneously hypertensive rats. The experiments were performed on the anesthetized male Wistar, Wistar-Kyoto (WKY), and spontaneously hypertensive rats (SHR). The abdominal aorta was cannulated and perfused with variable blood flow rates with subsequent determination of major characteristics of regional vascular function. The blockade of nitric oxide (NO) synthase resulted in the increase in hydraulic resistance of the hindlimb vascular bed in all series of the experiments. It was associated with the decrease in the intravascular pressure stability. The obtained results provide further evidence for an important role of NO in the formation of conductivity and stability of the arterial pressure both in normo- and hypertensive rats. However, the involvement of NO in the phenomenon of flow-dependent vasodilation in SHR is unlikely. The major difference between SHR and normotensive rats involved the ability of the resistive arteries of SHR to enhance vascular conductivity in response to blood flow enhancement. Presumably, there are some unidentified additional factors that are involved in the flow-dependent vasodilation in SHR.

Topics: Algorithms; Animals; Arteries; Blood Pressure; Catheterization; Enzyme Inhibitors; Hemodynamics; Hyperemia; Hypertension; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Vascular Resistance; Vasodilation

Neural activities trigger regional vasodilation in the brain. Diffusible messengers such as nitric oxide (NO) and prostanoids are considered to work as vasodilators in neurovascular coupling. However, their roles are still controversial. In the present study, cortical images of neural activities and vasodilation were recorded through the intact skull of C57BL/6 mice anesthetized with urethane. Flavoprotein fluorescence responses elicited by vibratory hindpaw stimulation were followed by darkening of arteriole images reflecting vasodilation in the somatosensory cortex. Vasodilation was also observed in light reflection images at the wavelength of 570 nm in the same mice. We perfused the surface of the cortex under the skull with 100 microM N(G)-nitro-l-arginine (l-NA), an inhibitor of NO synthase (NOS), and 10 microM indomethacin, an inhibitor of cyclooxygenase (COX). These drugs suppressed vasodilation without changing flavoprotein fluorescence responses. A mixture of l-NA and indomethacin almost completely eliminated vasodilation. In mice lacking neuronal NOS (nNOS), activity-dependent vasodilation was significantly suppressed compared with that in littermate control mice, while that in mice lacking cytosolic phospholipase A2 alpha (cPLA2alpha) was unchanged. These results indicate that NO works as a vasodilator in neurovascular coupling of the mouse somatosensory cortex.

Topics: Animals; Cerebral Arteries; Cerebrovascular Circulation; Cyclooxygenase 2 Inhibitors; Evoked Potentials, Somatosensory; Flavoproteins; Fluorescent Dyes; Group IV Phospholipases A2; Hyperemia; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitric Oxide; Nitric Oxide Synthase Type I; Nitroarginine; Physical Stimulation; Somatosensory Cortex; Vasodilation

Ghrelin has been recently identified as an endogenous ligand for growth hormone secretagogue receptor that regulates growth hormone secretion, increases appetite and contributes to energy homeostasis. Although this peptide is predominantly produced by the fasted stomach, little is known about its influence on the gastric mucosal integrity. The aim of the present study was (1) to investigate the effect of acylated ghrelin on the formation and healing of acute gastric mucosal lesions induced by ischemia-reperfusion and gastric mucosal blood flow in rats; (2) to analyse the effects of the deactivation of afferent sensory nerves with capsaicin and of the inhibition of nitric oxide (NO)-synthase by NG-nitro-l-arginine (l-NNA) on the ghrelin-induced protection; (3) to examine the influence of ghrelin on nuclear factor-kappa B (NF-kappaB) activation and on release of proinflammatory cytokines, such as tumor necrosis factor-alpha, (4) to assess the effect of ghrelin on the mRNA expression of constitutive nitric oxide synthase (cNOS), calcitonin gene related peptide (CGRP) and angiogenesis related proteins such as hypoxia inducible factor-1 alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF), and (5) to determine the effect of ischemia/reperfusion on the gastric mucosa expression of ghrelin in rats without and with administration of exogenous hormone. Wistar rats were exposed to 30 min of ischemia followed by 3 h of reperfusion. Ghrelin was administered in dose of 5, 10 or 20 mug/kg intraperitoneally (i.p.) 30 min prior exposure to ischemia/reperfusion and at 3 h after the end of ischemia, the mean lesion area was measured by planimetry and the changes in gastric blood flow were determined by hydrogen (H2)-gas clearance method. The healing of ischemia/reperfusion induced lesions was evaluated at 24 h or 6 days after the end of standard ischemia/reperfusion. The expression of cNOS, CGRP, HIF-1alpha, VEGF and ghrelin was evaluated by reverse transcription polymerase chain reaction or Western blot. Ghrelin significantly attenuated the ischemia/reperfusion-induced gastric lesions and accelerated the healing of these lesions while significantly raising the gastric blood flow. Deactivation of sensory nerves with capsaicin or inhibition of cNOS by L-NNA significantly attenuated the protective activity of ghrelin and accompanying increase in the GBF. Exogenous ghrelin significantly inhibited the activation of NF-kappaB and plasma TNF-alpha levels. The ghrelin

Topics: Animals; Calcitonin Gene-Related Peptide; Capsaicin; Enzyme Inhibitors; Gastric Mucosa; Gene Expression; Ghrelin; Hyperemia; Hypoxia-Inducible Factor 1, alpha Subunit; Injections, Intraperitoneal; Male; Neurons, Afferent; NF-kappa B; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Peptide Hormones; Rats; Rats, Wistar; Reperfusion Injury; RNA, Messenger; Stomach; Stomach Diseases; Tumor Necrosis Factor-alpha; Vascular Endothelial Growth Factor A

The role of different isoforms of nitric oxide synthase (NOS) in the gastric mucosal hyperemia, induced by 155 mM luminal hydrochloric acid (pH approximately 0.8) without a barrier breaker, was investigated. Rats were anesthetized with Inactin (120 mg/kg ip), and mice were anesthetized with Forene (2.2% in 40% oxygen gas at 150 ml/min); the gastric mucosa was exteriorized. Gastric mucosal blood flow was measured with laser-Doppler flowmetry (LDF) in rats treated with Nomega-nitro-l-arginine (l-NNA; unspecific NOS inhibitor), l-N6-(1-iminoethyl)lysine [l-NIL; inducible (i) NOS inhibitor], or S-methyl-l-thiocitrulline [SMTC; neuronal (n) NOS inhibitor], 10 mg/kg, followed by 3 mg. kg-1. h-1 iv, in iNOS-deficient (-/-) and nNOS(-/-) mice. mRNA was isolated from the gastric mucosa in iNOS(-/-) and wild-type (wt) mice, and real-time RT-PCR was performed. The effect of 155 mM acid on gastric mucosal permeability was determined by measuring the clearance of 51Cr-EDTA from blood to lumen. LDF increased by 48 +/- 13% during 155 mM HCl luminally, an increase that was abolished by l-NNA, SMTC, or l-NIL. In iNOS wt mice, LDF increased by 33 +/- 8% during luminal acid. The blood flow increase was attenuated substantially in iNOS(-/-) mice. RT-PCR revealed iNOS mRNA expression in the gastric mucosa in the iNOS wt groups. The blood flow increase in response to acid was not abolished in nNOS(-/-) mice (nNOS-sufficient mice, 39 +/- 18%; heterozygous mice, 25 +/- 19%; -/- mice, 19 +/- 7%). Mucosal permeability was transiently increased during 155 mM HCl. The results suggest that iNOS is constitutively expressed in the gastric mucosa and is involved in acid-induced hyperemia, suggesting a novel role for iNOS in gastric mucosal protection.

Topics: Administration, Topical; Animals; Enzyme Inhibitors; Female; Gastric Mucosa; Gene Expression Regulation, Enzymologic; Hydrochloric Acid; Hyperemia; Laser-Doppler Flowmetry; Male; Mice; Mice, Mutant Strains; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitroarginine; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Brain edema is a common fatal complication in acute liver failure. It is related to an acute change in brain osmolarity secondary to the glial accumulation of glutamine. Since high cerebral blood flow (CBF) precedes cerebral herniation in fulminant hepatic failure we first determined if an increase in brain water and glutamine are prerequisite to a rise in CBF in a model of ammonia-induced brain edema. Secondly, we determined if such a cerebral hyperperfusion is mediated by nitric oxide synthase (NOS).. Male rats received an end-to-side portacaval anastomosis (PCA). At 24 h, they were anesthetized with ketamine and infused with ammonium acetate (55 microM/kg per min). Studies were performed at 60, 90, 120, 150 and 180 min after starting the ammonia infusion and once the intracranial pressure had risen three-fold (mean 210'). Brain water (BW) was measured using the gravimetry method and CBF with the radioactive microsphere technique. Glutamine (GLN) in the CSF was sampled via a cisterna magna catheter. The neuronal NOS was specifically inhibited by 1-2-trifluoromethylphenyl imidazole (TRIM, 50 mg/kg intraperitoneally) and in separate studies nonspecifically by N-omega-nitro-L-arginine (L-NNA, 2 microg/kg per min intravenously). At 90', brain water was significantly increased (P < 0.015) as compared to the 60' group while CBF was significantly different at 150'. A significant correlation was observed between values of CBF and brain water (r = 0.88, n = 36, P < 0.001). Administration of either TRIM or L-NNA did not prevent the development of cerebral hyperperfu. sion and edema.. We observed that cerebral hyperemia follows an initial rise in brain water content, rather than in the cerebrospinal fluid concentration of glutamine. The rise in CBF further correlated with brain water accumulation and was of critical importance for the development of intracranial hypertension. The unique mechanism for the rise in CBF in hyperammonemia was not prevented by NOS inhibition indicating that NO is not the mediator of high CBF and intracranial hypertension.

Topics: Ammonia; Anesthesia, General; Animals; Arteries; Body Water; Brain; Brain Edema; Cerebrovascular Circulation; Enzyme Inhibitors; Glutamine; Hyperemia; Intracranial Pressure; Male; Nitric Oxide Synthase; Nitroarginine; Oxygen; Pentobarbital; Rats; Rats, Sprague-Dawley; Veins

Many properties of nitric oxide, NO, (localization, diffusiveness, half-life, vasodilatory affects) have supported its potential role in mediating the link between local cerebral activity and blood flow. However, evidence that both supports and refutes a role for NO in functional hyperemia have been presented. The present study employed multiple nitric oxide synthase inhibitors, two anesthetic regimes and laser-Doppler flowmetry to test the hypothesis that NO is critically involved in mediating the functional hyperemic response within rodent whisker-barrel cortex (WBC). In urethane anesthetized animals, functional hyperemic responses were obtained both before and after 1 mg/kg atropine infusion, 30 mg/kg i.v. L-NAME (N-Nitro-L-arginine methylester) infusion, 30 mg/kg L-NA (N-Nitro-L-arginine) infusion or 25 mg/kg 7-NI (7-nitroindazole). L-NAME was also tested in a group of animals pretreated with halothane before urethane anesthesia. Neither the magnitude of the blood flow response nor its time course was altered by NO blockade or atropine administration when compared to pre-infusion controls in urethane anesthetized rats. In contrast, animals that were pretreated with halothane exhibited a 33% inhibition of functional hyperemia after L-NAME administration. Taken together, these data do not support a primary role for NO in rat WBC functional hyperemia and suggest that previous reports of inhibition may have been secondary to the anesthesia employed.

Topics: Anesthesia, General; Anesthetics, Inhalation; Anesthetics, Intravenous; Animals; Atropine; Cerebrovascular Circulation; Enzyme Inhibitors; Halothane; Hyperemia; Indazoles; Male; Muscarinic Antagonists; Nerve Tissue Proteins; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Receptors, Muscarinic; Somatosensory Cortex; Touch; Urethane; Vasodilation; Vibrissae

Clinical studies have shown that low doses of aspirin (<300 mg/day) inhibit thromboxane A2 production and platelet aggregation but preserve prostacyclin synthesis. In contrast, high doses of aspirin (>1,000 mg/day) suppress the synthesis of both eicosanoids. Because the consequences of aspirin administration have never been investigated on coronary vasomotor tone in vivo, we investigated the effects of low and high doses of aspirin on systemic and coronary hemodynamics under basal conditions and after myocardial reactive hyperemia in conscious dogs. Dogs were instrumented with a Doppler flow probe and a hydraulic occluder. Coronary blood flow was measured in the conscious state at baseline and during myocardial reactive hyperemia after 10, 20, and 30 s of coronary occlusion. Thromboxane B2 serum concentrations, an index of platelet aggregation, decreased by >90% after long-term i.v. administration of aspirin, 100 mg/day for 7 days (low dose). Neither systemic and coronary hemodynamics nor reactive hyperemia were affected by the drug. After combined administration of this low dose of aspirin and of the nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine (L-NNA, 30 mg/kg/day/7 days), reactive hyperemia decreased to the same extent as when L-NNA was administered alone. After administration of a unique high-dose aspirin (1,000 mg, i.v.), myocardial reactive hyperemia was markedly reduced, and this effect was still observed after previous blockade of NOS and cyclooxygenase by L-NNA and diclofenac, respectively. Thus long-term treatment with a low antiaggregant dose of aspirin does not alter the ability of coronary vessels to dilate during myocardial reactive hyperemia in conscious dogs. In contrast, short-term administration of a high antiinflammatory dose of aspirin severely blunts myocardial reactive hyperemia through a mechanism that is independent of both cyclooxygenase and nitric oxide metabolic pathways.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aspirin; Bradykinin; Coronary Disease; Coronary Vessels; Cyclooxygenase Inhibitors; Diclofenac; Dogs; Dose-Response Relationship, Drug; Hyperemia; Male; Myocardium; Nitric Oxide Synthase; Nitroarginine; Salicylic Acid; Thromboxane B2; Time Factors

After ischaemic preconditioning (IP), obtained by short episodes of ischaemia, cardiac protection occurs due to a reduction in myocardial metabolism through the activation of A1 adenosine receptors. The antiarrhythmic effect of IP is attributed to an increase in the release of nitric oxide (NO) by the endothelium. On the basis of the above consideration the present investigation studies the changes induced by preconditioning in coronary reactive hyperaemia (RH) and how blockade of A1 receptors and inhibition of NO synthesis can modify these changes.. In anaesthetised goats, an electromagnetic flow-probe was placed around the left circumflex coronary artery. Preconditioning was obtained with two episodes of 2.5 min of coronary occlusion, separated by 5 min of reperfusion. RH was obtained with a 15 s occlusion. In a control group (n = 7) RH was studied before and after IP. In a second group (n = 7), 0.2 mg kg-1 of 8-cyclopentyl-dipropylxanthine, an A1 receptor blocker, and in a third group (n = 7) 10 mg kg-1 of NG-nitro-L-arginine (LNNA), an NO inhibitor, were given before IP. Reactive hyperaemia was again obtained before and after IP.. In the control group, after IP, the time to peak hyperaemic flow and total hyperaemic flow decreased by about 50% and 25%, respectively. The A1 receptor blockade alone did not change RH. During A1 blockade, IP reduced the time to peak of RH similar as in control (45%), but did not alter total hyperaemic flow. LNNA alone reduced resting flow and total hyperaemic flow. After NO inhibition, IP only reduced total hyperaemic flow by about 15%, but the time to peak flow was not affected.. IP alters RH by decreasing total hyperaemic flow and reducing the time to peak hyperaemic flow. While the former effect is attributed to a reduction in myocardial metabolism through the activation of the A1 receptors, the latter is likely to be due to an increased endothelial release of NO, suggesting that in addition to a protective effect on the myocardium, IP also exerts a direct effect on the responsiveness of the coronary vasculature (vascular preconditioning).

Topics: Adenosine; Analysis of Variance; Animals; Coronary Circulation; Endothelium, Vascular; Goats; Hyperemia; Ischemic Preconditioning, Myocardial; Myocardial Ischemia; Myocardium; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Purinergic P1 Receptor Antagonists; Regional Blood Flow; Xanthines

Crus II is an area of the cerebellar cortex that receives trigeminal afferents from the perioral region. We investigated the mechanisms of functional hyperemia in cerebellum using activation of crus II by somatosensory stimuli as a model. In particular, we sought to determine whether stimulation of the perioral region increases cerebellar blood flow (BFcrb) in crus II and, if so, whether the response depends on activation of 2-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-kainate receptors and nitric oxide (NO) production. Crus II was exposed in anesthetized rats, and the site was superfused with Ringer. Field potentials were recorded, and BFcrb was measured by laser-Doppler flowmetry. Crus II was activated by electrical stimulation of the perioral region (upper lip). Perioral stimulation evoked the characteristic field potentials in crus II and increased BFcrb (34 +/- 6%; 10 Hz-25 V; n = 6) without changing arterial pressure. The BFcrb increases were associated with a local increase in glucose utilization (74 +/- 8%; P < 0.05; n = 5) and were attenuated by the AMPA-kainate receptor antagonist 2, 3-dihydroxy-6-nitro-7-sulfamoylbenzo-[f]quinoxaline (-71 +/- 3%; 100 microM; P < 0.01; n = 5). The neuronal NO synthase inhibitor 7-nitroindazole (7-NI, 50 mg/kg; n = 5) virtually abolished the increases in BFcrb (-90 +/- 2%; P < 0.01) but did not affect the amplitude of the field potentials. In contrast, 7-NI attenuated the increase in neocortical cerebral blood flow produced by perioral stimulation by 52 +/- 6% (P < 0.05; n = 5). We conclude that crus II activation by somatosensory stimuli produces localized increases in local neural activity and BFcrb that are mediated by activation of glutamate receptors and NO. Unlike in neocortex, in cerebellum the vasodilation depends almost exclusively on NO. The findings underscore the unique role of NO in the mechanisms of synaptic function and blood flow regulation in cerebellum.

Topics: Animals; Blood Pressure; Brain Stem; Carbon Dioxide; Cerebellar Cortex; Cerebellum; Cerebrovascular Circulation; Electric Stimulation; Enzyme Inhibitors; Glucose; Hyperemia; Indazoles; Laser-Doppler Flowmetry; Male; Neuroprotective Agents; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxadiazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Somatosensory Cortex; Tetrodotoxin

We have recently reported that hypercholesterolemia reduces aerobic exercise capacity in mice and that this is associated with a reduced endothelium-dependent vasodilator function, endothelium-derived nitric oxide (EDNO) production, and urinary nitrate excretion. These findings led us to test the hypothesis that EDNO production contributes significantly to limb blood flow during exercise and to determine whether loss of EDNO production is responsible for the decline in exercise capacity observed in hypercholesterolemia.. Twelve-week-old wild-type (E+; n=9) and apoE-deficient (E-; n=9) C57BL/6J mice were treadmill-tested to measure indices defining exercise capacity on a metabolic chamber-enclosed treadmill capable of measuring oxygen uptake and carbon dioxide excretion. Urine was collected before and after treadmill exercise for determination of vascular NO production assessed by urinary nitrate excretion. The wild-type mice were then given nitro-L-arginine (E+LNA) in the drinking water (6 mg/dL) for 4 days before undergoing a second treadmill testing and urinary nitrate measurement. An additional set of 12-week-old wild-type mice was divided into 2 groups: 1 receiving regular water (E+; n=8) and 1 administered LNA for 4 days (E+LNA; n=8). These mice, along with an additional set of E mice (n=8), underwent treadmill testing to determine maximal oxygen uptake (VO2max). The mice were then cannulated such that the tip of the tubing was positioned in the ascending aorta. Fluorescent microspheres (20000) were infused into the carotid cannula while the mice were sedentary and again while approaching VO2max. When the mice were euthanized, the running muscles were collected and fluorescence intensity was measured to determine the peak-exercise redistribution of blood flow to the running muscles (expressed as percentage of total cardiac output, %COrm) during both states. Both E+LNA and E- mice demonstrated a markedly reduced postexercise urinary nitrate excretion, aerobic capacity, and %COrm at VO2max compared with E+.. EDNO contributes significantly to limb blood flow during exercise. Conditions that reduce EDNO production disturb the hyperemic response to exercise, resulting in a reduced exercise capacity.

Topics: Animals; Apolipoproteins E; Enzyme Inhibitors; Extremities; Female; Hypercholesterolemia; Hyperemia; Mice; Mice, Inbred C57BL; Motor Activity; Nitrates; Nitric Oxide; Nitroarginine; Physical Endurance; Regional Blood Flow

We evaluated in the in situ vascularly isolated canine diaphragm the role of nitric oxide (NO) in the regulation of basal vascular resistance and vascular responses to increased muscle activity (active hyperemia), brief occlusions of the phrenic artery (reactive hyperemia), and changes in arterial pressure. The vasculature of the left hemidiaphragm was either pump-perfused at a fixed flow rate or autoperfused with arterial blood from the femoral artery. Endothelial nitric oxide synthase (NOS) activity was inhibited by intraphrenic infusion of L-arginine analogues such as N(G)-nitro-L-arginine, N(G)-nitro-L-arginine methyl ester and argininosuccinic acid. Active hyperemia was produced by low (2 Hz) frequency stimulation of the left phrenic nerve. Reactive hyperemia was measured in response to 10, 20, 30, 60, and 120 sec duration occlusions of the left phrenic artery and was quantified in terms of postocclusive blood flow, vascular resistance, hyperemic duration, and hyperemic volume. Infusion of NOS inhibitors into the vasculature of the resting diaphragm increased phrenic vascular resistance significantly and to a similar extent. Reactive hyperemic volume and reactive hyperemic duration were also significantly attenuated after NOS inhibition, however, peak reactive hyperemic dilation was not influenced by NOS inhibition. It was also found that enhanced NO release contribute by about 41% to active dilation elicited by continuous 2 Hz stimulation. In addition, NOS inhibition had no effect on O2 consumption of the resting diaphragm, but significantly attenuated the rise in diaphragmatic O2 consumption during during 2 Hz stimulation. The decline in diaphragmatic O2 consumption was due to reduction in blood flow. These results indicate that NO release plays a significant role in the regulation of diaphragmatic vascular tone and O2 consumption.

Topics: Animals; Argininosuccinic Acid; Arterial Occlusive Diseases; Arteries; Blood Vessels; Dogs; Electric Stimulation; Enzyme Inhibitors; Hyperemia; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Oxygen Consumption; Phrenic Nerve; Regional Blood Flow; Respiratory Muscles; Vascular Resistance; Vasodilation

Temporary elevations in cortical cerebral blood flow (CBF) accompany cortical spreading depression (CSD) in anesthetized animals. We tested the hypothesis that nitric oxide (NO) is an important promotor of CSD-induced cortical hyperemia in urethan-anesthetized rabbits. CBF was measured at four time points by administration of 15-microm microspheres with the reference withdrawal technique. Intravenous administration of the nonspecific NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine increased mean arterial blood pressure and resting cerebrovascular resistance and attenuated CSD-induced hyperemia. Cortical CBF before intraperitoneal 7-nitroindazole (7-NI), a neuronal NOS inhibitor, was 42 +/- 8 and 124 +/- 19 ml x 100 g(-1) x min(-1) at baseline and during CSD, respectively (P < 0.05 by repeated-measures analysis of variance). After 7-NI administration, mean arterial blood pressure, CBF, and cerebrovascular resistance were unchanged from baseline values; cortical CBF was 38 +/- 4 and 90 +/- 8 ml x 100 g(-1) x min(-1) post-7-NI at rest and during a second CSD, respectively. Similar to N(omega)-nitro-L-arginine, 7-NI decreased the cortical hyperemic response during CSD (P < 0.05 by repeated-measures analysis of variance). We conclude that neuronal NOS promotes the temporary cortical hyperemia observed during CSD.

Topics: Analysis of Variance; Animals; Blood Pressure; Brain; Carbon Dioxide; Cerebral Cortex; Cerebrovascular Circulation; Cortical Spreading Depression; Female; Hemoglobins; Hyperemia; Microspheres; Neurons; Nitric Oxide; Nitroarginine; Organ Specificity; Oxygen; Partial Pressure; Rabbits; Regional Blood Flow; Time Factors; Vascular Resistance

Nitric oxide (NO) has been reported to play an important role in isoflurane-induced cerebral hyperemia in vivo. In the brain, there are two constitutive isoforms of NO synthase (NOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). Recently, the mutant mouse deficient in nNOS gene expression (nNOS knockout) has been developed. The present study was designed to examine the role of the two constitutive NOS isoforms in cerebral blood flow (CBF) response to isoflurane using this nNOS knockout mouse.. Regional CBF (rCBF) in the cerebral cortex was measured with laser-Doppler flowmetry in wild-type mice (129/SV or C57BL/6) and nNOS knockout mice during stepwise increases in the inspired concentration of isoflurane from 0.6 vol% to 1.2, 1.8, and 2.4 vol%. Subsequently, a NOS inhibitor, N omega-nitro-L-arginine (L-NNA), was administered intravenously (20 mg/kg), and 45 min later, the rCBF response to isoflurane was tested again. In separate groups of wild-type mice and the knockout mice, the inactive enantiomer, N omega-nitro-D-arginine (D-NNA) was administered intravenously in place of L-NNA. Brain NOS activity was measured with radio-labeled L-arginine to L-citrulline conversion after treatment with L-NNA and D-NNA.. Isoflurane produced dose-dependent increases in rCBF by 25 +/- 3%, 74 +/- 10%, and 108 +/- 14% (SEM) in 129/SV mice and by 32 +/- 2%, 71 +/- 3%, and 96 +/- 7% in C57BL/6 mice at 1.2, 1.8, and 2.4 vol%, respectively. These increases were attenuated at every anesthetic concentration by L-NNA but not by D-NNA. Brain NOS activity was decreased by 92 +/- 2% with L-NNA compared with D-NNA. In nNOS knockout mice, isoflurane increased rCBF by 67 +/- 8%, 88 +/- 12%, and 112 +/- 18% at 1.2, 1.8, and 2.4 vol%, respectively. The increase in rCBF at 1.2 vol% was significantly greater in the nNOS knockout mice than that in the wild-type mice. Administration of L-NNA in the knockout mice attenuated the rCBF response to isoflurane at 1.2 and 1.8 vol% but had no effect on the response at 2.4 vol%.. In nNOS knockout mice, the cerebral hyperemic response to isoflurane is preserved by compensatory mechanism(s) that is NO-independent at 2.4 vol%, although it may involve eNOS at 1.2 and 1.8 vol%. It is suggested that in wild-type mice, eNOS and nNOS contribute to isoflurane-induced increase in rCBF. At lower concentrations (1.2 and 1.8 vol%), eNOS may be involved, whereas at 2.4 vol%, nNOS may be involved.

Topics: Anesthetics, Inhalation; Animals; Brain; Cerebrovascular Circulation; Dose-Response Relationship, Drug; gamma-Aminobutyric Acid; Hyperemia; Isoflurane; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine

Electrical stimulation of cerebellar parallel fibers (PF) increases cerebellar blood flow (BFcrb), a response that is attenuated by glutamate receptor antagonists and NO synthase (NOS) inhibitors. We investigated whether administration of NO donors could counteract attenuation by NOS inhibitors of vasodilation produced by PF stimulation. In halothane-anesthetized rats the cerebellar cortex was exposed and superfused with Ringer solution. PF were stimulated with microelectrodes (100 microA, 30 Hz), and BFcrb was recorded by a laser-Doppler probe. During Ringer superfusion, PF stimulation increased BFcrb by 56 +/- 7% and hypercapnia by 72 +/- 5% (n = 5). Superfusion with the nonselective NOS inhibitor N-nitro-L-arginine (L-NNA, 1 mM) reduced resting BFcrb and attenuated the response to PF stimulation (-47 +/- 5%) and hypercapnia (-46 +/- 7%; PCO2 = 50-60 mmHg). After L-NNA, superfusion with the NO donors 3-morpholinosydnonimine (100 microM, n = 5) or S-nitroso-N-acetyl-penicillamine (5 microM, n = 5) reestablished resting BFcrb (P > 0.05 vs. before L-NNA) and reversed L-NNA-induced attenuation of the response to hypercapnia (P > 0.05 vs. before L-NNA) but not PF stimulation (P > 0.05 vs. after L-NNA). Similar results were obtained when NOS activity was inhibited with the inhibitor of neuronal NOS 7-nitroindazole (50 mg/kg i.p.). Like NO donors, the guanosine 3',5'-cyclic monophosphate analog 8-bromoguanosine 3',5'-cyclic monophosphate (n = 5), administered after L-NNA, restored resting BFcrb and counteracted inhibition of the response to hypercapnia but not PF stimulation. In contrast to NO donors and 8-bromoguanosine 3',5'-cyclic monophosphate, the NO-independent vasodilator papaverine (100 microM, n = 5) had no effect on attenuation of responses to PF stimulation or hypercapnia. Thus NO donors are unable to reverse the effect of NOS inhibition on vasodilation produced by PF stimulation. The data support the hypothesis that the vascular response to PF stimulation, at variance with hypercapnia, requires NOS activation and NO production. Thus NO plays an obligatory role in vasodilation produced by increased functional activity in cerebellar cortex.

Topics: Animals; Blood Pressure; Carbon Dioxide; Cerebellum; Cyclic GMP; Electric Stimulation; Enzyme Inhibitors; Glutamic Acid; Hyperemia; Indazoles; Male; Molsidomine; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxygen; Papaverine; Partial Pressure; Penicillamine; Rats; Rats, Sprague-Dawley; Regional Blood Flow; S-Nitroso-N-Acetylpenicillamine; Vasodilation

To elucidate the role of nitric oxide (NO) in the eye and the flicker-induced vascular response.. The blood flow in the retina and different parts of the optic nerve was compared in cats treated with the NO-synthase blocker, N(G)-nitro-L-arginine methyl ester and in control animals. In both groups, one of the eyes was dark-adapted, the other was subjected to 8 Hz flickering light. The regional blood flow was measured with the microsphere method.. In control animals, flickering light increased blood flow in the retina and optic nerve head by 39% and 256%, respectively. Pretreatment with N(G)-nitro-L-arginine methyl ester prevented this increase in retinal blood flow and markedly reduced the blood flow in the optic nerve heads.. NO release may mediate much of the vasodilating effect of flicker in cats, and play a role in maintaining normal vascular tone in the optic nerve head.

Topics: Animals; Blood Flow Velocity; Cats; Dark Adaptation; Enzyme Inhibitors; Hyperemia; Light; Microspheres; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Optic Disk; Optic Nerve; Photic Stimulation; Regional Blood Flow; Retina; Retinal Vessels; Vasodilation

The effects of intravenous (iv) bolus administrations of bradykinin (0.1-1 microgram.kg-1) on large and small coronary arteries were investigated in seven chronically instrumented conscious dogs. Bradykinin dose-dependently increased heart rate, left ventricular dP/dt max, coronary blood flow and coronary artery diameter and decreased aortic pressure. Subchronic inhibition of the nitric oxide synthase (NOS) pathway (N omega-nitro-L-arginine, 20 mg.kg-1.d-1 during 7 days) attenuated the systemic and coronary effects of bradykinin. HOE 140, a specific bradykinin B2 receptor antagonist, administered at a dose (30 micrograms/kg) sufficient to completely inhibit the systemic and coronary effects of exogenous bradykinin (1 microgram/kg, iv bolus), had no effect on baseline systemic and coronary hemodynamic parameters. HOE 140 had also no effect on the flow-dependent increase in large coronary artery diameter and on the relationship between flow debt and flow repayment volumes observed during myocardial reactive hyperemia. This lack of effect of HOE 140 persisted when experiments were repeated after NOS inhibition. We conclude that (a) exogenous bradykinin dilates large and small coronary arteries through a partially NO-mediated mechanism, and (b) endogenous bradykinin plays no role in the control of arterial pressure, heart rate, LV dP/dt max, basal and flow-stimulated coronary hemodynamics, both in control conditions and after subchronic inhibition of NOS in the conscious dog.

Topics: Acetylcholine; Animals; Blood Volume; Bradykinin; Bradykinin Receptor Antagonists; Coronary Circulation; Dogs; Heart Rate; Hyperemia; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroglycerin; Vasodilation; Vasodilator Agents

This study tested the hypothesis that overproduction of endogenous nitric oxide (NO) during endotoxemia may modulate coronary autoregulation and myocardial reactive hyperemia.. Hearts of endotoxin-pretreated rats and controls were isolated and arranged for perfusion in a Langendorff preparation. Autoregulation was studied by examining flow-pressure relations during stepwise changes in perfusion pressure. The contribution of nitric oxide was examined by perfusion with N omega-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthesis and methylene blue (MB), an inhibitor of soluble guanylate-cyclase.. Endotoxin-treated hearts showed massive coronary vasodilatation and autoregulatory function was impaired at perfusion pressures from 20 to 60 mmHg. Both NNLA and MB reduced coronary flow, improved autoregulation and eliminated differences in coronary flow and autoregulation between the control and endotoxin-treated group. Vasoconstriction with vasopressin, a direct smooth muscle constrictor, could not eliminate differences in autoregulation between groups. Reactive hyperemia following coronary occlusion in endotoxin-treated hearts showed decreased duration, flow repayment and repayment ratio. In the presence of NNLA or MB, however, no significant differences in reactive hyperemic flow patterns were present.. These observations suggest that massive coronary vasodilatation due to increased myocardial NO synthesis can result in autoregulatory dysfunction and altered myocardial reactive hyperemia during endotoxemia.

Topics: Animals; Coronary Circulation; Coronary Vessels; Endotoxemia; Guanylate Cyclase; Homeostasis; Hyperemia; Male; Methylene Blue; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Oxygen Consumption; Perfusion; Rats; Rats, Wistar; Vasodilator Agents

We used the parallel fibers (PF) system of the cerebellar cortex as a model to investigate the role of nitric oxide (NO) in the increases in blood flow elicited by neural activation. Rats were anesthetized with halothane and ventilated. The vermis was exposed, and the site was superfused with Ringer (37 degrees C; pH 7.3-7.4). PF were stimulated electrically (100 muA; 30 Hz), and the associated changes in cerebellar cortex blood flow (BFcrb) were monitored by laser-Doppler flowmetry. The field potentials evoked by PF stimulation were recorded using microelectrodes. During Ringer superfusion (n = 7), PF stimulation increased BFcrb (+ 52 +/- 4%). Topical application of the NO synthase (NOS) inhibitor N omega-nitro-L-arginine (L-NNA; 0.1-1 mM) attenuated the increases in BFcrb dose dependently and by 50 +/- 4% at 1 mM (n = 9; P < 0.001; analysis of variance and Tukey's test). L-NNA (1 mM) inhibited NOS catalytic activity, assessed ex vivo using the citrulline assay, by 95 +/- 9% (P < 0.001). L-NNA did not influence the field potentials evoked by PF stimulation. D-NNA (1 mM; n = 6), the inactive stereoisomer of nitroarginine, did not attenuate the BFcrb response (P > 0.05). Methylene blue (1 mM; n = 7) reduced the response by 41 +/- 9% (P < 0.01) without affecting NOS catalytic activity (P < 0.05). The increases in BFcrb were not affected by lesioning the NOS-containing nerve fibers innervating cerebral vessels, indicating that these nerves are not the source of NO. Thus the increases in BFcrb elicited by activation of PF are, in part, mediated by NO produced in the molecular layer during neural activity. The results indicated that NO participates in the coupling of function activity to blood flow and support the hypothesis that NO is one of the mediators responsible for functional hyperemia in the central nervous system.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Cerebellar Cortex; Electric Stimulation; Electrophysiology; Hyperemia; Male; Methylene Blue; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Regional Blood Flow

In the coronary bed vasodilation can be mediated by several mechanisms including endothelium-produced nitric oxide. To examine the contribution of nitric oxide, three different techniques to cause vasodilation in the coronary vessels were used in the anaesthetized dog: intracoronary injection of 1 microgram acetylcholine, sudden reduction of the aortic blood pressure inducing a myogenic response and transient occlusion followed by release of the left circumflex coronary artery causing reactive hyperaemia. Each manoeuvre was performed before and after intracoronary administration of 100 mg N-nitro-L-arginine, an inhibitor of the synthesis of nitric oxide. In contrast to previous investigations, the inhibition of nitric oxide synthesis was prevented from causing an increase in blood pressure by the use of a blood-pressure-compensating device. The results observed during each of the three techniques, suggest that the initial cause of the vasodilatation is not the result of the increase of the production of nitric oxide. However, subsequent to the initiation of vasodilation, an increase in the shear stress can result in an increase in the release of nitric oxide from the vascular endothelium, thus prolonging the vasodilatation obtained using each technique.

Topics: Acetylcholine; Animals; Arginine; Blood Flow Velocity; Blood Pressure; Coronary Circulation; Coronary Vasospasm; Coronary Vessels; Depression, Chemical; Dogs; Heart Rate; Hyperemia; Nitric Oxide; Nitroarginine; Vasodilation

The metabolites that mediate coronary reactive hyperemia have not been definitely identified. Although adenosine and endothelium derived substances seem to be involved, their relative contributions have not been defined yet. In the canine coronary circulation, we studied the relative participation of adenosine, nitric oxide and prostacyclin in reactive hyperemia, by measuring the changes produced by interfering with the synthesis or action of these metabolites. The dose-response curve for flow changes vs intracoronary administration of adenosine was displaced to the right after the inhibition of nitric oxide synthesis with N-omega-nitro-L-arginine, revealing that nitric oxide release partly mediates the vasodilator action of adenosine. The inhibition of PGI-2 synthesis with indomethacin did not modify reactive hyperemia. Interference with adenosine action, by administration of adenosine deaminase plus theophylline, decreased reactive hyperemia by 31.0 +/- 4.0% (p < 0.001). Inhibition of nitric oxide synthesis decreased reactive hyperemia by a larger (p < 0.005) magnitude, 41.0 +/- 3.9% (p < 0.001), revealing the existence of other stimuli for nitric oxide release in reactive hyperemia besides adenosine. Simultaneous inhibition of nitric oxide and PGI-2 syntheses and of adenosine action reduced reactive hyperemia, but the effect was not additive, reaching 49.5 +/- 4.5% of control. Since nitric oxide and adenosine are the most important mediators in reactive hyperemia so far described, our results suggest that other metabolites, acting directly or through mediators other than adenosine or nitric oxide, are responsible for about 50% of coronary reactive hyperemia.

Topics: Adenosine; Animals; Coronary Disease; Dogs; Endothelium, Vascular; Enzyme Inhibitors; Epoprostenol; Hyperemia; Neurotransmitter Agents; Nitric Oxide; Nitroarginine; Platelet Aggregation Inhibitors

De-endothelialization of the coronary vessels induced a 3-4-fold decrease in the level of hyperemia in anesthetised dogs. Infusion of L-arginine augmented the reactive hyperemia and the endothelium-dependent relaxation in response to acetylcholine administration. The reactive hyperemia seems to be wholly depending on the endothelium, being conditioned by the effect of endothelium-derived nitric oxide.

Topics: Acetylcholine; Animals; Arginine; Coronary Vessels; Dogs; Endothelium, Vascular; Female; Hyperemia; Male; Nitric Oxide; Nitroarginine; Papaverine; Saponins

To test the hypothesis that endothelium-derived products contribute to functional hyperemia in skeletal muscle, we infused nitric oxide synthase inhibitors, either 200 microM N omega-nitro-L-arginine (NNA) (N = 4) or 1 mM N gamma-monomethyl-L-arginine (NMMA) (N = 4), before and during 6 min of 4 Hz stimulation of canine gastrocnemius in situ. We infused saline (N = 4) as a control. NNA significantly decreased steady-level resting flow by 3.8 +/- 0.4 mL.kg-1.s-1. The increase in flow from rest to 5 min of stimulation was not changed by the nitric oxide synthase inhibitors. We also stimulated muscles for 60 min either with saline infusion (N = 4) or with the infusion of saline during the first 15 min and NNA for the remaining 45 min (n = 4). There was no difference in the flow during contractions. To clarify the effect of these inhibitors on canine vessels, we challenged rings of canine femoral artery with and without endothelium with acetylcholine and bradykinin (both 1 microM) before and after the addition of NNA and NMMA (both 10 microM). The nitric oxide synthase inhibitors decreased the relaxation accompanying acetylcholine. Both inhibitors caused only endothelium-intact rings to contract. Thus, the presence of a nitric oxide synthase inhibitor identified an endothelium-dependent contribution to the regulation of blood flow to skeletal muscle at rest but had no effect on functional hyperemia.

Topics: Acetylcholine; Amino Acid Oxidoreductases; Animals; Arginine; Blood Flow Velocity; Bradykinin; Dogs; Endothelium; Female; Femoral Artery; Hyperemia; Male; Muscles; Nitric Oxide Synthase; Nitroarginine; omega-N-Methylarginine; Oxygen Consumption; Vasoconstriction

To determine the role of an endothelium-derived relaxing factor (nitric oxide) in controlling basal coronary tone and coronary vasomotion after brief coronary occlusion (reactive hyperemia).. In 10 chronically instrumented conscious dogs, we studied the diameter changes of the large epicardial coronary artery and coronary blood flow in response to intracoronary administration of acetylcholine (0.1 and 1 microgram) and brief coronary occlusion for 5 and 20 s before and after intracoronary infusion of N-nitro-L-arginine (LNNA).. Intracoronary infusion of LNNA (1, 3, and 10 mg) decreased the diameter of the large epicardial coronary artery and coronary blood flow in a dose-dependent manner without altering arterial pressure and heart rate. LNNA (10 mg) significantly attenuated the increase in artery diameter and coronary blood flow by acetylcholine. The ratio of artery dilation to the blood flow response after acetylcholine was not affected by LNNA. LNNA (10 mg) significantly decreased the ratio of repayment to debt flow volume of reactive hyperemia, but did not affect the ratio of peak to resting flow; it also significantly attenuated the reactive dilation of the large epicardial coronary artery after reactive hyperemia. The ratio of artery dilation to repayment flow volume (micron/ml) during reactive hyperemia was attenuated significantly by LNNA.. These findings suggest that endothelium-derived nitric oxide may contribute to basal coronary tone and that reactive dilation of the large epicardial coronary artery during reactive hyperemia was caused by flow-mediated nitric oxide release, whereas coronary artery dilation after acetylcholine was caused largely by the direct receptor-mediated release of nitric oxide.

Topics: Acetylcholine; Animals; Arginine; Blood Flow Velocity; Consciousness; Coronary Circulation; Coronary Disease; Coronary Vessels; Dogs; Dose-Response Relationship, Drug; Endothelium, Vascular; Hyperemia; Nitric Oxide; Nitroarginine; Vasodilation

To investigate the role of endothelium-derived nitric oxide (EDNO) and adenosine in functional myocardial hyperemia, we examined the effect of NG-nitro-L-arginine (L-NNA) and 8-p-sulfophenyltheophylline (8-SPT) on coronary vasodilation in response to increased myocardial oxygen consumption in pentobarbital sodium-anesthetized dogs. L-NNA significantly attenuated the increase in coronary conductance from 28 +/- 6 to 16 +/- 2% with atrial pacing, from 69 +/- 5 to 36 +/- 6% with isoproterenol, and from 25 +/- 6 to 9 +/- 4% with constriction of the aorta. 8-SPT given alone attenuated the increase in coronary conductance to the same extent as L-NNA. The combined administration of L-NNA and 8-SPT did not further change coronary conductance. These findings suggest that EDNO and adenosine play an important role in functional hyperemia. EDNO-induced functional hyperemia appears to be dependent on adenosine receptor activation.

Topics: Adenosine; Animals; Arginine; Coronary Circulation; Dogs; Female; Hemodynamics; Hyperemia; Male; Nitric Oxide; Nitroarginine; Theophylline; Vascular Resistance

The role of nitric oxide (NO) in the response to 5% CO2 inhalation was investigated by measuring 1) regional cerebral blood flow (rCBF) by laser-Doppler flowmetry and pial vessel diameter through a closed cranial window after topical NG-nitro-L-arginine (L-NNA, 1 mM), and 2) the time-dependent changes in brain guanosine 3',5'-cyclic monophosphate (cGMP) levels after L-NNA (10 mg/kg ip). When L-NNA (but not NG-nitro-D-arginine) was applied topically for 30 or 60 min, the response to hypercapnia was significantly attenuated. A correlation was found between inhibition of brain NO synthase (NOS) activity and the rCBF response (r = 0.77; P < 0.01). However, L-NNA applied 15 min before hypercapnia did not attenuate the increase in rCBF but did attenuate the dilation to topical acetylcholine. Inhalation of CO2 (5%) elevated brain cGMP levels by 20-25%, and L-NNA reduced this response. These data from the rat suggest that 1) a product of NOS activity is associated with hypercapnic hyperemia and the attendant increase in brain cGMP levels, and 2) hypercapnic blood flow changes may not be dependent on endothelial NOS activity within pial vessels.

Topics: Acetylcholine; Administration, Inhalation; Administration, Topical; Animals; Arginine; Brain; Carbon Dioxide; Cerebral Cortex; Cerebrovascular Circulation; Cyclic GMP; Hypercapnia; Hyperemia; Male; Nitroarginine; Rats; Rats, Sprague-Dawley; Vasodilation

The effect of the inhibition of the endothelial release of nitric oxide (NO) on the hyperaemia which follows a 10 s coronary occlusion was studied in anaesthetized dogs. Aortic blood pressure was kept constant during the experiments using an arterial reservoir connected with the femoral arteries. The blood flow in the left circumflex coronary artery was recorded with an electromagnetic flow probe. A 10 s coronary occlusion was performed before and after intracoronary infusion of Nitro-L-arginine (LNNA), at the dose of 100 mg in 20 min. The effect of LNNA in preventing the release of NO by the endothelium was demonstrated by the reduced coronary hyperaemia which follows the intracoronary infusion of acetylcholine. After LNNA the baseline coronary flow was not altered. Following the release of the coronary occlusion the peak amplitude of the reactive hyperaemia was not significantly changed, while the duration was reduced to almost a half of the control. The results suggest that in the intact dog NO is not important in the regulation of the baseline coronary vasomotor tone. It may also be argued that the peak amplitude of the hyperaemia is not significantly affected by LNNA either because the inhibition of the release of nitric oxide is counteracted by a greater production of adenosine, or because a mechanism not affected by nitric oxide (e.g. a myogenic mechanism) is involved in the reactive hyperaemia. In contrast the reduction of the duration of the hyperaemia after the inhibitor may depend on a reduced effect of the shear stress of the blood on the endothelium during the reactive hyperaemia.

Topics: Animals; Arginine; Blood Pressure; Coronary Circulation; Dogs; Endothelium, Vascular; Heart Rate; Hyperemia; Nitric Oxide; Nitroarginine

To study the role of endothelium-derived relaxing factor (EDRF)--which participates in the regulation of coronary vascular tone, but has an unknown role in the transmural distribution of coronary flow--in transmural coronary flow distribution during steady basal flow and during reactive hyperemia in the left ventricular wall of the dog.. Sixteen mongrel dogs of either sex weighing between 14 and 24 kg were anesthetized with sodium pentobarbital. The lungs were mechanically ventilated and the thoraces were opened. Circumflex coronary flow was measured with an electromagnetic flowmeter, and its transmural distribution across four layers of the left ventricular wall was measured with radioactive microspheres. Measurements were done during steady basal flow and during peak reactive hyperemia before and after the inhibition of the EDRF synthesis with N-omega-nitro-L-arginine (NNLA). Mean aortic and systolic left ventricular pressures and heart rate were kept constant, and left ventricular end-diastolic pressure increased by only 3.3 mmHg during reactive hyperemia.. NNLA produced a mean decrease of steady basal flow of 22.3 +/- 0.9% (P < 0.01). Flow decreased in all layers of the wall; the decrease, however, was proportionally less in the subendocardium (P < 0.05). During reactive hyperemia (before NNLA), flow was redistributed to the subendocardium (compared with steady basal flow). Administration of NNLA reduced the magnitude of peak reactive flow to all layers in the wall, showing a relative enhancement of flow in the subendocardium.. These results suggest that the EDRF participates in the regulation of coronary bloodflow and its distribution across the left ventricular wall.

Topics: Animals; Arginine; Blood Flow Velocity; Coronary Circulation; Dogs; Female; Heart Ventricles; Hyperemia; Male; Nitric Oxide; Nitroarginine; Radionuclide Imaging; Rheology

The importance of nitric oxide (NO) in coronary blood flow (CBF) regulation was examined in anesthetized pigs. NO synthesis was inhibited by intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine (L-NNA). L-NMMA (30 mumol/min) reduced CBF (Doppler flowmetry) by 16.3% (13.1-20.2%; P < 0.001) and L-NNA (30 mumol/min) by 16.1% (13.9-18.9%; P < 0.001). During NO blockade, myocardial oxygen consumption was unaltered as an increase in oxygen extraction occurred due to a reduced partial pressure of oxygen and oxygen saturation in blood from the anterior interventricular vein. L-Arginine completely reestablished CBF after giving L-NMMA, but not after giving L-NNA. L-NNA reduced the coronary flow response to ADP by 66-83%, whereas the selected dose of L-NMMA did not affect it. The flow response to adenosine was not affected by either L-NMMA or L-NNA. L-NNA reduced reactive hyperemia after occluding the left anterior descending coronary artery for 10 and 30 s but not for 120 s. Our data show that NO produced in the coronary endothelium plays an important role in CBF regulation in vivo, accounting for approximately 16% of CBF and a major part of the flow response to ADP. NO also contributes to reactive hyperemia after brief, but not longer, ischemic periods.

Topics: Adenosine; Adenosine Diphosphate; Animals; Arginine; Coronary Circulation; Female; Hemodynamics; Hyperemia; Male; Myocardial Ischemia; Myocardium; Nitric Oxide; Nitroarginine; omega-N-Methylarginine; Oxygen Consumption; Swine; Time Factors

Acute and chronic effects of Nw-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide synthase, were examined on the hindquarter hemodynamics of conscious rabbits. After pharmacological autonomic reflex blockade on four experimental days (days 0, 1, 2, and 7), responses to aortic occlusion (balloon cuff, 5-80 s inflation), intra-aortic infusion of acetylcholine, adenosine, and sodium nitroprusside (SNP) were measured before and after vehicle (day 0) or L-NNA (16 mg/kg/h i.v., days 1, 2, and 7). On day 1, L-NNA raised the mean arterial pressure (MAP), and lowered the heart rate (HR) and hindquarter vascular conductance (HVC = abdominal aortic Doppler blood flow/MAP). On days 2 and 7, L-NNA only slowly raised the MAP. The dilator response to acetylcholine was inhibited by L-NNA on day 1 and before and after L-NNA on days 2 and 7. The responses to aortic occlusion, adenosine, or SNP infusion were unaffected by L-NNA treatment on any day. Thus, if nitric oxide synthase inhibition by L-NNA abolishes NO release, then (i) reactive hyperaemia is independent of NO, (ii) basal NO release normalises the arterial pressure in the short term but other factors become important in the long term, and (iii) the blockade by L-NNA of receptor-stimulated NO release by acetylcholine is only very slowly reversible.

Topics: Acetylcholine; Adenosine; Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Dose-Response Relationship, Drug; Female; Ganglionic Blockers; Heart Rate; Hemodynamics; Hindlimb; Hyperemia; Male; Mecamylamine; Muscle Tonus; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Rabbits; Regional Blood Flow

In the isolated perfused guinea pig heart coronary occlusion lasting 1-5 s is followed by reactive hyperaemia which is inhibited by 91-100% after pretreatment with a NO synthase inhibitor, NG-nitro-L-arginine (100 microM). Neither indomethacin (5 microM) nor 8-phenyltheophylline (10 microM) influences these responses. Therefore, the brief cardiac reactive hyperaemia seems to be predominantly if not entirely mediated by nitric oxide (NO).

Topics: Acetylcholine; Amino Acid Oxidoreductases; Animals; Arginine; Blood Pressure; Coronary Vessels; Female; Guinea Pigs; Hyperemia; In Vitro Techniques; Indomethacin; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Theophylline; Ventricular Function, Left; Ventricular Pressure

The endothelium plays a key role in the regulation of vasoreactivity. To assess its importance on coronary flow regulation, we studied the participation of endothelium-derived relaxing factor-nitric oxide (EDRF-NO) on coronary reactive hyperemia and on the hyperemia that occurs secondary to an increase in myocardial oxygen consumption. In 15 dogs, the reactive hyperemic response decreased substantially after inhibition of EDRF-NO synthesis with N-omega-nitro-L-arginine (P < 0.01). In contrast, the hyperemia secondary to an increase in myocardial oxygen consumption, characterized by a linear correlation between myocardial oxygen consumption and coronary flow, did not change significantly after inhibition of EDRF-NO production (regression analysis, P > 0.1). Thus EDRF-NO synthesis by the endothelium is an important mechanism mediating the reactive hyperemic response but it does not seem to be essential for the metabolic regulation of coronary vascular resistance during hyperemia induced by an increased metabolic demand on the myocardium.

Topics: Animals; Arginine; Coronary Circulation; Dogs; Hyperemia; Myocardium; Nitric Oxide; Nitroarginine; Nitroprusside; Oxygen Consumption; Vascular Resistance

We studied the effect of NG-nitro-L-arginine (L-NA) on reactive hyperemia in the vascularly isolated hemidiaphragm of anesthetized dogs pretreated with indomethacin. In nine animals, the diaphragm was autoperfused from the left femoral artery. Phrenic arterial flow was interrupted for 10-120 s during a control period and after 20 min of L-NA infusion (6 x 10(-4) M). Postocclusive flow and duration of hyperemia during the control period increased progressively with increasing occlusion duration. After L-NA infusion, baseline and postocclusive flow in response to all occlusions declined significantly compared with control values. However, when normalized as percentage of baseline flow, postocclusive flow remained similar to that during the control period. By comparison, the duration of reactive hyperemia was significantly shortened by L-NA infusion. In five animals, we repeated the same protocol during pump perfusion of the diaphragm at a fixed flow rate. L-NA infusion increased baseline and postocclusive phrenic resistance in response to all occlusion durations; however, postocclusive phrenic resistance as percentage of baseline remained similar to control values. In addition, hyperemia durations in response to 60- and 120-s occlusions were shortened significantly by L-NA infusion. We conclude that 1) endothelium-derived relaxing factor plays an important role in the regulation of baseline vasomotor tone in the diaphragm and 2) modulation of endothelium-derived relaxing factor release contributes to the reactive vasodilatory response to transient vascular occlusion in the diaphragm.

Topics: Animals; Arginine; Diaphragm; Dogs; Endothelium, Vascular; Hyperemia; Nitric Oxide; Nitroarginine; Phenylephrine; Vascular Resistance; Vasodilation

To assess the effect of endothelium-derived relaxing factor (EDRF) on diaphragmatic vascular resistance at rest and during contractions, we studied an in situ isolated diaphragm preparation in anesthetized and mechanically ventilated dogs. The arterial supply of the left diaphragm (phrenic artery) was catheterized and perfused with arterial blood at a fixed flow rate. Drugs were infused through a side port of the arterial catheter at 1/100th of the phrenic arterial flow. The inferior phrenic vein was catheterized to complete the isolation from the systemic circulation. Three sets of experiments were performed. In set 1 (n = 3), we infused endothelium-dependent (acetylcholine, ACh) and endothelium-independent (sodium nitroprusside, SNP) dilators at increasing concentrations. ACh and SNP infusion elicited a dose-dependent decline in phrenic vascular resistance (Rphr) at concentrations greater than 10(-8) M and 0.50 micrograms/ml, respectively. In set 2 (n = 15), we infused an inhibitor of EDRF synthesis and release, L-argininosuccinic acid (ArgSA), at increasing concentrations (10(-4), 3 x 10(-4), and 6 x 10(-4) M). ArgSA produced a dose-dependent increase in Rphr. Infusion of another EDRF inhibitor (NG-nitro-L-arginine, LNA, 6 x 10(-4) M) elicited increase in Rphr similar to that induced by ArgSA. In set 3 (n = 25), we infused ArgSA or LNA (6 x 10(-4) M) simultaneously with ACh and SNP and during sustained (2-Hz) contractions of the diaphragm. Both ArgSA and LNA completely reversed ACh vasodilation, whereas SNP vasodilation was reversed by 26 and 11%, respectively. ArgSA or LNA infusion during contractions reversed vasodilation by 48 and 52%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetylcholine; Animals; Arginine; Argininosuccinic Acid; Diaphragm; Dogs; Hyperemia; Muscle Contraction; Nitric Oxide; Nitroarginine; Nitroprusside; Vascular Resistance; Vasodilation