Nitric oxide in the pulmonary circulation.
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Administration, Inhalation↗
Biomedical subjects
S Adnot
Publications and source records attributed to S Adnot.
NO in the lung.
In the lung, nitric oxide (NO) derives from several cellular sources, forming networks of paracrine communication. In pulmonary vessels, NO produced by endothelial cells is a powerful vasodilator. In the airways, NO originates from epithelial cells and from adventitial nerve endings to induce smooth muscle relaxation. Activated macrophages can also produce large quantities of NO during lung immunological reactions. In the normal pulmonary circulation, NO not only mediates vasodilation, but also opposes vasoconstriction, prevents platelet adhesion, controls growth of smooth muscle and influences the composition of the extracellular matrix. During exposure to chronic hypoxia, impaired endothelial NO production contributes to the increased vasomotor tone and vascular remodelling leading to sustained pulmonary hypertension. Exogenous NO gas delivered via the airspaces is a selective pulmonary vasodilator. Inhaled NO is now used as a therapy to treat various forms of pulmonary hypertension and to improve arterial oxygenation during lung injury.
Animals↗
Protection from pulmonary hypertension with an orally active endothelin receptor antagonist in hypoxic rats.
The aim of this study was to investigate the potential role of endothelin (ET) in the development of chronic hypoxic pulmonary hypertension. Pulmonary vascular reactivity to ET-1 was first examined in isolated perfused lungs from normoxic and chronically hypoxic rats in the presence of bosentan, a new nonpeptide mixed antagonist of ETA and ETB receptors. The effect of chronic treatment with bosentan was then examined in rats that were exposed to chronic hypoxia and developed pulmonary hypertension. In lungs from normoxic rats, bosentan (10(-5) M) abolished the vasodilator responses to ET-1 (10(-10) M) or to the ETB-selective agonist IRL-1620 (10(-10) M) and attenuated the vasoconstrictor responses to 10(-9) M ET-1 (from 8.7 +/- 0.7 to 1.8 +/- 0.3 mmHg, P < 0.01) or 10(-9) M IRL-1620 (from 1.5 +/- 0.4 to 0.4 +/- 0.1 mmHg, P < 0.05). In lungs from chronically hypoxic rats, the pressor response to 3 x 10(-10) M ET-1 was abolished by bosentan and partially reduced by the selective ETA antagonist BQ-123. In conscious rats previously exposed to hypoxia for 15 days, pretreatment with bosentan (100 mg.kg-1.day-1 by gavage) for 3 days attenuated the increase in systemic arterial pressures and the concomitant decrease of cardiac output in response to an intravenous bolus of ET-1 (3 x 10(-10) M). In rats exposed to hypoxia for 15 days and simultaneously treated with bosentan, pulmonary arterial pressure was lower (P < 0.05) and right ventricular hypertrophy was less severe (P < 0.01) than in control hypoxic rats treated with vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Immunomodulation with low-dose immunoglobulins for moderate IgA nephropathy and Henoch-Schönlein purpura. Preliminary results of a prospective uncontrolled trial.
Recently, our group has shown that a 3-month course of intravenous immunoglobulin (2 g/kg/monthly) followed by 6 months of intramuscular immunoglobulins (IMIG, 16.5%, 0.35 ml/kg every 15 days) was able to slow or to stop the decline in the glomerular filtration rate, to reduce proteinuria, hematuria, leukocyturia and the histological index of activity on renal biopsy in patients with severe forms of IgA nephropathy (IGAN) and Henoch-Schönlein purpura (HSP). The aim of this open prospective trial was to evaluate the efficacy and safety of low-dose immunoglobulin therapy in moderate IGAN and HSP with permanent proteinuria. Fourteen patients with moderate IGAN [idiopathic IGAN: n = 11; chronic idiopathic HSP: n = 3] and permanent albuminuria were treated with polyvalent IMIG (16.5%) for 9 months (0.35 ml/kg once a week for 1 month, followed by 0.35 ml/kg every 15 days for a further 8 months). Eligibility criteria in the study were Lee histological stage I, II or III, albuminuria between 300 and 2,000 mg/day and a glomerular filtration rate > 70 ml/min/1.73 m2. IMIG were well tolerated and only 1 patient withdrew from the trial. No viral, renal or immunological side effects were observed. IMIG induced a significant decrease in albuminuria as well as in the histological activity index in the 11 cases in which a follow-up biopsy was performed. There was also a decrease in serum IgA, serum beta 2-microglobulin and IgA immune complex levels, and an increase in serum IgG1 levels. Twelve of the 13 evaluable patients improved during treatment.
Adjuvants, Immunologic↗
Haemodynamics and gas exchange before and after coil embolization of pulmonary arteriovenous malformations.
A complete description of haemodynamics and gas exchange before and after percutaneous coil embolization of multiple pulmonary arteriovenous malformations is reported in a 45 year old woman with hereditary haemorrhagic telangiectasis (HHT). Before treatment, whilst the patient complained of severe dyspnoea during daily activities, an intrapulmonary shunt of 31% was measured (inert gas elimination technique), together with a cardiac output (thermodilution technique) of 12.4 L.min-1, resulting in a resting arterial oxygen tension (PaO2) of 8.53 kPa. Effective occlusion of all visible pulmonary malformations resulted in a rapid and major improvement in exercise tolerance, whilst resting PaO2 remained almost unchanged. A second investigation performed 4 months after treatment revealed a persistent intrapulmonary shunt of 19%, a cardiac output of 7.35 L.min-1, and a resting PaO2 of 10.53 kPa. We conclude that major increases in cardiac output largely contribute to the maintenance of PaO2 in patients with multiple pulmonary arteriovenous malformations and intrapulmonary shunt. The benefit of coil embolization is due both to an improvement in arterial oxygenation and a normalization of cardiac output.
Arteriovenous Malformations↗
Decreased endothelium-dependent pulmonary vasodilator effect of calcitonin gene-related peptide in hypoxic rats contrasts with increased binding sites.
Levels of calcitonin gene-related peptide (CGRP), a vasodilator peptide present in nerves and airway endocrine cells of the rat respiratory tract, are increased in hypoxic lung and decreased in plasma, suggesting impaired CGRP release. We wanted to determine whether there was an adaptive functional response to reduced CGRP levels in hypoxia. Density of binding sites for CGRP were compared with its vascular actions following hypoxia, and with binding following administration of the sensory neurotoxin capsaicin to deplete neural CGRP. Autoradiography of lung sections incubated with 125I-labelled CGRP and other vasoactive peptides was used to quantify their binding sites, in male Wistar rats exposed to periods of hypoxia (inspiratory oxygen fraction (FI,O2) = 0.1) ranging 0-10 days (n = 5 each), in controls, and in rats treated neonatally with capsaicin. Relaxation to CGRP was compared in pulmonary artery of control and hypoxic rats. CGRP binding was seen in the vascular endothelium and was significantly elevated after 5 days of hypoxia (mean +/- SEM: control 4.6 +/- 0.4 versus hypoxic 16.6 +/- 2.4 amol.mm-2). CGRP-induced (5 x 10(-7)M) relaxation of pulmonary artery was reduced, compared with controls, following 8 and 21 days of hypoxia (mean +/- SEM) percentage of relaxation to phenylephrine: 78 +/- 3, 36 +/- 5 and 32 +/- 3, respectively) and was abolished by removal of endothelium. Capsaicin treatment also significantly elevated vascular CGRP binding. Atrial natriuretic peptide (ANP) binding levels were decreased in smooth muscle of all blood vessels after 7 days of hypoxia, but endothelin-1 (ET-1) and vasoactive intestinal peptide (VIP) binding was unchanged. We conclude that the vasodilator effects of CGRP are endothelium-dependent and, whilst they are reduced in hypoxic lung, this is not due to reduction in receptors, thereby implicating alterations in the nitric oxide guanylyl cyclase system. Furthermore, adaptive responses in some peptide binding sites occur in hypoxia, which may be due to changes in endogenous peptide levels.
Animals↗
Inhibition of nitric oxide synthesis in the forearm arterial bed of patients with advanced cirrhosis.
Increased vascular production of nitric oxide (NO) may contribute to the peripheral vasodilation and hyperdynamic state complicating advanced liver cirrhosis. In this study, we examined the effect on forearm blood flow of local brachial artery infusion of noradrenaline (NA) and NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO-synthase, in 10 alcoholic ascitic cirrhotic patients (patients with decompensated alcohol-induced liver disease: DALD group) and 10 patients with well-compensated alcohol-induced liver disease (CALD group). Forearm blood flow was measured by venous occlusion plethysmography. As compared with the CALD group, the DALD group had higher cardiac index and forearm blood flow as well as lower systemic blood pressure and vascular resistance. Infusions of NA and L-NMMA produced similar reduction in resting blood flow in the CALD group. However, in the DALD group, NA was significantly less effective than L-NMMA. The forearm vasoconstrictor response to NA was also significantly reduced in the DALD group when compared with the CALD group. In the DALD group, NA decreased forearm blood flow by 21.0 +/- 6.2% and increased vascular resistance by 37.2 +/- 12.3%, whereas respective changes in the CALD group were 41.8 +/- 6.2% (P < .01) and 77.8 +/- 9.9% (P < .02). In contrast, L-NMMA induced greater forearm vasoconstriction in the DALD group than in the CALD group. In decompensated patients, L-NMMA decreased forearm blood flow by 50.4 +/- 2.7% and increased vascular resistance by 115.9 +/- 14.4%, whereas changes in compensated patients were 38.2 +/- 4.9% (P < .05) and 77.4 +/- 16.2% (NS), respectively. These results are consistent with the hypothesis that increased vascular synthesis of NO contributes to the high dynamic state of patients with advanced cirrhosis.
Arginine↗
Treatment of pulmonary hypertension in patients with chronic obstructive pulmonary disease: position of vasodilators with special focus on urapidil.
Pulmonary hypertension, generally defined by a resting pulmonary artery mean pressure higher than 20 mmHg, is a common complication of advanced chronic obstructive pulmonary disease (COPD). Pulmonary hypertension in COPD is of the "precapillary type" and is almost exclusively accounted for by the increased pulmonary vascular resistance (PVR). Among the factors leading to an increased PVR, acute as well as chronic alveolar hypoxia is by far the most important. Pulmonary hypertension is usually mild (between 20 and 35 mmHg) in COPD patients, but pulmonary artery pressure (PAP) may increase markedly and suddenly during exercise, sleep and episodes of acute respiratory failure. These acute increases of afterload can favour the development of right heart failure. Furthermore, even if the progression of pulmonary hypertension is rather slow (PAP increases by + 0.5 mmHg/year as a mean), the level of PAP is a good indicator of prognosis in COPD patients. Consequently the treatment of pulmonary hypertension is justified in COPD. There are two treatments available so far, which are not mutually exclusive: vasodilators and long-term oxygen therapy (LTOT). LTOT may partly reverse hypoxic pulmonary vasoconstriction but is not always effective in reducing PAP in COPD. Patients with severe and persistent pulmonary hypertension despite oxygen and bronchodilator may be candidates for vasodilator therapy. Numerous vasodilators have been tested, but none has proved entirely satisfactory. Ideally the predominant vasodilator effect would occur in the pulmonary rather than in the systemic vascular bed, and systemic blood pressure should be maintained. The drug should not cause tachycardia and should be well tolerated. At the present time, inhaled nitric oxide (NO) is the only selective pulmonary vasodilator currently available, but NO inhalation is limited by toxicological consideration. Urapidil is known to be an alpha 1-adrenoceptor antagonist and an agonist of central 5HT1A-receptors, and should be considered as a vasodilator. Several studies have already demonstrated that this antihypertensive agent exerts favourable effects on pulmonary and cardiac haemodynamics when administered intravenously or orally to COPD patients with secondary pulmonary hypertension or cor pulmonale. Furthermore in patients with COPD or bronchial hyperreactivity no adverse effect is observed on ventilatory function, bronchial reactivity and gas exchange. Nevertheless, the potential benefit of this vasodilator needs to be confirmed in combination with LTOT by a pragmatic evaluation of its clinical efficacy and safety in COPD patients with secondary pulmonary hypertension.
Antihypertensive Agents↗
High-dose immunoglobulin therapy for severe IgA nephropathy and Henoch-Schönlein purpura.
OBJECTIVE: To determine if polyvalent IgG is promising therapy for severe IgG nephropathy. DESIGN: Open prospective cohort study. SETTING: Referral nephrology unit. PATIENTS: 11 adult patients with severe IgA nephropathy (9 who had idiopathic disease and 2 who had Henoch-Schönlein purpura) and indicators of poor prognosis. INTERVENTION: Patients were given high-dose immunoglobulins (2 g/kg each month) for 3 successive months, followed by intramuscular immunoglobulins (preparation content, 16.5%; 0.35 mL/kg every 15 days) for another 6 months. MEASUREMENTS: Histologic changes were analyzed by comparing pre- and post-therapy renal biopsy specimens blindly, using an activity index (14-point scale), a sclerosis index (10-point scale), and a semiquantitative immunofluorescence test of immune deposits. Proteinuria, hematuria, leukocyturia, enzymuria, and global renal function (creatinine and polyfructosan clearances) were evaluated before and after intervention. RESULTS: Proteinuria (median level before intervention, 5.20 g/d; median level after intervention, 2.25 g/d), hematuria, and leukocyturia decreased substantially. The decrease in glomerular filtration rate was greatly slowed or stopped (median rate of decline in glomerular filtration before, -3.78 mL/min per month; after, 0 mL/min per month). The histologic index of activity (median index before, 5; after, 2) and the staining intensity of glomerular IgA and C3 deposits also decreased. Immunoglobulin therapy was well tolerated. CONCLUSIONS: Immunoglobulin therapy may be effective in treating severe IgA nephropathy and protecting renal function. However, prospective controlled trials must confirm these preliminary results.
Adolescent↗
Continuous inhalation of nitric oxide protects against development of pulmonary hypertension in chronically hypoxic rats.
Exposure to hypoxia and subsequent development of pulmonary hypertension is associated with an impairment of the nitric oxide (NO) mediated response to endothelium-dependent vasodilators. Inhaled NO may reach resistive pulmonary vessels through an abluminal route. The aim of this study was to investigate if continuous inhalation of NO would attenuate the development of pulmonary hypertension in rats exposed to chronic hypoxia. In conscious rats previously exposed to 10% O2 for 3 wk, short-term inhalation of NO caused a dose-dependent decrease in pulmonary artery pressure (PAP) from 44 +/- 1 to 32 +/- 1 mmHg at 40 ppm with no changes in systemic arterial pressure, cardiac output, or heart rate. In normoxic rats, acute NO inhalation did not cause changes in PAP. In rats simultaneously exposed to 10% O2 and 10 ppm NO during 2 wk, right ventricular hypertrophy was less severe (P < 0.01), and the degree of muscularization of pulmonary vessels at both alveolar duct and alveolar wall levels was lower (P < 0.01) than in rats exposed to hypoxia alone. Tolerance to the pulmonary vasodilator effect of NO did not develop after prolonged inhalation. Brief discontinuation of NO after 2 wk of hypoxia plus NO caused a rapid increase in PAP. These data demonstrate that prolonged inhalation of low concentrations of NO induces sustained pulmonary vasodilation and reduces pulmonary vascular remodeling in response to chronic hypoxia.
Administration, Inhalation↗
Intravenously administered atrial natriuretic factor in patients with COPD. Effects on ventilation-perfusion relationships and pulmonary hemodynamics.
The potent pulmonary vasodilating property of atrial natriuretic factor (ANF) may alter gas exchange in patients with COPD. We examined the hemodynamic and gas exchange responses to intravenous infusion of ANF (0.01 and 0.03 ng/min/kg body weight) in eight stable patients with COPD studied during spontaneous breathing, using the inert gas elimination technique. When compared with baseline, ANF infusion was associated with a dose-dependent decrease in pulmonary artery pressure (from 27.3 +/- 2.5 to 23.9 +/- 1.8 and 20.2 +/- 1.7 mm Hg, respectively) and a dose-dependent increase in blood flow perfusing poorly ventilated and unventilated units (VA/Q < 0.1: from 5.80 +/- 2.05 to 7.25 +/- 2.5 and 12.0 +/- 5.4 percent of total blood flow, respectively; p = 0.02). However, PaO2 remained unchanged (70.2 +/- 3.6, 68.1 +/- 3.8 65.4 +/- 3.5 mm Hg, respectively) because of a significant increase in minute ventilation (VE) from 8.6 +/- 0.8 to 9.6 +/- 0.8 and 10.3 +/- 0.7 L/min (p < 0.002). Six additional COPD patients receiving intravenously administered ANF at the same dosages were studied during controlled mechanical ventilation using right heart catheterization. In these patients, pulmonary vasodilation was associated with a significant increase in venous admixture (from 12.7 +/- 2.4 to 14.4 +/- 2.9 and 17.5 +/- 3.5 percent of total blood flow, respectively; p < 0.02), and a dose-dependent reduction in arterial PO2 (from 117 +/- 17 to 110 +/- 15 and 96.4 +/- 8.8 mm Hg, respectively; p < 0.05). The present results show that ANF infusion is associated with alterations in the VA/Q relationship in patients with COPD. However, a decrease in arterial oxygenation may be prevented by an increase in VE.
Aged↗
Measurement of gastric intramucosal pH in patients with cirrhosis and portal hypertensive gastropathy.
OBJECTIVES: Patients with cirrhosis often have gastric mucosal lesions associated with portal hypertension. Microvascular changes due to portal hypertension may cause mucosal ischaemia. The decrease in intramucosal pH is used as an index of this condition. In this study we compared the gastric intramucosal pH in patients with cirrhosis and portal hypertension and in control group. METHODS: Estimates of pH were calculated using the Henderson-Hasselbalch equation, assuming that measured concentrations of CO2 in the gastric lumen (pCO2) and of HCO3- in arterial blood represented intramucosal CO2 and intramucosal HCO3- concentrations, respectively. Tonometer measurements of intragastric CO2, validated in vitro, were made in patients treated by famotidine (10 mg.h-1 continuous infusion) to suppress gastric acid secretion and minimize CO2 production from luminal gastric bicarbonate. Intramucosal pH was determined in 19 control patients (mean age: 50.2 years) and in 25 patients with cirrhosis and portal hypertensive gastropathy (mean age: 54.2 years). In the patients with cirrhosis the severity of mucosal and parietal abnormalities induced by portal hypertension were graded according to endoscopic score from 0 to 9 and endoscopic ultrasonography score from 0 to 3. RESULTS: The mean endoscopic and ultrasonographic scores were 5.0 and 1.8 respectively. The median gastric intramucosal pH of patients with cirrhosis (7.42; range: 7.36 to 7.53) was similar to that of the controls (7.42; range: 7.33-7.51). A positive correlation was found between intramucosal pH and severity of portal hypertensive gastropathy, in the antrum, but not in the fundus. CONCLUSION: These findings do not support the hypothesis that gastric mucosal lesions are the consequence of ischaemia in patients with cirrhosis.
Adult↗
[Nitric oxide, from vascular physiology to therapeutics].
Nitric oxide (NO) synthesised by endothelial cells, plays a key role in the control of vascular tone. Its synthesis from L-arginine is assured by NO-synthase, the activity of which is dependent on intracellular calcium concentrations, which are themselves modulated by pharmacological (acetylcholine, serotonin, bradykinin...) or physical factors (shearing forces exerted by blood flow). NO acts by stimulating a soluble guanylate-cyclase of the smooth muscle cells in the vessel wall. Its vasodilator effect is therefore mediated by an increase in intracellular cyclic GMP concentration. The synthesis or liberation of NO by the endothelium may be decreased or abolished during many pathological processes (hypercholesterolaemia, atherosclerosis, systemic or pulmonary hypertension...). The significance of this abnormality of NO-mediated endothelium-dependent vasodilation in different pathological conditions has not been established. However, it is probably significant in view of the different properties of NO: vaso-relaxation, antiaggregant and inhibition of vascular smooth muscle growth. It is not yet known whether this abnormality is a cause or a consequence of the underlying disease. From the therapeutic point of view, NO is an active metabolite of nitrate derivatives, sodium nitroprussiate and molsidomine which therefore share the same mode of action as the so-called "endothelium-dependent" vasodilatoe agents. The inhalation of NO, which is increasingly used in neonatal and adult intensive care units, is an alternative therapeutic approach in many conditions associated with pulmonary hypertension.
Administration, Inhalation↗
Optimal handling of blood samples for routine measurement of lactate and pyruvate.
Blood lactate and pyruvate are of critical importance for the diagnosis of mitochondrial diseases. To determine guidelines for adequate blood pyruvate and lactate determinations, intraindividual studies were carried out on 10 subjects, and the influences of venostasis, delay before deproteinization, and pH in the pyruvate assay were analyzed. Delays of 1 hour or more before deproteinization of samples induced major elevations of lactate-pyruvate ratios. The lactate-pyruvate ratio correlated positively with pH in the pyruvate assay, and inadequate pH appeared as a largely underestimated cause of misleading results, while venostasis was a minor source of errors.
Adult↗
Coronary vasodilating action of dobutamine in patients with idiopathic dilated cardiomyopathy.
To assess the coronary hemodynamic effects of dobutamine in patients with idiopathic dilated cardiomyopathy, dobutamine was infused at the incremental infusion rates of 25, 50, 100, and 200 micrograms/min into the left main coronary artery of nine patients undergoing cardiac catheterization. In response to dobutamine infusion, systemic hemodynamic effects were dose related. At the highest infusion rate cardiac index and left ventricular peak positive rate of rise in ventricular pressure increased from 2.33 +/- 0.54 to 2.97 +/- 0.65 L/min/m (p = 0.001) and from 690 +/- 177 to 1157 +/- 275 mm Hg/sec (p = 0.001), respectively. Left ventricular end-diastolic pressure decreased from 17 +/- 8 to 8 +/- 7 mm Hg (p = 0.001) and a trend toward decrease in left ventricular wall stress was observed (from 166 +/- 75 to 148 +/- 66 gm/cm2, not significant). Heart rate and mean arterial pressure remained unchanged. The coronary hemodynamic response to dobutamine infusion was also dose related. At the highest infusion rate coronary sinus blood flow increased from 133 +/- 35 to 179 +/- 47 ml/min (p < 0.01) and was associated with an increase in coronary oxygen blood content from 4.5 +/- 0.6 to 7.8 +/- 1.7 ml per 100 ml (p < 0.01) whereas myocardial oxygen consumption remained unchanged. During dobutamine infusion norepinephrine decreased in the femoral artery and in the coronary sinus from 1.03 +/- 0.34 to 0.641 +/- 0.179 ng/ml (p < 0.05) and from 1.76 +/- 0.98 to 1.38 +/- 0.65 ng/ml (p < 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Case 4-1993. Inhaled nitric oxide for right ventricular failure after heart transplantation.
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Administration, Inhalation↗
Intracoronary linsidomine abolishes acetylcholine-induced vasoconstriction of epicardial coronary arteries.
If the vasodilation of the epicardial coronary arteries caused by linsidomine (SIN-1), the active metabolite of molsidomine, is well established, few data are available concerning the effects of SIN-1 on the acetylcholine (ACh)-induced vasoconstriction of epicardial coronary arteries. Fourteen patients with mild lesions of the left anterior descending artery (LAD) were studied. Intracoronary blood flow velocity was measured by a Doppler probe placed in the proximal segment of the LAD, and cross-sectional arterial area was assessed by quantitative angiography. After initial hemodynamic parameters were measured, 12 mg papaverine was injected into the left main coronary artery. When hemodynamic parameters returned to baseline values, three increasing concentrations of ACh (5 x 10(-7), 10(-6), and 5 x 10(-6) M) were selectively administered into the LAD in a 3 min period for each concentration. While the infusion of ACh 5 x 10(-6) M was continued, 1 mg SIN-1 was injected as a bolus in the ostium of the left coronary artery. After the injection of papaverine, blood flow increased by 197 +/- 8%, with a trend toward vasoconstriction of the proximal and distal segments of the LAD (p = NS). The ACh injection induced a dose-dependent vasoconstriction, reaching 51 +/- 20% on the distal segment of the LAD at the maximum concentration (p < 0.001). After an initial increase in coronary blood flow of 47 +/- 10 and 28 +/- 11% during the first two concentrations of ACh, respectively, the values decreased after the last injection to the level of baseline values. The infusion of SIN-1 antagonized the ACh-induced vasoconstriction, leading to vasodilation of 7.5 +/- 3% (p < 0.005) and 16 +/- 7% (p < 0.001) of the proximal and distal segments of the LAD, respectively; this was associated with an increase in intracoronary blood flow by 42 +/- 8%. We conclude that intracoronary administration of SIN-1 can antagonize the ACh-induced vasoconstriction of epicardial coronary arteries.
Acetylcholine↗
Loss of endothelium-dependent relaxation in proximal pulmonary arteries from rats exposed to chronic hypoxia: effects of in vivo and in vitro supplementation with L-arginine.
To explore endothelium-dependent relaxation and the L-arginine (L-ARG)-nitric oxide (NO) pathway during chronic hypoxia, we examined isolated rings from large conduit pulmonary arteries and aorta from rats exposed to either room air (N), 3-week hypoxia (H), or 3-week H followed by 72-h recovery to normoxia (room air). We examined the vasodilatory actions of acetylcholine (ACh), ionophore A23187, and endothelin-3 (ET-3) on extrapulmonary left and right branches of pulmonary arteries and thoracic aorta precontracted by phenylephrine (PE 10(-6) M). Endothelium-dependent relaxation of N rat pulmonary arteries and aorta to ACh and A23187 was abolished in the presence of L-NG nitroarginine methyl ester (L-NAME 10(-4) M) or methylene blue (MB 10(-5) M) but was suppressed only partially by NG-monomethyl-L-arginine (L-NMMA 5 x 10(-4) M). In pulmonary arteries but not in aorta, ET-3 induced endothelium-dependent relaxation that was suppressed by L-NAME, MB, and L-NMMA. Pulmonary arteries from H rats did not relax with ET-3. As compared with those of N rats, they exhibited less relaxation to ACh and A23187, (47 +/- 3 vs. 89 +/- 2 and 53 +/- 2 vs. 85 +/- 4%, p < 0.001, respectively) but exhibited similar relaxation to the nonendothelium-dependent vasodilator linsidomine. In contrast, endothelial-relaxation did not differ between N and H rat aorta.2+ pretreatment with L-ARG.
Acetylcholine↗