Effects of nitric oxide synthase inhibitors, l-NG-nitroarginine and l-NG-nitroarginine methyl ester, on responses to vasodilators of the guinea-pig coronary vasculature (original) (raw)
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European Journal of Pharmacology, 1998
In the current investigation, the role of basal nitric oxide NO in modulating the vasorelaxant responses to pinacidil and Ž y8 y4. levcromakalim was examined in goat isolated coronary artery. Pinacidil 10-10 M elicited concentration-dependent relaxations of Ž. q the coronary artery ring segments with intact endothelium constricted with 30 mM K saline solution. The EC of the vasodilator was 50 y6 Ž y6. 2.57 = 10 M 95% CL, 1.9-3.46 = 10 M. The removal of endothelium by mechanical rubbing caused a rightward shift in the Ž y5 y5. concentration-response curve of pinacidil with a corresponding increase in EC value 1.90 = 10 M; 95% CL, 1.12-3.23 = 10 M. 50 Ž G Similar to endothelium removal, treatment of endothelium-intact rings either with the NO synthesis inhibitor L-NAME N-nitro-L-y5. Ž y6. arginine methyl ester; 3 = 10 M or the guanylate cyclase inhibitor, methylene blue 3 = 10 M resulted in a marked inhibition in the relaxant responses to pinacidil. Hence, the EC values of the potassium channel opener were significantly higher in tissues treated 50 Ž y6 y6. Ž y5 y5 either with L-NAME 7.41 = 10 M; 95% CL, 6.02-9.12 = 10 M or methylene blue 2.29 = 10 M; 95% CL, 1.58-3.31 = 10. Ž. M as compared to untreated controls. The ATP-sensitive potassium K channel blocker glibenclamide, which caused a significant ATP rightward shift in the concentration-relaxation curve of pinacidil in control tissues, was found to be less potent in antagonising the relaxant responses of the K channel opener in endothelium-denuded rings and in rings with intact endothelium but treated with either ATP L-NAME or methylene blue. In contrast to the observations made with pinacidil, the vasodilator responses to another K channel ATP y8 Ž opener, levcromakalim, were potentiated in the absence of basal NO. Thus, the EC of levcromakalim was 1.33 = 10 M 95% CL, 50 y8. 0.8-2.21 = 10 M in control tissues with intact endothelium, which was significantly higher than those obtained in endothelium-de-Ž y9 y9. Ž y9 prived rings 4.81 = 10 M; 95% CL, 4.04-5.73 = 10 M or endothelium intact rings treated either with L-NAME 2.63 = 10 M; y9. Ž y9 y9. 95% CL, 1.58-4.36 = 10 M or methylene blue 2.82 = 10 M; 95% CL, 1.7-4.68 = 10 M. The selective modulation by basal NO of the arterial relaxations elicited with the K channel openers was evident from the findings that papaverine-induced relaxations ATP were not affected in the absence of basal NO. Taken together, the results of the present study suggest that basal NO differentially modulates the interaction of pinacidil and levcromakalim with the K channels in goat coronary artery through a cGMP-dependent ATP pathway. q 1998 Elsevier Science B.V.
The nitroxyl anion (HNO) is a potent dilator of rat coronary vasculature
Cardiovascular Research, 2007
Objective: The nitroxyl anion (HNO) is the one-electron reduction product of NO U . This redox variant has been shown to be endogenously produced and to have effects that are pharmacologically distinct from NO U . This study investigates the vasodilator and chronotropic effects of HNO in the rat isolated coronary vasculature. Methods: Sprague-Dawley rat hearts were retrogradely perfused with Krebs' solution (8 ml/min) using the Langendorff technique. Perfusion pressure was raised using a combination of infusion of phenylephrine and bolus additions of the thromboxane mimetic U46619 to attain a baseline perfusion pressure of 100-120 mm Hg. The vasodilator effects of a nitroxyl anion donor, Angeli's salt, were examined in the absence and presence of HNO and NO U scavengers, K + channel inhibition, and soluble guanylate cyclase (sGC) inhibition. In addition, the inotropic and chronotropic effects of Angeli's salt were examined in hearts at resting perfusion pressure (50-60 mm Hg) and compared to responses evoked by acetylcholine and isoprenaline.
British Journal of Pharmacology, 1993
The effects of acute inhibition of nitric oxide (NO) synthase on cardiovascular responses to vasodilator challenges have already been described. We now report the responses to vasodilators during and after chronic NO synthase inhibition. 2 In conscious Brattleboro rats, the regional haemodynamic effects of 3 min infusions of acetylcholine (4 g min-'), sodium nitroprusside (15 fg min ') or adrenaline (0.2 ig min-') were assessed (from areas under or over curves (AUC, AOC)) under control conditions, 6 and 72 h after the addition of the NO synthase inhibitor, N0-monomethyl-L-arginine (L-NMMA) to the drinking water (1 mg ml-'), and 6, 24 and 48 h after the withdrawal of L-NMMA. In a separate group of Brattleboro rats, responses to acetylcholine, sodium nitroprusside and adrenaline were assessed before and 6 h after the onset of oral ingestion of the more potent nitric oxide synthase inhibitor, N0-nitro-L-arginine methyl ester (L-NAME; 0.05 mg ml-1). 3 Acetylcholine caused renal vasodilatation (87 ± 11 units) and mesenteric vasoconstriction (-31 ± 5 units), sodium nitroprusside caused vasodilatation in renal (96 ± 12 units), mesenteric (222 ± 13 units) and hindquarters (49 ± 15 units) vascular beds, whereas adrenaline caused hindquarters vasodilatation (92 ± 8 units). Seventy two h after the onset of oral ingestion of L-NMMA, acetylcholine had a decreased renal vasodilator (59 ± 9 units) effect, sodium nitroprusside had an increased renal vasodilator (142 ± 23 units) action, while adrenaline had a decreased hindquarters vasodilator (55 ± 6 units) influence. Twenty four h after withdrawal of L-NMMA, the renal vasodilator effect of acetylcholine was greater than the control response (106 ± 14 units), but the regional haemodynamic effects of sodium nitroprusside and adrenaline were not different from those under control conditions. Hence, the increased renal vasodilator response to acetylcholine was probably due to changes in muscarinic receptor-mediated mechanisms rather than to any increase in guanylyl cyclase or its sensitivity to NO.
British Journal of Pharmacology, 1996
We assessed whether a submaximal concentration (1 pM) of 5-hydroxytryptamine (5-HT) releases nitric oxide (NO) from the coronary endothelium in guinea-pig perfused heart (n = 5 or 6/group) by direct detection of NO in coronary effluent, and determined whether this accounts for the associated coronary dilatation. We also tested whether saponin is a selective and specific tool for examining the role of this mechanism in mediating agonist-induced coronary dilatation. 2 Continuous 5 min perfusion with 5-HT, or acetylcholine (ACh; 1 gM), substance P (1 nM) or sodium nitroprusside (SNP; 1 uM) increased coronary flow from baseline by 3.6 + 0.2, 3.4 + 0.2, 1.8 + 0.1 and 4.1+0.2 ml min-m g-, respectively (all P<0.05). Coronary effluent NO content, detected by chemiluminescence, was correspondingly increased from baseline by 715+85, 920+136, 1019+58 and 2333 + 114 pmol min-' g'-, respectively (all P<0.05). 3 Continuous perfusion for 30 min with NG-nitro-L-arginine methyl ester (L-NAME) 100 gM reduced basal coronary effluent NO content by 370+32 pmol min-' g-' and coronary flow by 7.5+0.5 ml min-' g-1 (both P<0.05). Saponin (three cycles of 2 min of 30 pg ml-' saponin perfusion interrupted by 2 min control perfusion) reduced basal coronary NO content by a similar amount (307+22 pmol min-' g-') but reduced basal coronary flow by only 0.6+0.2 ml min-' g-' (P<0.05 versus the effect of L-NAME). 4 The increases in coronary flow in response to (5-HT), ACh and substance P were reduced (all P<0.05) by 100 pM L-NAME to 1.2+0.3, 1.2+0.4 and 0.3+0.3 ml min-' g-', respectively. However, the flow increase in response to SNP was not reduced; it was in fact increased slightly to 4.8 +0.4 ml min-' g-' (P<0.05). 5 Similarly, after treatment with saponin, the increases in coronary flow in response to 5-HT, ACh and substance P were reduced to 2.1 + 0.3, 1.3 + 0.3 and 0.4 + 0.2 ml min-' g-', respectively (all P < 0.05). Again, the response to SNP was increased slightly to 4.6+0.5 ml min-' g-' (P<0.05). 6 L-NAME and saponin also inhibited 5-HT, ACh and substance P-induced NO release (P<0.05), without affecting equivalent responses to SNP. 7 For substance P, the change in coronary flow (ACF) correlated with log10 ANO in the presence and absence of saponin and L-NAME; ACF= 1.2(log ANO)-1.9; r = 0.92; P <0.05. For 5-HT the relationship was ACF = 2.2(log ANO-2.7; r = 0.79; P< 0.05, indicating that 5-HT causes a disproportionately greater increase in coronary flow per release of NO. This was taken to indicate that 5-HT relaxes coronary vasculature in part by releasing NO, but in part by additional mechanisms. ACh resembled 5-HT in this respect. 8 Saponin had no effect on cardiac systolic or diastolic contractile function assessed by the construction of Starling curves with an isochoric intraventricular balloon. 9 In conclusion, despite its minimal effect on basal coronary flow, saponin is an effective tool for revealing endothelium-dependent actions of coronary vasodilator substances and has selectivity in that it does not impair endothelium-independent vasodilatation or cardiac contractile function. 5-HT dilates guinea-pig coronary arteries largely by the release of NO from the coronary endothelium.
British Journal of Pharmacology, 1991
1 The effect of N-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide biosynthesis, on large coronary artery diameter and coronary blood flow was examined in anaesthetized greyhounds. The effects of L-NNA on the coronary vascular responses to acetylcholine (ACh), glyceryl trinitrate (GTN) and 5hydroxytryptamine (5-HT) were also assessed. 2 L-NNA (5 mg kg 1), infused into the left circumflex coronary artery, increased systemic mean arterial pressure and decreased the external diameter of the artery. Infusion of L-NNA decreased coronary blood flow in 5 of the 7 dogs tested and increased mean coronary resistance but neither of these effects was statistically significant. There was no change in heart rate.
Naunyn-Schmiedeberg’s Archives of Pharmacology, 1994
We investigated the relative contribution of basal and agonist stimulated EDRF/NO release to the adjustment of coronary tone and myocardial perfusion in conscious dogs by inhibiting coronary endothelial NO formation with NG-nitro-L-arginine methyl ester (L-NAME). Chronically instrumented conscious dogs (n = 9) were prepared for measurement of mean arterial blood pressure (MAP), heart rate (HR), coronary blood flow (CF) and diameter of the left circumflex (CDLc) and left anterior descending (CDLAD) coronary artery, respectively. Intracoronary infusions of L-NAME (30.3 mM; 0.25 ml x min-1) caused significant increases in MAP and decreases in HR. CDLc decreased by 3.8°70 from 3.01_+0.04 to 2.90+0.04 mm and CF decreases by 30% from 12.9_+0.2 to 9.1 +0.2 (aU). Peak reactive hyperemia (CFmax) evoked by 20-s-lasting occlusions of the left circumflex coronary artery decreased from 29.9+0.8 to 25.8_+ 1.0 aU and maximal flow-dependent coronary dilation were reduced from 2.04_+0.08 to 0.91 _+0.12% after inhibition of NO-synthesis. Intracoronary infusions of acetylcholine (ACh), adenosine (Ado), bradykinin (Bk), and papaverine (Pap) caused dose-dependent increases in CDLc and CE Infusion of L-NAME nearly abolished the dilator effect of Ado on CDLc and reduced those to ACh, Bk and Pap. Increases in CF to ACh, Ado and Bk but not to Pap were reduced by L-NAME. Subsequent intracoronary infusions of L-arginine (303 mM; 0.25 ml x min-1) reduced L-NAME-induced CF-changes partly, but did not reverse coronary constriction. These results suggest that inhibition of the continuous release of nitric oxide markedly reduces myocardial perfusion in vivo. Endogenous dilator mechanisms are likewise impaired. Thus, in the heart, nitric oxide deficiency probably cannot be fully compensated for by counterregulating mechanisms.
European Journal of Pharmacology, 2000
The present study examined the role of nitric oxide in coronary vascular tone and in the coronary vasodilatation in response to β-adrenoceptor stimulation and adenosine. In anesthetized goats, the effects of intracoronary and i.v. administration of the inhibitor of nitric oxide synthesis, Nw-nitro-l-arginine methyl ester (l-NAME), and those of isoproterenol, adenosine and acetylcholine on coronary blood flow, measured electromagnetically in the left circumflex coronary artery, were recorded. Intracoronary infusion of l-NAME (30–40 μg kg−1 min−1, four goats) reduced resting coronary blood flow by 14±3% (P<0.05) without changing arterial pressure and heart rate. l-NAME (40 mg kg−1, eight goats) i.v. reduced resting coronary blood flow by 19±4% (P<0.05), increased mean systemic arterial pressure by 22±3% (P<0.01) and decreased heart rate by 10±2% (P<0.05). These effects of l-NAME were partially, but significantly reversed by l-arginine (six goats). Isoproterenol (10–100 ng, eight goats), adenosine (0.3–10 μg, seven goats) and acetylcholine (3–100 ng, five goats), injected intracoronarily, increased coronary conductance in a dose-dependent way and, under control conditions, these increases for isoproterenol, ranged from 32±5% to 82±12%; for adenosine, 6±2% to 174±22%; and for acetylcholine, 39±5% to 145±15%. During i.v. l-NAME the increases in coronary conductance induced by isoproterenol and acetylcholine were significantly reduced by about 50 and 60% (P<0.05), respectively, whereas those induced by adenosine were significantly increased further (about 30–100%, P<0.05). During l-NAME plus l-arginine, the effects of isoproterenol, acetylcholine and adenosine on coronary conductance were not significantly different from those under control conditions. Therefore, it is suggested that in the coronary circulation: (a) nitric oxide may produce a basal vasodilator tone under normal conditions; (b) nitric oxide may be an intermediate in the vasodilatation due to β-adrenoceptor stimulation and acetylcholine, and (c) the vasodilatation due to adenosine is potentiated during reduction of nitric oxide production.
British Journal of Pharmacology, 1999
1 The endothelial modulation of the relaxant responses to the nitric oxide (NO) donor sodium nitroprusside (SNP) and the K ATP channel opener levcromakalim (LEM) and the interactions between these agents were analysed in isolated rat aorta. 2 LEM-induced relaxation was unchanged by endothelium removal or by the presence of L-NAME (10 74 M) or ODQ (10 76 M). In contrast, in KCl-(25 mM), but not in noradrenaline-(NA, 10 76 M) contracted arteries, SNP-induced relaxation was augmented by endothelium removal but not by L-NAME, indomethacin, glibenclamide nor charybdotoxin plus apamin.
European Journal of Pharmaceutical Sciences, 2014
The cardiovascular effects induced by a new organic nitrate were investigated in rats. The (Z)-ethyl 12nitrooxy-octadec-9-enoate (NCOE) was synthesized from ricinoleic acid, the major compound of the castor oil. NCOE induced significant and dose-dependent hypotension and bradycardia in normotensive rats. In rats pretreated with NCOE (60 mg/kg, i.v., once a day) for 4 consecutive days, hypotension induced by the nitrate was similar to that observed in rats that were not pretreated with the compound. The vasorelaxation induced by the compound was concentration-dependent (10 À10 -10 À3 M) in rat mesenteric artery rings, pre-contracted with phenylephrine (1 lM), with or without endothelium. Pre-incubation with PTIO (300 lM), a free radical form of NO (NO Å ) scavenger, attenuated the NCOE vasorelaxation potency. However, in the presence of L-cysteine (3 mM), a reduced form of NO (NO À ) scavenger, NCOE response was potentiated. NCOE effect was not changed in the presence of an inhibitor of cytochrome P450, proadifen (10 lM). On the other hand, the vasodilation was reduced in the presence of mitochondrial aldehyde dehydrogenase inhibitor (mtALDH), cyanamide (1 mM); soluble guanylyl cyclase inhibitor (sGC), ODQ (10 lM); and non-selective K + channels blocker, TEA (3 mM). In addition the NCOE-induced vasorelaxation was reduced by BK Ca (iberiotoxin, 100 nM) and K ATP selective (glibenclamide, 10 lM) blockers, however the effect was not modified by a K V blocker (4-aminopyridine, 1 mM). Furthermore, NCOE increased NO levels in rat aortic smooth muscle cultured cells, detected by NO-sensitive probe DAF-2DA, by flow cytometry. These results together suggest that NCOE induces short-lasting hypotension and bradycardia, and promotes vasorelaxation due to NO Å release through the compound metabolism via mtALDH and consequent sGC, K ATP and BK Ca activation. Furthermore, the compound was not able to induce tolerance.