Luis Monge

Regional differences in the arterial response to vasopressin : role of endothelial nitric oxide

1 . The isometric response to arginine‐vasopressin (10−10‐10−7 m) was studied in 2 mm long rabbit arterial segments isolated from several vascular beds (cutaneous, pial, renal, coronary, muscular, mesenteric and pulmonary). 2 . Vasopressin induced contraction in central ear (cutaneous), basilar (pial), renal, coronary and saphenous (muscular) arteries, but had no effect in mesenteric and pulmonary arteries; the order of potency for the contraction was: ear > basilar > renal > coronary > saphenous arteries. 3 . Treatment with the blocker of nitric oxide synthesis NG‐nitro‐L‐arginine methyl ester (L‐NAME; 10−6‐10−4 m) increased significantly (P < 0.05) the contraction to vasopressin in ear (148% of control), basilar (150% of control), renal (304% of control), coronary (437% of control) and saphenous (235% of control) arteries. Removal of the endothelium increased significantly (P < 0.05) the contraction to vasopressin in basilar (138% of control), renal (253% of control), coronary (637% of control) and saphenous (662% of control) arteries, but not in ear artery. Mesenteric and pulmonary arteries in the presence of L‐NAME or after endothelium removal did not respond to vasopressin, as occurred in control conditions. 4 . The specific antagonist for V1 vasopressin receptors d(CH2)5Tyr(Me)AVP (3 × 10−9‐10−7 m) was more potent (pA2 = 9.3–10.1) than the antagonist for both V1 and V2 vasopressin receptors desGly‐d(CH2)5‐D‐Tyr(Et)ValAVP (10−7‐10−6 m) (pA2 = 7.4–8.4) to block the contraction to vasopressin of ear, basilar, renal and coronary arteries. 5 . The specific V2 vasopressin agonist [deamino‐Cys1, D‐Arg8]‐ vasopressin (desmopressin) (10−10‐10−7 m) did not produce any effect in any of the arteries studied, with or without endothelium. 6 . In arteries precontracted with endothelin‐1, vasopressin or desmopressin did not produce relaxation. 7 . These results suggest: (a) most arterial beds studied (5 of 7) exhibit contraction to vasopressin with different intensity; (b) the vasoconstriction to this peptide is mediated mainly by stimulation of V1 vasopressin receptors, and (c) endothelial nitric oxide may inhibit the vasoconstriction to this peptide, especially in coronary and renal vasculatures.

Apelin effects in human splanchnic arteries. Role of nitric oxide and prostanoids.

Apelin effects were examined in human splanchnic arteries from liver donors (normal arteries) and from liver recipients. Segments 3 mm long were obtained from mesenteric arteries taken from liver donors (normal arteries), and from hepatic arteries taken from cirrhotic patients undergoing liver transplantation (liver recipients), and the segments were mounted in organ baths for isometric tension recording. In arteries under resting conditions, apelin (10(-10)-10(-6) M) caused no effect in any of the arteries tested. In arteries precontracted with the thromboxane A(2) analogue U46619 (10(-7)-10(-6) M), apelin (10(-10)-10(-6) M) produced concentration-dependent relaxation that was lower in hepatic than in mesenteric arteries, whereas sodium nitroprusside (10(-8)-10(-4) M) produced a similar relaxation in both types of arteries. The inhibitor of nitric oxide synthesis N(w)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) diminished the relaxation to apelin in mesenteric but not in hepatic arteries. The inhibitor of cyclooxygenase meclofenamate (10(-5) M) did not affect the relaxation provoked by apelin in both types of arteries. Therefore, apelin may produce relaxation in normal human splanchnic arteries, and this relaxation may be mediated in part by nitric oxide without involvement of prostanoids. This relaxation as well as the role of nitric oxide may be decreased in splanchnic arteries from cirrhotic patients.

Relaxation by urocortin of human saphenous veins

Urocortin, an endogenous peptide structurally related to corticotropin‐releasing factor (CRF), has potent cardiovascular effects, suggesting that it may be of significance in cardiovascular regulation. The objective of this study was to analyse the effects of urocortin and its action mechanisms on human blood vessels. To this, 3 mm long segments from human saphenous veins were prepared for isometric tension recording in an organ bath. In the segments at basal resting tone, urocortin did not produce any effect, but in the segments precontracted with endothelin‐1 (1 – 10 nM), urocortin (1 pM – 10 nM) produced concentration‐dependent relaxation. This relaxation was not modified by the inhibitor of nitric oxide synthase NG‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μM), but it was potentiated by the cyclo‐oxygenase inhibitor meclofenamate (10 μM) and it was reduced by the inhibitors of high‐conductance Ca2+‐dependent potassium channels tetraethylammonium (TEA, 10 mM) and charybdotoxin (100 nM). These results indicate that human saphenous veins are very sensitive to urocortin, which produces vascular relaxation by a mechanism independent of nitric oxide and dependent of high‐conductance Ca2+‐dependent potassium channels, and that it may be opposed by the release of vasoconstrictor prostanoids. Therefore, urocortin may be of significance for regulation of the venous circulation in humans.

Cerebral blood flow and cerebrovascular reactivity after inhibition of nitric oxide synthesis in conscious goats.

1 The role of nitric oxide in the cerebral circulation under basal conditions and after vasodilator stimulation was studied in instrumented, conscious goats, by examining the action of inhibiting endogenous nitric oxide production with NG‐nitro‐l‐arginine methyl ester (l‐NAME). 2 In 6 unanaesthetized goats, blood flow to one brain hemisphere (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. l‐NAME (35 mg kg−1 by i.v. bolus) decreased resting cerebral blood flow by 43 ± 3%, increased mean arterial pressure by 21 ± 2%, and decreased heart rate by 41 ± 2%; cerebrovascular resistance increased by 114 ± 13% (P < 0.01); the immediate addition of i.v. infusion of l‐NAME (0.15–0.20 mg kg−1 during 60–80 min) did not significantly modify these effects. Cerebral blood flow recovered at 72 h, arterial pressure and cerebrovascular resistance at 48 h, and heart rate at 6 days after l‐NAME treatment. 3 A second treatment with l‐NAME scheduled as above reproduced the immediate haemodynamic effects of the first treatment, which (except bradycardia) reversed with l‐arginine (200–300 mg kg−1 by i.v. bolus). 4 Acetylcholine (0.01–0.3 μg), sodium nitroprusside (3–100 μg) and diazoxide (0.3–9 mg), injected into the cerebral circulation of 5 conscious goats, produced dose‐dependent increases in cerebral blood flow, and decreases in cerebrovascular resistance; sodium nitroprusside (30 and 100 μg) also caused hypotension and tachycardia. 5 The reduction in cerebrovascular resistance from resting levels (in absolute values) to lower doses, but not to the highest dose, of acetylcholine was diminished, to sodium nitroprusside was increased, and to diazoxide was unaffected after l‐NAME, compared to control conditions. The effects on cerebrovascular resistance to acetycholine normalized within 24 h and to sodium nitroprusside within 48 h after l‐NAME treatment. 6 This study provides information about the evolution of the changes in cerebral blood flow and cerebrovascular reactivity after inhibition of endogenous nitric oxide in conscious animals. The results suggest: (a) endogenous nitric oxide is involved in regulation of the cerebral circulation by producing a resting vasodilator tone, (b) the cerebral vasodilatation to acetylcholine is mediated, at least in part, by nitric oxide release, and (c) inhibition of nitric oxide production induces supersensitivity of cerebral vasculature to nitrovasodilators.

Coronary vasoconstriction by endothelin-1 in anesthetized goats: role of endothelin receptors, nitric oxide and prostanoids

The role of endothelin ETA and ETB receptors as well as of nitric oxide (NO) and prostanoids in the effects of endothelin-1 on the coronary circulation was studied in anesthetized goats. Where blood flow in the left circumflex coronary artery (coronary blood flow) (electromagnetically measured), systemic arterial pressure, left ventricle pressure and d P/dt, and heart rate were recorded. Endothelin-1 (0.01-0.3 nmol), intracoronarily injected, produced marked, dose-dependent reductions in basal coronary blood flow, ranging from 5% for 0.01 nmol to 75% for 0.3 nmol; 0.1 and 0.3 nmol endothelin-1 also reduced systolic ventricle pressure and dP/dt. The effects of endothelin-1 on coronary blood flow were diminished during intracoronary infusion of BQ-123 (cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp). specific antagonist for endothelin ETA receptors. 2-16 nmol/min) in a dose-dependent way, but not during the infusion of BQ-788 (N-[N-[N-[(2.6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-1-leucyl]-1- (methoxycarbonyl)-D-tryptophyl]-D-norleucine monosodium, specific antagonist for endothelin ETB receptors. 2-4 nmol/min). IRL 1620 (Suc-[Glu9, Ala11.15]endothelin-1-(8-21), specific agonist for endothelin ETB receptors. 0.01-0.3 nmol), intracoronarily injected. slightly reduced basal coronary blood flow only when 0.1 and 0.3 nmol were applied (maximal reduction about 25%); 0.3 nmol IRL 1620 also reduced systolic ventricle pressure and dP/dt. The effects of IRL 1620 were not modified by BQ-123 or BQ-788. NG-nitro-1-arginine methyl ester (L-NAME, inhibitor of NO synthesis, 47 mg/kg by i.v. route) reduced resting coronary blood flow by 10% and increased mean systemic arterial pressure and systolic ventricle pressure by 22 and 20%. respectively, without changing systolic ventricle dP/dt and heart rate. With L-NAME, the reductions of coronary blood flow by endothelin-1 were potentiated (P < 0.05), and those by IRL 1620 were not changed (P > 0.05). Meclofenamate (cyclooxygenase inhibitor, 4-6 mg/kg by i.v. route) modified neither the basal values of hemodynamic variables nor the coronary effects of endothelin-1 and IRL 1620. Therefore, endothelin-1 produces marked coronary vasoconstriction, which may be mediated by endothelin ETA receptors, with no participation of endothelin ETB receptors. NO, but not prostanoids, may produce a basal coronary vasodilator tone and may inhibit endothelin-1-induced coronary vasoconstriction. Also, it is suggested that the coronary vasoconstriction by endothelin-1 may impair cardiac performance due to heart ischemia.

Cooling effects on nitric oxide production by rabbit ear and femoral arteries during cholinergic stimulation

1 Ear (cutaneous) and femoral (deep) arteries from rabbit were perfused at 37°C and 24°C (cooling) and the production of nitrite, as an index of nitric oxide production, was measured under basal conditions and cholinergic stimulation. 2 In both types of arteries under control conditions, the basal production of nitrite was similar at 24°C and 37°C. Compared with the control conditions, the basal production of nitrite was significantly lower in ear and femoral arteries without endothelium or treated with NG‐nitro‐L‐arginine methyl ester (L‐NAME, 10−4m) but it was similar in those treated with atropine (10−6m). 3 At 37°C, methacholine (10−7‐10−5 m) increased the production of nitrite in ear and femoral arteries; this increase persisted during 30–60 min and was practically abolished by L‐NAME (10−4m), atropine (10−6m), or removal of the endothelium. In ear arteries the total nitrite production to activation with methacholine was higher at 24°C than at 37°C due to this production persisted increased for a longer period (> 150 min), whereas in femoral arteries it was lower at 24°C than at 37°C. 4 It is suggested that: (a) the endothelium of rabbit ear and femoral arteries produce nitric oxide under basal conditions, which is increased by cholinergic stimulation, and (b) cooling potentiates endothelial nitric oxide production to cholinergic stimulation in cutaneous arteries, whereas it inhibits this production in deep arteries.

Effects of nitric oxide synthesis inhibition on the goat coronary circulation under basal conditions and after vasodilator stimulation

1 The role of nitric oxide in the coronary circulation under basal conditions and when exposed to various vasodilator stimuli was studied in instrumented, anaesthetized goats, by examining the action of inhibiting endogenous nitric oxide production with NG‐nitro‐l‐arginine methyl ester (l‐NAME). 2 In 12 goats, left circumflex coronary blood flow (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. l‐NAME (3–4, or 8–10 mg kg−1 injected i.v.) decreased resting coronary blood flow by 20 and 28%, increased mean arterial pressure by 23 and 30% and increased coronary vascular resistance by 47 and 65%, respectively, without affecting heart rate, or blood gases or pH. These haemodynamic effects were reversed by l‐arginine (200‐ 300 mg kg−1 by i.v. injection, 5 goats). 3 Acetylcholine (0.001–0.1 μg), sodium nitroprusside (0.01–0.3 mg), and diazoxide (0.1–3 mg), injected intracoronarily in 6 goats, produced dose‐dependent increases in coronary blood flow; sodium nitroprusside (0.1–0.3 mg) also caused hypotension and tachycardia. 4 During the effects of l‐NAME, the coronary vasodilatation to acetylcholine was attenuated, to sodium nitroprusside was increased, and to diazoxide was unaffected, in comparison with control conditions. The hypotensive effects of sodium nitroprusside were also increased during treatment with l‐NAME. 5 Graded coronary hyperaemic responses occurred after 5, 10 or 20 s of coronary occlusion. The magnitude of hyerpaemia for each occlusion duration was increased during treatment with l‐NAME, in comparison to control. 6 The results suggest: (a) endogenous nitric oxide is involved in regulation of coronary circulation by producing a basal vasodilator tone, (b) acetylcholine‐induced coronary vasodilatation is mediated, in part, by nitric oxide, and (c) inhibition of basal endogenous nitric oxide production induces supersensitivity of coronary vessels to nitrovasodilators and enhances hyperaemic responses after short periods of ischaemia of the myocardium.

Role of the endothelium in the response to cholinoceptor stimulation of rabbit ear and femoral arteries during cooling

1 The role of the endothelium in the effects of cooling on the response to cholinoceptor stimulation of the rabbit central ear (cutaneous) and femoral (non‐cutaneous) arteries was studied using 2 mm long cylindrical segments. 2 Concentration‐response curves for acetylcholine (10−9‐10−5 m), methacholine (10−9‐10−5 m) and sodium nitroprusside (10−9‐10−4 m) were isometrically recorded in arteries under conditions, with and without endothelium or following pretreatment with the nitric oxide‐synthesis inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10−6‐3 x 10−4 m) at 37°C and at 24°C (cooling). 3 Ear and femoral arteries showed endothelium‐dependent relaxation to acetylcholine and methacholine at 37°C and 24°C. The extent of relaxation of the control ear arteries, but not of the control femoral arteries, to acetylcholine and methacholine increased during cooling. 4 l‐NAME (10−6−3 × 10−4 m) reduced in a concentration‐dependent way the response of ear arteries to acetylcholine at both 37°C and 24°C, this reduction being more potent at 37°C. l‐Arginine (10−5‐10−3 m) reversed in a concentration‐dependent manner the inhibitor effects of 10−5 m l‐NAME at both temperatures. 5 Sodium nitroprusside caused a concentration‐dependent relaxation in both arteries that was endothelium‐independent. However, the extent of relaxation to this nitrovasodilator in ear and femoral arteries was lower at 24°C. 6 These results suggest that cooling augments the reactivity of cutaneous (ear) arteries, but not that of non‐cutaneous (femoral) arteries to cholinoceptor stimulation by endothelium‐mediated mechanisms. Cooling could therefore facilitate the stimulated release of endothelial nitric oxide in cutaneous vessels.

Coronary vasoconstriction produced by vasopressin in anesthetized goats. Role of vasopressin V1 and V2 receptors and nitric oxide.

To examine the role of vasopressin V1 and V2 receptors, nitric oxide and prostanoids in the coronary vascular effects of [Arg8]vasopressin, coronary blood flow was measured with an electromagnetic flow transducer placed around the left circumflex (23 goats) or anterior descending (11 goats) coronary artery and vasopressin (0.03-1 microg) was intracoronarily injected in 34 anesthetized, open-chest goats. Basal mean values for coronary blood flow, mean systemic arterial pressure and heart rate, were 34 +/- 2.38 ml/min, 89 +/- 3.34 mmHg and 80 +/- 3.06 beats/min, respectively. Vasopressin produced dose-dependent decreases in coronary blood flow and the maximal reduction of this flow, attained with 1 microg of vasopressin, was 14 +/- 1.49 ml/min (42 +/- 2.64% of basal flow) (P < 0.01). Desmopressin (0.03-1 microg; 8 goats) did not affect significantly coronary blood flow. The intracoronary infusion of the antagonist for vasopressin V1 receptors d(CH2)5Tyr (Me) arginine vasopressin (2 microg/min per kg, 6 animals) significantly diminished the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were reduced by 28%, P < 0.05). The mixed antagonist for vasopressin V1 and V2 receptors desGly-d(CH2)5-D-Tyr(Et)Val arginine vasopressin (0.2, 0.7 and 2 microg/min per kg, 9 animals) decreased in a dose-dependent manner the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were decreased by 61% with 2 microg/min per kg, P < 0.01). Intracoronary infusion of saline (vehicle, 3 goats) did not change the effects of vasopressin on coronary blood flow. Intravenous administration of the inhibitor of nitric oxide synthesis N-omega-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg, 9 animals) decreased resting coronary blood flow by 10% (P < 0.01) and augmented mean systemic arterial pressure by 20% (P < 0.01), without changing heart rate. During this treatment the reduction in coronary blood flow produced by vasopressin was higher than under control (the effects of 1 microg of vasopressin were increased by 28%, P < 0.01). Intravenous administration of the inhibitor of cyclooxygenase, meclofenamate (5 mg/kg, 7 animals), neither modified resting coronary blood flow, arterial pressure and heart rate nor the effects of vasopressin on this flow. These data indicate that vasopressin produces marked coronary vasoconstriction and suggest that: (a) it may be mediated by vasopressin V1 receptors, without involvement of vasopressin V2 receptors, (b) it is probably inhibited by nitric oxide under normal conditions and (c) it may be not modulated by prostanoids.

Cerebral vasoconstriction produced by vasopressin in conscious goats: role of vasopressin V1 and V2 receptors and nitric oxide

To examine the role of vasopressin V1 and V2 receptors, nitric oxide and prostanoids in the cerebrovascular effects of arginine vasopressin, cerebral blood flow was electromagnetically measured in awake goats. In 16 animals, vasopressin (0.03 – 1 μg), injected into the cerebral circulation, caused increments of resting cerebrovascular resistance which ranged from 18% (0.03 μg, P<0.01) to 79% (1 μg, P<0.01). Desmopressin (0.03 – 1 μg, four goats) did not affect significantly cerebrovascular resistance. The cerebrovascular resistance increases by vasopressin were reduced significantly by the antagonist for vasopressin V1 receptors d(CH2)5Tyr(Me)‐AVP in a rate depending way (five (six goats) and 15 (four goats) μg min−1), and by the mixed antagonist for vasopressin V1 and V2 receptors desGly‐d(CH2)5‐D‐Tyr(Et)Val‐AVP (5 μg min−1, four goats), and they were not significantly affected by the antagonist for vasopressin V2 receptors d(CH2)5, D‐Ile2, Ile4‐AVP (5 μg min−1, four goats). The inhibitor of nitric oxide synthesis Nw‐nitro‐L‐arginine methyl ester (L‐NAME, 47 mg kg−1 i.v., five goats) augmented cerebrovascular resistance by 130% (P<0.01), and for 24 h after this treatment the cerebrovascular effects of vasopressin were potentiated. The inhibitor of cyclo‐oxygenase meclofenamate (6 mg kg−1 i.v., five goats) did not modify significantly resting haemodynamic variables measured or the cerebrovascular effects of vasopressin. Therefore, the vasopressin‐induced cerebral vasoconstriction may be mediated by vasopressin V1 receptors, without involvement of vasopressin V2 receptors, and may be modulated by nitric oxide but not by prostanoids.