Jo Aikawa

Endothelin-1- and endothelin-3-induced vasorelaxation via common generation of endothelium-derived nitric oxide

The vasorelaxant effects by endothelin-1 (ET-1) and endothelin-3 (ET-3), and their mechanisms of action were studied in isolated porcine pulmonary arterial strips. ET-1 and ET-3 dose-dependently (10(-9) - 10(-8) M) relaxed vascular strips precontracted with norepinephrine only in the presence of endothelium. The maximal vasorelaxant effect by ET-1 was about 70% of that by ET-3. The ET-1- and ET-3- induced vasorelaxation was blocked by NG-nitro-L-arginine, an inhibitor of nitric oxide synthesis, and methylene blue, an inhibitor of soluble guanylate cyclase. The present data suggest that vascular smooth muscle relaxation induced by ET-1 and ET-3 is mainly ascribed to synthesis and release of nitric oxide from L-arginine in endothelium.

Effect of endothelin on angiotensin converting enzyme activity in cultured vascular smooth muscle cells

We evaluated the effect of endothelin-1 (ET) on the angiotensin converting enzyme (ACE) activity in rat aortic smooth muscle cells (VSMCs). ACE activity was determined by radioimmunoassay of the amount of angiotensin II generated after the addition of angiotensin I (500 pg/ml) to cultured VSMCs. The antibody used had less than 0.1% cross-reactivity with angiotensin I. ACE activity increased 1.9-fold 5 hr after the addition of 10(-6) M ET under serum-free conditions. This stimulatory effect of ET on ACE activity in VSMCs was completely inhibited by 10(-7) M captopril. Results suggested that the ACE present in SMCs is stimulated by ET.

Vascular Smooth Muscle Relaxation by α-Adrenoceptor Blocking Action of Dobutamine in Isolated Rabbit Aorta

We investigated the mechanism of vascular relaxation produced by dobutamine, a positive inotropic agent with beta 1-adrenergic action. Dobutamine concentration-dependently (10 nM-10 microM) relaxed ring segments of rabbit aorta partially precontracted with 1 microM phenylephrine (PE) but did not relax those precontracted with 40 mM K+ or 5 microM prostaglandin F2 alpha (PGF2 alpha). The relaxation was not completely inhibited by pretreatment with 10 microM propranolol. Dobutamine did not significantly increase tissue cyclic AMP levels concomitantly with relaxation as does isoproterenol (ISO) in rabbit aorta. Dobutamine produced a parallel rightward shift in concentration-response curves to PE. The Schild plot analysis resulted in a linear regression of a slope of 1.077 +/- 0.077, which was not significantly different from unity. The pA2 value of dobutamine as compared with PE in rabbit aorta was 6.81 +/- 0.03. Dobutamine causes arterial dilatation mediated not only through a beta-adrenergic action but also through an alpha-adrenergic blocking action in rabbit aorta.

Vascular smooth muscle relaxation by endothelium-dependent β1-adrenergic action

Abstract 1. Norepinephrine (NE) (10 −5 M) in rabbit aorta relaxed ring segments with endothelium precontracted with 10 −6 M NE, but not segments without endothelium. 2. The relaxation was inhibited with metoprolol and methylene blue, but not inhibited with yohimbine and indomethacin. 3. NE (10 −5 M) significantly elevated tissue c-GMP levels in segments with endothelium. 4. These studies suggest that the vascular relaxation by high doses of NE is mediated by the release of endothelium-derived relaxing factor (EDRF) induced by the stimulation of β 1 -adrenoceptor.

Vascular smooth muscle relaxation by alpha 1-adrenoceptor blocking action of denopamine in isolated rabbit aorta.

We investigated the mechanism of vascular relaxation by denopamine (Deno), an oral positive inotropic agent that has selective β1-adrenergic action. Deno relaxed, dose-dependently (0.1–30 μM), ring segments of rabbit aorta, which were partially precontracted with 1 μM phenylephrine (Phe) or norepinephrine (NE). but did not relax those precontracted with 5 μM prostaglandin F2α or 40 mM K+. The relaxation was not significantly inhibited by pretreatment with 10 μM propranolol or metoprolol. Deno produced parallel shifts in concentration–response curves to Phe, but this was not true for clonidine. The Schild plot analysis resulted in a linear regression of a slope of 1.075 ± 0.063. which was not significantly different from unity, and the pA2 value of Deno against Phe was 5.57 ± 0.02. The specific binding of [3H]prazosin to a rabbit aorta membrane preparation was displaced in a concentration-dependent manner by the simultaneous addition of Deno. The slope of a Hill plot was not significantly different from unity (1.102 ± 0.147). The pK1 value for Deno calculated from the displacement curve was 5.29 ± 0.17, which was not significantly different from the pA2 value of Deno. In conclusion, vascular smooth muscle relaxation by Deno was mediated by the blocking effect of α1-adrenoceptors. Thus, these findings suggest that Deno may he effective in the treatment of congestive heart failure because it elicits a positive inotropic effect by β1-adrenergic action and vasodilation by α1-adrenergic blocking action.

Acetylcholine-induced endothelium-dependent vascular smooth muscle relaxation in nitroglycerin-tolerant isolated rat aorta.

SummaryNitroglycerin (NTG) tolerance is recognized clinically, and its pharmacological mechanism has been thought to be due to a decrease in the accumulation of cyclic GMP (cGMP) which is a second messenger of NTG. Endothelium-derived relaxing factor (EDRF) also relaxes vascular smooth muscle through the activation of soluble guanylate cyclase and the production of cGMP. The purpose of this study was to investigate acetylcholine (ACh)-induced endothelium-dependent relaxation and cGMP response in NTG-tolerant isolated rat aorta. Ring strips prepared from the thoracic aorta of male Wistar rats were mounted in tissue baths and contracted with 10−6 M norepinephrine. NTG and ACh relaxation responses were compared before and after 1 h treatment with 5×10−4 M NTG. The chronological changes in tissue cGMP levels by 10−6 M NTG and ACh were compared between a control group (untreated) and NTG-tolerant group (treated with 5×10−4 M NTG for 1 h). The NTG dose-response curve shifted markedly to the right, but the ACh dose-response curve shifted to the left after the induction of NTG tolerance. In the control group, both NTG and ACh elevated the tissue cGMP levels, but in the NTG-tolerant group only ACh elevated cGMP significantly. However, in the NTG-tolerant group, the cGMP increase induced by ACh was smaller than that in the control group.These results suggest that NTG tolerance does not decrease, but rather augments ACh-induced endothelium-dependent vascular smooth muscle relaxation in isolated rat aorta.

Vascular relaxing mechanism of denopamine in isolated canine coronary, femoral, mesenteric, and renal arteries

SummaryWe investigated the mechanism of vascular relaxation produced by denopamine (deno), an oral positive inotropic agent that has selective β1-adrenergic action. Deno concentration-dependently (0.1 µM–30 µM) relaxed ring segments of canine femoral, mesenteric, and renal arteries which were partially precontracted with 1 µm phenylephrine or norepinephrine, but did not relax those precontracted with 5 µM prostaglandin F2α or 40 mM K+. The relaxation was not significantly inhibited by pretreatment with 10 µM propranolol or metoprolol. Deno produced a parallel rightward shift in concentration-response curves to phenylephrine in femoral and renal arteries. The Schild plot yielded linear regressions of slopes of 1.301 ± 0.106 and 0.823 ± 0.122, respectively, which were not significantly different from unity. The pA2 values of Deno against phenylephrine in femoral and renal arteries were 5.41 ± 0.03 and 5.76 ± 0.06, respectively.On the other hand, Deno concentration-dependently (10 nM–10 µM) relaxed ring segments of canine coronary arteries which were partially precontracted with 5 µM prostaglandin F2α. The relaxation was significantly inhibited by pretreatment with 10 µM metoprolol.In conclusion, vascular smooth muscle relaxation by Deno was mediated through β1-adrenergic action in canine coronary arteries and through the blocking effect of α-adrenoceptors in canine femoral, mesenteric, and renal arteries.

Effect of captopril on acetylcholine-induced relaxation in the presence of nitroglycerin tolerance in isolated rabbit aorta.

We investigated the effects of angiotensin converting enzyme inhibitors on acetylcholine-induced endothelium-dependent vasodilation in the presence of nitroglycerin tolerance in rings of rabbit thoracic aorta mounted in tissue baths and precontracted with 10(-6) M norepinephrine. The vasorelaxant effects of acetylcholine were measured before and after 1 h treatment with 5 x 10(-4) M nitroglycerin. The acetylcholine dose-response curve shifted to the right after the induction of nitroglycerin tolerance. Pretreatment with captopril (a sulfhydryl angiotensin converting enzyme inhibitor), but not with M-1 (a metabolite of delapril and a nonsulfhydryl angiotensin converting enzyme inhibitor) restored acetylcholine-induced relaxation. Pretreatment with N-acetylcysteine also restored reduced acetylcholine-induced relaxation. These results suggest that the sulfhydryl group plays a major role in restoration of reduced acetylcholine-induced vasodilation in the presence of nitroglycerin tolerance.