Effects of Ba(2+) on norepinephrine-induced contraction of rat thoracic aorta in vitro

The aim of this study was to examine the effect of exogenously applied BaCl(2) on the norepinephrine-induced contraction of the rat thoracic aorta. Exogenously applied BaCl(2) (0.3-1 mmol/l) slightly elevated the norepinephrine-induced sustained contraction of the rat thoracic aorta in the absence of nicardipine (1 micromol/l). In the aortic preparation pretreated with nicardipine (1 micromol/l), exogenous BaCl(2) (0.1-3 mmol/l) did not elevate the norepinephrine-induced sustained contraction, but the high concentration of BaCl(2) (10 mmol/l) slightly inhibited the norepinephrine-induced tone. In a Ca(2+)-free Krebs bi- carbonate solution (KBS) containing norepinephrine (1 micromol/l) or a Ca(2+)-free K(+)-rich (60 mmol/l) KBS, exogenously applied BaCl(2) (1-30 mmol/l) caused a sustained contraction of the rat thoracic aorta, and this sustained contraction was completely inhibited by nicardipine (1 micromol/l). Exogenous CaCl(2) (0.1-3 mmol/l) also caused a sustained contraction of the aortic preparation in a Ca(2+)- free KBS containing norephinephrine (1 micromol/l), but such a sustained contraction was partly inhibited by nicardipine (3 micromol/l). These results indicate that Ba(2+) elevates the norepinephrine-induced tone of the rat isolated thoracic aorta by permeating voltage-dependent Ca(2+) channels in the absence of nicardipine, but that Ba(2+) has a minor modification on the norepinephrine-induced sustained contraction of the nicardipine-pretreated preparation.     

Comparison of the inhibitory effects of nicorandil, nitroglycerin and isosorbide dinitrate on vascular smooth muscle of rabbit aorta

The inhibitory effects of nicorandil, nitroglycerin and isosorbide dinitrate on the contractions induced by 10(-6) M norepinephrine or by 65.4 mM K+ were compared in the vascular smooth muscle of rabbit aorta. These compounds relatively selectively inhibited the contraction induced by norepinephrine. Norepinephrine induced a sustained contraction in the aorta depolarized with high K+ and treated with 10(-6) M verapamil, and this contraction was also inhibited by these compounds. The increase in Ca2+ influx induced by norepinephrine, but not by high K+, was inhibited by the three compounds. The norepinephrine-induced transient contraction, which is due to release of stored Ca2+, was inhibited by these compounds. The inhibitory effects of nicorandil and nitroglycerin on this contraction were attenuated by high-K+ depolarization. Methylene blue (10(-5) M) antagonized and M&B 22948 (10(-5) M) potentiated the inhibitory effects of these compounds. These results suggest that nicorandil, nitroglycerin and isosorbide dinitrate have a similar mechanism of action. These compounds inhibit the norepinephrine-induced sustained contraction possibly by inhibiting the Ca2+ influx through receptor-linked Ca2+ channels, and inhibit the transient contraction by membrane hyperpolarization and also by direct inhibition of Ca2+ release although other mechanism of action may also be involved.     

Pharmacological studies on pinacidil, a new antihypertensive agent. 2. Studies on the hypotensive mechanism of pinacidil

Effects of pinacidil (PND) on the blood pressure of anesthetized cats and contraction of guinea-pig isolated hearts and blood vessels were compared with those of hydralazine (HDL) and nifedipine (NFD). PND showed a dose-dependent hypotensive effect and decrease of total peripheral resistance in a dose above 0.3 mg/kg (p.o.) in anesthetized cats. However, no involvement of the autonomic nervous system was presumed in the hypotensive effect of PND due to studies on autonomic responses. Although negative inotropic and chronotropic effects of PND in the isolated guinea-pig atria and heart (Langendorff method) were slight, PND caused a coronary vasodilation at a dose of 1 micrograms. PND inhibited the norepinephrine (NE) contracture of isolated guinea-pig thoracic aorta and portal vein at 10(-6)-10(-5) M, but concentrations of 10(-5)-10(-4) M were required for the inhibition of K contracture. In the isolated thoracic aorta, HDL markedly inhibited NE contracture, while NFD inhibited K contracture. These results suggest that the hypotensive effect of PND is more closely associated with the inhibition of Ca2+ influx caused by the receptor activation of Ca2+ release from intracellular storage sites than membrane potential-dependent Ca2+ influx.     

哇巴因对豚鼠主动脉环平滑肌作用及与Ca2+、去甲肾上腺素的相互关系

目的观察哇巴因（ouabain,Oua）对豚鼠血管平滑肌的作用，及其与Ca₂₊和去甲肾上腺素（NE）的相互作用关系。方法利用豚鼠离体胸主动脉环，观察药物对其张力的影响。结果无论有无内皮存在，Oua均能剂量依赖性地直接收缩血管平滑肌。在无钙溶液中，Oua不能引起血管收缩。Oua可使ＮＥ的量效曲线平行左移，E_max不变；Oua可使CaCl₂的量效曲线左移上移，E_max增大。硝苯地平和维拉帕米可使Ｏua所致的血管收缩曲线下降。结论Oua所致的血管收缩作用不依赖于血管内皮的存在，但依赖于细胞外钙，并且能被钙拮抗剂所拮抗；NE与Oua，Ca₂₊对血管平滑肌的收缩呈协同作用。     

Modification by decreased temperature and hypoxia of 45Ca movements in stimulated smooth muscle of rabbit aorta

In rabbit aortic smooth muscle, contractile responsiveness to 10(-6) M norepinephrine or 60 mM added K+ was inhibited by hypoxia (induced by 100% N2) or decreased bath temperature. Hypoxia increased K+-induced 45Ca efflux, inhibited K+-induced 45Ca uptake, and inhibited norepinephrine-induced 45Ca release; lowering bath temperature by 10 degrees C decreased resting 45Ca uptake and norepinephrine-induced 45Ca release by 30-40% and decreased the 45Ca uptake elicited with norepinephrine or K+ by more than two-thirds. Thus, hypoxia and temperature variations affect different Ca2+ components. Hypoxia decreases the norepinephrine-sensitive membrane Ca2+ fraction and the K+-stimulated mitochondrial Ca2+ fraction whereas decreased temperature most strongly inhibits membrane-associated Ca2+ uptake increases elicited with either norepinephrine or high K+.     

Synthesis and smooth muscle-selective relaxant activity of a piperidine analogue: 1-(4′-fluorophenacyl)-4-hydroxy-4-phenyl-piperidinium chloride

The antispasmodic and vasodilator activities of a newly synthesized piperidine derivative (1-(4'-fluorophenacyl)-4-hydroxy-4-phenyl-piperidinium chloride) were studied in vitro. The test compound exhibited a dose-dependent relaxant effect on the spontaneous and K+ (75 mM)-induced contractions of isolated rabbit jejunum with respective EC50 values of 0.01 mM (0.01-0.02, 95% Cl) and 0.30 mM (0.17-0.56). The Ca++ channel blocking (CCB) activity was confirmed when the test compound (0.1-0.2 mM) shifted the Ca++ dose-response curves to the right, similar to that produced by verapamil (0.1-1.0 microM), a standard CCB. In the isolated rabbit aorta, the test compound showed a dose-dependent vasodilator effect on K+ (75 mM)-induced contractions with an EC50 value of 0.08 mM (0.02-0.26) while also suppressed the norepinephrine (1 microM) control peak responses with EC50 value of 0.08 mM (0.05-0.13, n=5). When tested in Langendorff perfused rabbit heart preparation, the test compound exhibited a negligible inhibitory effect on the rate or force of atrial and ventricular contractions when tested up to 5 mM. The results show smooth muscle-selective relaxant effect of the test compound on intestinal and vascular preparations mediated possibly via blockade of voltage and receptor-operated Ca++ channels.     

Ca2+ channel blocking effects of hirsutine, an indole alkaloid from Uncaria genus, in the isolated rat aorta.

Ca2+ channel blocking activity of hirsutine and its pharmacological features were studied. Hirsutine (10(-6) to 3 x 10(-5) M) produced a dose-dependent relaxation of the isolated rat aorta contracted by norepinephrine and high K+ concentration. This effect was exhibited in the aorta strips with or without the endothelium, suggesting an involvement of vasodilative mechanisms not dependent on the endothelium. Hirsutine also inhibited the contractions induced by serotonin and Ca2+ channel activator YC-170, but not by Ca2+ ionophore A23187. The pA2 value of hirsutine was 6.6 +/- 0.1 (mean +/- S.E.; n = 4) in antagonizing cumulative dose-response curve for Ca2+ in the depolarized aorta strips. It is concluded that hirsutine apparently exhibits Ca2+ channel blocking activity mainly through inhibition of the voltage-dependent Ca2+ influx.     

Inhibitory effect of dichlorvos on arterial smooth muscle contraction

The effect of the organophosphate pesticide, dichlorvos, on the contractile responses of isolated rat tail arteries has been studied. Dichlorvos (10(-8)-10(-4) M) had no effect on baseline tension, but relaxed 10(-7) M norepinephrine (NE), 10(-7) M 5-HT or 100 mM KCl contractions dose-dependently. Dichlorvos also inhibited CaCl2 dose-response curves in K+-depolarized strips, as well as depressing both phasic and tonic components of NE-induced contractions. The results suggest a direct relaxant effect of dichlorvos on arterial smooth muscle by a mechanism probably related to interference with Ca2+ supply.     

雌酚酮衍生物EA204对离体兔血管平滑肌的舒张作用

目的探讨雌酚酮衍生物(EA204)对离体兔血管平滑肌的作用及其机制。方法以离体兔主动脉条为标本,观察了EA204对去甲肾上腺素(NE)、氯化钾(KCl)引起的兔主动脉条收缩的影响;对氯化钙(CaCl2)累积收缩量效曲线的影响,并与维拉帕米(Ver)相比较。通过对比格列苯脲(10μmol.L-1)孵育前后EA204对BaCl2、KCl的舒张量效曲线,研究EA204对钾通道的作用。结果EA204(10~3 mmol.L-1)可以剂量依赖性地抑制NE、KCl收缩的兔主动脉条;EA204(10μmol.L-1)或Ver(0.1μmol.L-1)都使CaCl2累积收缩量效曲线呈剂量依赖性右移,但EA204孵育后CaCl2量效曲线最大反应基本不变,而Ver使最大反应降低;加入格列苯脲(10μmol.L-1)孵育后EA204对BaCl2、KCl收缩的主动脉条的舒张量效曲线发生明显变化,EA204的舒张作用被抑制。结论EA204具有舒张离体兔血管平滑肌的作用,其作用机制与其钙通道阻断作用和钾通道开放作用有关。     

Mechanisms of hydrogen peroxide-induced relaxation in rabbit mesenteric small artery

The effects of hydrogen peroxide were studied on isolated rabbit mesenteric small artery; rabbit superior mesenteric artery and mouse aorta were also studied as reference tissues. For mesenteric small artery, hydrogen peroxide (1 to 100 microM) relaxed a norepinephrine-stimulated artery in a concentration-dependent manner. The relaxation was not significantly affected by removal of the endothelium and was less pronounced in arteries contracted with high-KCl solution plus norepinephrine than in those contracted with norepinephrine alone. The relaxation response to hydrogen peroxide was increased by isobutylmethylxanthine and zaprinast, inhibited by diclofenac, methylene blue and dithiothreitol and unaffected by atropine, tetraethylammonium, superoxide dismutase, deferoxamine, dimethyl sulfoxide or the Rp stereoisomer of adenosine cyclic monophosphothioate. Hydrogen peroxide shifted concentration-contractile response curves for norepinephrine to the right and downwards. Norepinephrine and caffeine elicited a transient, phasic contraction of the mesenteric small artery exposed for 0.5, 1 and 2 min to a Ca2+-free solution. Hydrogen peroxide inhibited the norepinephrine-induced contraction, and to a lesser extent the caffeine-induced contraction, and verapamil did not alter the contraction to norepinephrine. These pharmacological properties of hydrogen peroxide were similar to those of 8-bromo cGMP; 8-bromo cGMP inhibited more potently the norepinephrine-induced than the KCl-induced contraction and the contraction elicited by norepinephrine in Ca2+-free solution. The present results suggest that hydrogen peroxide induces endothelium-independent relaxation of the rabbit mesenteric small artery precontracted with norepinephrine. The effects of hydrogen peroxide may be at least in part mediated by cGMP and cyclooxygenase products in the vascular smooth muscles now used.     

Effects of magnesium on the action of vasodilatory agents

Studies have shown that alterations of the magnesium (Mg2+) concentration can alter the response of certain vasoactive compounds. Responses of rabbit thoracic aorta to verapamil, diltiazem, nitroglycerin and isoproterenol were examined in zero Mg2+ (0.0 M), N Mg2+ (1.2 mM), 2 N Mg2+ (2.4 mM) and 4 N Mg2+ (4.8 mM). Preconstriction was induced with norepinephrine and cumulative dose-response curves were obtained for the vasodilators. The dose-response curve for isoproterenol was shifted to the right in zero Mg2+ while there was no effect on the other vasodilators. Elevation of the Mg2+ concentration to 4.8 mM produced a shift to the left in the dose-response curves for diltiazem, nitroglycerin and isoproterenol with no effect on verapamil. Therefore, Mg2+ deficiency does not appear to affect the vasodilatory actions of the agents tested except for the beta-receptor agonist, isoproterenol. Elevated Mg2+, however, potentiated the actions of isoproterenol, nitroglycerin and diltiazem, but not verapamil.     

Effects of l-tetrahydropalmatine on isolated rabbit arterial strips

The effects of l-tetrahydropalmatine (THP) on isolated rabbit aortic, renal and superior mesenteric arterial strips were studied in comparison with verapamil (Ver). THP and Ver shifted the KCl, CaCl2, norepinephrine (NE) and 15-methyl prostaglandin F2 alpha dose-response curves to the right in a non-parallel fashion, and decreased the maximal response, showing noncompetitive antagonism. THP was less potent in dilating arterial strips than Ver. THP and Ver obviously inhibited the intracellular Ca2+-dependent component of NE-induced contraction of the aorta, but only slightly decreased the extracellular Ca2+-dependent component when the concentration of THP or Ver was very high (THP 0.1 mmol/L, Ver 10 mumol/L). The results suggest that THP, similar to Ver, mainly inhibits potential-operated calcium channels. THP and Ver were more potent in dilating renal and superior mesenteric arterial strips than aortic strips. The results indicate that the vasodilation effect of THP is similar to that of Ver and that THP probably has a calcium antagonistic effect.     

Pharmacological characteristics of receptor-operated and potential-operated Ca2+ channels in rat aorta

In the rat aorta activation of the potential-operated Ca2+ channels by 100 mM K+ resulted in a greater 45Ca2+ influx than stimulation of the receptor-operated Ca2+ channels by norepinephrine (NE, 3 X 10(-7) M) or angiotensin II (AII, 10(-7) M). 45Ca2+ influx induced by NE was inhibited by prazosin (10(-7) M) but not by yohimbine (10(-6) M) while that by AII was abolished by [Sar1, Ile8]AII (10(-8) M). These receptor antagonists had no effect on the 45Ca2+ influx produced by K+. Bay k 8644 enhanced the influxes to low concentrations of NE and K+ while it was additive with the maximal concentration of NE but not with K+. 3-Isobutyl-1-methyl-xanthine and forskolin inhibited both the influx and efflux of 45Ca2+ elicited by NE but were ineffective against those caused by K+. Nifedipine blocked the efflux of 45Ca2+ induced by K+ but not that evoked by NE. However, both types of Ca2+ channel exhibited the same sensitivity to inhibition by Ca2+ entry blockers (nifedipine/verapamil) on 45Ca2+ influxes. These data suggest that in the rat aorta, the receptor-operated calcium channels and potential-operated calcium channels share similar structural characteristics. However, they are gated separately and distinctly by their respective activators.     

薤白提取物对兔离体主动脉条的作用

本实验以离体兔主动脉条为标本 ,对薤白 (EA)的扩血管机制进行了探讨 .观察了薤白对去甲肾上腺素 (NE)、氯化钾 (KCl)和氯化钙 (CaCl2 )的剂量 效应曲线的影响及主动脉条的α受体及 β受体的作用 .观察了EA对NE引起的兔主动脉条两种收缩成分的影响 .结果表明EA能舒张已为氯化钙、高钾和去甲肾上腺素收缩的兔主动脉条 ,使NE、KCl、CaCl2 的剂量 效应曲线非平行右移 ,最大效应降低 .EA松弛血管平滑肌的作用不依赖于阻断α受体或 β受体 ,而与戊脉安 (Ver)相似 ,是通过阻断钙通道实现的 .但它们阻断钙通道的方式不同 .EA可能无选择性阻断电位依赖性钙通道和受体操纵性钙通道 .因此EA的扩血管机制与其对钙通道阻断作用有关 .     

The vasorelaxant effect of evocarpine in isolated aortic strips: mode of action

The effect of evocarpine (EVO), a quinolone alkaloid isolated from Evodiae fructus, on Ca2+-blocking activity has been examined. In the isolated rat thoracic aorta evocarpine significantly inhibited the contraction induced by 60 mM K+ with an IC50 of 9.8 microM, and that induced by external Ca2+ in the depolarized muscle in concentrations of 10-100 microM. The relaxant effect of evocarpine and verapamil was antagonized by Bay K8644. The increase of 45Ca2+-influx induced by 60 mM K+ was significantly inhibited by 100 microM evocarpine. In the isolated rabbit thoracic aorta 100 microM evocarpine had no effect on the norepinephrine-induced contraction in normal medium or on the phasic contraction in Ca2+-free medium or on the transient relaxation induced by activation of the Na+ pump. The content of cyclic AMP or cyclic GMP was unchanged. These results suggest that evocarpine inhibits Ca2+ influx through voltage-dependent calcium channels.     

Activation mechanisms of human renal artery: effects of KCl, norepinephrine and nitrendipine upon tension development and 45Ca influx

The activation of human vascular smooth muscle by KCl-induced depolarization or norepinephrine and the inhibition produced by nitrendipine were studied in the isolated human renal artery. The contractile response of arterial rings to 80 mM KCl was abolished when extracellular Ca2+ was removed, and was inhibited by nitrendipine (IC50 = 10(-8) M). In contrast, a residual, transient contractile response to norepinephrine remained when extracellular Ca2+ was removed and the norepinephrine-induced contractions obtained in the presence of extracellular Ca2+ were not blocked by nitrendipine. KCl caused a stimulation of 45Ca influx which was completely prevented by 10(-6) M nitrendipine. Norepinephrine also caused a stimulation of 45Ca influx; however, the norepinephrine-induced 45Ca influx was not prevented by 10(-6) M nitrendipine. These findings are consistent with the concept that depolarization-induced activation of the human renal artery is primarily dependent upon a stimulation of Ca2+ influx; whereas activation by norepinephrine involves the release of intracellular Ca2+ in addition to the activation of a separate, receptor-operated Ca2+ influx pathway.     

Comparison of the calcium-antagonistic effects of terodiline, nifedipine and verapamil

Studies were carried out on the Ca-antagonistic effects of terodiline and its enantiomers on the potassium-stimulated mesenteric and coronary arteries, on the spontaneous myogenic activity and norepinephrine- and acetylcholine-induced contractions of the protal vein and on electrically stimulated papillary muscle. The effects were compared with those of the Ca-antagonists, nifedipine and verapamil. Terodiline is relatively weak as a Ca-antagonist, having IC50-values between 5 X 10(-6) and 2 X 10(-5)M for all the tissues studied. Nifedipine is the most potent Ca-antagonist on vascular smooth muscle (IC50 3-6 X 10(-9) M), but is considerably less potent on the papillary muscle (IC50 10(-7)M). Verapamil is most potent on the papillary muscle (IC50 7 X 10(-8)M and the portal vein (IC50 6 X 10(-8)M, but is 10 times less potent on the mesenteric and coronary arteries (IC50 3-5 X 10(-7)M). Nifedipine is 1000 times and verapamil and (-)-terodiline 10 times more potent on the slow component of the K-induced contraction while (+/-)- and (+)-terodiline are almost as active on the fast as on the slow component of K-induced contractions on the mesenteric artery. Furthermore, (+/-)-and (+)-terodiline are 10 times more potent in antagonizing acetylcholine- and norepinephrine-induced contractions, whereas (-)-terodiline is equally potent and nifedipine and verapamil are 10 times more potent in blocking the myogenic activity of the portal vein. On the Ca2+-nifedipine and verapamil. However, nifedipine and verapamil, but not terodiline, in concentrations which blocked the maximal norepinephrine-induced response in non-depleted muscle, antagonized the contractions induced by norepinephrine together with Ca2+ in the Ca2+ depleted portal vein. These results show that terodiline blocks the uptake of Ca2+ and, in addition, blocks the utilization of some intracellular stores of Ca2+.     

The inhibitory effects of N2-dansyl-L-arginine-4-t-butylpiperidine amide (TI233) on contraction of vascular and intestinal smooth muscle.

Effects of N2-dansyl-L-arginine-4-t-butylpiperidine amide (TI233) on the contractions in vascular and intestinal smooth muscles were examined. High K-induced sustained contractions in the smooth muscles were inhibited by TI233 with an IC50 of 2.1 X 10(-5) M for rabbit aorta and 3.6 X 10(-6) M for guinea-pig taenia coli in a solution containing 1.5 mM Ca. Initial transient contraction induced by K in taenia coli was less sensitive to the inhibitory effect of TI233. When the Ca concentration in the medium was decreased to 0.3 mM, the concentration-inhibition curves for TI233 shifted to the left in both aorta and taenia coli. Increasing the Ca concentration to 7.5 mM shifted the curve to the right in the aorta. TI233 also inhibited the noradrenaline-induced contraction in the aorta (IC50 = 2.1 X 10(-5 M). In a hypoxic solution without added glucose, the inhibitory effect of TI233 on the K-induced contraction in aorta was augmented. In the presence of high concentrations (40 mM) of glucose in hypoxia, TI233 did not inhibit the noradrenaline-induced contraction of the aorta. Hypoxia and a high concentration of glucose also decreased the inhibitory effect of TI233 on the K-induced contraction in taenia coli. TI233 inhibited the K-induced increase in cellular Ca content measured by a modified lanthanum method. TI233 decreased oxygen consumption and ATP content of resting and K-stimulated aorta and taenia coli. It was concluded that TI233 inhibits the vascular and intestinal smooth muscle contraction by a Ca antagonistic action and also by inhibition of aerobic metabolism.     

Vasorelaxing effect in rat thoracic aorta caused by denudatin B, isolated from the Chinese herb, magnolia fargesii

Denudatin B is an antiplatelet agent isolated from the flower buds of Magnolia fargesii. We studied the effects of denudatin B on the vasoconstriction of rat thoracic aorta induced by high potassium (K+) solution, norepinephrine (NE) and caffeine, and to elucidate its mode of action. The contraction of rat aorta caused by high K+ (60 mM) and cumulative concentrations of CaCl2 (0.03-3 mM) was inhibited concentration dependently by denudatin B with an IC50 of 21.2 micrograms/ml. NE (3 microM)-induced phasic and tonic contractions of rat aorta were inhibited by pretreatment with denudatin B (10-100 micrograms/ml). The relaxing action of denudatin B persisted in denuded aorta, in Ca2(+)-free and EGTA (2 mM)-containing medium. The vasorelaxing effects were not affected by indomethacin (20 microM), hemoglobin (10 microM) or methylene blue (50 microM) and were not accompanied by PGI2 formation. In quin-2/AM-loaded cultured rat vascular smooth muscle cells, denudatin B (100 micrograms/ml) inhibited the increase of intracellular calcium caused by NE (3 microM) in the presence or absence of extracellular calcium. Denudatin B did not affect the caffeine (10 mM)-induced contraction and the increase in intracellular calcium. Denudatin B (100 micrograms/ml) increased the cGMP, but not the cAMP level in intact and denuded aorta. The 45Ca2+ influx induced in rat aorta by high K+ (60 mM) or NE (3 microM) was markedly inhibited by denudatin B in a concentration-dependent manner. These results indicate that denudatin B relaxed vascular smooth muscle by inhibiting the Ca2+ influx through voltage-gated and receptor-operated Ca2+ channels; its effect to increase cGMP may enhance the vasorelaxation.