Actions of isosorbide dinitrate on smooth muscle cells of rabbit vascular tissues

Effects of isosorbide dinitrate and diltiazem on Ca2+ flux and contraction in artery

We studied the effects of isosorbide dinitrate and diltiazem on histamine-stimulated 45Ca fluxes and contractions of isolated porcine coronary artery. Isosorbide dinitrate was slightly more potent as an inhibitor of intracellular compared to extracellular calcium-dependent contraction. Isosorbide dinitrate inhibited histamine-stimulated calcium efflux and intracellular calcium-dependent contraction over similar concentration ranges. Isosorbide dinitrate partially inhibited histamine-stimulated calcium influx, but this effect was significant only at high concentration and correlated weakly with inhibition of contraction that was dependent on extracellular calcium. Diltiazem more potently inhibited extracellular vs. intracellular calcium-dependent contraction. Diltiazem partially inhibited histamine-stimulated calcium efflux and intracellular calcium-dependent contraction to similar extents (55-60%) and produced similar concentration-response relationships for inhibition of histamine-stimulated calcium influx and extracellular calcium-dependent contraction. The data suggest that alterations of cellular calcium metabolism are major mechanisms of vascular smooth muscle relaxation by isosorbide dinitrate and diltiazem, but that the specific alterations differ for the two drugs. Isosorbide dinitrate may inhibit contraction primarily by enhancing intracellular calcium sequestration, but possibly also by inhibiting agonist-stimulated calcium influx at high isosorbide dinitrate concentrations. Diltiazem primarily inhibits stimulated calcium influx, but may also inhibit intracellular calcium release.

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.

Mechanism of vasodilation induced by alpha-human atrial natriuretic polypeptide in rabbit and guinea-pig renal arteries

Effects of alpha-human atrial natriuretic polypeptide (alpha-HANP) on electrical and mechanical properties of smooth muscle cells of the guinea-pig and rabbit renal arteries and of the guinea-pig mesenteric artery were investigated. alpha-HANP (up to 10 nM) modified neither the membrane potential nor resistance of smooth muscle cells of the guinea-pig and rabbit renal arteries. In the guinea-pig mesenteric and renal arteries, alpha-HANP (up to 10 nM) had no effect on the amplitude and facilitation (mesenteric artery) or depression (renal artery) of excitatory junction potentials nor on action potentials. In the guinea-pig renal artery, alpha-HANP (up to 10 nM) had no effect on the depolarization induced by noradrenaline (NA) (up to 10 microM) but markedly inhibited NA-induced contraction. alpha-HANP (10 nM) slightly inhibited the K-induced contraction. In the rabbit renal artery, alpha-HANP (10 nM) inhibited the NA-induced contraction and to a lesser extent the K-induced contraction. In the rabbit renal artery, the effects of alpha-HANP on the release of Ca from the cellular storage by two applications of NA, and its re-storage, were investigated in Ca-free solution containing 2 mM-EGTA. When 5 nM-alpha-HANP was applied before and during the first application of 0.5 microM-NA, the contraction was markedly inhibited but the contraction to a second application of 10 microM-NA was potentiated. If the first dose of NA was 10 microM the effect was very small. Under the same experimental procedures, nitroglycerine (10 microM) showed almost the same effects as alpha-HANP on the NA-induced contractions. When both the first (3 mM) and second (10 mM) contractions were evoked by caffeine in Ca-free solution, alpha-HANP (5 nM) and nitroglycerine (10 microM) inhibited both contractions to the same extent. In the rabbit renal artery, applications of alpha-HANP or nitroglycerine increased the amount of guanosine 3',5'-phosphate (cyclic GMP) in a dose-dependent manner. However, a much higher concentration of nitroglycerine was required (2 X 10(3) times). In the rabbit renal artery, hydrolysis of phosphatidyl inositol 4,5-bisphosphate (PI-P2) activated by 0.5 microM-NA was inhibited by alpha-HANP, in a dose-dependent manner, but activation by 10 microM-NA was not inhibited by alpha-HANP (up to 100 nM).(ABSTRACT TRUNCATED AT 400 WORDS)

Regional differences in the actions of verapamil and isosorbide dinitrate on rabbit and dog vascular smooth muscle

The effects of verapamil and isosorbide dinitrate (ISDN) alone or together on mechanical responses of the rabbit coronary artery and mesenteric vein, and the dog coronary artery have been investigated. Verapamil, in concentrations exceeding 10 nM consistently inhibited and at 10 microM, blocked the contraction evoked by excess concentrations of K in these tissues, but agonist-induced contraction was not modified by the presence or absence of Ca. In concentrations greater than 1 microM, verapamil depolarized the membrane by inhibiting the K-conductance of the membrane. ISDN had little effect on the rabbit coronary artery in concentrations below 10 microM. In contrast, in the rabbit mesenteric vein and dog coronary artery, ISDN in concentrations over 1 microM inhibited the contraction evoked by excess concentrations of K or by agonists. Species differences were apparent in the actions of ISDN on vascular tissues. When verapamil and ISDN were simultaneously applied to the rabbit mesenteric vein and dog coronary artery, the K-induced contraction was markedly inhibited by an amount exceeding that produced by the sum of the contractions evoked by the individual application of both agents. An enhanced vasodilating action induced by simultaneous applications of both agents indicates a possible clinical benefit for anti-anginal treatment.