Possible involvement of nitric oxide-cGMP pathway in the negative chronotropic effect of CD-832, a novel...

Effects of zaprinast, an inhibitor of guanosine 3', 5'-cyclic monophosphate (cGMP)-specific phosphodiesterase, and methylene blue, an inhibitor of soluble guanylate cyclase, on the negative chronotropic response to CD-832, a novel dihydropyridine derivative with a nitrate moiety, and nifedipine were examined with isolated guinea-pig right atria in the presence and absence of isoproterenol. CD-832 and nifedipine produced concentration-dependent negative chronotropic effects both in the absence and presence of isoproterenol. In the absence of isoproterenol, the concentration-response curves for CD-832 and nifedipine were neither potentiated by zaprinast nor inhibited by methylene blue. In the presence of isoproterenol (10[-8] M), zaprinast produced a three-fold leftward shift of the concentration-response curve for CD-832, while methylene blue produced a three-fold rightward shift. The concentration-response curve for nifedipine was not affected by these agents. SIN-1, a nitric oxide (NO) donor, had no chronotropic effect in the absence of isoproterenol, but had a concentration-dependent negative chronotropic effect in the presence of isoproterenol: the beating rate decreased to values close to that in the absence of isoproterenol. These findings suggest that NO-cGMP mediated pathway is involved in the negative chronotropic actions of CD-832 under beta-adrenergic stimulation.