Vasodilation profile of CD-832, a novel dihydropyridine derivative in rabbit aorta

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

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.

In-vitro negative chronotropic and inotropic effects of a novel dihydropyridine derivative, CD-832, in the guinea-pig: comparison with calcium-channel antagonists

The effects of CD-832 (4R-(-)-2-(nicotinoylamino)ethyl-3-nitroxypropyl-1,4-dihydro -2,6-dimethyl-4,3-nitrophenyl, 3,5-pyridine dicarboxylate) , a novel dihydropyridine derivative, on guinea-pig isolated myocardial preparations have been compared with those of Ca2+-channel antagonists. All ten compounds induced concentration-dependent negative chronotropic effects on preparations of isolated right atria and negative inotropic effects on isolated right ventricular papillary muscles. The order of potency for the negative chronotropic effect was CD-832 > nicardipine = gallopamil > clentiazem > nifedipine = efonidipine > amlodipine = semotiadil > verapamil > diltiazem; that for the negative inotropic effect was nicardipine = gallopamil > nifedipine > verapamil > CD-832 > diltiazem > clentiazem > efonidipine = semotiadil > amlodipine. The ratio of the EC50 (the concentration of Ca2+ antagonist having 50% of the maximum effect) for the negative inotropic effect divided by the EC50 for the negative chronotropic effect, considered to be an index of selectivity for negative chronotropic effect, was higher for CD-832, amlodipine, efonidipine and semotiadil than for the other Ca2+ antagonists. The ratio for CD-832, nifedipine, nicardipine, efonidipine, amlodipine, verapamil, gallopamil, diltiazem, clentiazem and semotiadil was 11.4, 0.29, 0.87, 35.4, 37.1, 0.65, 0.87, 0.92, 7.11 and 30.0, respectively. These findings indicate that CD-832 and the newly developed Ca2+ antagonists including amlodipine, efonidipine, semotiadil and clentiazem were selective for a negative chronotropic effect rather than for a negative inotropic effect. This 'chrono-selective' effect of these drugs might be of benefit in the treatment of cardiovascular disorders.