Isradipine: a potent calcium blocker with beneficial effects on platelet function and vascular prostacyclin production.

Calcium blockers inhibit platelet aggregation induced in vitro by various stimuli, such as ADP and collagen. In this study the in vitro effects of isradipine, a new dihydropyridine-derivative, and of nifedipine on platelet aggregation and malondialdehyde-production were tested. The lowest concentrations affecting ADP-induced platelet aggregation were 1.0 micrograms/ml isradipine and 12.5 micrograms/ml nifedipine. Both drugs exhibited an inhibitory action on malondialdehyde-production in concentrations 2 to 3 times lower than those affecting platelet aggregation. In vitro, PGI2-formation by rat aortic rings incubated with calcium blockers was increased in a dose-dependent manner. The lowest concentration of isradipine which increased PGI2-generation amounted 0.5 micrograms/ml. The corresponding value for nifedipine was 10 micrograms/ml. The findings demonstrate isradipine to be more potent than nifedipine in affecting in vitro platelet aggregation and enhancing PGI2-formation.