Effects of calcium entry blockers on human platelet metabolism measured by microcalorimetry.

1. The direct overall metabolic effects of calcium entry blockers on human platelets were evaluated using a sensitive microcalorimetric method. 2. The effect on platelet metabolism of four calcium entry blockers with different profiles of action was examined and compared with the relaxant response on human cerebral vessels in vitro. 3. Diltiazem (10(-8), 10(-4) M) and nifedipine (10(-10), 10(-6) M) were without effect on overall platelet metabolism. On the other hand flunarizine (10(-4) M) and verapamil (10(-4) M) significantly reduced metabolism, while lower concentrations of these agents did not change heat production. 4. The thermogenic response occurred at concentrations of the calcium entry blockers that were much higher than those observed during therapy and the concentrations which relax human cerebral arteries in vitro.