Effect of felodipine, a new calcium channel antagonist, on platelet function and fibrinolytic activity at rest and after exercise.

Fourteen healthy male volunteers (age 21-29 years, mean 23.7 years) were given placebo for 14 days followed immediately by felodipine 5 mg b.d. for a further 14 days. After each period of treatment blood for analysis was taken at rest and after exercise on a cycle ergometer. Platelet aggregation, plasma beta-thromboglobulin (B-TG), platelet factor 4 (PF-4), adrenaline and noradrenaline, and serum thromboxane B2 (TXB2), 6-keto-prostaglandin (F1 alpha (6-keto-PGF1 alpha), and euglobulin clot lysis time (ECLT), were measured on each occasion. The ECG, heart rate and blood pressure were monitored during the exercise tests. After felodipine therapy there was a significant decrease in the plasma level of PF-4 and B-TG at rest. This effect was maintained during exercise. There was no significant change in platelet aggregation, ECLT, TXB2 or 6-keto-PGF1 alpha at rest or during exercise. Irrespective of therapy, the plasma levels of adrenaline and noradrenaline were increased and the ECLT was decreased when measured immediately after exercise. Thus, felodipine in modest therapeutic dosage decreases the plasma levels of B-TG and PF-4, indicating an inhibitory effect on platelet on release. The effect also occurred during exercise. Felodipine did not change fibrinolytic activity or the production of TXB2 or 6-keto-PGF1 alpha.