Effects of three beta-blockers with different pharmacodynamic properties on platelet aggregation and platelet and...

The effects of three different types of beta-adrenoceptor blocking agents on platelet aggregation and on platelet and plasma cyclic AMP content have been studied in 14 patients with mild hypertension given each drug in turn for two weeks. The drugs were a non-selective blocking agent with high intrinsic sympathomimetic activity, pindolol, the nonspecific blocking agent propranolol, and the beta 1-selective metoprolol. The threshold values of ADP and adrenaline for irreversible platelet aggregation were significantly higher for pindolol and metoprolol than for propranolol. The cyclic AMP content of platelets was higher during pindolol and metoprolol than during propranolol treatment. Pindolol produced a substantial increase in plasma cyclic AMP relative to the other two drugs. Thus, platelet aggregation and cyclic AMP formation are influenced by beta-adrenoceptor blockade in proportion to intrinsic sympathomimetic activity and affinity for different beta-adrenoceptor subtypes.