Effect of metoprolol and propranolol on platelet aggregation and cAMP level in hypertensive patients

Summary Ten patients with uncomplicated moderate essential hypertension were recruited to evaluate the effect of the non-selective beta-blocker propranolol and the beta₁-selective beta-blocker metoprolol on platelet aggregation and cAMP formation. Five patients began treatment with propranolol 80 mg b. i. d. and 5 with metoprolol 100 mg b. i. d., and after 2 weeks the treatments were exchanged. ADP- and adrenaline-induced platelet aggregation and the basal level of platelet cAMP were measured at the end of each treatment period. Platelet aggregation was tested turbidometrically, using the threshold value for irreversible aggregation, and cAMP measurements were performed using a protein-binding assay.Both ADP and adrenaline thrshold values were significantly lower after propranolol than after metoprolol.The basal cAMP level was lower during propranolol than metoprolol treatment.The results indicate that platelet aggregation and basal cAMP level are influenced by beta-blockers in proportion to their affinity to different beta-adrenoceptors. This may be of value in the beta-blocker treatment of patients at high thrombotic risk.