Influence of propranolol and 4-hydroxypropranolol on platelet aggregation and thromboxane A2 generation

We examined in vitro effects of propranolol and its major metabolite, 4-hydroxypropranolol, on human platelets. Both propranolol and its 4-hydroxy metabolite had no significant direct effect on either platelet aggregation or TXA2 generation in therapeutic concentrations. Higher concentrations (greater than or equal to 10 micrograms/ml), however, reduced both parameters of platelet function. When propranolol and 4-hydroxypropranolol were incubated in combination with platelets in equal concentrations, there were synergistic effects on platelet aggregation and TXA2 generation. Neither propranolol nor 4-hydroxypropranolol inhibited platelet aggregation or TXA2 synthesis in sonicated platelets at any concentration, indicating that intact platelet membrane is necessary for their action.