The Peripheral Platelet Count and the Isoprenaline-Induced Splenic Platelet Pooling in Response to Beta-Adrenoceptor Blockade

Abstract

Previous reports showed that a single, oral dose of 50 mg metoprolol (a selective .beta.-1-receptor antagonist) caused a significant increase in the peripheral platelet count by releasing platelets from the spleen. In the present study 20 healthy volunteers received 50 mg metoprolol and 40 mg propranolol orally. The drugs induced a statistically significant increase in the platelet count lasting more than 5 h. The effect of metoprolol and propranolol on .beta. adrenoceptor mediated splenic platelet trapping was studied on 7 healthy subjects who received i.v. infusions of isoprenaline before and after the ingestion of these 2 .beta.-blocking drugs. The isoprenaline mediated decrease in the venous platelet count was diminished by propranolol and metoprolol but the former compound appeared to be more potent in this respect. Selective and non-selective .beta.-receptor blockade causes an increase in the peripheral platelet concentration during rest and during .beta.-adrenoceptor stimulation.