The Peripheral Platelet Count in Response to Adrenergic Alpha‐ and Beta‐1‐Receptor Stimulation

Abstract

The effect of adrenergic .alpha.- and .beta.-1-receptor stimulation on the peripheral platelet count was investigated. The experiments were carried out on 8 healthy male volunteers using radioisotopically labeled platelets. Three subjects received i.v. infusions of adrenaline [epinephrine] (0.09 .mu.g .times. kg-1 .times. min-1) before and after the ingestion of 40 mg propranolol. In response to the 1st infusion there was an instant increase in the venous platelet-bound radioactivity (PBR) which amounted to 12% over basal value. This effect of adrenaline seemed to be potentiated by propranolol pretreatment. Five subjects received i.v. infusions of the highly selective .beta.-1-receptor agonist H 133/22 (prenalterol, Hassle, Sweden). In response to a cumulative dose of 4.75 mg prenalterol a slight but significant (P < 0.05) decrease in PBR occurred. .alpha.-Receptor stimulation causes a depletion of platelets from the exchangeable splenic platelet pool resulting in a concomitant increase in the peripheral platelet count. .beta.-Receptor stimulation has an opposite effect on the spleen. The trapping of platelets by the spleen is mediated both via .beta.-1- and .beta.-2-receptors, but the effect of .beta.-2-receptor stimulation seems to predominate.