Heroin increases the density and sensitivity of platelet alpha 2-adrenoceptors in human addicts.

The density of platelet alpha 2-adrenoceptors, quantified by means of the binding of [3H]clonidine, and the aggregation response induced by adrenaline, was investigated in ten heroin addicts. The number of binding sites for [3H]clonidine was significantly increased during heroin abuse. Concomitantly, there was a potentiation of the adrenaline-induced platelet aggregation, which suggested that continuous heroin use (opiate dependence) is associated with supersensitive platelet alpha 2-adrenoceptors in human addicts. Spontaneous heroin withdrawal further increased in the same addicts the density of platelet alpha 2-adrenoceptors. These results suggest that platelet alpha 2-adrenoceptors may be used as a model to study receptor mechanisms of opiate dependence and withdrawal in humans.