?2-Adrenoceptor-mediated inhibition of platelet adenylate cyclase activity in heroin addicts in abstinence

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Abstract
The inhibition of basal and forskolin-stimulated platelet adenylate cyclase activity by (-)adrenaline was studied in ten heroin addicts during spontaneous withdrawal. Both basal and forskolin-stimulated enzyme activities were increased during heroin withdrawal and the inhibitory effect induced by (-)adrenaline was potentiated with parallel shifts to the left of the concentration-effect curves. The number of binding sites for [3H](-)adrenaline in platelet membranes was also increased during withdrawal. Treatment with clonidine markedly attenuated the inhibitory effect induced by (-)adrenaline on platelet adenylate cyclase activity. The results indicate that the heroin withdrawal syndrome induces supersensitivity of the platelet α2-adrenoceptor-adenylate cyclase system.