Abstract
[ 3H] dihydroergocyrptine, an α-adrenergic antagonist, binds specifically to sites on human platelet membranes. Prostaglandin E 1 (PGE 1) stimulates the production of cyclic AMP (cAMP) in human platelets. Alpha-adrenergic agonists, 1-epinephrine and 1-norepinephrine, and antagonists, phentolamine, phenoxybenzamine, and dihydroergocyrptine inhibit the binding of [ 3H] dihydroergocryptine. The α-adrenergic agonists inhibit PGE 1-stimulated cAMP production and the α-adrenergic antagonists phentolamine and dihydroergocryptine reverse this inhibition. The β-adrenergic agonist 1-isoproterenol and the β-adrenergic antagonists d1-propranolol and 1-alprenolol do not significantly alter binding or PGE 1-stimulated cAMP production. Clonidine, dopamine, and serotonin inhibit binding, but clonidine and dopamine are weak inhibitors of PGE 1-stimulated cAMP production, and serotonin is without effect. Tyramine, an amine without direct adrenergic activity fails to inhibit binding. Alpha-adrenergic agonists decrease the apparent affinity of a PGE 1-receptor activating cAMP production. The inhibition of PGE 1-stimulated cAMP production is a physiological measure of α-adrenergic agonist binding to the α-receptor.
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