REDUCTION OF ADENYLATE-CYCLASE ACTIVITY IN LYSATES OF HUMAN PLATELETS BY ALPHA-ADRENERGIC COMPONENT OF EPINEPHRINE

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  • 1 January 1976
    • journal article
    • research article
    • Vol. 2  (6) , 381-392
Abstract
The effects of the .alpha.- and .beta.-adrenergic components of epinephrine on adenylate cyclase activity were studied in lysates of human platelets. The .beta.-adrenergic component increased enzyme activity between 20 and 50%, whereas the .alpha.-adrenergic component caused a concentration-dependent reduction of adenylate cyclase activity. The maximal inhibition of adenylate cyclase was 50-60% with about 100 .mu.M epinephrine; about 1 .mu.M epinephrine caused half-maximal inhibition. The .alpha.-adrenergic reduction of adenylate cyclase activity appeared to be immediate and was specific for platelets from species in which .alpha.-adrenergic stimulation caused aggregation. Adenylate cyclase activity measured in the presence of prostaglandins or fluoride was also reduced by the .alpha.-adrenergic component of epinephrine, but the inhibitory effect was less than on basal activity. In contrast, the 5''-guanylylimidodiphosphate-stimulated enzyme was not affected by stimulation of .alpha.-adrenergic receptors.

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