Induction of human platelet fibrinogen receptors by epinephrine in the absence of released ADP

The ability of epinephrine to expose platelet fibrinogen receptors independent of released ADP was assessed using aspirin-treated, gel-filtered platelets. Similar to ADP-induced aggregation, platelet aggregation in response to epinephrine was accompanied by fibrinogen binding. Ten micromolar epinephrine induced a maximum number of platelet fibrinogen receptors in the absence of significant 14C-serotonin release. As indicated by Scatchard analysis, receptors exposed by both epinephrine and ADP had similar affinities for fibrinogen, but epinephrine induced approximately 30% fewer receptors than did ADP. This appears to correlate with the lesser degree of primary aggregation observed with this agent. Studies using phentolamine, a specific alpha-adrenergic antagonist, apyrase, or creatine phosphate/creatine kinase indicate that the exposure of platelet fibrinogen receptors by epinephrine was specific for platelet alpha-adrenergic receptor stimulation and was not the result of released ADP.