From the University of Florida College of Medicine, Department of Medicine and Pediatrics, and the Veterans Administration Medical Center, Gainesville, FL, USA
Abstract:
We examined relationships between epinephrine-induced slope of primary wave of aggregation and the alpha2-adrenoceptor status on platelets. A concentration (10-9 to 10-6 )-dependent increase in slope of primary wave with EC50 of epinephrine at 4.5 ± 0.4 × 10-7 was observed. In studies on epinephrine binding to alpha2adrenoceptors in competition with 3H-yohimbine to platelets, (IC50) of epinephrine was 4.8 ± 3.4 x 10-7 M. There was a significant (P<0.02) correlation between EC50 of epinephrine to evoke biological response and IC50 of epinephrine to bind to alpha2-adrenoceptors (r-0.75). There was no relationship between number of receptor sites or dissociation constant of 3H-yohimbine binding and primary wave of platelet aggregation. These data show that the slope of primary wave in response to epinephrine reflects alpha2-adrenoceptor binding of the agonist.