Epinephrine sensitizes human platelets in vivo and in vitro as studied by fibrinogen binding and P-selectin expression

Abstract

Epinephrine (Epi) infusion influences platelet activation markers in vivo, but in vitro studies have mainly examined supraphysiological Epi concentrations and have yielded conflicting results. In this study whole-blood flowcytometric measurements of platelet fibrinogen binding and P-selectin expression were used to compare enhancement of ADP (0.1 to 10 μmol/L)-induced platelet activation by Epi infusion in vivo (0.1 and 0.4 nmol · kg-1 · min-1) and by Epi in vitro (10 and 50 nmol/L) in nine healthy volunteers. ADP caused concentration-dependent increases in the percentage of platelets that bound fibrinogen (from 4.4±0.9% to 69.9±4.2%) and that expressed P-selectin (from 4.5±0.5% to 44.2±3.8%). Fibrinogen and P-selectin binding indices (FgBI and PSBI; calculated from mean fluorescence intensity and percentage of positive cells) also increased from 0.18±0.03 to 11.70±1.99 for FgBI and from 0.22±0.03 to 2.34±0.29 for PSBI. Epi concentration-dependently enhanced fibrinogen binding and P-selectin expression in vitro (by ≈30% at the midportion of the ADP curve at 10 nmol/L Epi; P