Alpha-2-adrenoreceptor density on intact platelets and adrenaline-induced platelet aggregation in endurance- and...

Alpha-2-adrenoreceptor density on intact platelets was evaluated in 17 sportsmen, 8 of whom were endurance-trained athletes. Receptor density was determined as being equivalent to 3H-Yohimbine, specifically bound on intact platelets. Adrenaline-induced aggregation of platelets in vitro was additionally ascertained. Bmax (maximal binding) and KD (dissociation constant) were significantly lower in endurance-trained athletes (148 fmol per 10(9) platelets, KD = 0.92 nmol) than in the nine nonendurance-trained individuals (284 fmol, KD = 1.79 nmol, P less than 0.01), amounting to 89 receptors per cell (endurance-trained subjects) and 171 (nonendurance-trained subjects). No significant change of receptor density or affinity was observed subsequent to exhaustive exercise in the group of eight endurance-trained individuals. Bmax values and oxygen uptake capacity correlated negatively (r = -0.78, P less than 0.001) and Bmax values and induced platelet aggregation in vitro positively (r = 0.79, P less than 0.001). Data may indicate a reduced sensitivity of platelets in endurance-trained subjects.