Alpha-2-adrenoreceptor density on intact platelets and adrenaline-induced platelet aggregation in endurance- and nonendurance-trained subjects.
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.
D000328:Adult; D001792:Blood Platelets / Q000032:analysis*; D004837:Epinephrine / Q000494:pharmacology*; D006801:Humans; D010807:Physical Endurance; D005082:Physical Exertion; D010974:Platelet Aggregation / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*; D013177:Sports; D014316:Tritium; D015016:Yohimbine / Q000097:blood*
D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D015016:Yohimbine; D004837:Epinephrine