Alpha 2- and beta 2-adrenoceptor downregulation in marathon runners.

The regulation of platelet alpha 2- and lymphocyte beta 2-adrenoceptor densities by alterations in endogenous catecholamines was examined. In order to activate the sympathetic nervous system eight trained male normotensive subjects carried out a marathon run. Adrenoceptor densities and plasma catecholamine concentrations were measured before and immediately after the run. Platelet alpha 2-adrenoceptor density and lymphocyte beta-adrenoceptor density decreased after the run (P less than 0.05), whereas both plasma noradrenaline and adrenaline concentrations increased (P less than 0.01). Mean arterial pressure decreased (P less than 0.05), and the heart rate increased (P less than 0.001). The data suggest that increases in endogenous catecholamine concentrations cause downregulation of both alpha- and beta-adrenoceptor densities on human blood cells.