REVERSIBLE DECREASE OF SURFACE BETA(2)-ADRENOCEPTOR NUMBER AND RESPONSE IN LYMPHOCYTES OF PATIENTS WITH PHEOCHROMOCYTOMA

To study the effect of chronic exposure to elevated plasma catecholami nes on surface beta(2)-adrenoceptor density, we measured these recepto rs in the lymphocytes of 9 patients with pheochromocytoma as well as i n 27 healthy control subjects. Binding experiments were performed on i ntact lymphocytes Using the hydrophilic ligand [H-3]-CGP12177. Lymphoc yte beta(2)-adrenergic response was also measured in three patients. b eta(2)-adrenoceptor density (p < 0.01), and isoproterenol-stimulated i ncrease in cAMP were reduced in patients with pheochromocytoma. Both p arameters normalized (p < 0.05) when patients were reevaluated 4 weeks after tumor removal, coinciding with normalization of plasma catechol amine levels. B-2-adrenoceptor density inversely correlated to log of plasma epinephrine (r=-0.95, p < 0.01) and to log of plasma norepineph rine (r=-0.58, p < 0.05) in patients. We conclude that chronic catecho lamine excess induces a decrease of lymphocyte beta(2)-adrenoceptor su rface number and response that is reversible upon normalization of pla sma catecholamine levels. This regulation is mainly dependent on plasm a levels of the hormone epinephrine, but norepinephrine may also play a regulatory role at supraphysiological levels.