Reversible Decrease of Surface ß₂-Adrenoceptor Number and Response in Lymphocytes of Patients with Pheochromocytoma

Abstract

To study the effect of chronic exposure to elevated plasma catecholamines on surface ß₂-adrenoceptor density, we measured these receptors in the lymphocytes of 9 patients with pheochromocytoma as well as in 27 healthy control subjects. Binding experiments were performed on intact lymphocytes using the hydrophilic ligand [³H]-CGP12177. Lymphocyte β₂-adrenergic response was also measured in three patients. ß₂-adrenoceptor density (p<0.01), and isoproterenol-stimulated increase in cAMP were reduced in patients with pheochromocytoma. Both parameters normalized (p<0.05) when patients were reevaluated 4 weeks after tumor removal, coinciding with normalization of plasma catecholamine levels. ß₂-adrenoceptor density inversely correlated to log of plasma epinephrine (r=-0.95, p<0.01) and to log of plasma norepinephrine (r=-0.58, p<0.05) in patients.

We conclude that chronic catecholamine excess induces a decrease of lymphocyte ß₂-adrenoceptor surface number and response that is reversible upon normalization of plasma catecholamine levels. This regulation is mainly dependent on plasma levels of the hormone epinephrine, but norepinephrine may also play a regulatory role at supraphysiological levels.

Key Words:

• pheochromocytoma
• surface β₂-adrenoceptors
• CGP12177
• catecholamines
• β₂-adrenergic response