Chronic and endogenous regulation of insulin receptors by catecholamines in adipocytes from patients with a phaeochromocytoma.

Insulin binding in adipocytes from patients with a phaeochromocytoma (PH) approached that of the controls (C) at low and higher concentrations of unlabeled insulin. The apparent receptor affinity was unchanged (ED50: PH 0.50 x 10(-9) M and C 0.60 x 10(-9) M). Scatchard analysis of the binding data using the negative cooperative model revealed a 46% decrease in the total number of receptors together with no changes in both K-e (PH 0.55 x 10(9) M-1 and C 0.36 x 10(9) M-1) and K-f (PH 0.13 x 10(9) M-1 and C 0.07 x 10(9) M-1). According to the two site model, an altered proportion in the two classes of insulin binding sites was detected. This was accompanied by a catecholamine-desensitization of the adipocytes to the antilipolytic action of insulin. These events could represent a final situation of a chronic and endogenous regulation by high levels of catecholamines of insulin receptors in human adipose tissue.