Effects of gluconeogenic hormones on insulin binding in intact human red blood cells

Modulation by dexamethasone of insulin binding and insulin receptor mRNA levels in U-937 human promonocytic cells

Treatment with 5 x 10(-6) M dexamethasone stimulated insulin binding in human promonocytic U-937 cells. When curvilinear Scatchard plots were examined according to the one-site model, only changes in affinity, but not in receptor numbers, were observed. However, when the two-site model was applied, an increase in both the affinity and the number of the high affinity-low capacity sites was observed, with maximum values at 15 h. By contrast, the low affinity-high capacity sites did not undergo significant alterations. Northern blot assays revealed two insulin receptor-related mRNAs of approximately 11 and 7 kb in size. Dexamethasone increased the levels of these RNAs, following similar kinetics to those of high affinity receptor expression. This suggests that the 11 and 7 kb species carry information for high affinity insulin receptors, and that in U-937 cells the expression of this receptor subclass is primarily regulated at the mRNA level.

Red blood cell insulin receptors in health and disease

CONTENTS

Structure and characteristics of erythrocyte insulin receptor. Red blood cell age and insulin receptors. Insulin receptors in human disease states. Obesity. Chronic renal failure. Acanthosis nigricans. Miscellaneous disease states. Insulin receptors in children. Insulin receptors in women during pregnancy. Insulin binding and other hormones. Comparison of biosynthetic insulin, pancreatic human insulin and porcine insulin binding to erythrocytes. Effect of exercise on insulin binding to red blood cells of normal human volunteers. Miscellaneous insulin binding studies. Insulin internalization and degradation. Insulin and erythrocyte metabolism. Summary and conclusion.

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.