Comparison of insulin binding to cells of fed and fasted obese patients: results in erythrocytes and monocytes.

The erythrocyte (RBC) has received recent interest as a cell model to examine insulin receptor status in humans. In the present study we have compared the insulin receptors on mature RBCs and monocytes of four hyperinsulinemic obese patients in the fed state and after a 14-day fast (less than 50 cal/day). Insulin binding in the basal (fed) state was described in RBC and monocytes due predominantly to a decrease in the receptor concentration in both cell types. After a 14-day fast, insulin binding to both RBCs and monocytes increased significantly in each patient. Maximal binding of [125I]iodoinsulin to RBCs increased by 29% (range, 20-46%), and binding to monocytes increased by 116% (range, 46-321%). In response to the fast, the concentration of insulin needed to inhibit binding by 50% decreased from 5 to 2 ng/ml in RBC and from 3 to 1 ng/ml in monocytes. Conventional and computer-fitted Scatchard analyses demonstrated no change in the receptor concentration of RBCs of any patient, whereas the receptor concentration of monocytes increased by more than 50% in two of the four patients and by 40% for the group. Thus, in response to the fast, the direction of the change in insulin binding was similar in the RBCs and monocytes, whereas the magnitude and, in certain patients, the mechanism of the binding increase differed.