Insulin binding to erythrocytes in diabetic patients

Insulin binding to circulating erythrocytes was studied in 32 maturity onset-type diabetic patients with varying degrees of insulin response to oral glucose. Specifically bound-insulin fraction to erythrocytes ranged from 4.9 to 12.7% at a tracer concentration of insulin. A negative correlation was found between the binding and fasting serum insulin concentration (r = -0.45). When the binding was compared with sum of serum insulin concentrations at 0, 30, 60, 90, and 120 min after the oral administration of 50 g glucose (sigma IRI), a better correlation was obtained (R = -0.63). Patients were classified into group A (sigma IRI less than or equal to 100 microunits/ml), group B (100 microunits/ml less than sigma IRI less than 200 muml) and group C (sigma IRI greater than or equal to 200 microunits/ml). Scatchard analysis of the competition data from each group indicated that erythrocytes from group a showed the highest concentration of receptors (60 sites/erythrocyte) while the lowest from group C (36 sites/erythrocyte). The receptor affinity was not significantly different among the groups. These results suggest that insulin receptors on human erythrocytes are regulated by the ambient insulin concentration as shown in receptors on insulin target cells. Therefore, erythrocytes seem useful for the study of insulin receptors in conditions associated with altered insulin sensitivity.