Insulin binding to erythrocytes of normal infants, children, and adults: variation with age and sex.

The assay of insulin receptors on erythrocytes requires only small amounts of blood and has made it possible to characterize insulin binding in infancy and childhood. To establish normal insulin-binding criteria, we studied 125I binding to insulin receptors on erythrocytes from a large number of normal subjects, including 15 term deliveries, 45 prepubertal children (aged 2 months-12 yr), 15 adult women, and 15 adult men. Insulin binding to cord erythrocytes was significantly higher at tracer and physiological insulin concentrations than binding to cells from any other age group (P less than 0.001). In the prepubertal children after the newborn period, insulin binding was not related to age or sex and did not differ significantly from the binding to cells from adult women. Erythrocytes from adult males, however, bound significantly higher amounts of insulin than did those from adult women or prepubertal children at all insulin concentrations tested (P less than 0.01). Increased binding to cord erythrocytes appeared to be due to an increase in receptor affinity, while the increased binding in adult males was primarily a result of increased receptor concentration. The data confirm previous reports of increased insulin binding to fetal cells and indicate that erythrocyte insulin binding stabilizes at levels similar to those in adult females by the age of 2 months. The increased binding of insulin to erythrocytes from adult males compared to binding to erythrocytes from children or adult females suggests that androgens may increase erythrocyte insulin binding over prepubertal levels.