Insulin binding to erythrocytes of nonpregnant women: a reevaluation, underlining the importance of body weights even in nonobese subjects.

Insulin binding to erythrocytes was measured in 18 healthy, non-obese women in the follicular phase and in 6 women in the mid-luteal phase of the same menstrual cycle. The presence of 55 nM and 220 nM monoclonal anti-IGF I receptor antibody (α-IR3) reduced only the number of low affinity binding sites for insulin by 20% and 33%, respectively. Women with relative body weights 110–119% had a lower number of high affinity receptors and an increased high affinity compared to women with relative body weights 91–109%. In women with relative body weights ≥ 100%, maximum specific binding and high affinity constants increased and the receptor numbers decreased from the follicular to the luteal phase, whereas in women with relative body weights < 100% the parameter changes were reverted. The data indicate: (1) erythrocytes contain two different classes of binding sites for insulin, (2) IGF I receptors might contribute to low-affinity binding of insulin to erythrocytes and (3) the relative body weight must be considered even for ‘non-obese’ control groups used in insulin binding studies of various clinical conditions.