Insulin Receptors in Human Circulating Lymphocytes: Application to the Study of Insulin Resistance in Man*

125I-insulin binds to circulating human lymphocytes and is displaced by unlabeled insulin. We have compared the binding and displacement curves of 125I-insulin from the circulating lymphocytes of normal subjects with those of insulin resistant obese and acromegalic patients and insulin sensitive hypopituitary subjects. The initial 125I-insulin binding (maximal percent 125I-insulin bound) for normal subjects had a mean value of 2.9 ng/ml (range 1.9–3.4) per 70 × 106 cells which is not statistically different from the other patient groups. For the normals, the Insulin-50% inhibition 125I-insulin bound (that concentration of insulin necessary to inhibit 50% of the maximal binding) had a mean value of 8.4 ng/ml (range 6.0–12.0 ng/ml). This value is significantly different from the obese patients but not from the acromegalic or the hypopituitary subjects. If the circulating lymphocyte mirrors the changes seen in the major metabolic sites of insulin action, these data suggest that an alteration in the insulin receptor may be in part responsible for the insulin resistance of obesity.