Effects of antiinsulin receptor autoantibody on the metabolism of rat adipocytes.

We have studied the effects of the serum from a patient with an unusual form of diabetic syndrome with extreme insulin resistance on the metabolism of rat adipocytes in vitro. This serum and IgG fractions from it inhibited the [125I]insulin binding to isolated adipocytes and stimulated the 2-deoxyglucose uptake, glucose oxidation, and the incorporation of amino acids into protein. In addition, these fractions inhibited the lipolysis induced by beta 1-24 ACTH in isolated adipocytes. The insulin-like effects of this serum and the effects of insulin were not additive at their maximal concentrations. The inhibition of [125I]insulin binding was due to a decrease in receptor affinity rather than to a change in receptor number by Scatchard plot analysis. Both the inhibition of insulin binding and the insulin-like effects on rat adipocytes were neutralized by antihuman IgG. In addition, these insulin-like effects were abolished by trypsin treatment of adipocytes. These facts suggest that this serum has a circulating antibody directed at or near the insulin receptor itself and that this antibody mimics the insulin effect on rat adipocytes by binding to the insulin receptor in vitro.