Receptor-mediated endocytosis of insulin: inhibition of [125I]iodoinsulin internalization in insulin resistant diabetic states of man.

We have used electron microscopic autoradiography to quantitatively study receptor-mediated endocytosis of [125I]insulin in freshly isolated monocytes from patients with non-insulin-dependent diabetes mellitus. In obese, non-obese, and lipoatrophic patients with diabetes, internalization of [125I]insulin was impaired at 30 min of incubation at 37 degrees C. By 60 min of incubation, however, internalization was indistinguishable from that of normals. In obese non-diabetic controls, internalization at 30 min was slightly less than internalization in normals but greater than that of the diabetic group. Dieting was associated with normalization of internalization in the obese group. We conclude that the rate of [125I]insulin internalization is impaired in non-insulin-dependent diabetes and compare this to previously reported results in insulin-dependent diabetes mellitus.