Objective To evaluate insulin receptor binding characteristics of urbanized South African black women with normal glucose tolerance and of patients with newly diagnosed untreated non-insulin-dependent diabetes mellitus (N1DDM).

Research Design and Methods Four groups of 10 subjects each were selected by the following criteria: group A, young (20-39 yr) nonobese (body mass index [BMI] 19.0-24.9 kg/m²) nondiabetic women; group B, middleaged (40–60 yr) nonobese nondiabetic women; group C, middle-aged obese (BMI>30.0 kg/m²) nondiabetic women; and group D, middle-aged obese newly diagnosed but untreated female patients with NIDDM. Insulin binding to monocyte receptors was determined by radioreceptor assay. Fasting plasma samples were analyzed for glucose, insulin, C-pep tide, and nones terified fatty acids.

Results In the four groups studied, maximum specific binding and receptor concentration were highest in group A, with a progressive and significant decrease in values through groups B and C to group D. Significant inverse correlations were obtained between maximum specific binding, 50% inhibition dose, and total receptor concentration on the one hand and glucose, insulin, and NEFA on the other.

Conclusions Our study of urban South African black women showed decreasing insulin-receptor activity with obesity and glucose intolerance. In patients with NIDDM, hyperglycemia and (β-cell dysfunction were associated with a reduction in receptor concentration. In this regard, our findings in South African blacks are consistent with results of similar studies of NIDDM in other communities.