Ethnic differences in the responsiveness of adipocyte lipolytic activity to insulin

Objective: The goal of this study was to quantify differences in lipid meta bolism and insulin sensitivity in black and white subjects to explain ethni c clinicopathological differences in type 2 diabetes. Research Methods and Procedures: The in vitro lipolytic activity of adipocy tes isolated from obese black and white women was measured in the presence of insulin and isoproterenol. Insulin resistance was assessed in vivo using the euglycemic hyperinsulinemic clamp technique. Results: Easting plasma levels of insulin and nonesterified fatty acid (NEF A) in black and white women were 67 +/- 5 pM vs. 152 +/- 20 pM (p < 0.01) a nd 863 +/- 93 mu M vs. 412 +/- 34 mu M (p < 0.01), respectively. Euglycemic hyperinsulinemic clamp studies showed that obese black subjects were more insulin-resistant than their white counterparts (glucose infusion rates: 1. 3 +/- 0.2 vs. 2.2 +/- 0.3 mg/kg per min; p < 0.05). Isolated adipocytes fro m white women were more responsive to insulin than those from black women w ith 0.7 nM insulin causing a 55 +/- 4% inhibition of isoproterenol-stimulat ed lipolysis compared with 27 +/- 10% in black women (p < 0.05). Discussion: The low responsiveness of adipocyte lipolytic activity to insul in in black women in the presence of a relative insulinopenia may account f or the high plasma NEFA levels seen in these women, which may, in turn, acc ount for their higher in vivo insulin resistance. High NEFA levels may also contribute to the low insulin secretory activity observed in the obese bla ck females. These data suggest that the pathogenesis of insulin resistance and type 2 diabetes within the black obese community is strongly influenced by their adipocyte metabolism.