Insulin sensitivity is not impaired in Mexican-American women without a family history of diabetes

OBJECTIVE - The purpose of this research was to compare insulin sensitivity in Mexican-Americans and non-Hispanic whites without a family history of diabetes to establish whether insulin resistance is a defect intrinsically related to subjects of Mexican origin. RESEARCH DESIGN AND METHODS - In study A, we compared insulin sensitivity in 12 Mexican-American and 12 non-Hispanic white women with normal glucose tolerance and no family history of diabetes. In study B, we compared insulin sensitivity in two groups of normal glucose-tolerant Mexican-Americans, nine with a positive (FHD+) and nine with a negative (FHD-) family history of diabetes. In both studies, the groups were closely matched for age, total body fat content, and fat topography. Insulin sensitivity was assessed with the euglycemic insulin clamp (20 mU · min^-1 · m² surface area) which was performed in combination with tritiated glucose infusion and indirect calorimetry. Total fat mass and fat-free mass (FFM) were assessed by a tritiated water dilution technique, and regional fat distribution was evaluated by anthropometry and magnetic resonance imaging. RESULTS - During a 4-h euglycemic insulin clamp (study A), rates (mg · min^-1 · kg FFM^-1) of total (6.32 ± 0.64 vs. 6.62 ± 0.81), oxidative (3.54 ± 0.24 vs 3.51 ± 0.19), and nonoxidative (2.78 ± 0.48 vs 3.11 ± 0.75) glucose utilization were similar in Mexican- Americans and non-Hispanic whites; hepatic glucose production (0.33 ± 0.13 vs 0.35 ± 0.13) was suppressed similarly in both groups. During a 2 h euglycemic insulin clamp (study B), Mexican-Americans with FHD+ had lower rates of insulin-mediated total (3.55 ± 0.39 vs 593 ± 0.59, P < 0.001), oxidative (331 ± 0.25 vs. 4.32 ± 0.17, P < 0.01), and nonoxidative (024 ± 0.28 vs 1.61 ± 0.49, P < 0.01) glucose disposal than subjects with FHD-; suppression of hepatic glucose production (0.24 ± 0.14 vs 0.18 ± 0.12) was similar in both groups. CONCLUSIONS - These results indicate that in the absence of a family history of non-insulin-dependent diabetes mellitus, Mexican-American women are not less sensitive to insulin than non-Hispanic white women.