INSULIN SENSITIVITY IS NOT IMPAIRED IN MEXICAN-AMERICAN WOMEN WITHOUTA FAMILY HISTORY OF DIABETES

OBJECTIVE - The purpose of this research was to compare insulin sensit ivity in Mexican-Americans and non-Hispanic whites without a family hi story of diabetes to establish whether insulin resistance is a defect intrinsically related to subjects of Mexican origin. RESEARCH DESIGN A ND METHODS - In study A, we compared insulin sensitivity in 12 Mexican -American and 12 non-Hispanic white women with normal glucose toleranc e and no family history of diabetes. In study B, we compared insulin s ensitivity in two groups of normal glucose-tolerant Mexican-Americans, nine with a positive (FHD+) and nine with a negative (FHD-) family hi story of diabetes. In both studies, the groups were closely matched fo r age, total body fat content, and fat topography. Insulin sensitivity was assessed with the euglycemic insulin clamp (20 mU . min(-1) . m(2 ) surface area) which was performed in combination with tritiated gluc ose infusion and indirect calorimetry. Total fat mass and fat-free mas s (FFM) were assessed by a tritiated water dilution technique, and reg ional fat distribution was evaluated by anthropometry and magnetic res onance 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. 6.6 2 +/- 0.81), oxidative (3.54 +/- 0.24 vs. 3.51 +/- 0.19), and nonoxida tive (2.78 +/- 0.48 vs. 3.11 +/- 0.75) glucose utilization were simila r in Mexican-Americans and non-Hispanic whites; hepatic glucose produc tion (0.33 +/- 0.13 vs. 0.35 +/- 0.13) was suppressed similarly in bot h groups. During a 2-h euglycemic insulin clamp (study B), Mexican-Ame ricans with FHD+ had lower rates of insulin-mediated total (3.55 +/- 0 .39 vs. 5.93 +/- 0.59, P < 0.001), oxidative (3.31 +/- 0.25 vs. 4.32 /- 0.17, P < 0.01), and nonoxidative (0.24 +/- 0.28 vs. 1.61 +/- 0.49, P < 0.01) glucose disposal than subjects with FHD-; suppression of he patic glucose production (0.24 +/- 0.14 vs. 0.18 +/- 0.12) was similar in both groups. CONCLUSIONS - These results indicate that in the abse nce of a family history of noninsulin-dependent diabetes mellitus, Mex ican-American women are not less sensitive to insulin than non-Hispani c white women.