Obese Premenopausal African-American Women With Normal and Impaired Glucose Tolerance Have a Similar Degree of Insulin Resistance but Differ in β-Cell Function

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Abstract
OBJECTIVE—To determine whether insulin resistance and secretion differ in obese premenopausal African-American women with and without glucose intolerance. RESEARCH DESIGN AND METHODS—A total of 63 women underwent oral glucose tolerance tests (OGTTs). A total of 48 women underwent frequently sampled intravenous glucose tolerance tests (FSIGTs). Insulin resistance was determined from the insulin sensitivity index (SI) from the FSIGT. Insulin secretion during the OGTT was determined by (I30 min − I0 min)/(G30 min − G0 min) and during the FSIGT by the acute insulin response to glucose (AIRg). The disposition index, the product of AIRg and SI, was used to determine whether AIRg was adequate to compensate for insulin resistance. Statistical analyses included one-way analysis of variance with Bonferroni corrections for multiple comparisons and regression analyses. RESULTS—The women were divided into three groups: nonobese glucose tolerant (n = 32), obese glucose tolerant (n = 17), and obese glucose intolerant (n = 14). The BMI of the three groups were 24.8 ± 2.3, 37.8 ± 5.5, and 42.0 ± 7.6 kg/m2 (mean ± SD), respectively (P < 0.0001). The ages of the three groups were 34.9 ± 8.4, 32.1 ± 5.0, and 41.1 ± 6.3 years (P = 0.011). SI was higher in the nonobese women than in the obese glucose-tolerant women (3.99 ± 1.44 vs. 2.66 ± 2.14 l · mU−1 · min−1, P = 0.03). SI was similar in the obese glucose-intolerant and obese glucose-tolerant women (2.12 ± 1.27 vs. 2.66 ± 2.14 l · mU−1 · min−1, P = 0.9). OGTT showed that insulin secretion was lower in the glucose-intolerant than the obese glucose-tolerant women (1.73 ± 1.38 vs. 3.62 ± 2.11, P = 0.005). FSIGT showed that AIRg was not significantly lower in glucose-intolerant than in obese glucose-tolerant women (807 ± 665 vs. 1,253 ± 655 mU · l−1 · min, P = 0.078). The disposition index was lower in glucose-intolerant than in obese glucose-tolerant women (1,324 ± 1,061 vs. 2,656 ± 1,415, P = 0.014). CONCLUSIONS—Obese premenopausal African-American women with and without glucose intolerance have a similar degree of insulin resistance but differ in insulin secretion.