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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 (S(I)) from the FSIGT. Insulin secretion during the OGTT was determined by (I(30 min) - I(0 min))/(G(30 min) - G(0 min)) and during the FSIGT by the acute insulin response to glucose (AIRg). The disposition index, the product of AIRg and S(I), 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/m(2) (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). S(I) was higher in the nonobese women than in the obese glucose-tolerant women (3.99 +/- 1.44 vs. 2.66 +/- 2.14 l x mU(-1) x min(-1), P = 0.03). S(I) was similar in the obese glucose-intolerant and obese glucose-tolerant women (2.12 +/- 1.27 vs. 2.66 +/- 2.14 l x mU(-1) x 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 x l(-1) x 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.

The purpose of this study was to determine the ability of air displacement plethysmography (ADP) to estimate body fatness in prepubertal and early pubertal African American and white children. One hundred nineteen nonoverweight and overweight boys (N = 56) and girls (N = 63), age (mean +/- SD) 9.8 +/- 1.7 y, body mass index 25.9 +/- 7.6 kg/m2 (range, 14.2-47.0 kg/m2), and mean percent body fat (%BF) by dual-energy x-ray absorptiometry (DXA) 39.2 +/- 11.7% (range, 12.2-57.5%), were studied. %BF by ADP was compared with DXA %BF estimates and with body fat by several field methods: skinfold thicknesses using the Slaughter et al. equations (Hum Biol 60: 709-723, 1988), bioelectrical impedance analysis (BIA) using the Houtkooper et al. equation (J Appl Physiol 72: 366-373, 1992), and a predictive equation using skinfold thicknesses, BIA, and weight (Goran et al.: Am J Clin Nutr 63: 299-305, 1996). All methods used to estimate %BF were significantly correlated with DXA (all p < 0.0001), with r2 ranging from 0.85 (skinfold measurements) to 0.95 (ADP). ADP using the Siri equation underestimated %BF by -1.9% (p < 0.001); the Bland-Altman limits of agreement (defined as +/-2 SD) were +/-7.4%. %BF by ADP-Siri underestimated %BF by DXA by 3.0% for girls (p < 0.001) and by 0.6% for boys (NS). Agreement between body fat estimation by ADP and DXA did not vary with age, race, or pubertal stage. Application of the age-adjusted Lohman model to ADP significantly increased the magnitude of the underestimation to -6.9% (p < 0.0001). Prediction of %BF by the Slaughter skinfold thickness equation showed no significant mean bias for the overall data, but significantly underestimated %BF in girls (-3.7%) while overestimating %BF in boys (+2.4%) with wide limits of agreement (+/-17.7%, p < 0.01 versus ADP). %BF by the Houtkooper BIA equation or Goran model underestimated %BF to a significantly greater degree than ADP (Houtkooper, -8.1%; Goran, -10.1%; both p < 0.0001 versus DXA or ADP). Determination of %BF from ADP using the Siri model slightly underestimates %BF as determined by DXA in girls, but appears to be superior to existing field methods both in accuracy and limits of agreement. Because of the ease with which it can be performed, ADP may prove useful for investigations of adiposity in children.

Objectives: African American children have greater bone mineral density (BMD) and bone mineral content (BMC) than white children. We examined the hypothesis that differences in insulin-like growth factors (IGFs) are important determinants of BMD during childhood., Methods: We measured IGFs and IGF binding proteins in 59 African American and 59 white girls matched for age, body mass index, socioeconomic status, and pubertal stage. BMD and BMC were determined by dual emission x-ray absorptiometry., Results: African American girls had greater total BMD (P <.001), BMC (P <.01), total IGF-1 (P <.001), and free IGF-1 (P <.01) than white girls. IGFBP-1, IGFBP-2, and IGFBP-3 were similar in both groups or lower in African Americans. IGF-1 was positively correlated with IGF-2 in white girls (P =.012) but was negatively correlated with IGF-2 in African Americans (P =.015). IGF-1 and free IGF-1 were positively correlated with BMD/BMC. Multiple regression analyses showed 80% of the variance in BMC could be accounted for by the use of body weight, height, and IGF-1 in the model. When IGF-1 was included as a factor, race did not add to the model's predictive power., Conclusion: IGF-1 and free IGF-1 are greater in African American than in white girls and may contribute to the greater BMD of African Americans.

African American women have a greater prevalence of obesity than Caucasian women, but the reasons for this difference are not known. We have investigated whether activity of the hypothalamic-pituitary adrenal axis plays a role in this phenomenon. Previous studies have shown that plasma ACTH immunoreactivity (ACTH-IR) of African American women, measured after ovine CRH (oCRH) stimulation, is significantly greater than ACTH-IR of Caucasian women, but is not accompanied by greater plasma cortisol concentrations. Analysis by high pressure liquid chromatography has demonstrated that after oCRH stimulation, the plasma ACTH-IR of African American women contains many nonintact ACTH fragments not found in Caucasians. To determine whether these racial differences in ACTH-IR secretion are an artifact of exogenous oCRH administration or are also found after a physiological stimulus for ACTH secretion, we measured hormones of the hypothalamic-pituitary adrenal axis before and after a standardized, maximal exercise treadmill test in 16 African American and 19 Caucasian healthy women matched for age, socioeconomic status, and body mass index. The intensity of exercise performed was similar in the two groups, as determined by duration of exercise, perceived intensity of exertion, plasma lactate, maximal heart rate, and maximum oxygen uptake. Basal ACTH-IR measured by RIA or immunoradiometric assay and cortisol were similar in African Americans and Caucasians. Plasma ACTH-IR, measured 10 min after completion of exercise, was significantly greater in African Americans than in Caucasians [by RIA: mean +/- SD ACTH-IR, 47.1 +/- 30.9 vs. 25.4 +/- 16.7 pmol/L (P < 0.01); by immunoradiometric assay: ACTH-IR, 45.9 +/- 43.2 vs. 21.1 +/- 14.6 pmol/L (P < 0.05)]. However, plasma cortisol after exercise was not different (450.2 +/- 157.7 vs. 483.6 +/- 180.4 nmol/L; P = 0.57). We conclude that ACTH-IR is significantly greater in African American than in Caucasian women after intense exercise. The ACTH-IR of African Americans and Caucasians does not appear to be equipotent at adrenal melanocortin-2 receptors, because the greater ACTH-IR of African Americans does not lead to greater cortisol secretion. Whether some components of the ACTH-IR detected in African Americans affect signal transduction of the hypothalamic melanocortin-4 receptors implicated in body weight regulation and thus predispose African American women to weight gain without altering plasma cortisol remains to be determined.