THE RELATIONSHIP IN AFRICAN-AMERICANS OF SEX-DIFFERENCES IN INSULIN-MEDIATED SUPPRESSION OF NONESTERIFIED FATTY-ACIDS TO SEX-DIFFERENCES INFASTING TRIGLYCERIDE LEVELS

Insulin is a potent antilipolytic hormone that promotes the deposition of fat and decreases the release of nonesterified fatty acids (NEFA) from adipose tissue. The purpose of this study was to investigate in A frican-Americans (AAs) sex differences in insulin-mediated suppression of plasma NEFA and fasting triglyceride (TG) levels. Ninety AAs, 44 m en and 46 women with a mean age of 34 +/- 8 years were classified by b ody mass index (BMI) into three groups: non-obese (22 men and 18 women ), obese (12 men and 10 women), and severely obese (10 men and 18 wome n). In each BMI group, women versus men had greater percent body fat ( non-obese, 30 +/- 6 v 18 +/- 6, P < .001; obese, 36 +/- 3 v 26 +/- 2, P < .001; and severely obese, 39 +/- 4 v 29 +/- 4, P < .001). An oral glucose tolerance test (OGTT) was performed with fasting TG levels and plasma insulin and NEFA concentrations obtained at 0, 30, 60, and 120 minutes. In women, insulin-mediated NEFA suppression was similar in e ach of the three BMI groups (non-obese, 85% +/- 14%; obese, 88% +/- 11 %; and severely obese, 87% +/- 10%; P = .8). In men, the percent suppr ession of NEFA declined with increasing obesity (non-obese, 83% +/- 14 %; obese, 71% +/- 21%; and severely obese, 68% +/- 16%; P = .04). Chan ges in NEFA suppression were reflected in the fasting TG levels. TG le vels in women were similar in each BMI group (non-obese, 71 +/- 39 mg/ dL; obese; 69 +/- 21; severely obese, 79 +/- 30; P = .7). In contrast, fasting TG levels for men were higher in the higher BMI groups. Plasm a TG levels in men were 87 +/- 41 mg/dL for obese, 113 +/- 65 for obes e, and 169 +/- 81 for severely obese (P = .001). These data demonstrat e sex differences in insulin-mediated NEFA metabolism. In AA women, th e maintenance of sensitivity to insulin-mediated suppression of NEFA r egardless of the degree of obesity may contribute to the normal plasma TG levels. For AA men, the resistance to insulin-mediated suppression of NEFA in the higher BMI categories may allow more NEFA to be releas ed from adipose tissue into the circulation and available to the liver for synthesis into TG-containing lipoproteins. Copyright (C) 1997 by W.B. Saunders Company.