Anti-lipolytic effects of insulin in African American and white prepubertal boys

Objective: Relative to whites, African Americans have lower circulating tri glycerides (TG) and greater high-density lipoprotein cholesterol. The metab olic basis for this difference is not known. This study was conducted to te st the hypothesis that insulin-induced suppression of free fatty acids (FFA ) results in lower serum TG in African American versus white prepubertal ch ildren. Research Methods and Procedures: Insulin, FFA, and TG were determined at ba seline and during a frequently sampled, intravenous glucose tolerance test in eight African American and eight white prepubertal males pair-matched fo r whole-body insulin sensitivity. Results: Baseline TG was lower in African Americans (0.43 +/- 0.10 vs. 0.79 +/- 0.37 mM/L; mean +/- SD; p < 0.01). African Americans had higher peak i nsulin (218 <plus/minus> 102 vs. 100 +/- 30 pM/L; mean +/- SD; p < 0.01) an d a greater acute insulin response (9282 <plus/minus> 4272 vs. 4230 +/- 132 6 pM/L X 10 minutes; mean +/- SD; p < 0.05). FFA and TG values determined a t the FFA nadir were lower in African Americans (0.26 <plus/minus> 0.02 vs. 0.30 +/- 0.03 mEq/L; mean +/- SD; p < 0.01 for FFA nadir and 0.39 <plus/mi nus> 0.07 vs. 0.77 +/- 0.33 mM/L; mean + SD; p < 0.05 for TG). Among all su bjects, FFA nadir was correlated with peak insulin (r = -0.54; p < 0.05). A fter adjusting for FFA nadir, neither baseline nor postchallenge TG differe d with ethnicity (p = 0.073 and 0.192, respectively). The ethnic difference in FFA nadir disappeared after adjusting for peak insulin (p = 0.073). Discussion: These data suggest that hyperinsulinemia-induced suppression of FFA among African Americans is a determinant of lower TG in this group.