Effects of an Intravenous Lipid Challenge and Free Fatty Acid Elevation on In Vivo Insulin Sensitivity in African American Versus Caucasian Adolescents

OBJECTIVE—African American youth have lower insulin sensitivity than their Caucasian peers, but the metabolic pathways responsible for this difference remain unknown. Free fatty acids (FFAs) are associated with insulin resistance through the Randle cycle. The present investigation determined whether elevating FFA is more deleterious to insulin sensitivity in African American than in Caucasian adolescents. RESEARCH DESIGN AND METHODS—Insulin sensitivity (3-h hyperinsulinemic-euglycemic clamp) was evaluated in 22 African American and 21 Caucasian adolescents on two occasions: 1) infusion of normal saline and 2) infusion of 20% intralipid. RESULTS—During intralipid infusion, fasting insulin and C-peptide concentrations increased while fasting glucose and basal glucose turnover did not change in either group. Insulin sensitivity decreased similarly in African American (normal saline 7.65 ± 0.61 vs. intralipid 5.15 ± 0.52 μmol · kg(−1) · min(−1) per pmol/l) and Caucasian subjects (normal saline 8.97 ± 0.85 vs. intralipid 5.96 ± 0.56 μmol · kg(−1) · min(−1) per pmol/l) (P < 0.001). CONCLUSIONS—African American and Caucasian adolescents respond to FFA elevation similarly through increased fasting insulin secretion to maintain fasting glucose homeostasis and reduced peripheral glucose uptake and insulin resistance. Thus, African American adolescents are not more susceptible to FFA-induced insulin resistance than Caucasian youth.