We studied the effect of acute hyperinsulinemia on amino acid (AA) utilization and oxidation rates independent of insulin-enhanced glucose utilization rate in fetal sheep. Metabolic studies were conducted in each fetus (n=11) under three experimental conditions. After Control period study (C), a fetal hyperinsulinemic-euglycemic-euaminoacidemic clamp was established (HI-euG-euAA), followed by a hyperinsulinemic-hypoglycemic-euaminoacidemic clamp to return glucose metabolic rates to control period values (HI-hypoG-euAA). Infusions of ³H₂0, L-[1-¹³C] leucine and ¹⁴C-U-glucose were administered to measure blood flow, leucine oxidation, and fetal glucose uptake, utilization and oxidation in each experimental period. Fetal glucose utilization rate increased 1.7-fold with hyperinsulinemia (5.8 +/- 0.8 mg/kg/min C, 10 +/- 1.3 HI-euG-euAA, p<0.0001), returning to control rates with hypoglycemia (7.1 +/- 0.9 HI-hypoG-euAA vs. C value above, p=0.15). Fetal glucose oxidation rate increased 1.9-fold with hyperinsulinemia (3.1 +/- 0.2 mg/kg/min C, 5.4 +/- 0.4 HI-euG-euAA, p<0.0001), and decreased to near control rates with hypoglycemia (4.0 +/- 0.3 HI-hypoG-euAA vs. C value above, p=0.006). AA utilization rates increased with hyperinsulinemia for all essential AA and most non-essential AA (p<0.001), and did not change when insulin-induced increases in glucose utilization returned to control rates. Leucine oxidation rate increased 1.7-fold with hyperinsulinemia (1.0 +/- 0.3 umol/min/kg C, 1.7 +/- 0.3 HI-euG-euAA, p<0.002) and did not change when glucose oxidation rate was decreased with hypoglycemia. These results demonstrate that in fetal sheep, insulin promotes AA utilization independently of its simultaneous effects on glucose metabolism, and in acute hyperinsulinemic conditions, protein oxidation does not change when insulin-induced glucose uptake is prevented.