Protein and glucose metabolic responses to hyperinsulinemia, hyperglycemia, and hyperaminoacidemia in obese men

Objective In insulin‐resistant states, resistance of protein anabolism occurs concurrently with that of glucose, but can be compensated for by abundant amino acid (AA) provision. This effect and its mechanism were sought in obesity. Methods Pancreatic clamps were performed in 8 lean and 11 obese men, following 5‐h postabsorptive, 3‐h infusions of octreotide, basal glucagon, and growth hormone, with clamped postprandial‐level insulin, glucose, and AA. Whole‐body [1‐13C]‐leucine and [3‐3H]‐glucose kinetics, skeletal muscle protein (2H5‐phenylalanine) fractional synthesis rates, and insulin signaling were determined. Results Clamp Δ insulin and Δ branched‐chain AA did not differ; fasting glucagon and growth hormone were maintained. Glucose uptake was 20% less in obese concurrent with less AktSer473, but also less IRS‐1Ser636/639 phosphorylation. Stimulation of whole‐body, myofibrillar, and sarcoplasmic protein synthesis was similar. Whole‐body protein catabolism suppression tended to be less (P=0.06), resulting in lesser net balance (1.09 ± 0.07 vs. 1.31 ± 0.08 μmol [kg FFM−1] min−1, P = 0.048). Increments in muscle S6K1Thr389 phosphorylation were less in the obese, but 4E‐BP1Ser65 did not differ. Conclusions Hyperaminoacidemia with hyperinsulinemia stimulated protein synthesis (possibly via nutrient signaling) normally in obesity, but suppression of proteolysis may be compromised. Whether long‐term high protein intakes could compensate for the insulin resistance of protein anabolism remains to be determined.