Insulin sensitivity of protein and glucose metabolism in human forearm skeletal muscle

R. J. Louard, D. A. Fryburg, R. A. Gelfand, E. J. Barrett

Research output: Contribution to journalArticlepeer-review

156 Scopus citations


Physiologic increases of insulin promote net amino acid uptake and protein anabolism in forearm skeletal muscle by restraining protein degradation. The sensitivity of this process to insulin is not known. Using the forearm perfusion method, we infused insulin locally in the brachial artery at rates of 0.00 (saline control), 0.01, 0.02, 0.035, or 0.05 mU/min per kg for 150 min to increase local forearm plasma insulin concentration by 0, ∼20, ∼35, ∼60, and ∼120 μU/ml (n = 35). L-[ring-2,6-3H]phenylalanine and L-[1-14C]leucine were infused systemically, and the net forearm balance, rate of appearance (Ra) and rate of disposal (Rd) of phenylalanine and leucine, and forearm glucose balance were measured basally and in response to insulin infusion. Compared to saline, increasing rates of insulin infusion progressively increased net forearm glucose uptake from 0.9 μmol/min per 100 ml (saline) to 1.0, 1.8, 2.4, and 4.7 μmol/min per 100 ml forearm, respectively. Net forearm balance for phenylalanine and leucine was significantly less negative than basal (P < 0.01 for each) in response to the lowest dose insulin infusion, 0.01 mU/min per kg, and all higher rates of insulin infusion. Phenylalanine and leucine Ra declined by ∼38 and 40% with the lowest dose insulin infusion. Higher doses of insulin produced no greater effect (decline in Ra varied between 26 and 42% for phenylalanine and 30-50% for leucine). In contrast, Rd for phenylalanine and leucine did not change with insulin. We conclude that even modest increases of plasma insulin can markedly suppress proteolysis, measured by phenylalanine Ra, in human forearm skeletal muscle. Further increments of insulin within the physiologic range augment glucose uptake but have little additional effect on phenylalanine Ra or balance. These results suggest that proteolysis in human skeletal muscle is more sensitive than glucose uptake to physiologic increments in insulin.

Original languageEnglish (US)
Pages (from-to)2348-2354
Number of pages7
JournalJournal of Clinical Investigation
Issue number6
StatePublished - Dec 1992
Externally publishedYes


  • Amino acid tracer kinetics
  • Forearm balance
  • Leucine
  • Phenylalanine
  • Proteolysis

ASJC Scopus subject areas

  • Medicine(all)


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