Differential regulation of amino acid exchange and protein dynamics across splanchnic and skeletal muscle beds by insulin in healthy human subjects.
Level 2 - randomized trial
Individual randomized controlled physiological trial
PubMed 9836512 · doi:10.2337/diabetes.47.12.1824
What was done
In 24 healthy human subjects after an overnight fast, researchers measured amino acid exchange and protein dynamics across the splanchnic and skeletal muscle (leg) beds using stable isotope tracers of phenylalanine, tyrosine, and leucine. Participants received saline or one of three insulin doses (0.25, 0.5, or 1.0 mU·kg⁻¹·min⁻¹).
What was found
After an overnight fast, muscle exhibited net amino acid release (breakdown exceeded synthesis), whereas the splanchnic bed exhibited net amino acid uptake (synthesis exceeded breakdown). Insulin infusion decreased muscle protein breakdown in a dose-dependent manner (P < 0.003) without altering muscle protein synthesis. In the splanchnic bed, insulin decreased protein synthesis (P < 0.03) without altering protein breakdown. Insulin also decreased leucine nitrogen flux significantly more than leucine carbon flux (P < 0.001), indicating increased leucine transamination that was greater in muscle than in the splanchnic bed. Exact kinetic rates and confidence intervals were not reported in the abstract.
Why it matters
This study demonstrates that insulin's acute anticatabolic action in the postabsorptive state is mediated primarily by the dose-dependent inhibition of skeletal muscle protein breakdown and a concurrent reduction in splanchnic protein synthesis, rather than stimulation of muscle protein synthesis.
Limits
The abstract describes a small sample (n = 24) of healthy individuals under acute fasting conditions, which limits applicability to fed states, chronic administration, or individuals with insulin resistance or diabetes. Specific numerical kinetic values were not reported in the abstract.
Cited by
- supports A published study by K. Sreekumaran Nair's group found that insulin is not required for muscle protein synthesis, but serves primarily to inhibit muscle protein breakdown.