Pharmacological vasodilation improves insulin-stimulated muscle protein anabolism but not glucose utilization in older adults.
Level 2 - randomized trial
Individual randomized trial
PubMed 20724580 · doi:10.2337/db10-0415
What was done
Twelve healthy, non-diabetic older adults (mean age 71 ± 2 years) were randomized to receive a local single-leg infusion of either insulin alone (Control) or insulin plus sodium nitroprusside (SNP) titrated to double leg blood flow. Investigators assessed leg blood flow via dye dilution, microvascular perfusion via contrast-enhanced ultrasound, Akt/mTORC1 signaling via Western blotting, and muscle protein synthesis, amino acid kinetics, and glucose kinetics via stable isotope techniques.
What was found
Blood flow, microvascular perfusion, phenylalanine delivery, and intracellular phenylalanine availability increased significantly only with SNP (P < 0.05). Akt phosphorylation increased in both groups but was significantly greater with SNP (P < 0.05). Muscle protein synthesis increased from 43 ± 6 to 129 ± 25 nmol · min⁻¹ · 100 ml leg⁻¹ in the SNP group (P < 0.05), compared to 41 ± 10 to 53 ± 8 in the Control group. Muscle net protein balance increased from -16 ± 3 to 26 ± 12 nmol · min⁻¹ · 100 ml leg⁻¹ with SNP (P < 0.05), versus -17 ± 3 to -2 ± 3 in Controls. Numerical values for glucose utilization were not reported in the abstract.
Why it matters
This study provides mechanistic evidence that age-related muscle anabolic resistance to insulin is linked to microvascular impairment, and that restoring blood flow and amino acid delivery can acutely rescue muscle protein synthesis in older adults.
Limits
The sample size is very small (n = 12 total, approximately 6 per group). The study evaluated acute local pharmacological infusion in a single leg, which cannot directly predict the safety, feasibility, or chronic effectiveness of systemic vasodilation interventions.
Cited by
- supports Aging impairs insulin-mediated capillary recruitment and vasodilation in skeletal muscle without necessarily causing overt glycemic insulin resistance.