Testosterone administration to elderly men increases skeletal muscle strength and protein synthesis

TLDR

Aging men lose muscle strength as serum testosterone declines. The study examined whether testosterone supplementation in elderly men enhances muscle protein synthesis, strength, and the intramuscular IGF‑I system. Elderly men with low testosterone received injections for four weeks to raise serum levels to those of younger men. Testosterone administration increased muscle strength and protein synthesis, upregulated IGF‑I mRNA, downregulated IGFBP‑4 mRNA, suggesting the IGF‑I pathway mediates the effect.

Abstract

Aging men develop a significant loss of muscle strength that occurs in conjunction with a decline in serum testosterone concentrations. We investigated the effects of testosterone administration to six healthy men [67 +/- 2 (SE) yr] on skeletal muscle protein synthesis, strength, and the intramuscular insulin-like growth factor I (IGF-I) system. Elderly men with serum testosterone concentrations of 480 ng/dl or less were given testosterone injections for 4 wk to produce serum concentrations equal to those of younger men. During testosterone administration muscle strength (isokinetic dynamometer) increased in both right and left hamstring and quadricep muscles as did the fractional synthetic rate of muscle protein (stable-isotope infusion). Ribonuclease protection assays done on total RNA from muscle showed that testosterone administration increased mRNA concentrations of IGF-I and decreased mRNA concentrations of insulin-like growth factor binding protein-4. We conclude that increasing testosterone concentrations in elderly men increases skeletal muscle protein synthesis and strength. This increase may be mediated by stimulation of the intramuscular IGF-I system.