Context: Alterations of protein turnover may contribute to the progressive decline of muscle mass with ageing.

Objective: The effects of near physiological recombinant growth hormone (GH) and /or testosterone (T) administration to older men on whole body protein kinetics (WBPK) and muscle gene expression.

Design, settings, and participants: A six months randomised, double blind, placebo controlled trial in twenty one healthy elderly men aged 65 to 75 years. Participants were randomised to receive placebo GH and placebo T (P), GH and placebo T (GH), T and placebo GH (T) or GH and T (GHT).

Interventions: Leucine rate of appearance (Ra, index of proteolysis), non-oxidative leucine disposal Rd (NOLD, an index of protein synthesis) and leucine oxidation rate were measured with an infusion of L- [1-¹³C] leucine. Muscle biopsies for the measurement of gene expression, body composition and aerobic capacity (VO₂max).

Results: Serum IGF-I levels increased significantly with GH and GHT (P < 0.001) compared to placebo. T increased significantly only in the T group (P = 0.028). Leucine Ra and NOLD increased with GH (P = 0.015, P = 0.019) and GHT (P = 0.017, P = 0.02) but leucine oxidation did not change significantly in any treatment group. Mid thigh muscle mass and VO₂max increased (P < 0.04) with GHT only. Expression of muscle function genes did not change significantly but the within group comparisons revealed a significant increase of androgen receptor expression in the GHT group (P = 0.001).

Conclusion: This study showed that 6 months treatment with low dose GH alone or with T in healthy elderly men produces comparable increments in whole body protein turnover and protein synthesis.