Acute Effects of Testosterone on Whole-Body Protein Metabolism in Hypogonadal and Eugonadal Conditions: A Randomized, Placebo-Controlled, Crossover Study.

Abstract

Chronic testosterone (T) substitution and short-term T administration positively affect protein metabolism, however, data on acute effects in humans are sparse. This study aimed to investigate T's acute effects on whole-body protein metabolism in hypogonadal and eugonadal conditions. We designed a randomized, double-blind, placebo-controlled, crossover study, including twelve healthy young males. Whole-body protein metabolism was evaluated during 1) eugonadism, and after medically-induced hypogonadism, with application of a gel on each trial day containing either 2) placebo, 3) T 50 mg, or 4) T 150 mg; under basal (5h basal period) and insulin-stimulated conditions (3h clamp). The main outcome measure was change in net protein balance. The net protein loss was 62% larger in the placebo-treated hypogonadal state compared with the eugonadal state during the basal period (-5.5 ±3.5 µmol/kg/h versus -3.4 ± 1.2 µmol/kg/h, p=0.038), but not during the clamp (p=0.06). Also, hypogonadism resulted in a 25% increase in whole-body urea flux (p=0.006). However, T did not result in any significant changes in protein breakdown, synthesis, or net balance during either the basal period or clamp (all p > 0.05). Protein breakdown was reduced during clamp compared to the basal period regardless of gonadal status or T exposure (all p≤0.001). In conclusion, the application of transdermal T did not counteract the negative effects of hypogonadism with no effects on protein metabolism within five hours of administration. Insulin (during clamp) mitigated the effects of hypogonadism. This study is the first to investigate acute protein-metabolic effects of T in hypogonadal men.