Effects of Testosterone on Mixed-Muscle Protein Synthesis and Proteome Dynamics During Energy Deficit

Area of Science:

• Endocrinology and Metabolism
• Muscle Physiology
• Nutritional Science

Background:

• The impact of testosterone on muscle protein metabolism and mass during caloric restriction remains unclear.
• Understanding these effects is crucial for managing muscle health in various physiological states.

Purpose of the Study:

• To investigate the effects of testosterone administration on mixed-muscle protein synthesis (MPS), proteome-wide fractional synthesis rates (FSR), and skeletal muscle mass.
• To determine these effects specifically during a period of significant energy deficit.

Main Methods:

• A randomized, double-blind, placebo-controlled trial involving 50 healthy men.
• Participants underwent a 28-day 55% energy deficit, receiving either 200 mg testosterone enanthate or a placebo weekly.
• Muscle biopsies and heavy water labeling were used to measure MPS and FSR, while D3-creatine dilution assessed muscle mass.

Main Results:

• Mixed-muscle protein synthesis was reduced during and after the energy deficit, with no significant difference between testosterone and placebo groups.
• A higher proportion of individual proteins showed increased FSR with testosterone at the end of the deficit period, suggesting a delayed anabolic effect.
• Muscle mass remained stable during the deficit but was significantly greater in the testosterone group during the recovery phase.

Conclusions:

• Exogenous testosterone demonstrated a delayed, broad stimulatory effect on muscle proteome synthesis rates during energy deficit.
• This effect contributed to greater muscle mass accretion during the subsequent recovery period.
• Testosterone may play a role in mitigating muscle loss and enhancing recovery post-deficit.