Myofibrillar Protein Synthesis Rates Do not Differ With Low and High Estradiol Concentrations Across the Menstrual...

Area of Science:

• Endocrinology
• Exercise Physiology
• Muscle Metabolism

Background:

• Skeletal muscle adaptation is influenced by sex hormones, but the effect of estradiol fluctuations during the menstrual cycle on myofibrillar protein synthesis (MyoPS) remains unclear.
• Understanding these hormonal influences is crucial for optimizing training and nutrition strategies.

Purpose of the Study:

• To compare MyoPS rates in postabsorptive and postprandial postexercise states during the early follicular (low estradiol) and late follicular (high estradiol) phases of the menstrual cycle.
• To investigate the acute regulatory role of estradiol on muscle protein synthesis.

Main Methods:

• A randomized, cross-over trial involving 17 healthy females comparing the early follicular and late follicular phases of the menstrual cycle.
• MyoPS was measured using L-[ring-2H5]-phenylalanine infusion during a 4-hour postprandial postexercise period following resistance exercise and amino acid ingestion.

Main Results:

• MyoPS rates increased postexercise and amino acid ingestion in both menstrual cycle phases, with no significant differences observed between the early and late follicular phases.
• Gene expression analysis revealed increased expression of protein synthesis and muscle remodeling genes in the late follicular phase compared to the early follicular phase.
• Moderate correlations were found between testosterone levels and overall MyoPS.

Conclusions:

• Elevated estradiol concentrations during the late follicular phase did not enhance myofibrillar protein synthesis rates.
• Estradiol does not appear to be a critical factor in the acute regulation of muscle mass in eumenorrheic females.
• While gene expression suggests a potential for muscle growth, MyoPS rates remain unaffected by acute estradiol fluctuations.