Effects of Lower- and Higher-Volume Resistance Exercise on Serum Total and Free Testosterone, Skeletal Muscle Testosterone and Dihydrotestosterone Content, and Skeletal Muscle Androgen Receptor mRNA Expression and Protein Content
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Testosterone is the primary sex steroid hormone within males. Its effects are ubiquitous, and can be categorized as either anabolic or androgenic. Testosterone exerts its effects on a specific nuclear androgen receptor (AR). Upon binding testosterone, the AR translocates to the nucleus of the cell. Once in the nucleus of the cell, the active AR complex binds to the androgen response element on DNA resulting in an up-regulation of gene expression. Androgen receptors are found in skeletal muscle which is responsive to testosterone. The binding of testosterone to the AR results in DNA binding, and subsequently promotes protein synthesis (anabolism) and a decrease in the breakdown of muscle tissue (catabolism). Both AR mRNA and protein expression and testosterone levels affect muscle protein balance. It is known that high intensity resistance exercise increase endogenous serum testosterone levels. Therefore, the purpose of this study was to examine the ability of a resistance exercise-induced elevation in serum and free testosterone to increase skeletal muscle testosterone, 5α-dihydrotestosterone (DHT), AR mRNA expression and protein content. In a randomized cross-over design, venous blood was obtained in male participants immediately before, after, and 30min, 1 hr, 2 hr, 3 hr, and 24 hr after a single bout of exercise. Muscle samples were also obtained immediately before, after, and 3 hr, 24 hr after exercise. Exercise bouts were either lower volume (LV) and consisted of a lower body resistance exercise program (knee extensions) or higher volume (HV) consisting of an upper body/lower body resistance exercise program (bench press, seated rows, shoulder press, knee extensions). Exercise bouts were separated by one week. From each blood sample, the levels of serum and total testosterone were determined. From each muscle sample, the concentration of testosterone, and dihydrotestosterone (DHT) was determined, along with the mRNA expression and protein content of the androgen receptor. Statistical analysis was performed by utilizing separate 2x4 and 2x7 (Session x Test) factorial analyses of variance (ANOVA) with repeated measures for muscle and blood analyses, respectively. Further analysis of the main effects was performed by separate one-way ANOVAs. Significant between-group differences were then determined involving the Tukey’s Post Hoc Test.