Title

Effect of resistance exercise on muscle steroidogenesis

Date of Completion

January 2008

Keywords

Health Sciences, Recreation

Degree

Ph.D.

Abstract

Circulating testosterone is elevated acutely following resistance exercise (RE) and is an important anabolic hormone for muscle adaptations to resistance training. Currently, no study has investigated the effect of RE on intracrine muscle testosterone production. Purpose. The purpose of this study was to examine the acute effect of heavy RE on muscle testosterone production and signaling in young resistance trained men and women. Methods. 15 young resistance trained men (n=8; 21±1 years, 175.3±6.7 cm, 90.8±11.6 kg) and women (n=7; 24±5 years, 164.6±6.7 cm, 76.4±15.6 kg) completed 6 sets of 10 repetitions of squats with 80% of their 1-repetition maximum. Before RE, and 10 min and 70 min after RE, muscle biopsies were obtained from the vastus lateralis. Before RE, after 3 and 6 sets of squats, and 5, 15, 30 and 70 min into recovery from RE blood samples were obtained using venipuncture from an anticubital vein. Muscle samples were analyzed for testosterone, 17β-hydroxysteroid dehydrogenase (HSD), 3β-HSD, and androgen receptor (AR) content. Blood samples were analyzed for the glucose, lactate, total and free testosterone concentrations. Results. AR was significantly (p≤0.05) reduced at 70 min post-exercise in men and at 10 min post-exercise in women compared to pre-exercise. No changes were found for muscle testosterone, 3β-HSD, and 17β-HSD concentrations; however, a change in protein migration in the Bis-Tris gel was observed for 17-17β-HSD post-exercise. Circulating total testosterone increased in men and free testosterone and lactate increased in men and women with exercise. Conclusion. These findings indicate that species differences in muscle testosterone production may exist between rats and humans. AR was significantly reduced by RE in men and women, but the timeline for this reduction showed gender differences. Women appeared to progress faster through the initial down-regulation in AR and returned to pre-levels at 70 minutes post-exercise. The findings of this study support the current paradigm on the acute AR response to RE but demonstrate that gender differences exist in the timeline of the AR response. This study expands on the current knowledge obtained from animal studies by examining resting and post-exercise muscle testosterone, steroidogenic enzyme, and AR responses in humans. ^