Although most people think of steroidogenic processes, such as the 5a-reduction of testosterone into dihydrotestosterone, as taking place in unwanted target tissue (the scalp, the prostate, etc…), this activity also takes place in skeletal muscle as well, as a reaction to exercise. DHT is, of course, the most potent male androgen, and has a host of beneficial effects for athletes (such as increased fat loss, strength, etc…)…and according to a recently published (rodent) study, it appears that endurance exercise preferentially increases intramuscular synthesis of this hormone.
Med Sci Sports Exerc. 2011 Apr 14. [Epub ahead of print]
Endurance Exercise Training Enhances Local Sex Steroidogenesis in Skeletal Muscle.
Aizawa K, Iemitsu M, Maeda S, Mesaki N, Ushida T, Akimoto T.
1 Laboratory of Regenerative Medical Engineering, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; 2 Ritsumeikan University Faculty of Sport and Health Science, Shiga, Japan; 3 University of Tsukuba, Tsukuba, Japan; 4 Tekikyo Heisei University, Ichihara, Japan.
Endurance training improves skeletal muscular function including energy metabolism and structure. Sex steroid hormones partly contribute to the exercise-induced muscular adaptations. Recently, we demonstrated that skeletal muscle containes steroidgenic converting enzymes to synthesize sex steroid hormones and an acute endurance exercise activates local steroidogenesis in skeletal muscle. However, whether chronic endurance training leads to enhanced steroidogenesis in skeletal muscle is unknown. Here we examined changes in steroidogenic enzymes and sex steroid hormones in the skeletal muscle following chronic endurance exercise training.
Eleven male rats were divided into 2 groups: sedentary (n=6), trained (n=5). Endurance training was performed on a treadmill (30 m/min, 30 min) at 5 days/wk for 12 weeks. The post-training harvesting were performed 48 h after the last exercise training.
The mRNA expressions of 3?-hydroxysteroid dehydrogenase (HSD), aromatase cytochrome P450 (P450arom) and 5?-reductase in the skeletal muscle of trained rats were significantly higher than that of sedentary rats (P < 0.05). The protein expressions of P450arom and 5?-reductase in the skeletal muscle of trained rats were also significantly higher than that of sedentary rats (P < 0.05). The muscular dihydrotestosterone (DHT) concentrations in the skeletal muscle of trained rats were significantly higher than that of sedentary rats (P 0.01), but no change in dehydroepiandrosterone (DHEA), total testosterone, free testosterone and estradiol. Furthermore, muscle weight corrected for BW of trained rats was moderately correlated with the level of muscular DHT concentration in trained rats (r = 0.41, P 0.05). CONCLUSION: Endurance exercise training enhances the muscular DHT concentration through 5?-reductase in the skeletal muscle of rats, suggesting that local bioactive androgen metabolism may participate in exercise training-induced skeletal muscular adaptation.