Steroidogenesis in the skeletal muscle

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Sex steroid hormones, such as testosterone and estradiol, play important roles in developing both strength and mass of skeletal muscle. Circulating dehydroepiandrosterone (DHEA)is peripherally taken up and converted to testosterone by 3B-hydroxysteroid dehydrogenase (HSD) and 17B-HSD, and testosterone, in turn, is irreversibly converted to estrogens by aromatase cytochrome P450 (P450arom). Although sex steroid hormones have been implicated in skeletal muscle regulation and adaptation, it is unclear whether skeletal muscles have a local steroidogenic enzymatic machinery capable of metabolizing circulating DHEA. First study, we investigate whether the three key steroidogenic enzymes are present in the skeletal muscle, and are capable of generating sex steroid hormones. These findings are novel and important in that they provide the first evidence showing that skeletal muscles are capable of locally synthesizing sex steroid hormones from circulating DHEA or testosterone. Second study, we examine sex differences in the levels of testosterone, estradiol, and steroidogenesis-related enzymes, such as 3B-HSD, 17B-HSD and P450arom, in the skeletal muscle at rest and after exercise. We studied the gastrocnemius muscles of resting rats(10 weeks old)and exercised rats(10 weeks old, treadmill running, 30 m/min, 30 min). A single bout of exercise can influence the steroidogenic system in skeletal muscle and these alterations differ between sexes. The acute exercise-induced alteration of steroidogenic enzymes may enhance the local steroidogenesis in the skeletal muscle in both sexes.