5-Alpha Reductase and Anabolic Effects of Testosterone

Approximately 40% of older male veterans have a low serum testosterone concentration. The latter is associated with diminished muscle strength and bone mineral density, depressed mood, low pain tolerance, frailty, and increased mortality. Replacement doses of testosterone have been administered to hypogonadal men for the purpose of reversing deficits in muscle and bone. Although testosterone is clearly important for maintaining muscle and bone in men, there are problems associated with T replacement. First, testosterone causes a number of undesired effects, including fluid retention, gynecomastia, worsening of sleep apnea, polycythemia, prostate enlargement and acceleration of early-stage prostate cancer. The anabolic effects obtained to date from testosterone replacement have been relatively modest, especially in older men. Our hypothesis is that combined treatment with a higher-than-replacement dose of testosterone and a 5- reductase inhibitor will produce substantial anabolic effects, while preventing testosterone-induced prostate enlargement and possibly other adverse effects.

We plan to investigate the efficacy and safety of combined treatment with testosterone and finasteride in older hypogonadal male veterans by conducting a 12-month randomized, placebo-controlled trial. We will administer a higher-than-replacement dose of testosterone plus the 5- reductase inhibitor finasteride to a group of hypogonadal, but otherwise healthy older men. We will determine whether this treatment is a safe and effective means to increase muscle mass and strength. Men aged 60 to 80, with circulating total testosterone 300 ng/dL or bioavailable testosterone 70 ng/dL, will be treated with 125 mg testosterone enanthate/week 5 mg finasteride/day for 1 year. We will assess the effects on body composition, 1- repetition maximum (1-RM) strength, grip strength, functional reach, bone mineral density, mood, cognition, hematopoiesis and prostate volume. We have chosen a moderately high dose of testosterone that may cause some adverse effects. We predict that finasteride will not block the anabolic effects of testosterone, but will block any prostate enlargement or symptoms and possibly other adverse effects as well.