INCREASE IN BONE-DENSITY AND LEAN BODY-MASS DURING TESTOSTERONE ADMINISTRATION IN MEN WITH ACQUIRED HYPOGONADISM

Acquired hypogonadism is being increasingly recognized in adult men. H owever, the effects of long term testosterone replacement on bone dens ity and body composition are largely unknown. We investigated 36 adult men with acquired hypogonadism (age, 22-69 yr; median, 58 yr), includ ing 29 men with central hypogonadism and 7 men with primary hypogonadi sm, and 44 age-matched eugonadal controls. Baseline evaluation include d body composition analysis by bioimpedance, determination of site-spe cific adipose area by dual energy quantitative computed tomography sca n (QCT) of the lumbar spine, and measurements of spinal hone mineral d ensity (BMD) using dual energy x-ray absortiometry, spinal trabecular BMD with QCT, and radial BMD with single photon absorptiometry. Percen t body fat was significantly greater in the hypogonadal men compared t o eugonadal men (mean +/- SEM, 26.4 +/- 1.1% vs. 19.2 +/- 0.8%; P < 0. 01). The mean trabecular BMD determined by QCT for the hypogonadal men was 115 +/- 6 mg K2HPO4/cc. Spinal BMD was significantly lower than t hat in eugonadal controls (1.006 +/- 0.024 vs. 1.109 +/- 0.028 g/cm(2) ; P = 0.02, respectively). Radial BMD was similar in both groups. Test osterone enanthate therapy was initiated in 29 hypogonadal men at a do se of 100 mg/week, and the subjects were evaluated at 6-month interval s for 18 months. During testosterone therapy the percent body fat decr eased 14 +/- 4%(P < 0.001). There was a 13 +/- 14% decrease in subcuta neous fat (P < 0.01) and a 7 +/- 2% increase in lean muscle mass (P = 0.01) during testosterone therapy. Spinal BRID and trabecular BMD incr eased by 5 +/- 1% (P < 0.001) and 14 +/- 3%(P < 0.001), respectively. Radial BMD did not change. Serum bone-specific alkaline phosphatase an d urinary deoxypyridinoline Excretion, markers of bone formation and r esorption, respectively, decreased significantly over the 18 months (P = 0.003 and P = 0.04, respectively). We conclude that testosterone th erapy given to adult men with acquired hypogonadism decreases sc fat a nd increases lean muscle mass. In addition, testosterone therapy reduc es bone remodeling and increases trabecular bone density. The benefici al effects of androgen administration on body composition and bone den sity may provide additional indications for testosterone therapy in hy pogonadal men.