Androgen treatment prevents loss of cancellous bone in the orchidectomized rat

This report describes histomorphometric evidence for an important role of androgens in maintaining cancellous bone balance at a remodeling site in vivo. Rats were orchiectomized (ORX) at 7 weeks of age and received either androgens or vehicle 1 week later (testosterone, 1-dehydrotestosterone, or 5-dihydrotestosterone) by subcutaneous pellet, producing controlled release of the drug for 3 weeks. Intact male rats and untreated ORX animals served as controls. After 4 weeks untreated ORX resulted in undetectable serum testosterone levels and marked atrophy of seminal vesicles compared with intact controls. Histomorphometry revealed severe cancellous osteopenia in the secondary spongiosa of the proximal tibial metaphysis. The length of bone surface lined by apparently "active" osteoblasts and number of osteoclasts per length of cancellous bone surface were increased following ORX. Testosterone treatment at 5 mg (per 21 days) produced subphysiologic serum testosterone levels. In contrast, 10 and 25 mg pellets resulted in serum testosterone ORX, and the degree of protection was dose dependent. 1-Dehydro- and 5-dihydrotestosterones displayed a bone-protective effect similar to that of testosterone. The results demonstrate that gonadal insufficiency results in a cancellous osteopenia that is preventable by testosterone treatment. Further, because a similar protective action was achieved using the nonaromatizable androgen 5-dihydrostestosterone, the results suggest that this bone-sparing effect is mediated by androgen rather than by metabolism of the androgen to an estrogen.