ANDROGEN RESISTANCE AND DEFICIENCY HAVE DIFFERENT EFFECTS ON THE GROWING SKELETON OF THE RAT

Mature male, female, and androgen-resistant testicular feminized (Tfm) male rats of the same strain were sacrificed at the age of 120 days. Young male and Tfm rats were orchidectomized (orch) at 1 month of age and sacrificed at 120 days. The right femora were dissected, cleaned, defatted, and scanned with the Hologic QDR-1000. Orch and Tfm rats had similar body weights that were intermediate between body weights of t heir normal male and female littermates. Serum IGF-I concentrations we re lowest in Tfm rats; IGF-1 concentrations in orch rats were not lowe r than in males. Dual-energy X-ray absorptiometry yielded the followin g results: Total femoral mass and area were lower in female, Tfm rats and in both orch groups compared with intact male rats. Femoral bone d ensity was, however, only decreased in orch rats. Bone density measure d in an area containing only cortical bone was not different between g roups. However, the density was lower in orch rats in an area containi ng both cancellous and cortical bone. This finding is consistent with a +/-50% decrease of cancellous bone volume in orch rats compared with all other groups at the proximal tibial metaphysis (an area containin g mainly cancellous bone). These data show that Tfm rats, despite havi ng lower IGF-I levels in serum, low body weight, and decreased femoral areas, manage-in contrast with orchidectomized rats-to maintain simil ar trabecular bone densities and volumes during growth. We conclude th at trabecular bone densities can be preserved in androgen-resistant ma le rats independent of bone or body growth velocity or IGF-I secretion . We postulate that the modest increase of estrogen concentration in t his animals and/or in situ aromatization may be responsible for the ma intenance of the cancellous bone.