EFFECT OF OVARIECTOMY ON CANCELLOUS BONE IN THE HYPOPHYSECTOMIZED RAT

This experiment studied the effects of hypophysectomy (HX) and ovariec tomy (OV) on cancellous bone in the proximal tibia and distal 5th lumb ar vertebra by dynamic histomorphometry. Forty-eight female Sprague-Da wley rats, 3 months of age, were divided into age-matched control, HX, OV, and HX + OV (HO) groups. Ten rats were sacrificed at 3 months of age as baseline controls, and the rest of the animals were sacrificed 5 weeks after the surgery. While the age-matched controls and OV rats significantly increased in body weight compared with the baseline cont rol rats, cancellous bone volumes in the proximal tibia and distal 5th lumbar vertebra increased in the age-matched control and decreased in the OV rats. In the HX and HO rats, body weight equaled baseline cont rol values, and their cancellous bone volumes were decreased with a po orer trabecular architecture in both bone sites. In all HX, OV, and HO rats, uterine weight and serum estradiol were significantly decreased . OV significantly increased longitudinal bone growth and the tissue- and surface-based bone formation and bone resorption parameters in bot h the proximal tibia and 5th lumbar vertebra (p < 0.05). HX alone or H O significantly decreased longitudinal bone growth and the tissue-base d bone formation rate without significantly affecting surface-based bo ne formation and bone resorption parameters when compared with the age -matched controls. No significant differences were detected in any var iable between the HX alone and HO rats. In this study, HX on OV rats d ecreased the longitudinal bone growth, cancellous bone turnover (tissu e-based), and cancellous bone volume in the proximal tibia and distal 5th lumbar vertebra in young rats at 5 weeks after surgery. We suggest that the bone loss in the HO rats was due primarily to pituitary horm one deficiency and that the effect of ovarian hormone deficiency on ca ncellous bone is pituitary hormone dependent.