EFFECTS OF 17-BETA-ESTRADIOL ADMINISTRATION ON CORTICAL AND CANCELLOUS BONE OF OVARIECTOMIZED RATS WITH AND WITHOUT HYPOPHYSECTOMY

Pituitary hormones are essential for bone growth and bone turnover, Hy pophysectomy (HX) diminishes mitogenesis and abolishes the high bone t urnover rate induced by ovariectomy (OV), It is not known whether the suppressive effect of estrogen on bone resorption is diminished or abo lished by HX, The present study investigates the effects of 17 beta-es tradiol (E-2) (20 mu g/wk) on cortical and cancellous bone mass and bo ne turnover as measured by histomorphometry in HX + OV (HO) rats. Spra gue-Dawley rats at 2 months of age were OV or HO and the experiment wa s performed over a 6 week period, Hypophysectomy + OV (HO) resulted in a cessation of periosteal bone formation, and longitudinal bone growt h and a decrease in cancellous bone volume, The tibial dry weight and tibial density were significantly lower in the HO than in the intact o r OV groups, Administration of E-2 to HO rats partially prevented canc ellous bone loss, whereas the same dosage of E-2 fully prevented cance llous bone loss in rats with OV alone, Nevertheless, cancellous bone v olume was higher in the HO + E-2 than in the HO-alone groups, Estradio l administration in HO rats did not suppress cancellous bone formation rate or the eroded surface as much as it did in the OV rats, The supp ressive effect of E-2 on periosteal bone formation rate and mineral ap position rate was also diminished in HO rats, However, factorial ANOVA showed that the effects of E-2 on increasing cancellous bone volume a nd decreasing periosteal bone formation rate and mineral apposition ra te were still significant in the HO rats, Tibial dry weight and tibial density did not differ between HO and HO + E-2 groups. In conclusion, we have demonstrated that the estrogen-induced effects of preventing cancellous bone loss, of suppressing bone formation, and resorption as seen in OV rats was diminished but not abolished in HO rats. (C) 1997 by Elsevier Science Inc.