EFFECTS OF ESTROGEN AND GROWTH-HORMONE ON SKELETON IN THE OVARIECTOMIZED RAT WITH HYPOPHYSECTOMY

To investigate whether growth hormone (GH) and 17 beta-estradiol (E-2) replacement can prevent osteopenia induced by pituitary and ovarian h ormone deficiency [by hypophysectomy and ovariectomy (HX+OV)], we admi nistered relatively low doses of GH (2.3 IU.kg(-1).day(-1)) and E-2 (1 00 mu g.kg(-1).wk(-1)) in experiment 1 and relatively high doses of GH (13.5 IU.kg(-1).day(-1)) and E-2 (3,500 mu g.kg(-1).wk(-1)) in experi ment 2 to 2-mo-old HX+OV Sprague-Dawley rats for 6 wk. Our data show t hat the HX+OV of rats results in diminished periosteal bone formation, longitudinal bone growth, and decreased cancellous bone volume. Admin istration of either the low or high dose of GH to these rats increased their systemic growth, serum levels of osteocalcin, and cortical bone formation. Either low or high doses of GH or E-2 alone only partially prevent cancellous bone loss. However, the combined treatment of GH p lus E-2 resulted in an additive increase in the cancellous bone mass. We conclude that the additive effect of GH plus E-2 on cancellous bone is attributed to the suppressive effect of E-2 on bone resorption and the anabolic effect of GH on bone formation.