Effects of estrogen and growth hormone on skeleton in the ovariectomized rat with hypophysectomy

To investigate whether growth hormone (GH) and 17beta-estradiol (E2) replacement can prevent osteopenia induced by pituitary and ovarian hormone deficiency [by hypophysectomy and ovariectomy (HX+OV)], we administered relatively low doses of GH (2.3 IU x kg(-1) x day(-1)) and E2 (100 microg x kg(-1) x wk(-1)) in experiment 1 and relatively high doses of GH (13.5 IU x kg(-1) x day(-1)) and E2 (3,500 microg x kg(-1) x wk(-1)) in experiment 2 to 2-mo-old HX+OV Sprague-Dawley rats for 6 wk. Our data show that the HX+OV of rats results in diminished periosteal bone formation, longitudinal bone growth, and decreased cancellous bone volume. Administration 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 E2 alone only partially prevent cancellous bone loss. However, the combined treatment of GH plus E2 resulted in an additive increase in the cancellous bone mass. We conclude that the additive effect of GH plus E2 on cancellous bone is attributed to the suppressive effect of E2 on bone resorption and the anabolic effect of GH on bone formation.