THE EFFECT OF 17-BETA-ESTRADIOL TREATMENT ON THE MASS AND THE TURNOVER OF BONE IN OVARIECTOMIZED RATS TAKING A MILD DOSE OF THYROXINE

We performed the dosing experiment to establish whether estrogen admin istration has any beneficial effects on the mass and the turnover of b one in ovariectomized rats taking a mild dose of thyroxin. Thirty-five Wistar rats, 28 weeks of age, received ovariectomies (OVX) or sham op erations and were divided into five groups. Group 1 was the sham group , Groups 2-5 were ovariectomized. Group 2 was the OVX-control, Group 3 treated with thyroxin 30 pg/kg/day (T4), Group 4, 17 beta-estradiol 0 .3 mg/kg/week (E2), and Group 5, the combination of T4 and E2. The dur ation of the experiment was 12 weeks. At the end of the experiment, se rum chemistries were measured. Bone minerals in the femur were determi ned with single photon absorptiometry and bone turnover was assessed h istomorphometrically. Alkaline-phosphatase increased in Group 3 (OVX-T 4), but it reduced in Groups 4 (OVX-E2) and 5 (OVX-T4 + E2). Bone mine rals decreased in Groups 2 (OVX) and 3. In Group 4, it was preserved a t the same level as in Group 1. Group 5 showed a significant increase of bone mass compared with Group 1. Eroded surface and osteoid surface increased in Groups 2 and 3 and they were reduced in Groups 4 and 5. Bone volume and mineral apposition rate were at a maximum in Group 5. This study demonstrated that 17 beta-estradiol was capable of preventi ng the bone mass decrease by regulating the turnover in ovariectomized rats taking a mild dose of thyroxin. Osteoblast function appeared to be stimulated in combination with 17 beta-estradiol and thyroxin.