EFFECTS OF A WEEKLY INJECTION OF HUMAN PARATHYROID-HORMONE-(1-34) ANDWITHDRAWAL ON BONE MASS, STRENGTH, AND TURNOVER IN MATURE OVARIECTOMIZED RATS

One hundred fifteen Wistar rats, 7 months off age, were ovariectomized (ovx) or sham-operated to evaluate the effects of a weekly injection of human parathyroid hormone (hPTH) and withdrawal on the bone mass, s trength, and turnover in mature ovariectomized rats. At 3 months, ovx rats were given a weekly injection of hPTH(1-34) at the respective dos es of 0 (vehicle), 10, and 90 mu g/kg body weight (BW) for 3 months. T hen, hPTH-treated rats were divided into two groups each: continuously treated groups, and the groups treated with vehicle only for another 3 months. Weekly hPTH injections at doses of 10 or 90 mu g/kg BW maint ained the lumbar BMD values and increased the values of the femoral co rtical bone, increasing the bone formation rates in the trabecular, en docortical, and periosteal envelopes. Trabecular osteoclasts were incr eased in the 90 mu g/kg dose group. Trabecular bone surface relative t o the volume was decreased by hPTH, The compressive load of the lumbar bone and the bending moment of the midfemur were increased. The lumba r compressive load values, corrected for BMD and volume, and the momen t of inertia of the midfemur were also increased. The intracortical po rosity values were not increased by the treatment. After withdrawal of hPTH treatment, the BMD values in both the lumbar and the midfemur we re reduced to ovx control levels. The bone mass stimulated by the 90 m u g/kg dose was reduced faster than that by the 10 mu g/kg dose. Howev er, the parameters of bone strength were still larger than those of th e ovx controls after cessation of the hPTH treatment. Thus, a weekly h PTH injection effectively stimulated the bone formation in both the tr abecular and cortical bone, leading to positive effects on mass and st ructure of the bone. These data suggest the possibility of benefits of both a lower frequency of hPTH injections as well as high-frequency i njections for human osteoporotics. (C) 1998 by Elsevier Science Inc. A ll rights reserved.