THE ANABOLIC EFFECTS OF PARATHYROID-HORMONE ON CORTICAL BONE MASS, DIMENSIONS AND STRENGTH-ASSESSED IN A SEXUALLY MATURE, OVARIECTOMIZED RAT MODEL

The aim of the study was to determine the effect of parathyroid hormon e (PTH), the antiresorptive agents estrogen and bisphosphonate (risedr onate), and also the combination of PTH with these antiresorptive drug s on femoral cortical bone mass, dimensions and strength in a sexually mature, ovariectomized rat model, A total of 138, 3-month-old Sprague -Dawley rats were randomized into seven groups: 1-sham operated (contr ol); 2-ovariectomized (OVX); 3-OVX plus estrogen; 4-OVX plus bisphosph onate (risedronate [NE]; 5-OVX plus hPTH (1-34); 6OVX plus hPTH (1-34) and estrogen; 7-OVX plus hPTH (1-34) and risedronate. Treatment regim ens were initiated 4 weeks after OVX and were continued for 5 and 15 w eeks for each treatment group, Changes in bone mass lash content), cro ss-sectional area, cortical thickness and dimensions and bone strength were assessed in middiaphyseal, femoral specimens, The results reveal ed that ovariectomy had no effect on cortical bone mass and biomechani cal competence, OVX rats treated with estrogen and also OVX rats treat ed with risedronate showed no significant difference from either OVX o r control groups, After only 5 weeks of treatment, hPTH monotherapy in creased ash content, cross-sectional area, cortical thickness and comp ressive bone strength (load) significantly, After 15 weeks of treatmen t, OVX rats treated with PTH monotherapy or PTH in combination with ri sedronate showed identical load-values, These values were significantl y higher than those seen in both control and OVX rats, However, PTH in combination with estrogen failed to augment cortical bone strength ov er control or OVX levels after therapy, No ''cortical steal'' phenomen on during PTH mono- or cotherapy was detected in this study on sexuall y mature OVX rats with cancellous osteopenia, However, the study focus ed solely on the weight-bearing femoral bone, These findings-from an e strogen-deplete rat model-provide support for PTH as a potentially eff ective agent for osteoporosis, but they need confirmation in a larger animal model with intracortical bone remodeling.