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 hormone (PTH), the antiresorptive agents estrogen and bisphosphonate (risedronate), and also the combination of PTH with these antiresorptive drugs 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 (control); 2-ovariectomized (OVX); 3-OVX plus estrogen; 4-OVX plus bisphosphonate (risedronate [NE]; 5-OVX plus hPTH (1-34); 6OVX plus hPTH (1-34) and estrogen; 7-OVX plus hPTH (1-34) and risedronate. Treatment regimens were initiated 4 weeks after OVX and were continued for 5 and 15 weeks for each treatment group, Changes in bone mass lash content), cross-sectional area, cortical thickness and dimensions and bone strength were assessed in middiaphyseal, femoral specimens, The results revealed that ovariectomy had no effect on cortical bone mass and biomechanical competence, OVX rats treated with estrogen and also OVX rats treated with risedronate showed no significant difference from either OVX or control groups, After only 5 weeks of treatment, hPTH monotherapy increased ash content, cross-sectional area, cortical thickness and compressive bone strength (load) significantly, After 15 weeks of treatment, OVX rats treated with PTH monotherapy or PTH in combination with risedronate showed identical load-values, These values were significantly higher than those seen in both control and OVX rats, However, PTH in combination with estrogen failed to augment cortical bone strength over control or OVX levels after therapy, No ''cortical steal'' phenomenon during PTH mono- or cotherapy was detected in this study on sexually mature OVX rats with cancellous osteopenia, However, the study focused solely on the weight-bearing femoral bone, These findings-from an estrogen-deplete rat model-provide support for PTH as a potentially effective agent for osteoporosis, but they need confirmation in a larger animal model with intracortical bone remodeling.