PTH HAS A MORE PRONOUNCED EFFECT ON VERTEBRAL BONE MASS AND BIOMECHANICAL COMPETENCE THAN ANTIRESORPTIVE AGENTS (ESTROGEN AND BISPHOSPHONATE) - ASSESSED IN SEXUALLY MATURE, OVARIECTOMIZED RATS

The aim of the study was to determine the effect of PTH, the antiresor ptive agents estrogen and bisphosphonate (Risedronate), and also the c ombination of PTH with the antiresorptive drugs on vertebral bone mass and biomechanical competence 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 (O VX); (3) OVX plus estrogen; (4) OVX plus bisphosphonate [Risedronate ( NE)]; (5) OVX plus hPTH (1-34); (6) OVX plus hPTH (1-34) and estrogen; and, finally, (7) OVX plus hPTH (1-34) and Risedronate. Treatment reg imens were initiated 4 weeks after OVX; and were continued for 5 and 1 5 weeks for each treatment group. Changes in bone mass (ash content) a nd biomechanical competence were assessed on lumbar vertebral body L(4 ). The results revealed that the Risedronate-treated OVX animals had a higher vertebral bone mass than the OVX group. hPTH (1-34) on its own had a pronounced anabolic effect and increased bone mass 20-25% and b one strength 70-80% over control levels. Neither combination therapy w ith estrogen nor with Risedronate provided any further advantage. The combination of PTH with Risedronate, though, seemed tea allow a contin ued increase in both bone mass and strength during the whole treatment period. The study has shown that in sexually mature but still growing ovariectomized rats, PTH alone has a pronounced anabolic effect on ve rtebral bone mass and strength which is not further augmented by co-th erapy with estrogen, while long-term co-therapy with Risedronate showe d a significant sustained increase in bone mass and strength throughou t the whole treatment period. It is concluded that PTH alone or in com bination with antiresorptive agents seems a promising therapeutic regi men for postmenopausal osteoporosis.