INFLUENCE OF TREADMILL RUNNING ON FEMORAL BONE IN YOUNG ORCHIECTOMIZED RATS

Forty 6-wk-old male Wistar rats weighing 308 +/- 24 g were divided int o two groups. On day 0, the 20 animals in one group were surgically ca strated and the other group was sham operated. Within each group, 10 r ats were selected for treadmill running (60% maximal O-2 consumption, 1 h/day, 6 days/wk for 15 wk). The 20 sedentary rats were used as cont rols. At the time the rats were killed (day 105), running had no signi ficant effect on femoral mechanical properties either in castrated or in sham-operated rats. Femoral bone density was lower in orchidectomiz ed than in sham-operated rats. Nevertheless, it was higher in exercise d than in sedentary rats. Femoral Ca content paralleled changes in bon e density. Treadmill running had no significant effect on plasma osteo calcin concentration but inhibited the increase in urinary deoxypyridi noline excretion observed in castrated rats. Image analysis (measured at the distal femoral diaphysis) revealed that these effects mainly re sulted from decreased trabecular bone resorption in castrated exercise d rats.