Effects of running exercise on the mandible and tibia of ovariectomized rats.

To examine the effects of running exercise on the mandible and tibia of ovariectomized (OVX) rats, 26-week-old sham-operated (Sham) and OVX rats 1 week post-ovariectomy were subjected to non-exercise (Sham-Cont and OVX-Cont) and exercise (Sham-Exc and OVX-Exc) for 8 weeks. OVX induced a significant decrease in alkaline phosphatase (ALP) and an increase in tartrate-resistant acid phosphatase (TRAP) activity and a reduction of 17beta-estradiol in the serum. In OVX-Cont rats, histology and bone mineral density (BMD) showed bone loss in the proximal tibia, and histology, soft X-ray photographs and bone marrow area (BMA) revealed enlargement of the bone marrow cavity in the neck of the condylar process. In OVX-Exc rats, exercise significantly increased ALP activity, decreased TRAP activity and markedly elevated serum progesterone levels. Histology and BMD in the tibia and histology, X-ray photographs and BMA in the mandible were comparable to those in Sham rats. In Sham-Exc rats, unexpected decreases were observed in serum enzymes and hormones, but the histology and BMD in the tibia and histology, X-ray photographs and BMA in the mandible were very similar to those in Sham-Cont rats, suggesting a decrease of bone turnover with no change of bone mass in the tibia and mandible. We conclude that exercise has a beneficial effect not only on bone loss in the tibia, but also on differential changes in the neck of the condylar process, perhaps by increasing serum levels of progesterone in OVX rats.