Short- and long-term effects of calcium and exercise on bone mineral density in ovariectomized rats

At the level of prevention of bone mineral loss produced by ovariectomy, th e aim of the present study was to determine the effect produced by suppleme ntation of Ca in the diet and a moderate exercise programme (treadmill), si multaneously or separately, in ovariectomized rats, an experimental model o f postmenopausal bone loss. Female Wistar rats (n 110, 15 weeks old) were d ivided into five groups: (1) OVX, rats ovariectomized at 15 weeks of age, f ed a standard diet; (2) SHAM, rats sham operated at 15 weeks of age, fed a standard diet; (3) OVX-EX, ovariectomized rats, fed a standard diet and per forming the established exercise programme; (4) OVX-Ca, ovariectomized rats fed a diet supplemented with Ca; (5) OVX-EXCa, ovariectomized rats with th e exercise programme and diet supplemented with Ca. The different treatment s were initiated 1 week after ovariectomy and were continued for 13 weeks f or subgroup 1 and 28 weeks for subgroup 2, to look at the interaction of ag e and time passed from ovariectomy on the treatments. Bone mineral density (BMD) was determined, at the end of the study, in the lumbar spine (L2, L3 and L4) and in the left femur using a densitometer. Bone turnover was also estimated at the end of the study, measuring the serum formation marker tot al alkaline phosphatase (AP) and the resorption marker serum tartrate-resis tant acid phosphatase (TRAP). As expected, OVX rats showed a significant de crease (P <0.05) in BMD, more pronounced in subgroup 2, and a significant i ncrease in AP and TRAP with regard to their respective SHAM group. The simu ltaneous treatment with Ca and exercise produced the best effects on lumbar and femoral BMD of ovariectomized rats, partially avoiding bone loss produ ced by ovariectomy, although it was not able to fully maintain BMD levels o f intact animals. This combined treatment produced a significant increase i n AP, both in subgroups 1 and 2, and a decrease in TRAP in subgroup 1, with regard to OVX group. The exercise treatment alone was able to produce an i ncrease in BMD with regard to OVX group only in subgroup 1 of rats (younger animals and less time from ovariectomy), but not in subgroup 2. In agreeme nt with this, there was an increase of AP in both subgroups, lower than tha t observed in animals submitted to exercise plus Ca supplement, and a decre ase of TRAP in subgroup 1, without significant changes in this marker in th e older rats. Ca treatment did not produce any significant effect on BMD in OVX rats in both subgroups of animals, showing a decrease of AP and TRAP l evels in the younger animals with no significant variations in markers of b one remodelling in the older female rats compared with their respective OVX group.