Effect of prostaglandin D2 on the femoral bone mineral density in ovariectomized rats.

We studied the effects of prostaglandin D2 (PGD2) on the femoral bone mineral density (BMD) and other related parameters in ovariectomized (OVx) and sham-operated rats. BMD was measured in vivo by dual energy X-ray absorptiometry (DXA) for the period of 36 days or 112 days after operation. When 9- or 10-week-old rats were used at the time of operation, the femoral BMD increased during these periods. Ovariectomy resulted in a marked suppression of this steady increase in BMD at both proximal and distal ends of the femur. Subcutaneous administration of a slow-release preparation of PGD2 on days 1 and 21 not only prevented the ovariectomy-induced suppression of BMD, but also augmented the steady increase in BMD of the sham-operated rats. When medication was started on day 70, the depressed rate of increase in BMD was restored to the control level. Serum calcitonin (CT) and parathyroid hormone (PTH) levels were not affected by either ovariectomy or by PGD2 administration. Body weight and bone length were increased, but uterine weight was decreased by ovariectomy. PGD2 administration showed no effects on these parameters. There was a significant increase in the fasting level of urinary hydroxyproline excretion after ovariectomy, and PGD2 administration had no significant effect on this parameter either. These results indicate that the prevention of osteopenia in OVx rats and the increase in BMD in sham-operated and post-OVx rats by PGD2 administration are due to its stimulatory effect on bone formation.