Osteopenia caused by ovariectomy in young female rats and prophylactic effects of 1,25-dihydroxyvitamin D3.

Young female rats were subjected to either bilateral ovariectomy or sham operation. One group of ovariectomized (ovx) animals was treated with the vitamin D metabolite 1,25(OH)2D3 after surgery. The effects of ovariectomy and 1,25(OH)2D3 treatment on different markers of bone formation (serum alkaline phosphatase, serum bone gla protein) and bone resorption (fasting urinary hydroxyproline) were determined. All rats were euthanized at 7 weeks post ovariectomy and their first lumbar vertebra were processed undecalcified for quantitative bone histomorphometry. A significant decrease in cancellous bone mass was noted in ovx compared with sham-operated rats. This bone loss was associated with increased biochemical markers of bone formation and bone resorption. Furthermore, ovariectomy led to elevated osteoblast perimeter and osteoid parameters as well as an increased osteoclast number. These data indicate that young growing rats develop osteopenia 7 weeks after ovariectomy which goes along with an accelerated bone turnover. Bone gla-protein, alkaline phosphatase and hydroxyproline can be useful markers in studies with ovx rats. Treatment with 1,25(OH)2D3 led to a lowered urinary hydroxyproline excretion and a significant decrease of osteoclast number whereas histomorphometrical indices of bone formation were nearly unchanged. Cancellous bone mass increased significantly in ovx rats treated with 1,25(OH)2D3 compared with non-treated rats. These results suggest that 1,25(OH)2D3 has a prophylactic effect with regard to bone loss in ovx rats which refers to a diminished bone resorption in the high bone turnover condition of ovx animals.