Autoradiographic study of the effect of 1,25-dihydroxyvitamin D3 on bone matrix synthesis in vitamin D replete rats.

An autoradiographic technique using pulse labels of [3H]proline was developed to assess the early effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on bone matrix synthesis in vitamin D replete rats. Rats, 7 days old, were given 0.25 2.5, or 25 ng of 1,25(OH)2D3 for vehicle alone subcutaneously on days 1, 3, and 5 of the experiment. Rats received a subcutaneous injection of 100 microCi [3H]proline on days 2 and 6 and were killed on day 7. Calvaria and tibia were processed for autoradiography, and morphometric methods were developed to measure the rate and amount of bone matrix formed during the experimental period. When compared to control values, the amount and rate of formation of new bone matrix were both signifIcantly decreased in rats receiving 25 ng of 1,25(OH)2D3 and slightly, but not significantly, decreased in rats receiving 2.5 ng. We conclude that administration of pharmacologic doses of 1,25(OH)2D3 to vitamin D replete rat pups impairs the formation of collagenous bone matrix.