Abstract
The effect of vitamin D on the change of bone contents of cyclic nucleotides and DNA was examined in rats fed a vitamin D deficient, low calcium diet. Daily administration of vitamin D3 (0.25 μg) to the animals for a week induced a significant increase of plasma calcium concentration as well as of bone DNA and cyclic AMP contents. After a single administration of vitamin D3 (0.25 μg), the earliest change observed was the elevation of plasma calcium levels, followed by an increase of the cyclic AMP content which was significant at 48 hr. Significant increase of the DNA content in bone was first observed at 72 hr. In contrast to the increase of cyclic AMP contents in bone, the level of cyclic GMP was almost constant. When the animals were switched to the same vitamin D deficient, high calcium (3%) diet containing lactose, their serum calcium concentrations were markedly elevated, while neither the cyclic AMP nor DNA contents were changed. These results indicate that although vitamin D administration leads to a change in the cyclic AMP and DNA contents of bone, these changes are not directly related to the early calcium mobilizing action of the vitamin. The bone change in the cyclic AMP and DNA contents appears to be due to a direct effect of vitamin D rather than to the elevation of serum calcium concentration.
