Effects of vitamin D on phosphate transport and incorporation into mucosal constituents of rat intestinal mucosa.

The effects of vitamin D on transport of inorganic phosphate into and across rat intestinal mucosa in vifro were studied, and the results used to interpret observations on incorporation of 32P-labeled phosphate into mucosal lipid, protein, and nucleic acids. Vitamin D given to intact rats increases phosphate transport in vifro selectively in the direction mucosa to serosa. The sterol in vivo acts directly in the intestine with no prior activation in other organs. 32Pi transport is via restricted channels in the mucosa, as indicated by the observation that the specific radioactivity of transported 32P-labeled phosphate is miscible with approximately one-third or less of the mucosal Pi pool. Because of this compartmentalization specific radioactivities of individual mucosal precursor pools of 32Pi are difficult or impossible to estimate. Consequently, effects of vitamin D on incorporation of 32P-labeled phosphate into mucosal constituents cannot be interpreted definitively in terms of rates of synthesis. The relative effects of vitamin D on calcium as compared to phosphate transport in various segments of intestine, and other evidence, suggests that the sterol influences separately these two intestinal transport mechanisms.