Effect of vitamin D3 and 1,25-dihydroxyvitamin D3 on intestinal transport of phosphate.

Dietary variations (low calcium, low calcium, low phosphorus, or high strontium) change phosphate transport by the jejunum according to their respective ability to increase or block the synthesis of 1,25-dihydroxyvitamin D3, suggesting that the action of this active sterol underlies the response of intestinal phosphate absorption to vitamin D. 1,25-(OH)2D3 stimulates the active entry of Pi at the mucosal border by its action on protein synthesis. It is attractive to speculate that 1,25-(OH)2D3 might induce the synthesis of a "phosphate carrier" protein in the plasma membrane. The interpretation that the enhancement of the maximal velocity of the "phosphate pump" by vitamin D is due to the creation of new pump sites would be consistent with this hypothesis.