In Vivo and in Vitro Effects of Vitamin D3 [1,25-(OH)2D3] on the Uptake of Phosphate by Isolated Chick Kidney Cells
Harrison and Harrison1 first proposed that vitamin D acts as an important regulator of phosphate homeostasis. Since then, it has has been demonstrated that the active form of the vitamin, 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], enhances, by an unknown mechanism, the intestinal absorption of phosphate2,3. The effect of 1,25-(OH)2D3 on the reabsorption of phosphate in the kidney is less clear. In some studies, infusion of the vitamin has been found to decrease phosphate excretion4,5, whereas in other investigations 1,25-(OH)2D3 has been reported to be Phosphaturie6 or without effect on urinary phosphate7. Some of the difficulties in resolving the apparent discrepancies stem, in part, from the complex interactions in the in vivo animal of the vitamin D metabolic and phosphate transport systems with various regulatory factors, including parathyroid hormone and other endocrines, dietary status, and calcium8,9. This prompted us to initiate studies on a simpler model system, namely, the isolated renal cell. In this report we will examine the effects of 1,25-(OH)2D3 on the uptake of phosphate by these isolated cells; first, after the vitamin is administered to a D-deficient chick in vivo, and second, when 1,25-(OH)2D3 is incubated with the cells in vitro.
KeywordsRenal Cell Phosphate Transport Phosphate Uptake Renal Handling Vitro Effect
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