Influence of Vitamin D Status and Chronic Administration on the Renal Tubular Effects of 1,25-Dihydroxy Vitamin D 3

Abstract

Abstract

Previous studies from this laboratory have demonstrated that the acute infusion of the vitamin D₃ derivative, 1,25-dihydroxy vitamin D₃ (1,25(OH)₂D₃) is antiphosphaturic when administered with small “permissive” amounts of parathyroid hormone (PTH). To determine the effect of chronic administration of this metabolite, studies were performed in both vitamin D-deficient (-D) and vitamin D-fed (+D) rats which had been pretreated with 1,25(OH)₂D₃ for 6 days and then infused with either the metabolite alone, the metabolite with a small “permissive” dose of parathyroid hormone (PTH) or neither. The results indicate that in the —D animals, 1,25(OH)₂D₃ infusion alone results in antiphosphaturia without the presence of PTH. However, in the +D rats, PTH was required, despite 1,25(OH)₂D₃ pretreatment, for the acute infusion of the metabolite to enhance phosphate reabsorption. Thus, both vitamin D and parathyroid status are important in determining the effect of 1,25(OH)₂D₃ on the renal tubular transport of phosphate.