Early and Direct Effect of 1,25-Dihydroxycholecalciferol on Calcium Uptake by Duodena of Rachitic Chicks

Abstract

Abstract

Injection of 1,25 dihydroxycholecalciferol (1,25(OH)²D₃, 10 μg) directly into the in situ ligated duodenal loop of rachitic chicks significantly elevated the tissue accumulation of ⁴⁷Ca within 20–30 min. The transfer of ⁴⁷Ca from lumen to blood, during the same time period, was not increased nor was there any measurable intestinal calcium-binding protein synthesized. Lesser amounts of 1,25(OH)₂D₃ (1 or 5 μg) did not result in any statistically significant elevation of ⁴⁷Ca tissue accumulation, nor did they have any effect on 47Ca transfer from lumen to blood (transmural). Ten micrograms of 1,24R,25(OH)₃D₃ was similarly effective in elevating tissue accumulation, whereas 24R,25(OH)₂D₃ and 25(OH)D₃ were not. These results provide additional evidence for an early and direct action of 1,25(OH)₂D₃ in altering intestinal epithelial membrane transport prior to the induction of synthesis of specific transport proteins.