Vitamin D and transfer of plasma calcium to intestinal lumen in chicks and rats

Abstract

The influence of vitamin D on the transfer of Ca47 from plasma to intestinal lumen in rachitic chicks and rats in vivo was studied. At 2. 5 min. after intravenous injection, the amount of Ca47 deposited into an intraluminal solution was measured. This and other determinations indicated that vitamin D significantly increased the plasma-to-lumen flux of Ca across chick ileum and rat duodenum by factors of 2. 7 and 1. 9, respectively. As expected, the lumen-to-plasma flux in both species was also enhanced by vitamin D. The influx effect was not due to a transmural electropotential difference from vitamin D administration or to differences in plasma Ca concentrations. These data suggested that the major direct effect of vitamin D is not on a unidirectionally oriented transport system of Ca but on an increased diffusional permeability, the latter perhaps manifested as a change in membrane structure and/or an effect on Ca carrier synthesis.