Vitamin D3 and unidirectional calcium fluxes across the rachitic chick duodenum

Abstract

The effect of vitamin D₃ on the unidirectional fluxes of calcium across the chick duodenum in vivo was studied. As the calcium concentration in the lumen was enhanced it was observed that both calcium efflux (lumen to plasma) and calcium influx (plasma to lumen) were increased in the rachitic and vitamin D₃-treated chick. Of significance, it was found that vitamin D₃ caused an increased efflux as well as increased influx of calcium, and the observed efflux/influx ratios at all levels of intraluminal calcium were not significantly affected by vitamin D₃. The present data are not consistent with the theory that vitamin D₃ operates through a unidirectionally oriented active transport system but can be more readily explained on the basis of a permeability change at the mucosal cell.