Effect of Vitamin D3 on the in vitro Transport of Calcium by the Chick Intestine

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Abstract
The effect of vitamin D3 treatment of the chick on concentrative transport of calcium by intestinal loops in vitro, on intestinal permeability to calcium in vitro and on calcium efflux from tied-off intestinal loops in situ was determined. Concentrative transport of calcium in vitro could not be demonstrated when chick intestine was incubated in K-H buffer (Na = 145 mM) but was observed when everted intestinal loops were incubated in a low sodium buffer (Na = 26 mM). In this low sodium medium, concentrative transport of calcium was observed only in the ileal segment and was greatly enhanced by vitamin D3 treatment of the chick. Vitamin D3 treatment was also shown to increase the permeability to calcium of the intestinal loop in vitro. In the in vitro preparations calcium was not transferred across the wall of the duodenum. In situ, however, the most rapid efflux of calcium occurred in the duodenal loop and was greatly enhanced by vitamin D treatment.