Transfer of Ca⁴⁵ across intestinal wall in vitro in relation to action of vitamin D and cortisol

The transfer of calcium across the intestinal wall of rats was measured in vitro by the device of everted intestinal loops with Ca 45 as an indicator. The conditions were developed so that the rate of diffusion of calcium across the intestinal wall as well as active transport against a concentration gradient could be determined. Vitamin D treatment increases the rate of diffusion of calcium across the intestinal wall. This action of vitamin D is exerted along the entire length of the small intestine and is not affected by inhibition of oxidative metabolism. The active transport of calcium on the other hand is localized to the proximal part of the intestine and is dependent on the energy of oxidative metabolism. Cortisol treatment antagonizes the vitamin D effect on the diffusion of calcium and also reduces the active transport of calcium. It is suggested that vitamin D and cortisol influence calcium transport by action on the permeability of cell surfaces to calcium.