Vitamin D3: Direct Action on the Small Intestine of the Rat

Vitamin D3 placed directly into loops of rat duodenum in vitamin D deficient animals increases markedly the subsequent transport of calcium by slices of the duodenal loop in vitro. Under similar conditions the same dose of vitamin given intravenously or placed in a jejunal loop has little or no effect on the duodenal tissue. Thus the vitamin acts directly on the small intestine without prior activation in another organ.