Requirement for vitamin D for the active transport of calcium by the intestine

¹ Department of Medicine, Columbia University College of Physicians and Surgeons; and the Presbyterian Hospital, New York City

The active transport of calcium from the mucosal to the serosal surfaces of everted gut-sacs of the rat is dependent on the dietary vitamin D. The active transfer in vitro is significantly increased one hour following the administration of calciferol by gastric tube to rats depleted of the vitamin. Vitamins D₂ and D₃ are approximately equally effective, whereas dihydrotachysterol (A.T. 10) is somewhat more effective than either of the vitamins D. Ultraviolet irradiation of intact rats also increases the active transport of calcium in vitro. Maintenance on a low calcium diet increases the active transfer, whereas thyroparathyroidectomy decreases it. Vitamin D is required to demonstrate both of these effects clearly. The results support the hypothesis that the active transfer is an adaptive mechanism which ensures adequate absorption when the requirement for calcium is increased, or when the diet is low in calcium.