CALCIUM-BINDING PROTEIN AND CALCIUM ABSORPTION AFTER VITAMIN D ADMINISTRATION

Intestinal absorption of calcium and the formation of calcium-binding protein (CaBP) as functions of time after vitamin D administration were studied in chicks and rats. Both calcium absorption and CaBP appear after vitamin D but the time courses of their appearance are different. The lag phase of calcium absorption after an oral 500-IU dose of vitamin D in chicks is about 10-16 hr depending on the calcium concentration of the diet. However, the lag phase of CaBP formation is 19-20 hr. The slopes of the two parameters between 20 and 100 hr after vitamin D are also different. Lowering the calcium concentration of the diet reduces the lag phase of calcium absorption from 16 to 10 hr after vitamin D but has no effect on the lag phase of CaBP formation. The data provide evidence that calcium absorption and CaBP formation as functions of vitamin D action are not directly related. Although CaBP is present when calcium absorption is initiated by vitamin D, some other factors seem to be involved in calcium transport. It has also been shown in this paper that the duodenum is the main site of calcium absorption in chick. © 1969.