Vitamin D-dependent calcium-binding protein. Response to some physiological and nutritional variables.

The effect of some physiological and nutritional variables on the vitamin D-dependent calcium-binding protein content of duodenal mucosa of .chicks was assessed. Calciumbinding protein, originally detected in vitamin Da-treated rachitic chicks, is also present in normally raised chicks; however, the concentration of calcium-binding protein in the vitamin Da-treated rachitic chick mucosa exceeded that in normal mucosa. 47Ca absorption by a duodenal loop and the calcium-binding protein content of duodenal mucosa decreased at a similar rate when chicks given a single dose of vitamin DS were replaced on a rachitogenic diet. Chicks adapted to a low calcium intake absorbed more calcium and had a greater concentration of duodenal calcium-binding protein than chicks on a normal diet. Further, content of mucosal calcium-binding protein was greater in younger than more mature birds, the same in pullets and cockerels of the same age, and greater in laying than in nonlaying hens. Estrogen (diethylstilbesterol), a hormone prominent in the process of egg laying, did not induce the formation of calcium-binding protein. Vitamin Da was more effective in calcium-binding protein formation than vitamin D2 which fact coincides with their relative physiological effects. The relationship between these studies and the implication of a role of calcium-binding protein in calcium translocation is discussed.