The effect of age and 1,25-dihydroxyvitamin D3 treatment on the intestinal calcium-binding protein of suckling rats.

The intestinal level of the vitamin D-dependent duodenal calcium-binding protein was assayed by an equilibrated column technique in rat embryos, neonates, and pups. Calcium-binding protein was undetectable in unborn, newborn, and 1- to 2-day-old rats i.e., the level was lower than in severely vitamin D-deficient animals. Calcium-binding protein was detected after the animals were 5-days old and thereafter rose monotonically as a function of body weight. Treatment with 1,25-dihydroxyvitamin D₃ failed to raise the calcium-binding protein levels of newborn or 1-day-old rats, but doubled the level in 11- or 12-day-old pups. Plasma calcium was raised in all treated animals. The failure to detect calcium-binding protein in vitamin D-replete suckling animals provides evidence for a dissociation between calcium absorption and calcium binding protein.