Vitamin D-dependent calcium-binding protein of rat intestine: changes during postnatal development and sensitivity to 1,25-dihydroxycholecalciferol.

To study the role of the vitamin D-endocrine system during the perinatal period, we monitored vitamin D-dependent calcium-binding protein (CaBP) in rat intestine by radial immunodiffusion and polyacrylamide disc gel electrophoresis. Small amounts of CaBp were present 2 days before birth; these levels increased 74-fold by day 38 after birth. Approximately 80% of the increase in CaBP concentration occurred in a 5-day period at the time of weaning (days 17--22 after birth). Before this period, the concentration of CaBP was comparable to that found in rachitic (adult) rats. Administration of 1,25-dihydroxycholecalciferol to suckling rats on days 15 and/or 16 was followed by a premature increase in the amount of intestinal CaBP. These data demonstrate that although vitamin D-dependent CaBP is low in preweaned rats, the rat intestine is responsive to exogeneous 1,25-dihydroxyvitamin D3 at least as early as day 15 after birth. The close temporal correspondence between the increases in CaBP and previously reported changes in calcium transport and vitamin D metabolism suggest that the vitamin D-endocrine system plays a role in postnatal intestinal maturation and adaptation during the weaning period.