Intestinal maturation: in vivo loss of calcium in suckling and adult rats.

Intestinal permeability to Ca is greater in infant than in older rats, predisposing the infant rat to hypocalcemia. The present studies compared in suckling and adult rats the amount of Ca lost into the intestinal lumen in relation to plasma Ca during an acute 2-h in vivo recirculation perfusion of the jejunum and ileum with an isotonic NaCl solution either free of or containing CaCl2. Rats had been injected with radioactive 45CaCl2 24 h prior to the perfusion. Secretion of Ca was determined from rate of appearance of 45Ca into the lumen. During perfusion of the solution free of Ca, rate of secretion of Ca into the intestinal lumen (both jejunum and ileum) was about the same in the suckling and the adult rats, about 7.3 mumol/2 h. However, rate of secretion based on body weight was 10-fold greater in the suckling than in the adult rats. The relatively greater loss of Ca in suckling rats resulted in a significant drop of serum Ca, from 2.95 mumol/ml to 2.02 mumol/ml. In adult rats serum Ca was maintained to within normal limits. During perfusion of solutions containing 2 mmol/L of CaCl2, all rats absorbed Ca, and absorption rates were greater in the jejunum and ileum of the suckling than of the adult rats. Thus, because of the possibility of excessive loss of Ca through the intestinal tract, it appears advisable to allow young infants enough dietary Ca to maintain concentration of ionized Ca in the intestinal lumen to above that in serum.