In vivo intestinal calcium transport in infant rats: normal and growth retarded.

We compared the in vivo transport of calcium (Ca) in the jejunum + ileum of 1-, 2-, 3-, 4-, and 6-week old rats. In normal rats, net absorption and the estimated bidirectional fluxes of Ca (lumen-to mucosa and mucosa-to-lumen) normalized for differences in size of the intestine (mumoles/hour per g weight) were similar in the 1-, 2-, and 3-week old rats and significantly lower in the 6-week old than in the younger rats. Growth retardation (pups raised with mothers fed a diet deficient in protein) appeared to have suppressed net absorption and the bidirectional fluxes of calcium in the 4- and 6-week old rats, but to have slightly enhanced net absorption and the bidirectional fluxes in the 1-, 2-, and 3-week old rats. These findings suggested a change in the mechanism(s) for intestinal transport of Ca during maturation. Rate of gain in body weight expressed as g/day increased with age from 1.4 g/day between 1 and 2 weeks, to 6.1 g/day between 4 and 6 weeks of age. There was no correlation between rate of net Ca absorption from the jejunum + ileum and gain in body weight expressed as g/day or as percent per day.