Age-related changes in rat intestinal transport of D-glucose, sodium, and water

Experiments were performed with everted sacs of jejunum and ileum and brush-border membrane vesicles from four different age groups of rats: very young, young, adult, and old. The changes with age in several parameters, such as cell electrolyte and D-glucose concentrations, cell volume, net D-glucose, Na+ and water transport, and D-glucose uptake into vesicles, were studied. Differences in transport activities in the four age groups of animals were observed. In the jejunum the greatest transport was found in young rats and less in adult, very young, and old rats. In the ileum, the greatest transport activity was found in very young and young rats, while in adult and old animals transport activity was negligible. The cell volume of the enterocyte was significantly smaller in old rats. Changes in cell electrolytes (increased Na+ and decreased K+) were observed only in the jejunum of old rats. The overshoot of D-glucose in brush-border membrane vesicles varied considerably in the four different age groups of animals. In other words, the capacity for sugar uptake into vesicles is greater in young rats than in very young or adult animals. In old rats there was no overshoot, and a slow linear increase of sugar entry was observed. The results indicate that the changes in D-glucose transport with age might be explained in part by the changes in the amount of sugar that crosses the brush-border membrane of the enterocyte.