Changes in intestinal glucose transport over the lifespan of the rat.

Age-related changes in intestinal glucose absorption were studied using everted intestinal sacs and brush border membrane vesicles prepared from male F344 rats. Glucose uptake by everted intestinal sacs was greatest in young (2-3-month-old) as compared with adult (12-14-month-old) and old (24-month-old) rats. The greatest decrease in glucose uptake occurred between 2 and 12 months. The addition of phloridzin reduced glucose uptake to similar levels in all age groups, suggesting that the age-related change was in the carrier-mediated component of glucose transport. In order to localize the site of decreased carrier-mediated glucose transport, experiments were performed using brush border membrane vesicles. Vesicular glucose uptake in the presence of Na was significantly greater in vesicles prepared from 2-month-old rats (133 +/- 18 pmol/mg/s), compared with those prepared from 12-month-old rats (82 +/- 13 pmol/mg/s). Kinetic studies performed under non-equilibrium conditions demonstrated that the major effect of age was on the Na-dependent component of the brush border transport system. There was a reduction in the Vmax from 335 +/- 37 pmol/mg/s in the young to 217 +/- 22 pmol/mg/s in the adult, but there was no change in the Km. Isotope exchange studies performed under equilibrium conditions confirmed a decrease in the activity of the glucose transporter with age. No age-related changes in Na uptake by brush border membrane vesicles were observed. These findings suggest that a decrease in the number and/or activity of Na-linked glucose carriers may account for the decrease in intestinal glucose transport with age.