Changes in metabolite transport by small intestine and kidney of young and old rats

We have studied the influence of the ageing phenomenon on metabolite absorption by the small intestine and the kidney of the rat, using isolated brush-border membrane vesicles prepared from 2 groups, one composed of 2 month, and the other of 24 month, animals. "Overshoot", which is typical of Na(+)-glucose cotransporter activity, disappeared in the duodenum and decreased in the kidney of the old rats. Short-circuiting of vesicles with valinomycin showed that, in the presence of K+ and valinomycin, "overshoot" decreased in both groups by about the same percentage. The Na(+)-dependent uptake of aspartate and phenylalanine showed contrasting pictures in the jejunum and kidney of the aged animals: aspartate transport decreased only in the kidney, while phenylalanine uptake was negatively affected in the jejunum. Na(+)-dependent citrate uptake, studied in renal brush-border membrane vesicles, was lower in the old rats. The Km values determined for Na(+)-dependent D-glucose and citrate uptake in the kidney did not meaningfully differ between the two groups. A continuous decrease in Na(+)-dependent D-glucose and citrate uptake in the rat kidney, during ageing, was demonstrated.