Development of colonic fluid and electrolyte transport: influence of weaning pattern.

The purpose of this study was to investigate the normal postnatal development of electrolyte and water transport in the large intestines of rats aged 10-20 days, to focus on the events taking place around the time of weaning, and to study the influence of different feeding patterns at the time of weaning on the normal development of the transport mechanisms in the large intestine. The net absorption of sodium, potassium, and water was investigated by using in vivo luminal isotonic perfusion in rats aged 12-40 days. The activity of the active transport enzyme Na-KATPase in the colonic mucosa of rats aged 10-40 days was determined. We found a significant decrease in the net absorption of electrolytes and water that was greatest around the time of weaning. Since the NaKATPase activity was lower in 10-16-day-old rats than in 40-day-old rats, we suggest that the high sodium and water uptake in the colon of suckling rats is independent of the sodium pump. Changes in the feeding patterns around the time of weaning, such as prolonged suckling, were associated with a significantly higher net absorption of electrolytes and water than in rats that were normally weaned at 20 days of age. The Na-KATPase activity was not significantly influenced by the weaning pattern.