Regulation of Amiloride-sensitive Na+ Transport in Immature Rat Distal Colon by Aldosterone

The effects of dietary changes and plasma aldosterone levels on channel-mediated electrogenic amiloride-sensitive Na+ transport were examined in the distal colon of immature and adult rats. The decrease of the short-circuit current after amiloride addition (ISCamil) was used as a measure of electrogenic Na+ absorption. Plasma aldosterone levels were six to eight times higher between d 15 and 30 than in younger suckling or prepubertal rats. In adult rats, the plasma aldosterone was approximately 30 times lower than in young animals kept on the same standard diet. ISCamil followed the developmental profile of plasma aldosterone. ISCamil increased between d 10 and 20, reached a plateau between d 20 and 25, then decreased and entirely disappeared after d 30. ISCamil was zero in adult distal colon but was induced if dietary Na+ intake decreased below 100 mumol Na+/(100 g body wt.d) and plasma aldosterone increased above 200-300 pg/mL. Adrenalectomy, or high Na+ intake, inhibited ISCamil and significantly depressed plasma aldosterone in 20- and 25-d-old rats. Premature weaning decreased ISCamil without appreciable changes in plasma aldosterone in 18- and 20-d-old rats, prolonged suckling inhibited ISCamil and caused a significant depression of plasma aldosterone. We conclude from these results that the postnatal changes of distal colonic Na+ transport are regulated predominantly by circulating aldosterone and dietary Na+ intake.