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 (I-SC(amil)) 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. I-SC(amil) followed the developmental profile of plasma aldosterone. I-SC(amil) increased between d 10 and 20, reached a plateau between d 20 and 25, then decreased and entirely disappeared after d 30. I-SC(amil) was zero in adult distal colon but was induced if dietary Na+ intake decreased below 100 mu mol Na+/(100 g body wt . d) and plasma aldosterone increased above 200-300 pg/mL. Adrenalectomy, or high Na+ intake, inhibited I-SC (amil) and significantly depressed plasma aldosterone in 20- and 25-d-old rats. Premature weaning decreased I-SC(amil) without appreciable changes in plasma aldosterone in 18- and 20-d-old rats, prolonged suckling inhibited I-SC(amil) 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.