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Mechanisms for colonic sodium transport during ontogeny: loss of an amiloride-sensitive sodium pathway
Y Finkel1, A C Eklöf, A Aperia
1Department of Pediatrics, St. Göran's Children's Hospital, Karolinska Institute, Stockholm, Sweden.
Insights
Young rats absorb more sodium and water through their colons than adult rats. This difference is due to developmental changes in sodium transport mechanisms, particularly amiloride-sensitive uptake in developing colons.
Area of Science:
- Physiology
- Developmental Biology
- Gastroenterology
Background:
- Net colonic sodium and fluid absorption is higher in suckling and weanling rats compared to adult rats.
- Understanding the developmental changes in colonic transport mechanisms is crucial for explaining growth differences.
Purpose of the Study:
- To investigate the mechanisms underlying the age-dependent differences in net colonic sodium and fluid absorption in rats.
Main Methods:
- In vivo colon perfusion was performed in rats aged 14 to 80 days.
- The effects of amiloride and cyclic adenosine monophosphate (cAMP) on net sodium (Na) and water transport were assessed.
Main Results:
- Net Na and water uptake decreased exponentially with age, from 14 to 80 days.
- Amiloride reversed net Na transport to secretion in 20-day-old rats but had no effect in 40-day-old rats.
- cAMP increased net Na uptake in young rats and decreased it in older rats, with no effect in amiloride-treated young rats.
Conclusions:
- Significant quantitative and regulatory changes occur in colonic Na transport pathways during development.
- The high amiloride-sensitive sodium uptake in the young colon is likely adaptive, supporting sodium accretion for rapid postnatal growth.
Abstract:
Net colonic sodium and fluid absorption is higher in suckling and weanling rats than in adult rats. This study was undertaken to investigate the mechanisms behind these differences. In vivo perfusion of the colon was performed in 14- to 80-day-old rats. Net Na and water uptake decreased exponentially from 14 to 80 days of age. Na uptake was 402 +/- 73 micrograms Eq/min/g DT in 20-day-old rats and 116 +/- 6 mu Eq/min/g DT in 40-day-old rats. After amiloride treatment, net Na transport was reversed to net secretion (-79 +/- 36 mu Eq/min/g DT) in 20-day-old rats. Amiloride had no effect on the net Na transport in 40-day-old rats. cAMP stimulation significantly increased the net Na uptake in 20-day-old rats and significantly reduced the net Na uptake in 80-day-old rats. cAMP did not increase the net uptake in amiloride-treated 20-day-old rats. We conclude that there are both quantitative and regulatory changes in the pathways for colonic Na transport during development, and we speculate that the large amiloride-sensitive sodium uptake in the young colon is adaptive and contributes to the sodium accretion necessary for rapid growth during late postnatal development.