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In vivo intestinal bicarbonate transport in infant rats
Insights
Bicarbonate absorption in rat jejunum decreases with age, while ileal transport shifts from absorption to secretion. Metabolic acidosis significantly alters bicarbonate transport in both segments.
Area of Science:
- Physiology
- Gastroenterology
- Developmental Biology
Background:
- Bicarbonate (HCO3-) transport is crucial for maintaining intestinal homeostasis.
- Age-related changes in intestinal function are not fully understood.
- Understanding bicarbonate transport dynamics is vital for pediatric and geriatric gastrointestinal health.
Purpose of the Study:
- To investigate age-dependent changes in jejunal and ileal bicarbonate transport in rats.
- To examine the effects of metabolic acidosis on bicarbonate transport.
- To assess the influence of glucose and acetazolamide on bicarbonate absorption.
Main Methods:
- In vivo, one-pass perfusion technique used in two-, three-, and eight-week-old rats.
- Segments of jejunum and ileum were perfused with isotonic and hypertonic solutions.
- Net bicarbonate absorption and secretion rates were quantified.
Main Results:
- Jejunal bicarbonate absorption was significantly higher in younger rats (2-3 weeks) compared to older rats (8 weeks).
- Ileal bicarbonate transport showed age-dependent variability, with net absorption in younger rats and net secretion in older rats.
- Perfusion with a hypertonic solution induced metabolic acidosis in younger rats, leading to increased bicarbonate secretion in both jejunum and ileum.
Conclusions:
- Intestinal bicarbonate transport exhibits significant age-related plasticity.
- Metabolic acidosis profoundly impacts bicarbonate secretion, particularly in younger animals.
- Glucose and acetazolamide did not significantly alter net bicarbonate absorption in this model.
Abstract:
Transport of bicarbonate (HCO3-) was studied in segments of the jejunum and ileum in two-, three-, and eight-wk-old rats using and in vivo, one-pass perfusion technique. From isotonic solutions the net absorption of HCO3-(/B5mol/hr/g dry wt) in the jejunal segments was about twice as gret (P-0.01) in the two- and three- as in the eight-wk-old rats. In ileal segments, HCO3-transport was quite variable; in the two- and three-wk-old rats, there was net absorption, whereas in the eight-wk-old rats, there was net secretion. In both segments, net absorption was unaffected by addition of glucose (5 mmoles/liter), or acetazolamide (10 mmoles/liter) to the perfusion solution. Perfusion of a hypertonic old rats induced metabolic acidosis, which was associated with net secretion of relatively large amounts of bicarbonate into the lumen of both segments. Perfusion of the hypertonic solution in the eight-wk-old rats did not change blood acid-base status. In these rats, net absorption of bicarbonate in the jejunum was decreased, and net secretion in the ileum was enhanced in comparison to values noted during perfusion of the isotonic solution.