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Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect
G D Potter1, R Lester, S M Burlingame
1Department of Medicine, University of Texas Medical School, Houston 77225.
Insights
Infant rabbit colons do not respond to taurodeoxycholic acid (TDCA) with secretion, unlike adult colons. This lack of response occurs when the infant ileum cannot yet transport bile acids, suggesting developmental differences in colon function.
Area of Science:
- Gastroenterology
- Physiology
- Developmental Biology
Background:
- Impaired ileal bile acid absorption in adults causes colonic fluid secretion and diarrhea.
- The infant ileum exhibits immature bile acid transport capabilities.
Purpose of the Study:
- To investigate the effect of taurodeoxycholic acid (TDCA) on ion transport in the distal colon of infant rabbits.
- To compare the response of infant and adult rabbit colon to TDCA exposure.
Main Methods:
- Distal colons from infant (7-10 days old) and adult rabbits were mounted in Ussing chambers.
- Mucosal or serosal surfaces were exposed to varying concentrations of TDCA.
- Short-circuit current (Isc) and ion flux were measured to assess ion transport.
- Microscopy was used to evaluate epithelial integrity.
Main Results:
- Adult rabbit colon showed increased short-circuit current and chloride secretion in response to TDCA.
- Infant rabbit colon exhibited a reduction in Isc with TDCA exposure, without altered ion flux.
- Infant colon remained responsive to other secretagogues like theophylline and carbachol.
- TDCA did not cause significant epithelial damage in infant colon.
Conclusions:
- The infant rabbit distal colon lacks a secretory response to TDCA during the neonatal period.
- This developmental difference in colonic response to bile acids correlates with the ileum's inability to transport bile acids in infants.
- The findings highlight developmental changes in intestinal ion transport regulation.
Abstract:
Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.