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Comparative Study
. 2000 Feb;46(2):218-24.
doi: 10.1136/gut.46.2.218.

Mucin secretion is modulated by luminal factors in the isolated vascularly perfused rat colon

A Barcelo  1 , J Claustre, F Moro, J A Chayvialle, J C Cuber, P Plaisancié
Affiliations
Comparative Study

Mucin secretion is modulated by luminal factors in the isolated vascularly perfused rat colon

A Barcelo et al. Gut. 2000 Feb.

Abstract

Background: Mucins play an important protective role in the colonic mucosa. Luminal factors modulating colonic mucus release have been not fully identified.

Aim: To determine the effect of some dietary compounds on mucus discharge in rat colon.

Methods: An isolated vascularly perfused rat colon model was used. Mucus secretion was induced by a variety of luminal factors administered as a bolus of 1 ml for 30 minutes in the colonic loop. Mucin release was evaluated using a sandwich enzyme linked immunosorbent assay supported by histological analysis.

Results: The three dietary fibres tested in this study (pectin, gum arabic, and cellulose) did not provoke mucus secretion. Luminal administration of sodium alginate (an algal polysaccharide used as a food additive) or ulvan (a sulphated algal polymer) induced a dose dependent increase in mucin discharge over the concentration range 1-25 mg/l (p<0.05 for 25 mg/l alginate and p<0.05 for 10 and 25 mg/l ulvan). Glucuronic acid and galacturonic acid, which are major constituents of a variety of fibres, produced significant mucin secretion (p<0.05). Hydrogen sulphide and mercaptoacetate, two sulphides produced in the colonic lumen by microbial fermentation of sulphated polysaccharides, did not modify mucin secretion. Among the short chain fatty acids, acetate (5-100 mM) induced a dose dependent release of mucus (p<0.05 for 100 mM acetate). Interestingly, butyrate at a concentration of 5 mM produced colonic mucin secretion (p<0.05), but increasing its concentration to 100 mM provoked a gradual decrease in mucus discharge. Propionate (5-100 mM) did not induce mucin release. Several dietary phenolic compounds (quercetin, epicatechin, resveratrol) did not provoke mucus discharge.

Conclusions: Two algal polysaccharides (alginate and ulvan), two uronic acids (glucuronic acid and galacturonic acid), and the short chain fatty acids acetate and butyrate induce mucin secretion in rat colon. Taken together, these data suggest that some food constituents and their fermentation products may regulate the secretory function of colonic goblet cells.

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Figures

Figure 1
Figure 1
Colonic mucin-like immunoreactivity (µg/mg DNA) to luminal administration of increasing amounts of ulvan in the isolated perfused rat colon. The secretion of mucin was evaluated by a sandwich ELISA as described in Materials and methods. Data are mean (SE). *p<0.05 v controls.
Figure 2
Figure 2
Thin section histology of perfused rat colon. Bar = 10 µm. (A) Crypt of a control preparation. This colonic loop underwent a 10 minute equilibration period, followed by a 30 minute period during which 1 ml isotonic saline was administered to the lumen of the colonic loop. Goblet cells (alcian blue/periodic acid-Schiff stained) are filled with mucus. Arrows indicate examples of stained mucus cells. (B) Colonic crypt after administration of ulvan (25 mg/l) for 30 minutes. Stained mucus cells exhibit deep apical membrane cavitation (arrow) from which streams of stained mucus (asterisk) emerged to join the mucus blanket in the crypt lumen. (C) Crypt of perfused rat colon after 30 minutes of stimulation with 5 mM butyrate. Numerous mucus cells with deep cavitation of the apical surface are easily observed.
Figure 3
Figure 3
Effects of two uronic acids on colonic mucus cells. (A) Effects of glucuronic acid (25 mg/l) and galacturonic acid (25 mg/l) on luminal mucin secretion in the isolated vascularly perfused rat colon. *p<0.05 v the control group. (B) Effects of glucuronic acid (25 mg/l) and galacturonic acid (25 mg/l) on the percentage of cavitated mucus cells. The colonic mucosa was analysed by light microscopy as described in Materials and methods. Some 500-1000 stained mucus cells per slide were evaluated for the presence of apical membrane cavitation. A mucus cell with clear apical indentation into the intracellular store was taken as showing signs of cavitation. Data are mean (SE). *p<0.05 compared with the control group.
Figure 4
Figure 4
Effects of increasing the concentration of butyrate on colonic mucin secretion as evaluated by using a sandwich enzyme linked immunosorbent assay and by histological analysis. Data are mean (SE). *p<0.05 v the control group.
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