Luminal mucin in the large intestine of mice, rats and guinea pigs.

The luminal and epithelial mucin was studied histochemically in the large intestine of mice (Mus musculus), rats (Rattus rattus) and guinea pigs (Cavia porcellus) using freeze-substitution and vapor-fixation methods. Neutral mucin decreased and acid mucin increased in the epithelium from the cecum to the distal colon. Vacuolated cells contained more acid mucin than goblet cells. Luminal mucin always contained neutral mucin, which formed the main constituents in the cecum and in the proximal colon. Sialo-mucin increased from the cecum to the distal colon. Sulfo-mucin appeared only in the distal colon. Except in the cecum a luminal mucin layer (LML) was found at the epithelial surface. In the proximal colon LML was not entirely continuous and varied in composition and thickness (182.4 +/- 170.1, 150.5 +/- 110.4, 30.0 +/- 28.9 (micrometer), in mice, rats and guinea pigs, respectively), and contained many bacteria. In the distal colon LML was compact, homogeneous and thin (33.6 +/- 18.8, 16.1 +/- 7.3, 29.1 +/- 20.0 (micrometer), in mice, rats and guinea pigs, respectively) containing few bacteria. Possible functions of the luminal mucin and their regional differentiations were discussed.