Histamine and mast cell distribution in the gastrointestinal wall of the rat: comparison between germ-free and conventional rats.

The distributions of histamine and mast cells in the intestinal mucosa have been studied in conventional (CV) and germ-free (GF) rats. Both distributions do not appear to be uniform throughout the gastrointestinal tract. The presence of digestive microflora influences these distributions: more histamine and mucosal mast cells are present in the small intestine of CV than in GF rats. Paradoxically the opposite is observed in the large intestine. Differences in mast cell counts in the crypt area of the small intestine (higher in CV than in GF rats) confirm the role of microflora on crypt cell proliferation due to a mild chronic inflammation. In the large intestine, however, the microflora appears to have a more complex influence and could act indirectly on histamine turnover.