Immunocytochemical study of intestinal endocrine cells in germ-free mice

Morphological and functional modifications have been described in the gastrointestinal tract of germ-free rodents in comparison to their conventional counterparts. These differences have been related to the absence of normal flora, but peptides and biogenic amines may also be involved. Enteroglucagon-, peptide YY-, somatostatin-, serotonin-, neurotensin-, chole-cystokinin-, and secretin-producing cells were studied by immunocytochemistry in the ileum, cecum and colon of 10 germ-free, 10 conventional and 5 conventionalized CFW adult male mice. In the cecum and colon of germfree mice, enteroglucagon- and peptide YY-positive cells appeared enlarged, were globular in shape and strongly immunostained. Enlarged and strongly immunostained serotonin- and neurotensin-positive cells were also seen in some germ-free mice. Somatostatin-positive cells and all the endocrine cells of the ileum were similar in the 3 groups, and no cholecystokinin- or secretin-positive cells were observed. Our results are consistent with higher enteroglucagon and peptide YY production in germ-free mice that may be related to the lower cellular renewal rates and slower gastrointestinal transit reported in these animals. Locally produced biogenic amines and peptides may be important factors in the mediation of the effect of the intestinal flora on gastrointestinal structure and function and germ-free mice seem to be a good model for the study of the mechanisms involved.