Increased intracellular content of enteroglucagon in proximal colon is related to intestinal adaptation to germ-free status

Changes in the frequency of endocrine cells are evidence of intestinal adaptation to germ-free (GF) status. Not only the distribution of these cells along the intestine, but also the differences in intracellular content of these regulatory peptides may be explored to explain functional and structural aspects of GF intestinal adaptation. Focusing on the endocrine L-cells, we analyzed the intracellular content of enteroglucagon (EG) and peptide YY (PYY) throughout the intestine of the 14 GF and 14 conventional (CV) mice by using immunohistochemistry and the supra-optimal dilution technique. The percentage of EG-immunoreactive cells, but not of PYY-immunoreactive cells stained at supra-optimal dilution was significantly higher in the proximal colon of GF mice than in the CV counterparts (P < 0.05). Since the content of co-stored PYY did not differ between GF and CV mice, the higher content of EG was compatible with a selective cellular response. Moreover, in the cecum of GF mice, the density of EG-immunoreactive cells was significantly higher than that of PYY-immunoreactive cells (P < 0.05). These results are consistent with preferential production of EG by L-cells at the expense of PYY in the proximal colon and in the enlarged cecum of GF mice. In addition, they may reflect the dynamics of the GF intestinal epithelium and/or be correlated with the higher serum levels of these peptides. The role of endocrine cells needs to be better studied in human and other experimental adaptative conditions in order to elucidate the regulatory mechanisms of intestinal functions.