Withdrawal of butyrate from the colonic mucosa triggers "mass apoptosis" primarily in the G0/G1 phase of the cell cycle.

Butyrate exerts a trophic effect on the colonocytes and plays a protective role in ulcerative colitis. In the present study, we investigated the effect of butyrate withdrawal on the colonic mucosa of the guinea-pig. The samples were mounted in Ussing chambers and bathed for 45, 60, 90 and 150 min with standard Ringer solution with or without sodium butyrate. Light and electron microscopy for morphology, electrophysiological methods for testing tissue function, histochemistry using the TUNEL method for localization of apoptotic cells and flow cytometry for cell cycle analysis were applied. Morphological observations revealed that butyrate deprivation caused a time-dependent hypoplasia and a rapid triggering of massive apoptosis as substantiated by the TUNEL assay. The epithelium, however, did not show discontinuities at any time. Electrophysiological data confirmed that no leakage of the epithelium had occurred. In the control specimens, the mucosa underwent a moderate reduction in height; apoptotic epithelial cells were infrequently observed. Cell cycle analysis of colonocytes isolated from the mucosa deprived of butyrate revealed a decrease in the percentage of cells occupying each phase of the cycle, especially the G0/G1 phase. Thus, in the absence of butyrate, apoptosis was enhanced and cell renewal reduced. The trophic protective action exerted by butyrate in both physiological and pathological conditions could derive from its capacity to modulate survival and death of colonocytes.