WITHDRAWAL OF BUTYRATE FROM THE COLONIC MUCOSA TRIGGERS MASS APOPTOSIS PRIMARILY IN THE G(0) G(1), PHASE OF THE CELL-CYCLE/

Butyrate exerts a trophic effect on the colonocytes and plays a protec tive 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, 6 0, 90 and 150 min with standard Ringer solution with or without sodium butyrate. Light and electron microscopy for morphology, electrophysio logical methods for testing tissue function, histochemistry using the TUNEL method for localization of apoptotic cells and flow cytometry fo r cell cycle analysis were applied. Morphological observations reveale d that butyrate deprivation caused a time-dependent hypoplasia and a r apid triggering of massive apoptosis as substantiated by the TUNEL ass ay. 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 modera te reduction in height; apoptotic epithelial cells were infrequently o bserved. Cell cycle analysis of co lonocytes isolated from the mucosa deprived of butyrate revealed a decrease in the percentage of cells oc cupying each phase of the cycle, especially the G(0)/G(1) phase. Thus, in the absence of butyrate, apoptosis was enhanced and cell renewal r educed. The trophic protective action exerted by butyrate in both phys iological and pathological conditions could derive from its capacity t o modulate survival and death of colonocytes.