Bax is required for increased enterocyte apoptosis after massive small bowel resection

Background. Massive small bowel resection (SBR) increases rates of both ent erocyte proliferation and apoptosis. Previous studies have demonstrated inc reased intestinal expression of proapoptotic bar mRNA and protein, as well as the appearance of an 18-kd bar cleavage product within 12 hours of SBR. This study tested the hypothesis that bar is required for postresection inc reases in enterocyte apoptosis. Methods. Male bax-null and C57Bl/6 (control) mice underwent either a 50% pr oximal SBR or sham operation. After 3 days, the remnant ileum was harvested and weighted. Apoptotic indexes, proliferation indexes, villus heights, an d crypt depths were determined. Results. The usual adaptive increases in ileal wet weight, crypt depth, and rate of proliferation occurred in both the control and bar-null mice. Rese ction significantly increased the rate of apoptosis in the control mice; ho wever, it failed to alter the apoptotic index in the bar-null mice. Conclusions. Bar is necessary for the increase in apoptosis that occurs aft er SBR, but its absence has no significant effect on short-term adaptation. These findings suggest that enterocyte proliferation and apoptosis are dif ferentially regulated during intestinal adaptation.