Effect of massive small bowel resection on the Bax/Bcl-w ratio and enterocyte apoptosis

Following small bowel resection (SBR), the remnant intestine undergoes adap tation. Enterocyte proliferation is increased and counterbalanced by increa sed rates of apoptosis. To elucidate a mechanism for in creased enterocyte apoptosis, this study tested the hypothesis that the ratio between pro-apop totic Bax and pro-survival Bcl-w correlates with the apoptosis that occurs following SBR. Mice (C57Bl/6; n = 76) underwent a 50% proximal SBR or sham operation. After 12 hours and 1, 2, 3, and 7 days, the ileum was removed, t he apoptotic index (apoptotic bodies/crypt) was recorded, and the messenger RNA and protein for Bax and Bcl-w were quantified. The apoptotic index was equivalent in the sham and SBR mice at 12 hours; however, it was significa ntly elevated following SBR at every other day measured. The ratio of Bar t o Bcl-w messenger RNA relative to sham operation increased after SBR at 24 hours, decreased by day 3, and returned to baseline levels by 1 week. The p rotein ratio showed an increase by day 1, which remained elevated through d ay 7. An augmented ratio of Bax to Bcl-w messenger RNA and protein correspo nded with the increase in enterocyte apoptosis. Alterations in the expressi on ratio of these genes may play a role in establishing a new homeostatic s et point between proliferation and apoptosis during adaptation.