Upregulation of apolipoprotein A-IV gene expression in residual ileum after massive small bowel resection requires the biliary secretion in rats.

Small bowel resection results in adaptation of residual intestine, but little is known about the postresectional response of apolipoproteins synthesized mainly in the small intestine. We have investigated the postresectional response of apolipoprotein A-1 and A-IV gene expression in residual ileum and assessed the mechanism of response, particularly the role of biliary secretion. Time course of changes in apolipoprotein A-1 and A-IV mRNA levels was examined by Northern blotting in the residual terminal ileum for 24 hr after 85% jejunoileal resection in fasted rats. Localization of these mRNAs was studied using in situ hybridization histochemistry. Effect of biliary diversion on the postresectional response of mRNAs and proteins was estimated by Northern blotting and immunoblotting, respectively. Apolipoprotein A-IV mRNA began increasing at 1 hr postresection, achieved a maximum by 12 hr (5-fold increase) and remained stable to 24 hr, while apolipoprotein A-1 mRNA did not change. Apolipoprotein A-IV mRNA accumulated predominantly in the upper part of ileal villi and increased its intensity postresection, and apolipoprotein A-1 mRNA was detected in the villus base to tip. The postresectional increase in apolipoprotein A-IV MRNA and protein was completely abolished by concurrent biliary diversion. The results suggest that the enterocytes in the ileal villi rapidly adapt to massive small bowel resection by increase in apolipoprotein A-IV gene expression which is mediated by biliary constituents but not luminal nutrients.