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Abstract
Expression of endogenous heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), a proven intestinal cytoprotective molecule, was examined in intestinal epithelial cells (IEC) in vitro, and in intestine undergoing ischemia/reperfusion (I/R) injury in vivo. In vitro, cells were exposed to anoxia for 90 min followed by reoxygenation for 1-3 h (A/R). In vivo, total midgut I/R injury was produced in rats by occlusion of the superior mesenteric artery for 30 or 90 min followed by reperfusion for 4 h. In situ hybridization and immunohistochemistry were used to study HB-EGF mRNA expression and protein production. In vitro, normal IEC had no detectable HB-EGF mRNA or protein expression. After anoxia, cells expressed HB-EGF mRNA and protein, with expression reaching a peak 2-3 h after reoxygenation. In vivo, only very low levels of HB-EGF mRNA and no detectable protein were found in normal intestine. Four hours after I/R, HB-EGF protein was detected in villous epithelia subjected to 30 min but not 90 min of ischemia, whereas HB-EGF mRNA was highly expressed after both ischemic intervals. Endogenous HB-EGF is immediately upregulated in IEC after A/R injury and in intestine after I/R injury. Thus, HB-EGF acts as an immediate early gene under these conditions.