Ischemia-reperfusion injury in rats affects hydraulic conductivity in two phases that are temporally and mechanistically separate

Abstract

Ischemia-reperfusion (IR) injury is a major insult to postcapillary venules. We hypothesized that IR increases postcapillary venular hydraulic conductivity and that IR-mediated changes in hydraulic conductivity result from temporally and mechanistically separate processes. A microcannulation technique was used to determine hydraulic conductivity (L_p) in rat mesenteric postcapillary venules serially throughout ischemia (45 min) and reperfusion (5 h) induced by superior mesenteric artery occlusion and release. Mesenteric IR resulted in a biphasic increase in L_p. White blood cell (WBC) adhesion slowly increased with maximal adhesion corresponding to the second peak ( P < 0.005). After IR, tissue was harvested for RT-PCR analysis of ICAM-1, E-selectin, and P-selectin mRNA. Intercellular adhesion molecule-1 (ICAM-1) mRNA in the gut showed the most significant upregulation. Quantitative real-time PCR revealed that ICAM-1 mRNA was upregulated 60-fold in the gut. An ICAM-1 antibody was therefore used to determine the effect of WBC adhesion on L_pduring IR. ICAM-1 inhibition attenuated L_pduring the first peak and completely blocked the second peak ( P < 0.005). When rats were fed a tungsten diet to inhibit xanthine oxidase and then underwent IR, L_pwas dramatically attenuated during the first peak and mildly decreased the second peak ( P < 0.005). Inhibition of xanthine oxidase by oxypurinol decreased L_pduring IR by over 60% ( P < 0.002). Tempol, a superoxide dismutase mimetic, decreased L_pduring IR by over 30% ( P < 0.01). We conclude that IR induces a biphasic increase in postcapillary hydraulic conductivity. Reactive oxygen species impact both the first transient peak and the sustained second peak. However, the second peak is also dependent on WBC-endothelial cell adhesion. These serial measurements of postcapillary hydraulic conductivity may lead the way for optimal timing of pharmaceutical therapies in IR injury.