Effects Of Ischemic Preconditioning With Different Pressures And Cycle Times On Hepatic And Kidney Ischemia/Reperfusion Injury Model Of CO₂ Pneumoperitoneum In Rats

Objective: To investigate the protective effects of ischemic preconditioning with different CO₂ pressures and cycle times of on hepatic and kidney ischemia/reperfusion injury in a rat model of CO₂ pneumoperitoneum.Methods: Part One: Thirty healthy male SD rats were randomly divided into five groups, control group（C Group） was subjected to sham operation, the pneumoperitoneum group（Pp Group） was subjected to a 60-minutes pneumoperitoneum with a pressure of 10 mm Hg, and the ischemic preconditioning groups（IP Groups） were subjected to ischemic preconditioning prior to the induction of pneumoperitoneum. The ischemic preconditioning was defined as three cycles of 5-minutes pneumoperitoneum with 5 mm Hg（L-IP Group）, 10 mm Hg（M-IP Group） or 15 mm Hg（H-IP Group） intra-abdominal pressure each, followed immediately by a 5-minutes desufflation. Sixty minutes after deflation, hepatic tissues were collected at the end of the experiment to observe the pathological variations with HE staining. Malondialdehyde（MDA）, superoxide dismutase（SOD） and total antioxidant capacity（T-AOC） were measured by spectrophotometry. Protein expressions of Bcl-2 and Bax in the hepatic tissues were detected by immunohistochemistry and western blot. Meanwhile, the expression of interleukin-1β（IL-1β） and interleukin-6（IL-6） m RNA were determined by RT-PCR.Part Two:Thirty male SD rats were randomly divided into five groups（n=6 in each group）: Sham group, Pneumoperitoneum（Pp） group, Ischemic preconditioning group 1（IP1）, Ischemia preconditioning group 3（IP3）, and Ischemic preconditioning group 5（IP5）. Sham group was subjected to sham operation. Other groups were subjected to CO₂ pneumoperitoneum for 60 minutes with 10 mm Hg intra-abdominal pressure and then deflation. IP1, IP3 and IP5 group were subjected to preconditioning prior to pneumoperitoneum/deflation, which was consisted of 5 minutes of pneumoperitoneum, followed immediately by 5 minutes of deflation, and respectively for 1 cycle or 3,5 cycles. Sixty minutes after deflation, the kidney pathological changes were observed by using light microscopy. Kidney tissue samples were also taken for measuring of MDA, SOD and T-AOC. The expression of Bcl-2 and Bax were determined by immunohistochemistry and western blot.Results: Part One: Pathological changes of hepatic injury were found in both Pp group and IP groups, but the injury was milder in IP groups than that in Pp group. The activity of SOD and T-AOC were significantly higher and MDA were significantly lower in all IP groups than that in Pp group（P<0.05）, the expression of Bcl-2 protein elevated, and the expression of Bax protein and IL-1β、IL-6 m RNA decreased, especially in M-IP group.Part Two:Microscopic examination showed edema, degeneration and necrosis of ischemia renal tubule endothelial cells, tubular ectasia, congestion, and infiltration of neutrophils in Pp group. Histological damage of tubular in IP1, IP3, IP5 groups were much lighter than that of Pp group（P<0.05）. Compared with Pp group, levels of MDA in kidney were remarkably decreased in IP1, IP3 and IP5 groups,whereas kindey SOD and T-AOC values increased significantly（P<0.05）. Immunohistochemistry and western blot results showed an increase in the expression of Bcl-2 and a decrease in the expression of Bax in IP3 group, as compared to Pp group（P <0.05）.Conclusion: CO₂ ischemic preconditioning had protective effects on liver and kidney against ischemia/reperfusion injury in a rat model of CO₂ pneumoperitoneum in pressure/time dependent manner, and 10 mm Hg intra-abdominal pressures was more effective in reducing hepatic injury, 3 cycles was more effective in reducing kidney injury. The reduction of oxygen free radicals, up-regulation of Bcl-2 protein expression and down-regulation of Bax protein and IL-1β, IL-6 m RNA expression were involved in the underlying mechanism.