Effect of ischemic preconditioning on rat liver microcirculation monitored with laser Doppler flowmetry.

Background: Ischemic preconditioning (IP) may protect the liver from ischemia-reperfusion (I-R) injury during liver resection. This study investigated the effect of IP on hepatic microcirculation (HM) and analyzed the objective parameters of the HM using laser Doppler flowmetry (LDF).
Methods: We used male Wistar rats (250-280 g) that underwent normothermic, segmental liver ischemia. The animals were divided into eight groups: 30, 45, 60, and 90 min of ischemia with, or without, IP. Five minutes ischemia and 10 min reperfusion, in two cycles, were used to elicit IP. Changes of the hepatic microcirculation were studied by LDF with on-line computer monitoring and processing. Histological alterations, liver enzymes, bilirubin, and TNF-alpha level were all measured simultaneously.
Results: Reperfusion was assessed by post-ischemia flux plateau maximum (PM) and by the area under the reperfusion-curve (RA). Both PM and RA are inversely correlated with the duration of ischemia. The groups with IP had significantly (P < 0.05) higher flow values than groups without preconditioning. IP before liver ischemia resulted in significantly (P < 0.05) lower TNF-alpha levels at the end of the 30-min reperfusion. Lower serum ALT, LDH, and bilirubin levels could only be observed at 45 and 60 min I-R during the first post-operative day. On the seventh post-operative day there were no significant differences between the I-R and IP + IR groups in any of these parameters.
Conclusion: The benefit of ischemic preconditioning on hepatic microcirculation was well demonstrated with this method, which has never been described before, in this context. Changes in hepatic microcirculation can be precisely investigated by laser Doppler flowmetry using the standardization and transformation described in this paper.