MICROCIRCULATORY FAILURE DETERMINES LETHAL HEPATOCYTE INJURY IN ISCHEMIC-REPERFUSED RAT LIVERS

The contribution of microcirculatory failure to ischemia/reperfusion i njury in isolated perfused rat livers was investigated using intravita l epifluorescence videomicroscopy. The degree of microvascular shut-do wn during reperfusion was modulated by the reperfusion conditions: flo w-controlled (10 ml/min), in which microcirculatory failure is minimiz ed by maintenance of constant flow through the liver, and pressure-con trolled, in which microvascular shut-down is allowed to occur. Livers underwent 60 min of ischemia, 90 min of ischemia, or no ischemia (cont rol). Perfused sinusoids and dead hepatocytes were quantified in 10 st andardized microsopic fields (9000 mum2) per liver during off-line vid eo playback. With flow-controlled reperfusion, microvascular (sinusoid ) shut-down was largely avoided; a maximum of 21% of the sinusoids fai led to conduct flow. Pressure-controlled reperfusion, however, resulte d in early and severe shut-down. A significant decrease of approximate ly 20-30% was found after 60 min of ischemia and 30 min of reperfusion , while, after 90-min ischemia and 90-min reperfusion, 90% of the sinu soids failed to conduct flow. The appearance of dead hepatocytes corre lated well with the number of perfused sinusoids (r = -0.78 for flow c ontrolled, r = -0.97 for pressure-controlled). Only an occasional dead hepatocyte was observed with control perfusion, while up to 50% stain ed with propidium iodide following 90-min ischemia and 90-min reperfus ion under pressure-controlled conditions. These results indicate that loss of sinusoidal flow can be ameliorated by flow-controlled reperfus ion; moreover, hepatocyte necrosis during reperfusion is highly depend ent upon the integrity of the microcirculation.