Microvascular dysfunction in hepatic ischemia-reperfusion injury in pigs

Although hepatic ischemia-reperfusion (I/R) injury has been investigated for more than two decades, histopathological documentation is limited. As a result, three pig livers with I/R injury and three control livers were injected with colored media, cut into 14 segments, and examined by light microscopy together with microscopic map making. In livers with I/R injury, lobules were identified as being occluded or unoccluded. The proportion of the occluded lobules increased in a caudocephalic fashion, while that of the unoccluded lobules decreased (chi(2) for linear trend, P<0.0001). Especially in the occluded lobules, swollen hepatic plates displayed various forms of cellular distortion. Collapsed sinusoids containing leukocyte aggregation and shrunken central veins were observed together with reduced caliber of the contiguous sublobular veins. Portal vein constriction with loosening of the surrounding stroma suggestive of edema and hepatic artery dilation were also seen. Isolated arterioles and transintimal vasal outlets of the hepatic vein's vasa venarum were dilated and frequently observed. In conclusion, I/R injury affected the liver parenchyma, the microvasculature, and its surrounding stroma. The heterogeneous distribution of occluded and unoccluded lobules is suggested due to the difference of vascular structure in various liver segments. The constrictive/obstructive changes in the portosinusoidal-hepatic vascular profile suggest a definite increase in resistance at presinusoidal, sinusoidal, and proximal postsinusoidal levels, resulting in an expansion of the arterial shunt circulation.