Persistence of impaired hepatic microcirculation after nonarterialized liver transplantation in the rat

The nonarterialized orthotopic rat liver transplant (NOLT) is a frequently used model in transplantation research that was recently used to investigate microcirculatory alterations during acute rejection, which occurs within 7 days. The present study sought to establish whether NOLT represents a reasonable model for the study of the hepatic microcirculation beyond the immediate reperfusion phase.

Three groups of animals were studied: sham-operated control (n = 8), NOLT (n = 7) and arterialized orthotopic liver transplant (AOLT; n = 8). The hepatic microcirculation was investigated by intravital fluorescence microscopy and laser Doppler flowmetry (LDF) on day 7 postoperatively. Liver histology and plasma levels of liver enzymes were also assessed.

Plasma levels of aspartate aminotransferase, alanine aminotransferase, and bilirubin were significantly higher in NOLT than in AOLT and control animals. The low LDF signal recorded from the surface of the NOLT liver (92 +/- 25 vs. 210 +/- 25 and 172 +/- 14 PU in AOLT and control liver, respectively; p < 0.05) was associated with heterogeneous perfusion at both the lobular and sinusoidal levels (density of perfused sinusoids (n/40,000 microm(2)): 5.8 +/- 0.8, 8.1 +/- 0.3, 8.0 +/- 0.3, respectively; p < 0.05). The percentage of hyperfluorescent Ho342-stained hepatocytes (apoptotic) ranged between 2 and 5% and was not significantly different between groups. The lack of post-transplant arterial supply was associated with an increased hepatic cord width-to-sinusoid diameter ratio (3.77 +/- 0.3, 2.02 +/- 0.04, and 1.72 +/- 0.06 in NOLT, AOLT, and control animals, respectively; p < 0.001 vs. control and AOLT) and increased temporary leukocyte adherence to the walls of the terminal hepatic venules. Intense vitamin A autofluorescence around shunt- and large-diameter, slow-velocity vessels was occasionally encountered in the NOLT liver, which coincided with mild fibrosis and bile ductular proliferation. In the well-perfused areas, both AOLT and NOLT were associated with a significant rise in sinusoidal RBC(vel), which was more marked in the NOLT group.

Our data indicate that NOLT represents an inappropriate model for the long-term study of the hepatic microcirculation. Lack of a post-transplant arterial supply may lead to persistent microvascular perfusion failure, hepatocellular/endothelial cell swelling, and microvascular anomalies related to bile duct injury. Recovery from microcirculatory alterations induced by cold preservation/reperfusion injury appears to depend on an intact hepatic arterial blood supply.