Increased sinusoidal wall permeability and liver fatty change after two-thirds hepatectomy: an ultrastructural study in the rat.

Accumulation of lipids in the hepatocyte cytoplasm after partial hepatectomy (PH) has long been recognized, but the mechanism behind this phenomenon is still poorly understood. In this study, rats subjected to a standard two-thirds PH showed early and marked increase in portal venous pressure (P < .01). On scanning electron microscopy, the regenerating liver fixed by portal perfusion under hemodynamic conditions identical to that found in vivo during the first 24 hours showed a significant (P < .01) 10-fold increase in the sinusoidal wall porosity (percentage open area by fenestrations). This was paralleled by the disappearance of the sieve-plate arrangement of small fenestrations and by a significant decrease in the number of fenestrations per micrometers squared of sinusoidal surface at 6 (P < .01) and 12 hours (P < .05). In addition, there were major changes in the frequency and distribution of all three classes of fenestrations. At 6 and 12 hours, there was a marked decrease of small class 1 fenestrations and a marked increase of intermediate class 2 fenestrations and large class 3 fenestrations (P < .0001). A concurrent accumulation of lipid droplets in the hepatocyte cytoplasm produced a 20-fold increase in the hepatocyte total lipid volume. A statistically significant linear correlation (r = 0.907; P < .01) was found between the amount of intracellular lipids and the data quantitating the changes in porosity of liver sinusoids at 24 hours. It is concluded that an increased sinusoidal wall permeability to lipids may be the primum moves in the pathogenesis of transient liver fatty change after PH in the rat.