Structural changes in endothelial cells of developing rat liver in the transition from fetal to postnatal life.

Endothelial fenestrae in the microcirculatory walls of fetal (18th and 21st days), newborn (1st and 5th days), and adult rat livers have been studied by an interactive analysis of scanning electron microscope images. Our results show that liver endothelial cells contain different fenestration patterns depending on both their specific location in the liver acinus and the developing period. Portal vessels have a continuous endothelium in both fetal and postnatal livers as in the adult liver. Endothelial cells in central veins change from highly fenestrated in the fetal and neonatal livers to continuous in the adult liver. The number of fenestrae per square micrometer of endothelium is similar along the sinusoidal network of fetal liver, but increases in the zone 3 sinusoids of newborn liver through the adult liver, where it has tripled the number in the zone 1 sinusoids. Porosity values in sinusoidal endothelium progressively decrease in the fetal to postnatal transition due to the disappearance of large fenestrae (greater than 250 nm) which accompanies the residual hemopoietic activity. While we do not known which factors specifically regulate these fenestration patterns, their configuration in fetal liver, before hepatic tissue has assumed its heterogeneous functioning postnatally, is worthy of note.