Fine structure of perisinusoidal cells in developing human and mouse liver.

The fine structure of hepatic perisinusoidal cells was studied in human fetuses and in mouse embryos and fetuses. The perisinusoidal cells differed in structure from the sinusoidal lining cells, and occasionally mitosis of perisinusoidal cells was observed suggesting that these cells are independent and self-proliferating at the stage of development studied. Unlike perisinusoidal cells of the normal mature liver, those of the developing liver contained only sparse and small lipid droplets. They possessed a well developed rough endoplasmic reticulum and Golgi complex, and many microtubules. Collagen fibrils appeared in close proximity to perisinusoidal cells. In perisinusoidal cells of the mouse liver development of the rough endoplasmic reticulum and Golgi complex, accumulation of microtubules and increase of collagen fibrils progressed with the time of gestation. The thick cytoplasmic processes of the perisinusoidal cells frequently encircled the sinusoids, and 5-6 nm thick filaments appeared at the cell periphery. Perisinusoidal cells and hepatocytes were frequently linked by junctional elements. These findings strongly suggest that the perisinusoidal cells are responsible for the production of type III collagen. Also they may indicate that these cells reinforce the sinusoides, influence the sinusoidal blood flow by contractile activity and participate in the maintenance of the parenchymal organisation in the developing liver.