Congenital portacaval shunt in rats: liver adaptation to lack of portal vein--a light and electron microscopic study.

In five rats with congenital portacaval shunt, liver atrophy, hyperplastic foci in the periportal zone, atrophic hepatocytes in the centrolobular zone, well-preserved hepatocyte ultrastructure with abundant rough endoplasmic reticulum, packed mitochondria and numerous peroxisomes were observed as in surgical portacaval shunt. However, portal triads were abnormal in contrast to surgical shunt. In large portal triads, hepatic arteries were prominent, bile ducts numerous and portal veins were lacking. Instead, small or large capillaries were seen in the portal tracts usually at the periphery. These capillaries appeared to be in continuity with nearby sinusoids presenting the ultrastructural characteristics of capillaries. These observations suggest that absence of the portal vein is compensated by formation of neocapillaries. It is assumed that these capillaries originate from periportal sinusoids and are necessary to distribute blood to all sinusoids and form a reservoir to lower arterial pressure.