A study of liver regeneration using fetal rat liver tissue transplanted into the spleen.

The liver morphology of fetal hepatic tissue transplanted into an ectopic location was investigated over one year period. Fetal liver fragments prepared from a maternal rat on the 18th or 19th day of pregnancy were injected into the splenic parenchyma of syngeneic rats using a 21 gauge needle. Histologically, the fetal liver did not essentially show any apparent lobular architecture or cord structure. The transplanted fetal hepatic tissues survived and formed hepatic cords in the spleen instead of undergoing degeneration and necrosis. Three characteristic features became complete during the 4 weeks following transplantation, namely; clumps of hepatocytes with obvious hepatic cords and sinusoids, markedly proliferating bile ducts and proliferating individual hepatocytes. Macroscopic nodules of the hepatocytes on the spleen were seen at about 6 months after transplantation. When the differentiation of the transplanted fetal hepatic tissue was compared with the development of a normal neonatal liver after birth, it was delayed by only about one week, while there was no proliferation of bile ducts in the normal neonatal liver. This experimental model provides a useful system for investigating liver regeneration and the mechanism of cell growth.