Sinusoidal Capillarization and Arterial Blood Supply Continuously Proceed with the Advance of the Stages of Hepatocarcinogenesis in the Rat

Hepatocellular carcinoma (HCC) is supplied only with arterial blood and has capillaries instead of sinusoids, unlike the normal hepatic tissue. In order to reveal the sequential changes of sinusoidal structure and blood supply during hepatocarcinogenesis, we examined hyperplastic nodules (HPN), atypical hyperplastic nodules (AHPN) and HCC in F344 rats fed with 2‐acetylaminofluorene for 25–35 weeks. The extent of arterial blood supply and the degree of sinusoidal capillarization were assessed by the staining of hepatic nodules with arterially infused ink and by immunohistochemical and ultrastructural analyses of the sinusoids, respectively. The proportion of arterialized nodules was 47% in HPN, 57% in AHPN and 85% in HCC, which indicates that arterialization begins at the stage of HPN and a few HCC still receive portal venous blood. The proportion of Factor‐VIII‐related antigen (F‐VIII)‐positive nodules was 25% in HPN, 40% in AHPN and 100% in HCC. Non‐arterialized nodules did not express F‐VIII, while some F‐VIII‐negative nodules were already arterialized. Electron microscopically, non‐arterialized HPN exhibited normal features of sinusoids, while arterialized HPN showed disappearance of Kupffer cells and partial defenestration of sinusoidal endothelial cells. In non‐arterialized and arterialized AHPN, basement membrane became continuous and lipid droplet‐containing stellate cells were no longer seen. In HCC, endothelial fenestrae were diminished and basement membrane became thick. The present study has demonstrated that sinusoids are altered in the following order as hepatocarcinogenesis advances from HPN to HCC; onset of arterialization and decrease of endothelial fenestrae, expression of F‐VIII by endothelial cells, disappearance of Kupffer cells, diminution of lipid droplets in stellate cells and thickening of basement membrane.