Canine hepatic vein branches associated with subendothelial mast cells and an adventitial lymphatic plexus.

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Abstract
Branches of the hepatic veins in the dog are equipped with peculiar, periodically arranged sphincter muscles which are known to constrict in response to hematogenous shock agents, causing the severe hepatic congestion characteristic of this species. As was confirmed in this study, the sphincters are more strongly and effectively disposed in the peripheral portion of the veins, including the sublobular and central veins. Mast cells were numerous around the sublobular branches, being specifically gathered beneath the endothelium as recorded by FUJITA (1964). The present observation light-microscopically extended his findings, particularly with regard to the distribution of the mast cells along the entire course of the hepatic vein branches.sbd.from the proximal trunks through the sublobular veins to the central veins. In addition, mast cell condensation was especially pronounced in the peripheral branches, apparently in accordance with the development of the sphincters. Electron microscopy observation confirmed the subendothelial location of the mast cells and revealed that, through an endothelial gap, the cells may extend a microprocess into the venous lumen, thus enabling the direct direction of hematogenous agents. A suspension of a bacterium, Listeria monocytogenes, was injected into the dog livers to induce hepatitis, and the resulting pathologically altered parts of the organ were examined light-microscopically. A heavy infiltration of inflammatory cells was found around the peripheral branches of the hepatic veins. The lymphatics accompanying the veins often contained lymphocytes and macrophages at two days after the injection. At five days, the lymphatics were extremely distended and twisted. The subendothelial mast cells were not encountered at the sites of severe cell infiltration. It is suggested that the hepatic vein branches, together with their subendothelial mast cell sheath and adventitial lymphatics, form a functional and defensive unit in the canine liver. The mast cells, with their histamine and other bioactive agents, not only induce the constriction of the venous sphincters and the outflow of the fluid component of the blood into the lymphatics, but also presumably attract infiltrating cells around the veins and thereafter regulate their functions. The possibilty was proposed that the flowing fluid may effectively carry the immune-related substances released from the infiltrating cells into the lymphatics and the systemic circulation.

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