In vivo microscopy of liver microvasculature in rainbow trout (Oncorhynchus mykiss)

Morphological change is an excellent biomarker of exposure to toxicants because it is the integration of biochemical and physiological injury. Zonal patterns of necrosis in the liver have also allowed mammalian pathologists to suggest the mechanism of toxicity for certain compounds. Unfortunately, the necrotic patterns in fish are not well understood because we cannot unequivocally identify portal (afferent) from hepatic (efferent) venules in histologic sections. In vivo microscopy does allow such analysis. Mature trout were surgically implanted with dorsal aortic and portal vein catheters, and in vivo microscopy of the liver surface performed through a window in the side of anesthetized, artificially ventilated animals. Blood flow patterns were recorded on video tape by injecting fluorescein solutions. Video images were digitized and superimposed to reveal the interaction between arterial and venous vessels. We found a repeating pattern of alternation between afferent and efferent regions of the microvascular bed. The hepatic parenchyma near the convex laterorostral surface is drained by superficially placed hepatic venules. Afferent venules reach this area by passing from deeper within the liver. Arteriole distribution appeared to closely parallel portal venule distribution. Melanomacrophages were associated with arterioles. Many of these characteristics are common with the mammalian liver. However, correlation of the dimensions of cells and vascular elements between histologic sections and in vivo images are needed before we can assign terms such as periportal or pericentral to routine histologic analyses.