Periductal fibrosis and lipocytes (fat-storing cells or ito cells) during biliary atresia in the lamprey

Transmission and scanning electron microscopy were utilized to follow the degeneration of bile ducts of lampreys (Petromyzon marinus L.) during metamorphosis. The convoluted bile ducts of larval lampreys are surrounded by rich sinusoids, but this intimate biliovascular relationship is lost during metamorphosis because the bile duct degeneration is accompanied by the development of thick periductal fibrosis. Lipocytes, which are present not only in the parenchyma but also in the interstitial tissue of the liver, increase in number in the periductal fibrous tissue, and their processes are directly opposed to collagen fibrils. Fibrillar materials in the dilated cisternae of the rough endoplasmic reticulum and the nuclear envelope of lipocytes are believed to be excreted by exocytosis in a manner similar to such excretion by fibroblasts. The findings suggest that lipocytes are responsible for the periductal fibrosis during biliary atresia in lampreys. This animal might prove to be an interesting model in which to study the biology and fibrogenic potential of lipocytes.