LIVER OF JUVENILE ATLANTIC SALMON, SALMO-SALAR L - A LIGHT, TRANSMISSION, AND SCANNING ELECTRON-MICROSCOPIC STUDY, WITH SPECIAL REFERENCE TO THE SINUSOID

Background: This report provides a detailed description of sinusoidal and perisinusoidal structures in the normal liver of the juvenile Atla ntic salmon (Salmo salar L.), a teleost species. Methods: The liver wa s studied by Light, transmission, and scanning electron microscopy, an d organ specimens were sampled after retrograde, whole-body perfusion through the dorsal aorta using 3% glutaraldehyde. Detailed characteriz ation of perisinusoidal stellate cells also included immunohistochemic al staining for desmin and evaluation of autofluorescence of the same cells upon excitation in ultraviolet (UV) light. Results: The sinusoid is lined by one cell type only: the endothelial cell. No intraluminal pit cells or Kupffer cells are present. The space of Disse contains r eticulin fibres, visualized by Gomori's silver stain, and perisinusoid al stellate cells (PSC). PSC exhibited autofluorescence in UV light, i ndicating that these cells store vitamin A in cytoplasmic lipid drople ts. Immunohistochemically, PSC were found negative for desmin. The spa ce of Disse, extending deep down between adjacent hepatocytes, receive s long, slender microvilli from parenchymal cells. In addition to scat tered macrophages, interhepatocytic cells (IHC) are found perisinusoid ally. Hepatocytes of Atlantic salmon form branching and anastomosing t ubules. Conclusions: The sinusoids of Atlantic salmon liver are lined by a fenestrated endothelium, with PSC located in the space of Disse, with macrophages and IHC as inhabitants of;the interhepatocytic space. IHC show ultrastructural similarities to mammalian pit cells and tele ostean large granular lymphocytes, as well as to piscine monocytes. PS C might be storage cells for vitamin A in Atlantic salmon as shown by autofluorescence in these cells, while immunohistochemical studies ind icate that desmin does not seem to be an adequate immunohistochemical marker for PSC in the juvenile Atlantic salmon. Methodologically, fixa tion for electron microscopy was performed by a new and convenient per fusion method: arterial retrograde whole body perfusion. Liver specime ns intended for scanning electron microscopy were fractured at room te mperature after prolonged osmium postfixation, leaving hepatocytes int act and producing images well suited to document the three-dimensional structure of cells and tissue. (C) 1994 Wiley-Liss, Inc.