REVALUATION ON THE TYPES AND PATTERN OF DISTRIBUTION OF SINUSOIDAL FENESTRATIONS IN THE LOBULE OF NORMAL RAT-LIVER

Background: There is a need to identify the existence of large fenestr ations and to evaluate the type and pattern of the distribution of sin usoidal fenestrations in the hepatic lobule. Methods: The sinusoidal f enestrations in the rat liver lobule were investigated by scanning ele ctron microscopy of perfusion-fixed specimens and by transmission elec tron microscopy of freeze-fracture replicas from immersion-fixed speci mens. Ringer solution used for precleaning was equilibrated with 84%/1 6% O-2/CO2 at 37 degrees C, and the perfusion pressure was maintained at 5-10 mmHg in the portal vein. Results: The fenestrations were recog nized on the luminal surface of sinusoids on the basis of regional dif ference in size and distribution within the lobule and divided into th ree types: small, medium-sized, and Targe, The small fenestrations wer e numerous in each region, The number of medium-sized fenestrations wa s large in the pericentral and intermediate regions, while that of lar ge fenestrations was predominant in the intermediate region, Based on the occurrence of fenestrations, the sinusoids were also divided into three types, The type I sinusoid mainly showed small fenestrations and was predominant in the periportal region, The type II sinusoid showed small and medium-sized fenestrations and was predominant in the peric entral region, The type III sinusoid showed all the types of fenestrat ions including large ones and was predominant in the intermediate regi on. The images showing dumbbell-shaped or irregularly shaped margins w ere observed between small or medium-sized fenestrations on the freeze -fracture replica. Conclusions: 1) The fenestrations are divided into three types according to the size and pattern of distribution within t he lobule, 2) The sinusoids are also divided into three types based on the distribution pattern of each type of fenestrations, 3) The small fenestrations are evenly distributed throughout the entire lobule, whi le the medium-sized and large fenestrations show the regional differen ce within the lobule, 4) The large fenestrations exist as real structu res of the endothelial lining cells of sinusoids and may result from t he fusion of contiguous smaller ones. (C) 1997 Wiley-Liss, Inc.