[Studies on cerebral scavenger cells (fluorescent granular perithelial cells) - especially uptake and digestion of...

Small cerebral vessels including capillaries are provided with the specific barrier (blood brain barrier) for a transport of substances from blood to cerebral tissue. However, it is also established that fat soluble substances are easily permeable in this barrier. Along cerebral small vessels, the cells having intracellular fluorescent granules are distributed and named "fluorescent granular perithelia (F.G.P.)" by the authors. They are potent in the uptake capacity for exogenous substances as reported in the previous papers. In this study, 24 male Wistar rats aged 8 months and 2.5 years old were employed. They were fed with a fat rich chow (Oriental Co.) containing 10% lard, 2% cholesterol and methylthiouracil for one day and fifteen days. Half of them was subcutaneously injected with 5 mg/kg of elastase (Eisai Co.) dissolved in physiological saline once a day. To clarify the effect of elastase on fat incorporated by F.G.P., 4 rats aged 2.5 years were fed with a fat rich chow for 2 days. After then, they were fed with ordinal rat chow for 3 days with or without elastase injection. After decapitation, cerebral cortex of rats was removed in cold physiological saline and sliced with a blade. Half of the sliced specimens was prepared by the authors' method (Mato and Ookawara, 1979) and stained with hematoxylin eosin, periodic acid Schiff reaction and sudan black B for a light microscopical observation. The other half of the specimens was immersed in a mixture containing 2% paraformaldehyde and 2.5% glutaraldehyde buffered with 0.1M phosphate solution (pH 7.4) for 10 h. The specimens were then postfixed with osmium tetroxide buffered with the same solution for 2h. The other procedures for embedding and cutting were the same as in a routine method. Following findings were obtained at the light and electron microscopical levels; when they were fed with a fat rich chow, fat in blood passed through vascular walls and was taken up by F.G.P.. The quantity of fatty deposits in F.G.P. was different depending on age of rats employed for the experiment. The deposits in F.G.P. increased with advancing of age. That is, in old rats a lot of deposits were chiefly distributed in inclusion bodies at one and fifteen days after the administration. The difference in quantity of deposits between young and old rats was not only based on the permeability of vessels, but on the digestion capacity of F.G.P. for fat. On the other hand, Elastase, a specific enzyme for lysis and synthesis of elastic components, prepared by Eisai Co., made a suppressive effect to the permeability of cerebral small vessels and facilitated markedly the digestion capacity of F.G.P. for fat, although the mechanism remained unsettled. From this standpoint, F.G.P. are also designated as "cerebral scavenger cells".