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Biomedical subjects

A Brouwer

Publications and source records attributed to A Brouwer.

At least 163 records · Page 9Linked to original sources
PubMed1984

Early and differential decrease in natural retinoid levels in C57BL/Rij and DBA/2 mice by 3,4,3',4'-tetrachlorobiphenyl.

3,4,3',4'-Tetrachlorobiphenyl (TCB) administered by weekly ip injections of 1.5 to 100 mg kg-1 for 4 weeks induced a dose dependent decrease in retinoids in female C57BL/Rij and DBA/2 mice (5 to 7 weeks of age). However, the response differed between the two strains of mice. In C57BL/Rij mice, a dose dependent decrease in liver retinol (up to 60%), retinyl palmitate (up to 40%), and serum retinol (up to 80%) occurred, while in DBA/2 mice a decrease in serum retinol (up to 80%) only was observed. The effects of 3,4,3',4'-TCB on retinoid levels were more pronounced than on toxicity (e.g., decrease in thymus and body weight, increase in liver weight, and induction of AHH activity). This finding suggests that reduction in retinoid levels is a very sensitive parameter for the toxicity of polychlorinated biphenyls (PCBs). In addition, in these experiments the induction of aryl hydrocarbon hydroxylase (AHH) did not correlate with the decrease in retinoid levels in C57BL/Rij and DBA/2 mice, suggesting that the mixed function oxidase (MFO) system is not involved.

Animals↗
PubMed1984

[Initial findings with magnetic resonance tomography of mediastinal and hilar tumors].

Twenty-six tumours of the mediastinum and hilar regions were examined by magnetic resonance; the technique and initial experience in distinguishing normal from pathological appearances are described. ECG triggering has proved essential, whereas respiratory triggering was found to be unnecessary. Spin-echo images were found to be best for tumour delineation but, for further characterisation, the inversion recovery mode and multi-echo technique were most satisfactory. In general, the space-occupying lesion was seen as well as it would be with CT. The advantages of the new method are the excellent differentiation of vascular structures and the ability to image in multiple planes, whereas CT possesses better resolution which, in some cases, may be of diagnostic advantage.

Adult↗
PubMed1984

Distribution of thiol-protein disulfide oxidoreductase, insulin-glucagon proteinase and cathepsin D in different cell types of the rat liver.

Cathepsin D (EC 3.4.23.5), the insulin and glucagon degrading proteinase (IGP, EC 3.4.22.-) and the thiol-protein disulfide oxidoreductase (TPO, EC 1.8.4.2, 5.3.4.1) participate in the intracellular protein degradation, the last one also in post-protein-synthetic processing. The distribution of these enzymes was determined in isolated liver parenchymal cells, Kupffer cells and endothelial cells by means of immunochemical methods in order to further characterize these cell types. The cathepsin D content, expressed as microgram enzyme per mg protein, is about 3 fold higher in endothelial cells and about 5 to 24 fold higher in Kupffer cells than in parenchymal cells. This result confirms an earlier report which is based on the activity determination. The TPO concentration is highest in parenchymal cells with half of that concentration in Kupffer cells and one third in endothelial cells. About 0.5% of the total liver protein is represented by this enzyme. The IGP has been found to be totally absent in non-parenchymal cells. It represents, therefore, together with the glucose-6-phosphatase a valuable marker enzyme for parenchymal cells of rat liver.

Animals↗
PubMed1983

Applicability of solidified water (hydrogel) in laboratory animal care.

Hydrogel was used to provide water in a solid state to rats and mice under laboratory conditions. Hydrogel was easy to handle and readily consumed by the animals. In studies extending over 10 months, no adverse effects on the condition of the animals were observed. Consumption of hydrogel as the sole source of water for nearly 2 months had no effect on the concentration of selected fecal aerobic microorganisms. Histopathological changes were not observed in the tissues of rats and mice kept for periods up to 7 months on hydrogel as the sole source of fluids. The survival time of rats and mice kept on hydrogel after exposure to supralethal doses of total body irradiation did not differ significantly from that of control animals given drinking water in bottles.

Animal Husbandry↗
PubMed1982

Endocytosis of lactate dehydrogenase isoenzyme M4 in rats in vivo. Experiments with enzyme labelled with O-(4-diazo-3,5-di[125I]iodobenzoyl)sucrose.

1. Pig lactate dehydrogenase isoenzyme M4 was labelled with O-(4-diazo-3,5-di[125I]iodobenzoyl)sucrose and injected intravenously into rats. Previous work has shown that this label does not influence the clearance of the enzyme (half-life about 26 min) and that it is retained within the lysosomes for several hours after endocytosis and breakdown of the protein [De Jong, Bouma & Gruber (1981) Biochem. J. 198, 45--51]. 2. The distribution of the radioactivity over a large number of tissues was determined 2 h after injection. A high percentage of the injected dose was found in liver (41%), spleen (10%) and bone including marrow (21%). 3. Autoradiography indicated uptake of the enzyme mainly by Kupffer cells of the liver, by spleen macrophages and by bone marrow macrophages. 4. Liver cells were isolated 1 h after injection of the enzyme. Kupffer cells, endothelial cells and parenchymal cells were found to endocytose the enzyme at rates corresponding to 4230, 35 and 25 ml of plasma/day per g of cell protein, respectively. 5. Previous injection of carbon particles greatly reduced the uptake of the enzyme by liver and spleen, but the uptake by bone marrow was not significantly changed.

Animals↗
PubMed1982

Inhibition of cysteine proteinase activity by Z-Phe-Phe-diazomethane and of aspartic proteinase activity by pepstatin in different organs from some animals and isolated cells from rat liver.

Two methods have been developed to discriminate simultaneously between the main part of cysteine proteinase activity (cathepsin L) and all aspartic proteinase activity (mainly cathepsin D) in rat organs, using Z-Phe-Phe-CHN2 which at 5 mumol/l completely inhibits cathepsin L from rat liver and, on the other hand, pepstatin which at 0.5 mumol/l completely inhibits cathepsin D. Substrates are double-labeled cytosol proteins from rat liver at pH 3.0 or azocasein in 3 mol/l urea at pH 5.0. Several organs from rat, pigeon, frog and carp have been investigated using these methods. Especially kidneys from rat, frog and carp contain a high Z-Phe-Phe-CHN2 inhibited activity. Investigating the different liver cell types we could confirm earlier findings that Kupffer cells and endothelial cells contain more pepstatin inhibited activity than parenchymal cells.

Animals↗
PubMed1982

Endocytosis of heat-denatured albumin by cultured rat Kupffer cells.

Purified Kupffer cells were obtained by centrifugal elutriation of sinusoidal cells isolated by pronase treatment of the rat liver. The endocytosis of radioactively labeled heat-aggregated colloidal albumin (CA 125I) was investigated in maintenance cultures of the purified Kupffer cells. The endocytic capacity of the cells was studied during 4 days of culture. Maximum uptake was observed after 24 hr of culture, with a gradual decline during the following days. When the uptake was measured after incubation with increasing concentrations of CA 125I, a saturation effect was observed. This finding and the observed high rate of uptake are strong indications that receptor sites on the cell membrane are involved in the mechanism of endocytosis. The uptake of CA 125I by Kupffer cells was inhibited by the metabolic inhibitors fluoride and antimycin A, indicating that endocytosis of CA 125I is dependent on energy derived from both glycolysis and mitochondrial respiration. The mechanism of internalization may also require the action of microfilaments as well as intact microtubules, since both cytochalasin B and colchicine inhibited the uptake of CA 125I. The intracellular degradation of CA 125I by Kupffer cells was strongly inhibited by chloroquine but not by colchicine. The degradation of ingested CA 125I occurred within the Kupffer cell lysosomes.

Animals↗
PubMed1981

Clearance capacity of rat liver Kupffer, Endothelial, and parenchymal cells.

The clearance of five radioactively labeled test substances--polyvinylpyrrolidone, colloidal albumin, antimony sulfur colloid, endotoxin, and heparin--by the reticuloendothelial system was studied after i.v. injection of these substances into rats. The participation of parenchymal, Kupffer, and endothelial liver cells could be determined after isolation and purification of these cell classes. Only endotoxin was almost exclusively taken up by Kupffer cells. All other substances were also taken up by both endothelial and parenchymal cells. From the rate of uptake, expressed as the endocytic index, it appeared that all substances, with the exception of polyvinylpyrrolidone, were taken up by adsorptive endocytosis. Although the specific rate of uptake by parenchymal cells was always slower than that shown by both Kupffer and endothelial cells, the total contribution of parenchymal cells to the clearance of polyvinylpyrrolidone, antimony sulfur colloid, and heparin by the liver was even greater than that of the other two cell classes. The results demonstrate that nonphagocytosing parenchymal and endothelial cells make an important contribution to the clearance of the various test substances which, in addition, is highly dependent on the nature of the substance used. This necessitates a revision of present concepts of clearance by the reticuloendothelial system.

Albumins↗
PubMed1980

Fluid endocytosis by rat liver and spleen. Experiments with 125I-labelled poly(vinylpyrrolidone) in vivo.

1. Rates of fluid endocytosis of rat liver, spleen, hepatocytes and sinusoidal liver cells have been determined, by using 125I-labelled poly(vinylpyrrolidone) as marker. Poly(vinylpyrrolidone) was injected intravenously into rats, and plasma clearance and uptake by liver and spleen were estimated. From these data, rates of fluid endocytosis of 1.2 and 1.8 ml of plasma/g of protein per day were calculated for liver and spleen respectively. Essentially the same results were found in nephrectomized rats. 2. Hepatocytes and sinusoidal cells were separately isolated by the collagenase/Pronase method, and sinusoidal cells were further fractionated by centrifugal elutriation. Hepatocytes, sinusoidal cells, Kupffer cells and endothelial cells showed rates of fluid endocytosis of 0.96, 9.0, 19 and 13 ml of plasma/g of cell protein per day respectively. Total-body X-irradiation did not influence uptake of poly(vinylpyrrolidone) by spleen, indicating that spleen lymphocytes are not significantly involved in fluid endocytosis. 3. For liver a rate constant of exocytosis of 5% per day was found, whereas for spleen no significant loss of accumulated label could be demonstrated during a 21-day period. 4. Distribution of label over a great number of organs and tissues was measured 9 days after the injection. Liver, skin, bone and muscle together contained about 70% of the label present in the carcass; only spleen and lymph nodes contained more label per g fresh weight of tissue than liver.

Animals↗
PubMedDate not supplied

Maintenance cultures of Kupffer cells isolated from rats of various ages: ultrastructure, enzyme cytochemistry, and endocytosis.

Sinusoidal liver cells were isolated from the livers of 3-, 12-, 30-, and 36-month-old female BN/BiRij rats by enzymatic digestion. The Kupffer cells in the sinusoidal cel suspensions were purified by centrifugal elutriation and kept in maintenance culture for periods of up to about 3 weeks. The viability and yield of Kupffer cells per gram of body weight did not change with the age of the donor rat. The ultrastructural, cytochemical, and functional characteristics of Kupffer cells as observed in perfusion-fixed liver were retained during several days of maintenance culture. The consistent observation of worm-like structures in cultured Kupffer cells indicated the reformation of the specific fuzzy coat of the cells during culture. Endogenous peroxidatic and acid phosphatase activities were evident in cultured Kupffer cells and showed the same localization as observed in perfusion-fixed liver. Kupffer cells in culture were able to endocytose colloidal carbon, latex particles (0.8 micron), horseradish peroxidase, and endotoxin, indicating the reappearance of different types of specific membrane receptors. The ultrastructural appearance of Kupffer cells was not markedly influenced by the age of the donor rat. However, with increasing age, the lysosomes showed increasing amounts of electron dense lipid-like material and iron in the form of ferritin. No qualitative age-related changes in the enzymes tested or in the endocytic capacity of the Kupffer cells were observed. On the basis of these observations, maintenance cultures of purified Kupffer cells can be considered as a valuable model for studying Kupffer cell functions, also in relation to aging phenomena.

Aging↗
PubMedDate not supplied

Age-related changes in the endocytic capacity of rat liver Kupffer and endothelial cells.

There are many indications that the functional capacity of the reticuloendothelial system (RES) declines with age. The aim of this study was to investigate the cellular basis of age-related changes in the clearance function of the RES. The experiments were focused mainly on Kupffer and endothelial cells of the liver which represent a major part of the RES and are primarily responsible for clearance of colloidal material from the circulation. The clearance capacity of the RES was tested clinically and experimentally by intravenous injection of colloids, such as radiolabeled heat-aggregated colloidal albumin. Age-related changes in the endocytosis of 125I-labeled colloidal albumin (CA) in rats were determined by clearance and organ distribution of different doses of intravenously injected CA, uptake of CA by Kupffer and endothelial liver cells in vivo as determined after isolation of the cells from injected rats and kinetic studies on CA uptake by Kupffer cells in culture. The results show that, at a low dose, the clearance of CA is primarily determined by liver blood flow. At a higher saturating dose, plasma clearance and uptake by the liver are not significantly decreased with age. Endocytosis by endothelial cells, which accounts for about 60% of that of the whole liver, is also unchanged with age. In contrast, a significant decrease in endocytic capacity was observed for Kupffer cells in vivo. This age-related functional decline was also observed in Kupffer cells which were isolated from rats of different ages and maintained in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMedDate not supplied

Rat liver endothelial cells have a greater capacity than Kupffer cells to endocytose N-acetylglucosamine- and mannose-terminated glycoproteins.

The capacity of rat liver Kupffer and endothelial cells to endocytose glycoproteins with N-acetylglucosamine- or mannose-terminated oligosaccharide chains was studied. For this purpose, agalactoorosomucoid, ahexosaminoorosomucoid and horseradish peroxidase were used as ligands. A reliable determination of the amount of ligand endocytosed in vivo or in vitro was made possible by using the recently developed cold pronase method for the isolation and purification of Kupffer and endothelial cells. Both cell types participated in the uptake of the ligands in vivo as well as in vitro, but their endocytic capacity was several times greater in vivo than in vitro. Under both conditions, endothelial cells possessed a greater capacity to endocytose the ligands than did Kupffer cells. Since the total number of endothelial cells in the liver is at least twice the number of Kupffer cells, the contribution of endothelial cells to the liver uptake of N-acetylglucosamine-terminated glycoproteins in vivo was estimated to be 3 to 7 times higher than that of the Kupffer cells. In vitro experiments showed that the uptake of the glycoproteins followed saturation kinetics and was strongly inhibited at 4 degrees C and in the presence of mannan. Ultrastructural investigations revealed that horseradish peroxidase was taken up by all Kupffer and endothelial cells. These results emphasize the important role liver endothelial cells play in the clearance of specific glycoproteins from the circulation.

Animals↗