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Biomedical subjects

A Brouwer

Publications and source records attributed to A Brouwer.

At least 127 records · Page 7Linked to original sources
PubMed1991

Thyroxine and 3,3',5-triiodothyronine are glucuronidated in rat liver by different uridine diphosphate-glucuronyltransferases.

Male Wistar rats were treated with 50 mg 3,3',4,4'-tetrachlorobiphenyl (TCB)/kg BW or vehicle. After 4 days, the livers were isolated and perfused for 90 min with 2 nM [125I]T3 or 10 nM [125I]T4 in Krebs-Ringer medium containing 1% albumin. Deiodination and conjugation products and remaining substrates were determined in bile and medium samples by Sephadex LH-20 chromatography and HPLC. TCB treatment did not affect hepatic uptake and metabolism of T3. However, biliary excretion of T4 glucuronide was strongly increased by TCB, resulting in an augmented T4 disappearance from the medium, although initial hepatic uptake of T4 was not altered. Measurement of the microsomal UDP-glucuronyltransferase (UDPGT) activities confirmed that T4 UDPGT was induced by TCB, whereas T3 glucuronidation was unaffected. T3 UDPGT activity showed a discontinuous variation, which completely matched the genetic heterogeneity in androsterone glucuronidation in Wistar rats. These results indicate that different isozymes catalyze the glucuronidation of T3 and T4.

Animals↗
PubMed1990

Distribution of lecithin-retinol acyltransferase activity in different types of rat liver cells and subcellular fractions.

It is now well documented that lecithin-retinol acyltransferase (LRAT) is the physiologically important enzyme activity involved in the esterification of retinol in the liver. However, no information regarding the cellular distribution of this enzyme in the liver is presently available. This study characterizes the distribution of LRAT activity in the different types of rat liver cells. Purified preparations of isolated parenchymal, fat-storing, and Kupffer + endothelial cells were isolated from rat livers and the LRAT activity present in microsomes prepared from each of these cell fractions was determined. The fat-storing cells were found to contain the highest level of LRAT specific activity (383 +/- 54 pmol retinyl ester formed min-1.mg-1 versus 163 +/- 22 pmol retinyl ester formed min-1.mg-1 for whole liver microsomes). The level of LRAT specific activity in parenchymal cell microsomes (158 +/- 53 pmol retinyl ester formed min-1.mg-1) was very similar to LRAT levels in whole liver microsomes. The Kuppfer + endothelial cell microsome fractions were found to contain LRAT, at low levels of activity. These results indicate that the fat-storing cells are very enriched in LRAT but the parenchymal cells also posses significant levels of LRAT activity.

Acyltransferases↗
PubMed1990

Sinusoidal endothelial cells of the liver: fine structure and function in relation to age.

Liver endothelial cells form a continuous lining of the liver capillaries, or sinusoids, separating parenchymal cells and fat-storing cells from sinusoidal blood. Liver sinusoidal endothelial cells differ in fine structure from endothelial cells lining larger blood vessels and from other capillary endothelia in that they lack a distinct basement membrane and also contain open pores, or fenestrae, in the thin cytoplasmic projections which constitute the sinusoidal wall. This distinctive morphology supports the protective role played by liver endothelium, the cells forming a general barrier against pathogenic agents and serving as a selective sieve for substances passing from the blood to parenchymal and fat-storing cells, and vice versa. Sinusoidal endothelial cells, furthermore, significantly participate in the metabolic and clearance functions of the liver. They have been shown to be involved in the endocytosis and metabolism of a wide range of macromolecules, including glycoproteins, lipoproteins, extracellular matrix components, and inert colloids, establishing endothelial cells as a vital link in the complex network of cellular interactions and cooperation in the liver. Fine structural studies in combination with the development of cell isolation and culture techniques from both experimental animal and human liver have greatly contributed to the elucidation of these endothelial cell functions. Morphological and biochemical investigations have both revealed little changes with age except for an accumulation of iron ferritin and a decrease in the activities of glucose-6-phosphatase, Mg-ATPase, and in glucagon-stimulated adenylcyclase. Future studies are likely to disclose more fully the role of sinusoidal endothelial cells in the regulation of liver hemodynamics, in liver metabolism and blood clearance, in the maintenance of hepatic structure, in the pathogenesis of various liver diseases, and in the aging process in the liver.

Aging↗
PubMed1990

Comparative endotoxin-induced hepatic injury in young and aged rats.

Recent studies have demonstrated that aged rats are more susceptible to the lethal effects of endotoxin (ET) than young rats. The early (15 min to 7 h) hepatic ultrastructural and biochemical changes induced by ET in young (6 months) and aged (24 months) rats were evaluated to elucidate cell populations and/or the mechanisms that may be responsible for the previously observed differential effects. Aged rats given ET had significantly increased numbers of neutrophils in hepatic sinusoids at 30 min and thereafter as compared with ET-treated young rats. Morphologic evidence of coagulation within hepatic sinusoids, including aggregates of fibrin enmeshed among polymorphonuclear leukocytes and platelet aggregates, was frequently observed in ET-treated aged rats but not in ET-treated young rats. In contrast, Kupffer cells of ET-treated young rats frequently contained phagocytized neutrophils and platelets, whereas this phenomenon was rarely observed in Kupffer cells of ET-treated aged rats. Hepatocellular morphologic injury was more pronounced and occurred at earlier time periods in ET-treated aged rats, and was accompanied by significant increase in hepatic transaminases. ET-treated aged rats had an earlier onset and greater severity of endothelial cell injury than did ET-treated young rats. The results of this study indicate a greater aggregation of blood elements in the hepatic sinusoids of aged rats following the intravenous administration of ET, which suggests that a greater diminution in microcirculation was induced in aged rats by ET. Additionally, the increased phagocytosis of inflammatory cells by Kupffer cells of young rats may be a mechanism which affords protection against endotoxin-induced lethality.

Aging↗
PubMed1990

3,4,3',4'-Tetrachlorobiphenyl distribution and induced effects in the rat adrenal gland. Localization in the zona fasciculata.

The distribution of radiolabeled 3,4,3',4'-tetrachlorobiphenyl (TCB) and TCB-induced effects on serum and adrenal gland retinoid content, and adrenal gland morphology was studied by liquid scintillation counting, high performance liquid chromatography, light microscopic autoradiography, and transmission electron microscopy. Adult, female WAG/Rij rats received a single intraperitoneal injection of either vehicle (corn oil), 15 mg TCB/kg, or 200 mg TCB/kg body weight and were sacrificed (N = 3 per group) at 1, 3, 7, and 14 days after treatment. One rat of the high dose group that was sacrificed at each sampling time had received radiolabeled compound (containing 1.85 mCi of 3H-TCB). At day 1, the adrenal gland had the greatest concentration of radioactivity (dpm x 10(-6)/gm wet tissue) of any organ examined. There was a selective distribution of radiolabeled compound to the zona fasciculata accompanied by morphometric evidence of hypertrophy of the zona fasciculata. The vast majority of 3H-TCB present in the adrenal gland was parent compound at all time periods. Serum retinol content was significantly decreased in the high dose group by 61 and 54% at days 3 and 7, respectively. No significant decrease in adrenal gland retinoid content occurred at any time in this study, but in contrast, adrenal gland retinol and retinyl palmitate content was increased. Serum cortisol levels were transiently decreased in the high dose group. Ultrastructural alterations were only observed in cells of the zona fasciculata. Predominant changes included mitochondrial hypertrophy and concentric whorling lamellar arrays of the membranes of the outer mitochondrial compartment and mitochondrial cristae. The results of this study indicate that the rat adrenal gland is an early target organ after TCB intoxication, and that there is an early and selective distribution of TCB in the rat adrenal gland accompanied by morphologic alterations in the sites of compound localization. The results further suggest that the observed morphologic changes did not result from hypovitaminosis A.

Animals↗
PubMed1990

Light- and immunoelectron microscopic visualization of in vivo endocytosis of low density lipoprotein by hepatocytes and Kupffer cells in rat liver.

The in vivo interaction of low density lipoproteins (LDL) with the liver was investigated by visualizing the endocytic route using light- and immunoelectron microscopic methods in control and 17 alpha-ethinyl estradiol (EE)-treated rats. The fluorescent dye dioctadecyl indocarbocyanine perchlorate allowed the visualization of LDL at the light microscopic level. Cryoimmunocytochemistry using antibodies against apolipoprotein B was applied at the electron microscopic level. In treated, as well as in EE-treated rats, dioctadecyl indocarbocyanine perchlorate-LDL was taken up by Kupffer cells to a substantial extent. Parenchymal cell uptake was strongly increased after EE treatment and at 10 minutes after injection, LDL was found to be attached to the microvilli of the parenchymal cells and some LDL was already localized in multivesicular structures. At later time points, substantial labeling in multivesicular structures, vesicles near bile canaliculi, and also inside bile canaliculi was observed. A low amount of labeling was found in lysosomes. In untreated rats, label was also observed in the aforementioned structures, but at a much lower level. The biliary appearance of LDL was quantified in rats equipped with permanent catheters in the bile duct, duodenum, and heart. After administration of [125I]tyraminecellobiose-LDL in control rats, about 5% of the injected dose was secreted into the bile during the first 3 hours after injection. This value was about 25% for EE-treated rats. The radioactivity secreted into the bile was trichloroacetic acid-precipitable and high molecular weight bands were immunoreactive for apolipoprotein B as revealed by Western blotting. The described events were not observed when methylated [125I]tyraminecellobiose-LDL was administered. It is concluded that, in rat liver, a significant portion of apolipoprotein B derived from LDL is directly transported to the bile. Since this pathway is enhanced in EE-treated rats, it appears to be a route specific for liver parenchymal cells, dependent on uptake via the LDL receptor.

Animals↗
PubMed1989

Marked alterations in retinoid homeostasis of Sprague-Dawley rats induced by a single i.p. dose of 10 micrograms/kg of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Interference of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in retinoid homeostasis was investigated in Sprague-Dawley rats with a low (dietary induced) retinoid status, that were fed a [3H]retinol-containing diet (37 MBq, 10,000 IU/kg diet) for 21 days to facilitate determination of retinoid concentrations in various tissues. The rats were exposed to a single i.p. dose of 10 micrograms TCDD/kg body weight in corn oil, or to corn oil at day 7 of [3H]retinol supplementation. TCDD induced significant reductions in retinol and retinyl ester concentrations and [3H] retinol-derived radioactivity in the liver, the lung, the intestine and the adrenals to 3-5%, 40-45%, 37%, and 56% of control values, respectively, at 14 days after exposure. In contrast, the retinoid concentrations and the amount of [3H]retinol-derived radioactivity in the kidney and serum of TCDD-treated rats was increased to 440% and 140% of corn oil-treated controls, respectively, at the termination time of the experiment. Analysis of the amount of serum retinol binding protein (RBP) by gel-permeation chromatography revealed an 150% increase in the free fraction of retinol-RBP, i.e., uncoupled to transthyretin (TTR), in serum of TCDD-treated rats. In addition, urinary excretion of [3H]retinol-derived radioactivity was significantly enhanced (to 140% of controls) by TCDD. These data indicate that TCDD induces an increased mobilization of retinoids from hepatic and extrahepatic storage sites into serum accompanied by an enhanced elimination via the kidney into the urine of rats.

Adrenal Glands↗
PubMed1989

Platelet participation in the increased severity of endotoxin-induced pulmonary injury in aged rats.

Recent studies have demonstrated that aged rats are more susceptible to the lethal effects of endotoxin as compared with young rats. The morphogenesis of early endotoxin-induced pulmonary injury in young (6 months) and aged (24 months) rats was examined by combined light and transmission electron microscopy to elucidate cell populations that may be responsible for these effects. Pulmonary endothelial cell injury was of greater severity and occurred at earlier time periods in aged rats as compared with young rats. Platelet sequestration and aggregation were observed only in aged rats in this study, and occurred in conjunction with the initial degenerative changes in the endothelium. Morphological evidence of granulocyte degranulation and fragmentation was also observed only in aged rats. These results suggest that pulmonary endothelial cells of aged rats are more susceptible to endotoxin-induced injury and that platelets may play an important role in the enhancement of initial endothelial damage. Furthermore, the extent of injury to the endothelial cell population may play an important role in accounting for differences in endotoxin-induced mortality between young and aged rats.

Aging↗
PubMed1989

Genotoxic effects of intragastrically administered benzo[a]pyrene in rat liver and intestinal cells.

The genotoxic effects of intragastrically administered benzo[a]pyrene (BaP) were studied in isolated rat liver and intestinal cells. We found that BaP was unable to induce unscheduled DNA synthesis in rat parenchymal liver cells in vivo. In contrast, alkaline elution showed that at 5 h after administration of BaP a considerable number of alkali-labile sites was present in the DNA of both intestinal cells and parenchymal liver cells, but not in that of non-parenchymal liver cells. The possibility is discussed that these sites were induced by radical intermediates, generated during the metabolization of BaP.

Animals↗
PubMed1989

3,4,3',4'-tetrachlorobiphenyl-induced effects in the rat liver. I. Serum and hepatic retinoid reduction and morphologic changes.

The distribution of 3,4,3',4'-tetrachlorobiphenyl (TCB), its effects on serum and hepatic retinoid, content and liver morphology were investigated in adult female WAG/Rij rats. Animals received a single intraperitoneal injection of either a corn oil vehicle, 15 or 200 mg TCB/kg body weight and were killed at 1, 3, 7, and 14 days after treatment. One rat of the high-dose group that had received 200 mg TCB/kg containing 1.85 mCi of 3H-TCB was sacrificed at each sampling time. There was a significant increase in liver weight when expressed as a percentage of body weight in the high-dose group at day 3 (122% of controls), day 7 (116% of controls), and day 14 (110% of controls). There was a rapid rise in the amount of 3H-TCB present in the liver that peaked at day 7 followed by a rapid decline in the amount of radiolabelled material by day 14. Greater than 90% of the radiolabelled material in the liver was parent compound. TCB treatment induced a significant decrease in serum retinol content in the high-dose group at day 3 (39% of controls) and day 7 (46% of controls) following exposure. There was a significant decrease in hepatic retinol content in the high-dose group at day 3 (34% of controls), day 7 (25% of controls), and day 14 (42% of controls) following exposure. TCB treatment induced a significant decrease in hepatic retinyl palmitate content in the high-dose group at day 7 (56% of controls) following exposure. Ultrastructural alterations in hepatocytes included the proliferation and vesiculation of endoplasmic reticulum, and mitochondrial enlargement with paracrystalline inclusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

3,4,3',4'-tetrachlorobiphenyl-induced effects in the rat liver. II. Electron microscopic autoradiographic localization of 3H-TCB.

Recent results (3) indicate that 200 mg 3,4,3',4'-tetrachlorobiphenyl induces hepatomegaly accompanied by significant decreases in serum and hepatic retinoid content and hepatocyte morphologic alterations of proliferated and vesiculated endoplasmic reticulum and megamitochondria with paracrystalline inclusions. There was also an associated change in the number, size, and distribution of lipid droplets in hepatocytes and fat-storing cells. Electron microscopic autoradiographic techniques were utilized to determine the cellular and subcellular distribution of 3H-3,4,3',4'-tetrachlorobiphenyl (3H-TCB) in the adult rat liver and determine if there is any relationship between subcellular morphologic change and radiolabel localization. Adult female WAG/Rij rats received a single intraperitoneal injection of 200 mg TCB/kg containing 1.85 mCi of 3H-TCB and were sacrificed at 1, 3, 7, and 14 days following exposure. The vast majority of 3H-TCB-derived radioactivity was located in the hepatocyte at all time points examined, ranging from 79-86% of the total number of autoradiographic grains counted over the liver cells. Sequential order of radiolabel localization per liver cell type at 1, 3, and 7 days was hepatocyte much greater than Kupffer cell greater than fat-storing cell greater than endothelial cell. At day 14, the sequential order of radiolabel localization per liver cell type was hepatocyte much greater than fat-storing cell greater than Kupffer cell greater than endothelial cell, which indicates that there was some shift movement of label over time. The lipid droplet, mitochondria, and endoplasmic reticulum were the subcellular structures or organelles of hepatocytes having the highest number of 3H-TCB-derived grains at all time periods examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Nitrosylated high density lipoprotein is recognized by a scavenger receptor in rat liver.

In order to assess the presence of specific recognition sites for high density lipoprotein (HDL) in vivo, HDL was nitrosylated with tetranitromethane and the decay and liver uptake were compared with that of native HDL. The association of intravenously injected nitrosylated HDL (TNM-HDL) with liver was greatly increased as compared to native HDL. Using a cold cell isolation method, it became evident that the liver endothelial cells were responsible for the increased uptake of the modified HDL. The involvement of the endothelial cells in the uptake of TNM-HDL from the circulation could also be demonstrated morphologically by using the fluorescent dye dioctadecyl-tetramethyl-indocarbocyanine perchlorate (Dil) to label HDL. In vitro competition studies with isolated liver endothelial cells indicated that unlabeled modified HDL and acetylated LDL displaced iodine-labeled TNM-HDL, while no competition was seen with LDL and a slight displacement was seen with unlabeled native HDL. Nonlipoprotein competitors of the scavenger receptor such as fucoidin and polyinosinic acid blocked the interaction of TNM-HDL with the liver endothelial cells. Also the degradation of TNM-HDL was blocked by low concentrations of chloroquine. It can be concluded that a scavenger receptor on liver endothelial cells is involved in the clearance of tetranitromethane-modified HDL, which excludes the possibility of using TNM-HDL in vivo to assess the non-receptor-dependent uptake of HDL. The use of nitrosylated HDL in vitro as a low affinity control is limited to cell types that do not possess scavenger receptors, because cell types with scavenger receptors will recognize and internalize TNM-HDL by a high affinity scavenger pathway.

Animals↗
PubMed1988

Interaction in vivo and in vitro of apolipoprotein E-free high-density lipoprotein with parenchymal, endothelial and Kupffer cells from rat liver.

The interaction of apolipoprotein (apo) E-free high-density lipoprotein (HDL) with parenchymal, endothelial and Kupffer cells from liver was characterized. At 10 min after injection of radiolabelled HDL into rats, 1.0 +/- 0.1% of the radioactivity was associated with the liver. Subfractionation of the liver into parenchymal, endothelial and Kupffer cells, by a low-temperature cell-isolation procedure, indicated that 77.8 +/- 2.4% of the total liver-associated radioactivity was recovered with parenchymal cells, 10.8 +/- 0.8% with endothelial cells and 11.3 +/- 1.7% with Kupffer cells. It can be concluded that inside the liver a substantial part of HDL becomes associated with endothelial and Kupffer cells in addition to parenchymal cells. With freshly isolated parenchymal, endothelial and Kupffer cells the binding properties for apo E-free HDL were determined. For parenchymal, endothelial and Kupffer cells, evidence was obtained for a saturable, specific, high-affinity binding site with Kd and Bmax. values respectively in the ranges 10-20 micrograms of HDL/ml and 25-50 ng of HDL/mg of cell protein. In all three cell types nitrosylated HDL and low-density lipoproteins did not compete for the binding of native HDL, indicating that lipids and apo B are not involved in specific apo E-free HDL binding. Very-low-density lipoproteins (VLDL), however, did compete for HDL binding. The competition of VLDL with apo E-free HDL could not be explained by label exchange or by transfer of radioactive lipids or apolipoproteins between HDL and VLDL, and it is therefore suggested that competition is exerted by the presence of apo Cs in VLDL. The results presented here provide evidence for a high-affinity recognition site for HDL on parenchymal, liver endothelial and Kupffer cells, with identical recognition properties on the three cell types. HDL is expected to deliver cholesterol from peripheral cells, including endothelial and Kupffer cells, to the liver hepatocytes, where cholesterol can be converted into bile acids and thereby irreversibly removed from the circulation. The observed identical recognition properties of the HDL high-affinity site on liver parenchymal, endothelial and Kupffer cells suggest that one receptor may mediate both cholesterol efflux and cholesterol influx, and that the regulation of this bidirectional cholesterol (ester) flux lies beyond the initial binding of HDL to the receptor.

Animals↗