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U Marti

Publications and source records attributed to U Marti.

At least 37 records · Page 2Linked to original sources
PubMed1995

The overexpression of proliferating cell nuclear antigen in biliary cirrhosis in the rat and its relationship with epidermal growth factor receptor.

Chronic bile duct obstruction in the rat leads to biliary cirrhosis but maintained hepatocellular mass. We have previously demonstrated translocation of epidermal growth factor receptor to nuclei. It remained unclear, however, whether this was due to hepatocyte proliferation and/or altered handling of epidermal growth factor receptor. Therefore, in the present investigation we stereologically estimated expression of proliferating cell nuclear antigen, a marker of the S phase of teh cell cycle at 1, 2, 3, 7, 14, 21 and 28 days after bile duct ligation. Proliferating cell nuclear antigen positive hepatocytes averaged 2.1 +/- 3.6% in sham-operated control animals. This increased to 20.7 +/- 6.4, 26.8 +/- 18.7, 31.3 +/- 23.9, 42.3 +/- 16.6 and 24.7 +/- 28.0% 3, 7, 14, 21 and 28 days after bile duct ligation, respectively (p<0.005 by ANOVA). This was correlated with the number of epidermal growth factor receptor positive nuclei (rs = 0.737) and inversely with the maximal binding capacity of epidermal growth factor to a crude plasma membrane fraction (rs = 0.697) reported previously. We conclude that bile duct ligation in the rat induces a significant hepatocellular proliferation as assessed by proliferating cell nuclear antigen expression and that this process could, at least in part, be related to increased nuclear expression of the epidermal growth factor receptor.

Analysis of Variance↗
PubMed1995

Characterization of mechanisms causing hypoalbuminemia in rats with long-term bile duct ligation.

Albumin kinetics and albumin synthesis were studied in rats with chronic bile duct ligation and compared with pair-fed control rats. The plasma albumin concentration was significantly reduced in bile duct ligated rats as compared to control rats, averaging 35 +/- 1 vs 40 +/- 2 g/l after 2 weeks and 28 +/- 3 vs 38 +/- 5 g/l after 4 weeks of bile duct ligation. Two weeks after bile duct ligation, the transcapillary escape rate of albumin was increased by 60% in bile duct ligated rats, whereas the plasma volume was unchanged. Albumin synthesis expressed as a fraction of total liver protein synthesis, as assessed by the 'flooding' dose method using [3H]phenylalanine, was decreased by 46% in bile duct ligated rats. However, absolute albumin synthesis expressed per 100 g body weight was not different from control rats. Four weeks after bile duct ligation, the transcapillary escape rate of albumin was no longer different, whereas the plasma volume was increased by 38% in bile duct ligated rats. At this time point, albumin synthesis as a fraction of total liver protein synthesis was decreased by 60% in bile duct ligated rats, and absolute albumin synthesis expressed per 100 g body weight averaged 80 +/- 8 vs 53 +/- 12 mg/(day x 100 g) in control and bile duct ligated rats (p < 0.05). The hepatic steady-state levels of albumin mRNA determined by Northern blot analysis were decreased in bile duct ligated rats at both 2 and 4 weeks after surgery. The studies suggest that reduced plasma albumin concentrations in bile duct ligated rats are caused by increased capillary permeability and lack of compensatory increase in albumin synthesis 2 weeks, and by increased plasma volume and decreased albumin synthesis 4 weeks after surgery.

Animals↗
PubMed1995

Acinar and cellular distribution and mRNA expression of the epidermal growth factor receptor are changed during liver regeneration.

The epidermal growth factor receptor shows acinar heterogeneity with a portal-to-central concentration gradient. Immunohistochemical analysis showed that the strong cytoplasmic staining for epidermal growth factor receptor found in normal hepatocytes disappears over time after partial hepatectomy or sham operation, however, with different time courses. Four hours after surgery, 84.3 +/- 3.5% (mean +/- SD) of the hepatocytes in animals after sham operation showed strong cytoplasmic staining vs. 21.8 +/- 19.0% in animals after partial hepatectomy. After 12 h, the cytoplasmic staining in animals after sham operation was further reduced to 39.0 +/- 22.6% vs. 20.0 +/- 5.5% in animals after partial hepatectomy. At the same time point, we found staining for the epidermal growth factor receptor in nuclei of 21.8 +/- 14.8% and 3.0 +/- 3.9% of the hepatocytes in animals after partial hepatectomy and animals after sham operation, respectively. Northern blot analysis revealed comparable changes in expression of the epidermal growth factor receptor mRNA in animals after partial hepatectomy and in animals after sham operation. No changes were evident in animals after sham operation, however, if the abdominal incisions were shortened. This suggests that at least part of the changes found in animals with sham operation are due to acute phase events and/or surgical stress. In conclusion, partial hepatectomy induces changes in the intracellular and acinar fate of the epidermal growth factor receptor, drives the receptor to the nuclei, and affects the expression of the epidermal growth factor receptor mRNA.

Animals↗
PubMed1994

Hepatocellular Na+/H+ exchange is activated early, transiently and at a posttranscriptional level during rat liver regeneration.

In hepatocytes in vitro, Na+/H+ exchange, an important regulator of intracellular pH, is activated by epidermal growth factor, but its activity during liver regeneration in vivo is unknown. We therefore compared activity and regulation of Na+/H+ exchange in hepatocytes isolated after two-thirds partial hepatectomy or sham surgery, respectively, by measuring intracellular pH (fluorimetry) and steady state Na+/H+ exchange mRNA levels (Northern blotting). Resting intracellular pH increased from 7.06 +/- 0.02 to 7.12 +/- 0.02 (p < 0.05) 2 hr but not 20 hr after partial hepatectomy. Na+/H+ exchange-mediated rates of intracellular pH recovery from an acid load increased from 0.075 +/- 0.018 to 0.151 +/- 0.018 pH units/min (p < 0.05) 2 hr but not 20 hr after partial hepatectomy. Because intracellular buffering capacity was not affected, this reflects increased Na+/H+ exchange activity. The inverse relationship between Na+/H+ exchange activity and intracellular pH was shifted by about 0.1 pH units toward more alkaline pH values 2 hr but not 20 hr after partial hepatectomy, whereas steady-state Na+/H+ exchange mRNA levels remained unchanged. In conclusion, hepatocellular Na+/H+ exchange is activated early, transiently and at a posttranscriptional level during liver regeneration induced in the rat by partial hepatectomy.

Animals↗
PubMed1994

Hepatocellular Na+/H+ exchange is activated at transcriptional and posttranscriptional levels in rat biliary cirrhosis.

BACKGROUND/AIMS: Rat hepatocyte Na+/H+ exchange is activated in vitro by growth factors and in vivo following partial hepatectomy. This study explored by which mechanism(s) it is activated in a cirrhosis model characterized by chronic stimulation of hepatocyte proliferation. METHODS: Rat hepatocytes were isolated 4 weeks after bile duct ligation or sham operation. Intracellular pH (pHi) was fluorimetrically determined, and plasma membranes and messenger RNA (mRNA) were prepared from isolated hepatocytes by standard methods. RESULTS: Resting pHi was higher in bile duct-ligated than in control rats (7.42 +/- 0.03 vs. 7.06 +/- 0.04; P < 0.001). Although plasma membrane lipid composition and intracellular buffering capacity were similar, initial Na+/H+ exchange-mediated rates of pHi recovery following acid loading were higher in bile duct-ligated than in control rats (0.098 +/- 0.011 vs. 0.055 +/- 0.005 pH units/min; P < 0.05). The antiporter's set point was shifted approximately 0.3 pH units towards more alkaline values and its steady-state mRNA levels were doubled after bile duct ligation. CONCLUSIONS: Hepatocellular Na+/H+ exchange is transcriptionally and posttranscriptionally activated in rat biliary cirrhosis further supporting a relationship between hepatocyte proliferation and Na+/H+ exchange activation.

Animals↗
PubMed1994

Differential effect of micronodular and biliary cirrhosis on epidermal growth factor receptor expression in the rat.

Cirrhosis is characterized by fibrogenesis, hepatocyte necrosis and the formation of regenerative nodules. Modulation of the epidermal growth factor receptor is an early event during regeneration. We have recently demonstrated alterations in the epidermal growth factor receptor during the development of biliary cirrhosis. The aim of the present study was to compare epidermal growth factor receptor distribution, expression and binding in biliary cirrhosis to that occurring in micronodular cirrhosis induced by phenobarbital/CCl4 exposition. Biliary cirrhosis and micronodular cirrhosis had similar functional impairment as assessed by the aminopyrine breath test. Epidermal growth factor receptor binding capacity was reduced in both models (control vs micronodular cirrhosis vs biliary cirrhosis: (mean +/- 1 SD) 60 +/- 22 vs 16 +/- 12 vs 27 +/- 9 fmol/mg protein, p < 0.05), while the binding constant was increased in biliary cirrhosis only. The receptor mass in plasma membrane, determined by Western blotting, was not changed. Distribution of epidermal growth factor receptor was assessed immunohistochemically on tissue sections. In both models, cytoplasmic staining was decreased and basolateral plasma membrane labeling was maintained. Nuclear localization was found in biliary cirrhosis only. In conclusion, in both models, cirrhosis induces an alteration in the binding properties, but not in the number of epidermal growth factor receptors in the plasma membrane. The loss of cytoplasmic epidermal growth factor receptor could reflect alterations in expression and/or in intracellular trafficking. This is supported by the reduced mRNA steady state levels for epidermal growth factor receptor which were found in both models, presumably representing down-regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Handling of epidermal growth factor and number of epidermal growth factor receptors are changed in aged male rats.

In the aged liver, cell proliferation and induction of DNA synthesis by epidermal growth factor is impaired. Changes in the hepatic handling of epidermal growth factor may be important for these effects. I compared epidermal growth factor handling in the livers of young and old rats. Epidermal growth factor binding capacity of plasma membranes was reduced from 1.30 +/- 0.15 to 0.51 +/- 0.19 pmol/mg in young and old animals, respectively. Intracellular handling of epidermal growth factor was assessed by means of portal injection of 125I-labeled epidermal growth factor and collection of bile samples. The extraction of epidermal growth factor showed no significant difference. After 60 min the remaining radioactivity in the aged liver was half that in young liver. The total radioactivity secreted into bile was reduced from 16.5% +/- 5.7% to 10.0% +/- 2.3% of the injected dose in young and old animals, respectively. Per gram of liver and per 10(6) cpm injected, the old animals secreted only 30.9% of the amount secreted by young animals. The secretion of immunologically intact epidermal growth factor into bile was reduced from 1.6% +/- 0.8% to 0.78% +/- 0.2% of the injected dose in the young and old animals, respectively. Perfusion experiments showed that in aged liver the amount of total radioactivity secreted into the perfusate was increased to 133.6% that of the young liver. Per gram of liver and per 10(6) cpm injected, however, we found a reduction to 80.7%. Exocytosis at the canalicular and basolateral membrane appeared to be differently affected by aging.

Aging↗
PubMed1992

Epidermal growth factor receptor in chronic bile duct obstructed rats: implications for maintenance of hepatocellular mass.

Changes of the number and properties of the epidermal growth factor (EGF) receptor occur during liver regeneration and may be of importance in the maintenance of hepatocellular mass in liver cirrhosis. We therefore studied the changes in the number and distribution of EGF receptor in the development of liver cirrhosis induced by bile duct ligation. Receptor binding assays demonstrated a marked decrease in the binding capacity of crude plasma membrane fractions from 45 +/- SD 16 to 19 +/- 10 fmol/mg protein (p < 0.001) in control and bile duct ligated livers, respectively while the Kd increased after 3 days of bile duct ligation from 0.5 +/- 0.2 to 1.4 +/- 0.6 nmol/l. Total receptor concentration in the same membrane fractions, as assessed by Western blot analysis, was not changed. The expression of EGF receptor mRNA was reduced to about one third of control levels after 28 days of bile obstruction. Immunohistochemistry, performed using monoclonal antibodies against EGF receptor, showed a strong labeling of cytoplasm (87 +/- 3% positive) and plasma membranes (84 +/- 24%) but no labeling of nuclei in control livers. In bile duct ligated rats, in contrast, cytoplasmic staining was decreased (15 +/- 12%) already after 3 days of bile obstruction; labeling of canalicular membranes and nuclei appeared after 14 days. The shift of EGF receptor from plasma membranes to nuclei supports the notion that EGF receptor is involved in the maintenance of hepatocellular mass in this model of liver cirrhosis. This concept is supported by the finding of decreased mRNA for EGF receptor presumably representing down-regulation as seen in regenerating rat liver.

Animals↗
PubMed1991

Caloric restriction affects liver microsomal monooxygenases differentially in aging male rats.

Caloric restriction (CR) extends life span and retards the onset of physiological changes and pathologies associated with aging, but the underlying mechanisms remain unresolved. This study demonstrates that CR postpones the documented age-related declines in and/or enhances the activity and microsomal concentration of several liver monooxygenases in male rats, i.e., NADPH cytochrome P-450 reductase, total cytochromes P-450. However, the relative concentration of cytochrome P-450b+C did not exhibit statistically significant changes, whereas another isozyme, the male specific P-450h, declined significantly in both ad libitum-fed and CR rats as a function of increasing age. While CR appears to retard age-associated changes in certain liver enzymes, this effect is by no means universal. The hepatic monooxygenases constitute a well-characterized enzyme system in which to examine the perturbation of the aging process by CR.

Aging↗
PubMed1991

Acinar heterogeneity of the epidermal growth factor receptor in the liver of male rats.

Epidermal growth factor is cleared from the circulation by the liver, forming a very steep portal-to-central sequestration gradient. It was unknown whether this was due to the position within the liver acinus or whether it was due to functional differences in the hepatocytes. Experiments were undertaken to elucidate the lobular distribution and heterogeneity of the epidermal growth factor receptor in rat liver. Immunocytochemistry showed a predominantly higher staining density over periportal localized hepatocytes. Receptor binding studies with isolated, cultured hepatocytes, enriched in periportal or perivenous located cells, were performed. Our data revealed high- and low-affinity binding sites with a kd of 26 pM and 0.87 nM, respectively, for periportal hepatocytes. The high-affinity receptors were restricted to the periportal hepatocytes only, whereas the number of low-affinity receptors showed a 3 to 4-fold concentration gradient between both cell populations.

Animals↗
PubMed1991

Localization of epidermal growth factor receptor in hepatocyte nuclei.

Experiments undertaken to investigate the binding of epidermal growth factor by hepatocyte nuclei showed that: (a) isolated nuclei from both normal and regenerating rat liver are capable of binding 125I-epidermal growth factor, (b) the nuclear epidermal growth factor-binding protein is similar in molecular weight to the plasma membrane epidermal growth factor receptor, (c) monoclonal antibodies produced against the plasma membrane epidermal growth factor receptor recognize the nuclear epidermal growth factor receptor and (d) the nuclear receptor has an affinity for epidermal growth factor comparable to that of the plasma membrane receptor, but fewer (approximately 10%) nuclear receptors are available per protein unit compared with the plasma membrane.

Animals↗
PubMed1990

Induction of cytochrome P450 by phenobarbital in rat liver visualized by monoclonal antibody immunoelectron microscopy in situ.

A panel of murine monoclonal antibodies was produced against phenobarbital-inducible cytochrome P450-PB of rat liver in order to establish specific immunological tools for studying the induction process in situ by immunoelectron microscopy and in vitro by a novel ELISA. Antibody 573/64 was found to be useful for both approaches. The immunolabeling procedure with protein A-colloidal gold applied to Lowicryl K4M-embedded rat liver revealed the rough ER as the primary site of cytochrome P450-PB induction. This organelle showed the highest labeling density 12 h after administration of phenobarbital while after maximal enzyme induction at day 5 the labeling density was highest in the smooth ER. Maximal increase in cytochrome P450-PB was 21-fold by morphometric analysis and 15-fold by ELISA. In addition, the enzyme apparently does neither recycle through the Golgi apparatus nor is it degraded in lysosomes when maximally induced.

Animals↗
PubMed1989

Biological effects of epidermal growth factor, with emphasis on the gastrointestinal tract and liver: an update.

Epidermal growth factor (EGF) is a 6,000 Da polypeptide hormone produced by glands of the gastrointestinal tract, namely the salivary and Brunner's glands. It is found in a wide variety of external secretions as well as in blood and amniotic fluid. In fetal and neonatal life, EGF appears to play an important role in the development of the oral cavity, lungs, gastrointestinal tract and eyelids. Its presence in cells of the central nervous system suggests that it also plays a role in modulating the development of this system. In adult animals, the function of EGF is much less well understood. In rodents, it apparently modulates acid secretion from parietal cells in the stomach, and it undoubtedly plays an important role in wound healing, either through its localization within skin or by the licking of wounds with EGF-containing saliva. Considerable evidence now suggests that it may be one of the key factors in initiating liver regeneration after partial hepatectomy or chemical injury. The liver appears to be the principal organ which regulates the circulating level of EGF. In fact, EGF is cleared so efficiently by the liver that only the peripheral cells of the lobule (zone 1) sequester EGF, and little remains in the circulation for cells in the more distal zones (zones 2 and 3). In the liver, EGF normally binds to a plasma membrane receptor and is internalized within the liver cell, where the vast majority of EGF and its receptor are destroyed in lysosomes. A small but consistent quantity of EGF enters the bile intact. In the regenerating liver, however, the lysosomal pathway appears to be shut down, and the EGF is diverted to hepatocyte nuclei prior to the initiation of DNA synthesis. Nuclear EGF is found free as well as bound to a high-molecular-weight protein which has many characteristics identical to the plasma membrane EGF receptor. The plasma membrane receptor is a large transmembrane glycoprotein of 170,000 Da containing four domains: an extracellular EGF-binding portion, a hydrophobic membrane-spanning segment, a proximal cytoplasmic domain which binds ATP and protein substrates containing tyrosine for phosphorylation and a terminal cytoplasmic portion with 3 tyrosines which undergo autophosphorylation after EGF binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1989

Effect of oxidative iodination of epidermal growth factor on its binding and secretion by hepatocytes.

Experiments were undertaken to determine whether the method of iodination of epidermal growth factor (EGF) affects its binding to rat liver plasma membranes and its uptake, processing, and secretion into bile by intact rat hepatocytes. EGF was iodinated using one of three oxidative reagents: chloramine T (CT), lactoperoxidase (LP), or monochloride (MC). Quantitative receptor binding studies on plasma membranes isolated from male rat livers with either CT-, LP-or MC-125I-EGF indicated no significant difference in the apparent binding constants of the three preparations. To determine whether these three preparations were capable of forming a covalent-like complex with the EGF receptor, they were individually incubated with isolated plasma membranes and subjected to polyacrylamide gel electrophoresis under reducing conditions, followed by autoradiography. Each preparation formed a major radioactive protein band of approximately 180 kD, identified as the EGF receptor by immunoprecipitation with monoclonal anti-EGF receptor antibodies. Furthermore, even unlabeled EGF incubated with plasma membranes formed this same 180 kD band, as revealed on Western blots using anti-EGF antibody. The biliary secretion of CT-, LP-, and MC-125I-EGF was compared by injecting each one into rat portal veins and measuring the total and immunoprecipitable radioactivity in bile. The amount of immunologically intact CT-125I-EGF in bile was significantly greater than the others, whereas MC-125I-EGF transport was significantly reduced. We conclude that the method of iodination does not affect the covalent-like binding properties of EGF. Furthermore, since unlabeled EGF displayed these same binding properties, oxidative iodination procedures per se do not account for the covalent-like association between EGF and its receptor. However, the method of iodination used did affect the intracellular transport and processing of EGF by hepatocytes. The structural modification responsible for this alteration in transport properties has yet to be determined.

Animals↗
PubMed1987

Morphometry and immunocytochemistry.

The use of morphometry (and stereology), especially in conjunction with immunocytochemistry, in surgical and experimental pathology is reviewed. The combined use of morphometry and immunocytochemistry permits the study of secretory products and the distinction between cells that produce them, e.g., as in the pancreas. Several examples to illustrate the application of immunocytochemical techniques in morphometry are presented. For example, using this approach on the pancreas, it was shown that not only B cells, but also A and D cells, seem to undergo pathologic changes in a prediabetic organism. Since morphologic alterations may be distributional as well as quantitative, a model for the assessment and statistical evaluation of the distribution of objects within an area is discussed. Similar procedures were used to analyze the distribution of cytochrome P-450 molecules along intracellular membranes; however, special labeling techniques were necessary for this quantification in the electron microscope. Immunoenzyme cytochemically stained secretions can also be studied morphometrically, and microdensitometry and microfluorometry can also be used to quantify immunocytochemical reactions, as is shown in the analysis of the intralobular distribution of NADPH-cytochrome P-450 reductase in the rat liver. Finally, the BIVAS semiautomatic system for morphometric measurements, developed at the Department of Pathology of the University of Basel, is briefly described.

Animals↗