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H Krell

Publications and source records attributed to H Krell.

At least 19 recordsLinked to original sources
PubMed1996

Bile ductular proliferation and altered leukotriene elimination in thioacetamide-induced fibrosis of rat liver.

BACKGROUND/AIMS: Liver fibrosis is accompanied by both bile ductular proliferation and inflammation under various conditions. The functional consequences and the interrelationships between these changes are unknown. Altered biliary elimination and retention of cholephilic mediators may be a factor in fibrogenesis. Therefore, the relationship between fibrosis, ductular proliferation and functional changes in biliary elimination was studied. METHODS: Micronodular liver fibrosis was induced by thioacetamide in rats. The relative amount of bile ductular epithelial cells was determined by microscopic morphometry. The functional changes in bile secretion and metabolism of leukotriene C4 were assessed in isolated perfused livers of treated rats. RESULTS: Pretreatment with thioacetamide in vivo resulted in enhanced bile fluid formation in subsequently isolated and perfused livers. Infusion of isoproterenol into the portal vein stimulated bile flow. Both unstimulated and isoproterenol-stimulated bile flows were increased in fibrotic livers and were correlated with liver content of bile ductular epithelia. In contrast, biliary secretion of infused leukotriene C4 was lowered in correlation with that of taurocholate. Enhanced metabolism resulted in a shift of the major fraction in bile from leukotriene C4 to leukotriene D4. CONCLUSIONS: Thioacetamide-induced liver fibrosis is associated with an increased number of functionally intact bile ductules that are responsive to isoproterenol stimulating bile fluid formation. In contrast, biliary secretion of cysteinyl-leukotrienes and taurocholate is inhibited and the relative amount of leukotriene D4 is increased. Bile ductular proliferation as well as retention and altered metabolism of leukotrienes are factors associated with the development of liver fibrosis.

Animals↗
PubMed1996

Increased biliary secretion of cysteinyl-leukotrienes in human bile duct obstruction.

BACKGROUND/AIMS: The pathophysiological role of leukotrienes in liver disease is not well understood. Redistribution or enhanced formation in cholestatic states may result in increased hepatic concentrations that are expected to contribute to liver injury. To disclose the potential role of cysteinyl-leukotrienes in chronic liver diseases, we studied biliary and urinary secretion in the model situation of relief of bile duct obstruction. METHODS: Concentrations of cysteinyl-leukotrienes were determined in bile and urine of patients with extrahepatic biliary obstruction in the course of therapeutic decompression by endoscopic or transhepatic techniques. Leukotrienes were measured by radioimmunoassay after HPLC separation. Concentrations of bile acids in bile and serum were measured for comparison. RESULTS: Bile collected 2 h after decompression contained high concentrations of leukotrienes (57.5 +/- 22 microM). Biliary secretion decreased over 24 h reaching equilibrium values after 48-72 h (2.8 +/- 1.7 mM and 6.4 +/- 6.6 microM, respectively). Total bile acid concentration in serum followed a similar time course. In contrast, biliary bile acid concentration showed high interindividual variations. Bile contained all leukotriene C4, D4, E4 and NAc-LTE4, but LTC4 was predominant. Urinary leukotriene secretion in cholestasis (199.7 pmol/mmol creatinine) was less than 7% of maximal biliary secretion. It further decreased to 116.4 pmol/mmol creatinine within 72 h. Urine also contained all species of cysteinyl-leukotrienes, but the relative amounts of LTE4 and NAc-LTE4 were higher than in bile. CONCLUSIONS: Formation of cysteinyl-leukotrienes is increased in obstructive jaundice resulting in increased urinary excretion before and both biliary and urinary excretion after relief of the obstruction. Predominance of LTC4 suggests that the secreted leukotrienes are newly formed. Increased synthesis and retention of hepatic cysteinyl-leukotrienes may contribute to hepatic and extrahepatic consequences of cholestasis.

Aged↗
PubMed1995

Different pathomechanisms of altered biliary leukotriene C4 elimination in isolated perfused rat livers.

Hepatic retention of cysteinyl leukotrienes is a consequence of impaired bile secretion and may be involved in the pathogenesis of intrahepatic cholestasis. In order to assess the mechanisms of altered biliary leukotriene elimination, we studied the secretion and metabolic pattern of leukotriene C4 (LTC4) in bile early in the alterations of bile formation by xenobiotics. To this end, rats were pretreated with alpha-naphthylisothiocyanate (ANIT), ethionine (ETH), or estradiol valerate (EV) at doses which did not increase serum marker enzymes of cholestasis. Bile secretion was assessed in perfused livers isolated from the treated rats. In all models, the access of [14C]sucrose into bile was increased, indicating increased permeability of the bile tract. Biliary recovery of radioactivity infused as [3H]LTC4 was decreased by ANIT and ETH while 3H-efflux into the perfusate was increased concomitantly. The secretion rate of 3H-radioactivity into bile was correlated with that of [14C]taurocholate infused at the same time. After pretreatment with ANIT (but not in the other models) the venous efflux of [3H]LTC4-ANIT pretreatment was increased [14C]sucrose clearance into bile associated with greatly enhanced biliary access of [32P]phosphate. Thus, altered charge selectivity of the paracellular pathway appears to be a prerequisite for reflux of cholephilic anions. HPLC analysis of [3H]LTC4-derived radioactivity in bile revealed that in all models of altered bile secretion the relative amount of LTD4 in bile was elevated. These results demonstrate differential changes in hepatobiliary transport and metabolism of LTC4 in developing cholestasis. ANIT inhibits leukotriene secretion by increasing paracellular permeability with loss of charge selectivity. In contrast, ETH treatment inhibits transcellular transport while treatment with EV only results in enhanced LTC4 metabolism.

1-Naphthylisothiocyanate↗
PubMed1993

Cholestasis: pathophysiology and pathobiochemistry.

Clinical and morphological diagnosis of cholestasis involves a variety of different parameters, but bile fluid formation and composition of bile are usually not accessible in patients. In contrast, a pathophysiological definition of cholestasis can be based on current knowledge on the mechanisms of bile formation. Hence, causes of cholestasis may be localized in each step of the process of bile formation. 1. Inhibition of fluid formation reduces maximal secretory capacity. 2. Inhibition of the transcellular hepatobiliary transport may involve transport carriers, binding proteins, and the systems of biotransformation. 3. Mechanical obstruction or regurgitation of bile constituents due to increased permeability of the bile tract may inhibit the biliary elimination of cholephilic compounds. Consequences of the inhibition of biliary elimination are retention in the liver and the whole organism of potentially toxic compounds. Among these are endogenous compounds such as bile acids and cysteinyl-leukotrienes, but xenobiotics as well may become more toxic in cholestasis. The composition of bile and portal venous blood is altered. In experimental animals, changes in secretory function can already be observed before clinically used indicator enzymes of cholestasis increase. This functional inhibition of biliary elimination can be characterized as "subclinical" cholestasis that may, nevertheless, inhibit the elimination and potentiate the toxicity of cholephilic endo- and xenobiotics.

Bile↗
PubMed1993

Stimulation of bile flow and inhibition of biliary secretion of taurocholate and leukotriene C4 in thioacetamide-induced liver fibrosis.

In order to study the relation of hepatic fibrogenesis to biliary elimination, female Uje:WIST rats were treated with thioacetamide (TAA). This treatment results in single cell necrosis, fibrosis, nodular parenchyma und proliferation of bile ducts. In isolated perfused livers from pretreated rats, liver hemodynamics, bile flow, and secretion of taurocholate and leukotriene C4 were determined. After TAA-pretreatment, sinusoidal efflux of glucose and pyruvate was reduced increasing lactate/pyruvate ratio threefold. Biliary secretion of [14C]taurocholate and [3H]leukotriene C4 was lowered by 47% and 35%, respectively, compared to controls. In contrast, basal bile flow was increased after TAA-treatment. The beta-adrenergic agonist isoproterenol stimulated bile flow threefold over controls. The increased stimulation was correlated with increased liver weight after TAA-treatment. We postulate that both increased bile flow and stimulation by isoproterenol are due to proliferation of bile ducts and increased ductular bile secretion partially compensating for disturbed hepatocellular secretion.

Animals↗
PubMed1991

Increased paracellular permeability in intrahepatic cholestasis induced by carmustine (BCNU) in rats.

Carmustine [i.e., 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)] is a drug with cholestatic potency both in experimental animals and in humans. To study the mechanisms involved in the development of the hepatic lesions, early changes in liver function in rats pretreated with the drug were investigated. Dosages and sampling times that did not result in hepatocellular injury, as indicated by release of marker enzymes, were applied. In isolated perfused livers from pretreated rats, bile flow and maximal secretion rate of taurocholate were decreased. An increase in biliary [14C]sucrose clearance suggested enhanced permeability of the bile tract and was correlated with increased inorganic phosphate concentration in bile. To assess the contribution of paracellular and transcellular pathways of sucrose, [14C]sucrose access into bile was analyzed by biliary off-kinetics after omission of the radioactive marker from the perfusion medium. An improved method was developed to quantitate the permeability of the bile tract by applying the classical flow equation to the paracellular portion of biliary sucrose clearance. With this method it was shown that pretreatment of rats with BCNU resulted in an increase in both diffusion and convection of paracellular sucrose from perfusate into bile. Accordingly, the fast access of horseradish peroxidase from perfusate into bile was facilitated in isolated perfused livers of BCNU-treated rats. The results indicate that an increase in paracellular permeability is an early alteration that may contribute to the development of hepatotoxic lesions caused by BCNU. It is shown that inert solute clearance can be used to assess paracellular permeability if the paracellular fraction is determined.

1-Naphthylisothiocyanate↗
PubMed1989

Hemodynamic and metabolic responses to leukotriene C4 in isolated perfused rat liver.

Responses of isolated perfused rat liver to leukotriene C4 were studied in order to assess the mechanisms involved in leukotriene-mediated liver injury. Infusion of leukotriene C4 (11 and 44 pmoles per min per gm liver weight) into the portal vein resulted in a rise in portal pressure, a decrease in oxygen consumption, an increase in hepatic glucose and lactate efflux and lactate/pyruvate ratio in the perfusate and a small decrease in bile flow. Isoproterenol (1 microM) counteracted the effects of leukotriene C4 on respiration and portal pressure, whereas bile flow and glucose efflux were reversibly stimulated. The same changes were observed upon withdrawal of leukotriene C4. The release of glucose was correlated with the increase in oxygen consumption upon both isoproterenol addition and withdrawal of leukotriene C4. These results are indicative of leukotriene C4-induced microcirculatory redistribution of perfusate flow. Since, in the presence of nitroprusside (50 microM), both the effects of leukotriene C4 and their reversal by isoproterenol were diminished, a vascular site of action can be assumed. Accordingly, the accompanying metabolic responses can be explained by gradual changes in oxygen supply to parts of the liver. Reversibility of the leukotriene C4 effects and lack of short-term impairment of viability of the isolated liver suggest that leukotriene-mediated liver injury is a long-term effect related to events subsequent to microcirculatory changes.

Animals↗
PubMed1987

Quantitative estimation of transcellular and paracellular pathways of biliary sucrose in isolated perfused rat liver.

A method was developed to estimate the relative contributions of paracellular and transcellular pathways to the total biliary clearance of sucrose in isolated perfused rat liver. When livers were perfused with a sucrose-containing medium (1 mM), biliary sucrose concentration reached an equilibrium of 165 +/- 27 microM within 10 min, without further significant change up to 40 min. After removal of sucrose from the perfusate, the decrease of the sucrose concentration in bile was found to obey biphasic first-order kinetics, showing a rapid initial decrease (half-life 3.3 +/- 0.5 min) and then a slower decrease (half-life 29.4 +/- 5.7 min). Both phases of decrease were further characterized. Pretreating rats with the cholestatic agents alpha-naphthyl isothiocyanate (ANIT), oestradiol valerate (OV) and colchicine increased the biliary equilibrium concentration and decreased the half-life of the fast phase of the biliary sucrose elimination. The slow phase was unaffected in the livers of ANIT- and OV-treated rats. The slow phase of biliary sucrose efflux was sensitive to colchicine treatment. A close correlation was observed between the slow-phase fraction of the biliary sucrose and the corresponding sucrose content of the liver. By quantitative analysis of the efflux kinetics the relative contribution of the paracellular pathway to the biliary clearance of sucrose was estimated to be 83 +/- 2% in control livers, which increased to about 90% in livers of pretreated animals. These results are important in view of the use of sucrose in evaluating the paracellular-pathway permeability in intra- and extra-hepatic cholestasis.

Animals↗
PubMed1987

Drug-induced intrahepatic cholestasis: characterization of different pathomechanisms.

The pathogenesis of intrahepatic cholestasis in rats was studied using isolated perfused livers as an experimental model. Three basic mechanisms were differentiated: Permeabilization of the bilio-sinusoidal barrier associated with electron microscopic alterations of the tight junctional complexes was found in livers of rats treated with alpha-naphthylisothiocyanate (ANIT, 250 mg/kg body weight). Consequences of these alterations were: reflux of bile constituents such as taurocholate and sulfobromophthalein and increased access to the biliary space of paracellular markers such as inulin and sucrose. The clear-cut mechanism of ANIT cholestasis was used to distinguish other mechanisms of intrahepatic cholestasis. Inhibition of the basic process of fluid secretion was found to be the primary event in the development of cholestasis induced by estrogens. After 5 days of treating rats with ethinyl estradiol (5 mg/kg/day), bile flow was diminished in isolated livers while the permeability of the biliary tract to sucrose and inulin was not affected. Accordingly, the maximal concentration of taurocholate in bile was increased, indicating that its secretion was sustained. The same effect was observed after 1 week of treatment with the depot estrogen estradiol valerate (1 mg/kg/week). After 3 weeks of treatment, however, the taurocholate concentration in bile was lowered and the clearance of sucrose was increased. Bile flow remained at the same cholestatic level for 20 weeks. These results suggest that estrogens have the potency to increase tight junctional permeability only in a second step in the development of cholestasis, following the inhibition of bile flow. An additional mode of secretory inhibition was induced by lowering the concentration of Ca2+ in the perfusate of isolated liver.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Naphthylisothiocyanate↗
PubMed1987

Increase in biliary permeability subsequent to intrahepatic cholestasis by estradiol valerate in rats.

To clarify the role of biliary permeability in estrogen-induced intrahepatic cholestasis, long-term experiments were performed in rats using estradiol 17 beta-valerate. Bile flow, secretion of taurocholate, biliary clearance of [14C]sucrose and [14C]inulin, and phosphate concentration in bile were determined in hemoglobin-free perfused livers excised from male rats pretreated for different time periods. Basal and taurocholate-stimulated bile flow were already reduced during the first 7-10 days of treatment and remained at the lower level for more than 12 wk. In contrast, the concentration of taurocholate in bile was elevated at 7 and 10 days but was lower than in controls after 3 wk. An increase in [14C]sucrose clearance after 3 wk indicated a moderate increase in the permeability of a paracellular pathway. The concentration of phosphate in bile was also increased after 3 wk. Detailed analysis of biliary sucrose and inulin clearances revealed that the diffusion permeability coefficient (k = 0.14) did not increase during the first 10 days of treatment but did increase to greater than 0.4 after 3 wk of treating rats with estradiol 17 beta-valerate. From the temporal sequence of the cholestatic responses it is concluded that the altered permeability of the biliary tree is not the primary event but occurs subsequent to the cholestasis induced by estrogens.

Animals↗
PubMed1986

On the state of calcium ions in isolated rat liver mitochondria. V. Development of a rapidly dischargeable pool of mitochondrial calcium during calcium-induced transition.

Ruthenium red-induced calcium efflux from rat liver mitochondria is accelerated in the course of calcium-mediated mitochondrial transition. Analysis of the efflux patterns reveals biexponential kinetics consisting of the native slow phase preceded by a faster phase developing in the presence of calcium. The data are consistent with a progressive transformation of mitochondrial calcium into a rapidly dischargeable pool prior to spontaneous calcium release. Analysis of the efflux pattern is proposed as a method to discriminate between different mechanisms of modulation of ruthenium red-induced calcium efflux. Thus, it is shown that acetate, in contrast to phosphate, stimulates ruthenium red-induced calcium efflux due to the development of the rapidly dischargeable pool of calcium.

Animals↗
PubMed1985

Regulation of canalicular bile formation by alpha-adrenergic action and by external ATP in the isolated perfused rat liver.

In isolated perfused rat liver, addition of adrenaline induced a complex response of bile flow including rapid, reversible stimulation (1/2-2 min), reversible inhibition (2-10 min), and prolonged stimulation. Both the reversible stimulation and the inhibition were mimicked by the alpha-sympathomimetic agonist phenylephrine but not by the beta-agonist isoproterenol. The reversible stimulation was a very early effect being terminated prior to all other alpha-adrenergic responses of liver. External ATP considerably lowered bile flow while inducing release of glucose and lactate, inhibition of respiration, and a reversible efflux of Ca2+. Variations of mannitol clearance parallel to those of bile flow indicate a canalicular origin of all changes.

Adenosine Triphosphate↗
PubMed1985

On the state of calcium ions in isolated rat liver mitochondria IV. Prevention of phosphate-induced mitochondrial destruction by ruthenium red-insensitive calcium release.

Ruthenium red prevented the spontaneous calcium release and the accompanying mitochondrial destruction occurring in calcium-loaded mitochondria in the presence of phosphate. Under these conditions delta pH and membrane potential delta psi were preserved and the ruthenium red-induced calcium efflux was low and at a constant rate. On prolonged incubation with calcium prior to addition of ruthenium red increasingly more mitochondrial calcium developed into a pool rapidly dischargeable by ruthenium red. This development was accompanied by stimulation of respiration which was, however, not abolished by ruthenium red as could have been expected if it had been caused by calcium cycling. Calcium therefore altered mitochondria by a different mechanism than by cycling across the inner membrane.

Animals↗
PubMed1984

On the state of calcium ions in isolated rat liver mitochondria. I. Ion fluxes and volume changes upon Ca2+ uptake under various ionic conditions.

As to functional consequences of Ca2+ uptake in isolated rat liver mitochondria, we simultaneously measured 3H2O and [14C]sucrose spaces, monovalent cation distribution, membrane potential and delta pH across the inner membrane, and [32P]phosphate and 45Ca2+ content in parallel incubations of different ionic composition. Without added Ca2+ and phosphate, mitochondrial matrix volume, membrane potential, and delta pH depended on the concentration and permeability of monovalent cations. Despite large differences in membrane potential, maximal Ca2+ uptake was identical under all conditions. Ca2+ uptake never provoked a volume change from which an osmotic active state of mitochondrial Ca2+ could be concluded. If matrix volume shrunk this could be totally accounted for by the loss of alkali ions exchanging for calcium ions. Even phosphate taken up in conjunction with Ca2+ was osmotically silent. Volume increases here occurring if K+ was permeabilized, solely resulted from K+ uptake, though this condition may give rise to irreversible mitochondrial damage with Ca2+ and phosphate release. As mitochondrial Ca2+ is bound, an electro-chemical equilibrium across the membrane is impossible for this ion. This has to be considered in any model describing equilibria of Ca2+ with mitochondria, though present models neglect this state of mitochondrial Ca2+.

Animals↗
PubMed1984

On the state of calcium ions in isolated rat liver mitochondria. II. Effects of phosphate and pH on Ca2+-induced Ca2+ release.

At high K+ concentration, the effect of phosphate on Ca2+ uptake and release was studied in isolated rat liver mitochondria. Phosphate stimulated uptake at moderately high Ca2+ concentration, and inhibited release at high pH. At low pH, phosphate accelerated Ca2+ release. Ca2+ was released after a lag phase. The time of onset and the velocity of Ca2+ release depended on Ca2+ concentration. Ca2+ release was associated with mitochondrial swelling and destruction of the permeability barrier for sucrose and for chloride. Mg2+ inhibited Ca2+ release and the accompanying events. Ruthenium red and EGTA protected mitochondria from the destructive Ca2+ release and induced an immediate, slow release of Ca2+ and phosphate. Destructive Ca2+ release depended on the time of preincubation of respiration-inhibited mitochondria in the presence of Ca2+, prior to respiration-initiated Ca2+ uptake. The presence of phosphate and mitochondrial energization antagonized the destructive effect of calcium ions. Ca2+ release by acetoacetate also depended on pH. At pH 6.8, phosphate-stimulated Ca2+ release by acetoacetate, while it inhibited the acetoacetate effect at pH 7.6. The results suggest that an essential cause for the destruction of mitochondrial integrity is an increase in the intramitochondrial concentration of free calcium ions under the influence of phosphate.

Acetoacetates↗