Cell swelling increases bile flow and taurocholate excretion into bile in isolated perfused rat liver.
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ABSTRACT:
SUBMITTER: Hallbrucker C
PROVIDER: S-EPMC1130729 | biostudies-other | 1992 Feb
REPOSITORIES: biostudies-other
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Project description:An increase of the hepatocellular hydratation state, induced by hypotonic exposure, amino acids or tauroursodeoxycholate, was shown to increase within minutes the Vmax of transcellular taurocholate transport and excretion into bile [Häussinger, Hallbrucker, Saha, Lang and Gerok (1992) Biochem. J. 288, 681-689]. This stimulatory effect of cell swelling on taurocholate excretion into bile is abolished in the presence of colchicine (5 microM). On the other hand, colchicine did not affect the stimulatory action of hypotonic cell swelling on 14CO2 production from [1-14C]glycine or [1-14C]glucose. Likewise, volume regulatory K+ fluxes following anisotonic exposure were not influenced in the presence of colchicine. Lumicolchicine (5 microM), a stereoisomer of colchicine without an inhibitory effect on microtubules, did not abolish the stimulation of taurocholate excretion into bile following hypo-osmotic exposure. Hypertonic cell shrinkage decreased taurocholate excretion into bile by about 35%; this effect was fully reversible upon normotonic re-exposure. With colchicine pretreatment, however, the hypertonicity-induced inhibition of taurocholate excretion was blunted and was no longer reversible upon normotonic re-exposure. The results suggest that stimulation of taurocholate excretion into bile in response to cell swelling involves a colchicine-sensitive, probably microtubule-dependent, mechanism, but not the stimulation of other cell-volume-sensitive pathways such as glycine oxidation or the pentose-phosphate shunt. It is hypothesized that the swelling-induced stimulation of taurocholate excretion into bile is due to a microtubule-dependent insertion of bile acid transporter molecules into the canalicular membrane.
| S-EPMC1132532 | biostudies-other
Project description:Exposure of isolated single-pass-perfused rat liver to hypo-osmotic media resulted in liver cell swelling and an inhibition of release of branched-chain amino acids. Similarly, cell swelling inhibited [3H]leucine release from perfused livers from rats in which liver proteins were prelabelled in vivo by intraperitoneal injection of L-[4,5-3H]leucine 16-20 h before the experiment. The effects of cell swelling on [3H]leucine release were fully reversible. [3H]Leucine release was also inhibited when cell swelling was induced by addition of glutamine (0.5-2 mM). There was a close relationship between the inhibition of [3H]leucine release and the degree of liver cell swelling, regardless of whether cell swelling was induced by hypo-osmotic perfusion or addition of glutamine. The data suggest that the known anti-proteolytic effect of glutamine is in large part due to glutamine-induced hepatocyte swelling.
| S-EPMC1149682 | biostudies-other
Project description:Perfusion of an isolated rat kidney with labelled bile acids, in a protein-free medium, resulted in the urinary excretion of the labelled bile acid, 3% being converted into polar metabolities in 1h. These metabolities were neither glycine nor taurine conjugates, nor bile acid glucuronides, and on solovolysis yielded the free bile acid. On t.l.c. the metabolite of [24-14C]lithocholic acid had the mobility of lithocholate 3-sulphate. The principal metabolite of [24-14C]chenodeoxycholic acid had the mobility of chenodeoxycholate 7-sulphate; trace amounts appeared as chenodeoxycholate 3-sulphate. [35S]sulphate was incorporated in chenodeoxycholic acid by the kidney, resulting in a similar pattern of sulphation. No disulphate salt of chenodeoxycholic acid was detected. These findings lend support to the hypothesis that renal synthesis may account for some of the bile acid sulphates present in urine in the cholestatic syndrome in man.
| S-EPMC1163754 | biostudies-other
Project description:High concentrations of urea were shown to induce a paradoxical regulatory volume decrease response with K(+) channel opening and subsequent hepatocyte shrinkage (Hallbrucker, C., vom Dahl, S., Ritter, M., Lang, F., and Häussinger, D. (1994) Pflügers Arch. 428, 552-560), although the hepatocyte plasma membrane is thought to be freely permeable to urea. The underlying mechanisms remained unclear. As shown in the present study, urea (100 mmol/liter) induced within 1 min an activation of ?(1) integrins followed by an activation of focal adhesion kinase, c-Src, p38(MAPK), extracellular signal-regulated kinases, and c-Jun N-terminal kinase. Because ?(5)?(1) integrin is known to act as a volume/osmosensor in hepatocytes, which becomes activated in response to hepatocyte swelling, the findings suggest that urea at high concentrations induces a nonosmotic activating perturbation of this osmosensor, thereby triggering a volume regulatory K(+) efflux. In line with this, similar to hypo-osmotic hepatocyte swelling, urea induced an inhibition of hepatic proteolysis, which was sensitive to p38(MAPK) inhibition. Molecular dynamics simulations of a three-dimensional model of the ectodomain of ?(5)?(1) integrin in water, urea, or thiourea solutions revealed significant conformational changes of ?(5)?(1) integrin in urea and thiourea solutions, in contrast to the simulation of ?(5)?(1) in water. These changes lead to an unbending of the integrin structure around the genu, which may suggest activation, whereas the structures of single domains remained essentially unchanged. It is concluded that urea at high concentrations affects hepatic metabolism through direct activation of the ?(5)?(1) integrin system.
| S-EPMC2937967 | biostudies-literature
Project description:Aristolochic acids are natural nitro-compounds found globally in the plant genus Aristolochia that have been implicated in the severe illness in humans termed aristolochic acid nephropathy (AAN). Aristolochic acids undergo nitroreduction, among other metabolic reactions, and active intermediates arise that are carcinogenic. Previous experiments with rats showed that aristolochic acid I (AA-I), after oral administration or injection, is subjected to detoxication reactions to give aristolochic acid Ia, aristolactam Ia, aristolactam I, and their glucuronide and sulfate conjugates that can be found in urine and feces. Results obtained with whole rats do not clearly define the role of liver and kidney in such metabolic transformation. In this study, in order to determine the specific role of the kidney on the renal disposition of AA-I and to study the biotransformations suffered by AA-I in this organ, isolated kidneys of rats were perfused with AA-I. AA-I and metabolite concentrations were determined in perfusates and urine using HPLC procedures. The isolated perfused rat kidney model showed that AA-I distributes rapidly and extensively in kidney tissues by uptake from the peritubular capillaries and the tubules. It was also established that the kidney is able to metabolize AA-I into aristolochic acid Ia, aristolochic acid Ia O-sulfate, aristolactam Ia, aristolactam I, and aristolactam Ia O-glucuronide. Rapid demethylation and sulfation of AA-I in the kidney generate aristolochic acid Ia and its sulfate conjugate that are voided to the urine. Reduction reactions to give the aristolactam metabolites occur to a slower rate. Renal clearances showed that filtered AA-I is reabsorbed at the tubules, whereas the metabolites are secreted. The unconjugated metabolites produced in the renal tissues are transported to both urine and perfusate, whereas the conjugated metabolites are almost exclusively secreted to the urine.
| S-EPMC3276251 | biostudies-literature
Project description:Ischemic post-conditioning (iPoCo) by coronary re-occlusion/reperfusion during immediate reperfusion after prolonged myocardial ischemia reduces infarct size. Mechanical manipulation of culprit lesions, however, carries the risk of coronary microembolization which may obscure iPoCo's cardioprotection. Pharmacological post-conditioning with exogenous triiodothyronine (T3) could serve as an alternative conditioning strategy. Similar to iPoCo, T3 may activate cardioprotective prosurvival pathways. We aimed to study T3's impact on infarct size and its underlying signal transduction. Hearts were isolated from male Lewis rats (200-380 g), buffer-perfused and subjected to 30 min/120 min global zero-flow ischemia/reperfusion (I/R). In additional hearts, either iPoCo (2 × 30 s/30 s I/R) was performed or T3 (100-500 µg/L) infused at reperfusion. Infarct size was demarcated with triphenyl tetrazolium chloride staining and calculated as percent of ventricular mass. Infarct size was reduced with iPoCo to 16 ± 7% vs. 36 ± 4% with I/R only. The maximum infarct size reduction was observed with 300 µg/L T3 (14 ± 2%). T3 increased the phosphorylation of protein kinase B and mitogen extracellular-regulated-kinase 1/2, both key enzymes of the reperfusion injury salvage kinase (RISK) pathway. Pharmacological RISK blockade (RISK-BL) during reperfusion abrogated T3's cardioprotection (35 ± 10%). Adult ventricular cardiomyocytes were isolated from buffer-perfused rat hearts and exposed to 30 min/5 min hypoxia/reoxygenation (H/R); reoxygenation was initiated without or with T3, respectively, and without or with RISK-BL, respectively. Maximal preservation of viability was observed with 500 µg/L T3 after H/R (27 ± 4% of all cells vs. 5 ± 3% in time-matched controls). Again, RISK-BL abrogated protection (11 ± 3%). Mitochondria were isolated at early reperfusion from buffer-perfused rat hearts without or with iPoCo or 300 µg/L T3, respectively, at reperfusion. T3 improved mitochondrial function (i.e.: increased respiration, adenosine triphosphate production, calcium retention capacity, and decreased reactive oxygen species formation) to a similar extent as iPoCo. T3 at reperfusion reduces infarct size by activation of the RISK pathway. T3's protection is a cardiomyocyte phenomenon and targets mitochondria.
| S-EPMC8055637 | biostudies-literature
Project description:1. Loading the isolated perfused liver from well-fed rats with xylitol (20mm) caused a depletion of adenine nucleotides and P(i) and an accumulation of alpha-glycerophosphate. The ATP content fell to 66% of the control value after 10min and to 32% after 80min. The ADP and AMP contents also fell. After 80min 63% of the total adenine nucleotides and 59% of the P(i) had been lost. 2. The alpha-glycerophosphate content rose from 0.13 to 4.74mumol/g at 10min and reached 8.02mumol/g at 40min. 3. Xylitol was rapidly metabolized, the main products being glucose, lactate and pyruvate. 4. The [lactate]/[pyruvate] ratio in the presence of xylitol rose to 30-40. 5. On perfusion of livers from starved animals the main product of xylitol metabolism was glucose and the mean ratio xylitol removed/glucose formed was 1.29 (corrected for endogenous glucose and lactate production). This is close to the predicted value of 1.2. 6. Evidence is presented indicating that the loss of adenine nucleotides caused by xylitol is not due to the increased ATP consumption but to the accumulation of alpha-glycerophosphate and depletion of P(i). 7. The loss of adenine nucleotides accounts for the hyperuricaemia which can occur after xylitol infusion in man. 8. The relevance of the findings to the clinical use of xylitol as an energy source is discussed.
| S-EPMC1177829 | biostudies-other
Project description:The output of proteins into bile was studied by using isolated perfused rat livers. Replacement of rat blood with defined perfusion media deprived the liver of rat serum proteins (albumin, immunoglobulin A) and resulted in a rapid decline in the amounts of these proteins in bile. When bovine serum albumin was incorporated into the perfusion medium it appeared in bile within 20 min and the amount in the bile was determined by the concentration of the protein in the perfusion medium. The use of a defined perfusion medium also deprived the livers of bile salts and the amounts of these, and of plasma-membrane enzymes [5'-nucleotidase (EC 3.1.3.5) and phosphodiesterase I], in bile declined rapidly. Introduction of micelle-forming bile salts (taurocholate or glycodeoxycholate) to the perfusion medium 80 min after liver isolation markedly increased the output of plasma-membrane enzymes but had no effect on the other proteins. The magnitude of this response was dependent on the bile salt used and its concentration in bile; there was little effect on plasma-membrane enzyme output until the critical micellar concentration of the bile salt had been exceeded in the bile. A bile salt analogue, taurodehydrocholate, which does not form micelles, did not produce the enhanced output of plasma-membrane enzymes. This work supports the view that the output of plasma-membrane enzymes in bile is a consequence of bile salt output and also provides evidence for mechanisms by which serum proteins enter the bile.
| S-EPMC1154256 | biostudies-other
Project description:The new immunosuppressive agent sirolimus generally is combined in transplant patients with cyclosporine and tacrolimus which both exhibit cholestatic effects. Nothing is known about possible cholestatic effects of these combinations which might be important for biliary excretion of endogenous compounds as well as of immunosuppressants. Rats were daily treated with sirolimus (1 mg kg(-1) p.o.), cyclosporine (10 mg kg(-1) i.p.), tacrolimus (1 mg kg(-1) i.p.), or a combination of sirolimus with cyclosporine or tacrolimus. After 14 days a bile fistula was installed to investigate the effects of the immunosuppressants and their combinations on bile flow and on biliary excretion of bile salts, cholesterol, and immunosuppressants. Cyclosporine as well as tacrolimus reduced bile flow (-22%; -18%), biliary excretion of bile salts (-15%;-36%) and cholesterol (-15%; -47%). Sirolimus decreased bile flow by 10%, but had no effect on cholesterol or bile salt excretion. Combination of sirolimus/cyclosporine decreased bile flow and biliary bile salt excretion to the same extent as cyclosporine alone, but led to a 2 fold increase of biliary cholesterol excretion. Combination of sirolimus/tacrolimus reduced bile flow only by 7.5% and did not change biliary bile salt and cholesterol excretion. Sirolimus enhanced blood concentrations of cyclosporine (+40%) and tacrolimus (+57%). Sirolimus blood concentration was increased by cyclosporine (+400%), but was not affected by tacrolimus. We conclude that a combination of sirolimus/tacrolimus could be the better alternative to the cotreatment of sirolimus/cyclosporine in cholestatic patients and in those facing difficulties in reaching therapeutic ranges of sirolimus blood concentration.
| S-EPMC1573383 | biostudies-other
Project description:Fibrates are hypolipidemic drugs that act as activators of peroxisome proliferator-activated receptor ? (PPAR?). In both humans and rodents, females were reported to be less responsive to fibrates than males. Previous studies on fibrates and PPAR? usually involved male mice, but little has been done in females. The present study aimed to provide the first comprehensive analysis of the effects of clofibrate (CLOF) and PPAR? on bile acid (BA) homeostasis in female mice. Study in WT male mice showed that a 4-day CLOF treatment increased liver weight, bile flow, and biliary BA excretion, but decreased total BAs in both serum and liver. In contrast, WT female mice were less susceptible to these CLOF-mediated responses observed in males. In WT female mice, CLOF decreased total BAs in the liver, but had little effect on the mRNAs of hepatic BA-related genes. Next, a comparative analysis between WT and PPAR?-null female mice showed that lack of PPAR? in female mice decreased total BAs in serum, but had little effect on total BAs in liver or bile. However, lack of PPAR? in female mice increased mRNAs of BA synthetic enzymes (Cyp7a1, Cyp8b1, Cyp27a1, and Cyp7b1) and transporters (Ntcp, Oatp1a1, Oatp1b2, and Mrp3). Furthermore, the increase of Cyp7a1 in PPAR?-null female mice was associated with an increase in liver Fxr-Shp-Lrh-1 signaling. In conclusion, female mice are resistant to CLOF-mediated effects on BA metabolism observed in males, which could be attributed to PPAR?-mediated suppression in females on genes involved in BA synthesis and transport.
| S-EPMC5915336 | biostudies-literature