Portacaval Shunted Rats Research Articles

Brain cholinergic impairment in liver failure

The cholinergic system is involved in specific behavioural responses and cognitive processes. Here, we examined potential alterations in the brain levels of key cholinergic enzymes in cirrhotic patients and animal models with liver failure. An increase (∼30%) in the activity of the acetylcholine-hydrolyzing enzyme, acetylcholinesterase (AChE) is observed in the brain cortex from patients deceased from hepatic coma, while the activity of the acetylcholine-synthesizing enzyme, choline acetyltransferase, remains unaffected. In agreement with the human data, AChE activity in brain cortical extracts of bile duct ligated (BDL) rats was increased (∼20%) compared to controls. A hyperammonemic diet did not result in any further increase of AChE levels in the BDL model, and no change was observed in hyperammonemic diet rats without liver disease. Portacaval shunted rats which display increased levels of cerebral ammonia did not show any brain cholinergic abnormalities, confirming that high ammonia levels do not play a role in brain AChE changes. A selective increase of tetrameric AChE, the major AChE species involved in hydrolysis of acetylcholine in the brain, was detected in both cirrhotic humans and BDL rats. Histological examination of BDL and non-ligated rat brains shows that the subcellular localization of both AChE and choline acetyltransferase, and thus the accessibility to their substrates, appears unaltered by the pathological condition. The BDL-induced increase in AChE activity was not parallelled by an increase in mRNA levels. Increased AChE in BDL cirrhotic rats leads to a pronounced decrease (∼50–60%) in the levels of acetylcholine. Finally, we demonstrate that the AChE inhibitor rivastigmine is able to improve memory deficits in BDL rats. One week treatment with rivastigmine (0.6 mg/kg; once a day, orally, for a week) resulted in a 25% of inhibition in the enzymatic activity of AChE with no change in protein composition, as assessed by sucrose density gradient fractionation and western blotting analysis. In conclusion, this study is the first direct evidence of a cholinergic imbalance in the brain as a consequence of liver failure and points to the possible role of the cholinergic system in the pathogenesis of hepatic encephalopathy.

Plasma redox status is impaired in the portacaval shunted rat – the risk of the reduced antioxidant ability

BackgroundPortacaval shunting in rats produces a reduction of hepatic oxidant scavenging ability. Since this imbalance in hepatic oxidant/antioxidant homeostasis could coexist with systemic changes of oxidant stress/antioxidant status, plasma oxidants and antioxidant redox status in plasma of portacaval shunted-rats were determined.ResultsMale Wistar male: Control (n = 11) and with portacaval shunt (PCS; n = 11) were used. Plasma levels of the oxidant serum advanced oxidation protein products (AOPP), lipid hydroperoxides (LOOH), the antioxidant total thiol (GSH) and total antioxidant status (TAX) were measured. Albumin, ammonia, Aspartate-aminotransferase (AST), Alanine-aminotransferase (ALT), thiostatin and alpha-1-acid glycoprotein (α1-AGP) were also assayed 4 weeks after the operation. AOPPs were significantly higher (50.51 ± 17.87 vs. 36.25 ± 7.21 μM; p = 0.02) and TAX was significantly lower (0.65 ± 0.03 vs. 0.73 ± 0.06 mM; p = 0.007) in PCS compared to control rats. Also, there was hypoalbuminemia (2.54 ± 0.08 vs. 2.89 ± 0.18 g/dl; p = 0.0001) and hyperammonemia (274.00 ± 92.25 vs. 104.00 ± 48.05 μM; p = 0.0001) and an increase of thiostatin (0.23 ± 0.04 vs. 0.09 ± 0.01 mg/ml; p = 0.001) in rats with a portacaval shunt. The serum concentration of ammonia is correlated with albumin levels (r = 0.624; p = 0.04) and TAX correlates with liver weight (r = 0.729; p = 0.017) and albumin levels (r = 0.79; p = 0.007)ConclusionThese findings suggest that in rats with a portacaval shunt a systemic reduction of oxidant scavenging ability, correlated with hyperammonemia, is principally produced. It could be hypothesized, therefore, that the reduced antioxidant defences would mediate a systemic inflammation.

Hyperammonaemia alters the mechanisms by which metabotropic glutamate receptors in nucleus accumbens modulate motor function

Activation of metabotropic glutamate receptors by injecting (S)3,5-dihydroxyphenylglycine (DHPG) in nucleus accumbens (NAcc) increases motor activity by different mechanisms in control rats and in rats with chronic liver failure due to portacaval shunt. In control rats DHPG increases extracellular dopamine in NAcc and induces locomotion by activating the 'normal' circuit: NAcc-->ventral pallidum-->medial-dorsal thalamus-->prefrontal cortex, which is not activated in portacaval shunt rats. In these rats, DHPG activates an 'alternative' circuit: NAcc-->substantia nigra pars reticulata-->ventro-medial thalamus-->prefrontal cortex, which is not activated in control rats. The reasons by which liver failure leads to activation of this 'alternative' circuit remain unclear. The aim of this work was to assess whether hyperammonaemia could be responsible for the alterations found in chronic liver failure. We injected DHPG in NAcc of control or hyperammonaemic rats and analysed, by in vivo brain microdialysis, the neurochemical responses of the 'normal' and 'alternative' circuits. In hyperammonaemic rats DHPG injection in NAcc activates both the 'normal' and 'alternative' circuits. In hyperammonaemia, activation of the 'alternative' circuit and increased motor response following metabotropic glutamate receptors activation in NAcc seem due to an increase in extracellular glutamate which activates AMPA receptors.

Motor activity is modulated via different neuronal circuits in rats with chronic liver failure than in normal rats

The mechanisms by which liver failure alters motor function remain unclear. It has been suggested that liver disease alters the neuronal circuit between basal ganglia and cortex that modulates motor function. Activation of group I metabotropic glutamate receptors in the nucleus accumbens (NAcc) by injecting (S)-3,5-dihydroxyphenylglycine (DHPG) activates this circuit and induces locomotion We analysed by in vivo brain microdialysis the function of the circuits that modulate motor function in rats with liver failure due to portacaval shunt (PCS). We inserted cannulae in the NAcc and microdialysis probes in the NAcc, ventral pallidum (VP), substantia nigra pars reticulata (SNr), medio-dorsal thalamus (MDT), ventro-medial thalamus (VMT) or prefrontal cortex (PFCx). We injected DHPG in the NAcc and analysed extracellular neurotransmitters concentration in these areas. The results indicate that in control rats DHPG induces locomotion by activating the 'normal' neuronal circuit: NAcc --> VP --> MDT --> PFCx. In PCS rats this circuit is not activated. In PCS rats, DHPG injection activates an 'alternative' circuit: NAcc --> SNr --> VMT --> PFCx. This circuit is not activated in control rats. DHPG injection increases dopamine in the NAcc of control but not of PCS rats, and glutamate in PCS but not in control rats. DHPG-induced increase in dopamine would activate the 'normal' neuronal circuit, while an increase in glutamate would activate the 'alternative' circuit. The identification of the mechanisms responsible for altered motor function and coordination in liver disease would allow designing treatments to improve motor function in patients with hepatic encephalopathy.

Glutamate‐induced activation of nitric oxide synthase is impaired in cerebral cortexin vivoin rats with chronic liver failure

It has been proposed that impairment of the glutamate-nitric oxide-cyclic guanosine monophosphate (cGMP) pathway in brain contributes to cognitive impairment in hepatic encephalopathy. The aims of this work were to assess whether the function of this pathway and of nitric oxide synthase (NOS) are altered in cerebral cortex in vivo in rats with chronic liver failure due to portacaval shunt (PCS) and whether these alterations are due to hyperammonemia. The glutamate-nitric oxide-cGMP pathway function and NOS activation by NMDA was analysed by in vivo microdialysis in cerebral cortex of PCS and control rats and in rats with hyperammonemia without liver failure. Similar studies were done in cortical slices from these rats and in cultured cortical neurons exposed to ammonia. Basal NOS activity, nitrites and cGMP are increased in cortex of rats with hyperammonemia or liver failure. These increases seem due to increased inducible nitric oxide synthase expression. NOS activation by NMDA is impaired in cerebral cortex in both animal models and in neurons exposed to ammonia. Chronic liver failure increases basal NOS activity, nitric oxide and cGMP but reduces activation of NOS induced by NMDA receptors activation. Hyperammonemia is responsible for both effects which will lead, independently, to alterations contributing to neurological alterations in hepatic encephalopathy.

Inflammation and hepatic encephalopathy

One of the neurological alterations in patients with minimal or overt hepatic encephalopathy is cognitive impairment. This impairment is reproduced in rats with chronic liver failure due to portacaval shunt (PCS). These rats show decreased ability to learn a conditional discrimination task in a Y-maze, likely due to reduced function of the glutamate-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in brain. It has been proposed that inflammation exacerbates the neuropsychological alterations induced by hyperammonemia, suggesting that inflammation-associated alterations may contribute to cognitive impairment in hepatic encephalopathy. This study assessed whether treatment with an anti-inflammatory drug, ibuprofen, is able to restore the function of the glutamate-NO-cGMP pathway in cerebral cortex in brain in vivo and/or learning ability in PCS rats. We show that PCS rats have increased levels of interleukin-6 and increased activities of cyclooxygenase and of inducible NO synthase in cerebral cortex, indicating the presence of inflammation. Chronic treatment with ibuprofen normalizes cyclooxygenase and inducible NO synthase activities but not interleukin-6 levels. Moreover, ibuprofen normalizes the function of the glutamate-NO-cGMP pathway in cerebral cortex in vivo and completely restores the ability of rats with chronic liver failure to learn the Y-maze task. This supports that inflammation contributes to the cognitive impairment in hepatic encephalopathy. the results reported point to the possible therapeutic utility of decreasing inflammation in the treatment of the cognitive deficits in patients with minimal or overt hepatic encephalopathy.

Hypolocomotion in rats with chronic liver failure is due to increased glutamate and activation of metabotropic glutamate receptors in substantia nigra

Patients with hepatic encephalopathy show altered motor function, psychomotor slowing and hypokinesia. The underlying mechanisms remain unclear. This work's aims were: (1) to analyse in rats with chronic liver failure due to portacaval shunt (PCS) the neurochemical alterations in the basal ganglia-thalamus-cortex circuits; (2) to correlate these alterations with those in motor function and (3) to normalize motor activity of PCS rats by pharmacological means. Extracellular neurotransmitters levels were analysed by in vivo brain microdialysis. Motor activity was determined by counting crossings in open field. Extracellular glutamate is increased in substantia nigra pars reticulata (SNr) of PCS rats. Blocking metabotropic receptor 1 (mGluR1) in SNr normalizes motor activity in PCS rats. In ventro-medial thalamus of PCS rats GABA is increased and it is normalized by blocking mGluR1 in SNr. Blocking mGluR1 in SNr increases and mGluR1 activation reduces glutamate in motor cortex and motor activity. Increased extracellular glutamate and activation of mGluR1 in SNr are responsible for reduced motor activity in rats with chronic liver failure. Blocking mGluR1 in SNr normalizes motor activity in PCS rats, suggesting that, under appropriate conditions, similar treatments could be useful to treat the psychomotor slowing and hypokinesia in patients with hepatic encephalopathy.

Sustained Citalopram Treatment in Experimental Hepatic Encephalopathy: Effects on Entrainment to the Light‐Dark Cycle and Melatonin

Patients with chronic hepatic encephalopathy often display altered diurnal rhythm as well as other affective disturbances which motivate treatment with antidepressants. We investigated the effects of sustained treatment with citalopram (10 mg/kg daily, 10 days) on 24-hr behavioural open-field activities in portacaval-shunted (PCS) rats and sham-operated control rats. In addition, the daytime and nighttime serum melatonin levels, as well as the serum concentrations of the enantiomers of citalopram and its metabolites, were analyzed. Untreated PCS rats showed reduced locomotor and rearing activities during nighttime. Citalopram treatment resulted in elevated behavioural activity in the PCS rats during night, indicative of an improved entrainment to the light-dark cycle, whereas no behavioural effect could be observed in sham rats. Higher melatonin levels in both PCS and sham rats were observed during nighttime compared with daytime, but the untreated PCS rats also showed higher daytime melatonin level than the corresponding sham group. Citalopram treatment seemed not to have any major effect on the melatonin levels. Higher serum levels of both citalopram and metabolites were observed in PCS rats as compared to sham rats. An altered ratio between the S- and R-enantiomers could also be observed in the PCS rats. In conclusion, the present data support the contention of a disturbed diurnal rhythm, and that the melatonin activity may be altered, in chronic hepatic encephalopathy. The citalopram treatment resulted in similar behavioural performances and daytime serum melatonin levels in PCS rats and controls, although pharmacokinetic differences were present between the groups.

Quantitative Studies of Liver Atrophy After Portacaval Shunt in the Rat

It is well known that portacaval shunting ultimately leads to a decrease in liver volume and hepatic function, but the mechanism is uncertain. The aim of the present study was to evaluate the effect of portacaval shunting (PCS) upon the morphological changes that occur in the liver in rats after port caval anastomosis. Sixty-six male rats underwent either PCS (n = 35) or sham operations (n = 31). Hormone levels were determined in blood samples taken just before removal and weighing of the livers. Hematoxylin and eosin-stained sections were used for quantitative morphometric analysis. Apoptosis, mitosis, and cellular organelles also were assessed quantitatively. There was a significant reduction in the liver mass together with testosterone levels in PCS rats in comparison with sham rats. The distance between presinusoidal and postsinusoidal vessels was reduced from 500 mum in the sham rats to 299 mum in the PCS rats (P = 0.000001). Within the same group, there was a significant reduction in the area of hepatocyte nuclei in zone 3 in comparison with zone 1. Electron microscopy revealed a highly significant (P = 0.0007) reduction in the membrane-bound cytoplasmic organelles of zone 3 hepatocytes in PCS rats in comparison with the sham rats. Apoptosis was increased in zone 3 in PCS rats (P = 0.00001), whereas in zone 1 of the same group, there was an associated increased in mitosis (P = 0.000001). Overall, the degree of apoptosis was in excess of mitosis, resulting in a general loss of liver mass. Morphometric analysis at cellular and subcellular levels confirms the morphological findings of liver atrophy in PCS rats. The mechanism of atrophy is a complex one. Portacaval shunting leads to hepatic atrophy that, in turn, results in microcirculatory and hormonal changes that further contribute to liver cell loss in this animal model.

Soy protein diet prevents hypermethioninemia caused by portacaval shunt in rats

In hepatic disorders, abnormal plasma amino acid profiles are observed. In this study, we examined whether soy protein isolate (SPI) improved plasma methionine concentration in the model animals. Portacaval shunt (PCS) increased alanine aminotransferase (ALT) activity and methionine concentration in blood of rats fed a 40% casein diet supplemented with 0.6% methionine (casein-M diet). A 40% SPI diet supplemented with 1.28% methionine (SPI-M diet), which contained the same amount of methionine as that in 40% casein-M diet, normalized plasma ALT activity and methionine level in PCS rats. These effects of a SPI diet may be due to its amino acid composition, since an amino acid mixture diet mimicking a 40% SPI-M diet was also effective to hypermethioninemia of PCS rats. To find key enzymes for the beneficial effect of soy protein, we examined effects of a 40% SPI-M or casein-M diet on the activities of three methionine-metabolizing enzymes in liver of PCS rats. A SPI-M diet stimulated only the activity of cystathionine gamma-lyase, compared with a casein-M diet. A SPI diet has a preventive effect on hypermethioninemia, at least in part, by stimulating cystathionine gamma-lyase activity in liver and may be used for nutritional management of liver disorders with hypermethioninemia.

Open‐Field Behavioural Alterations in Liver‐Impaired and Sham‐Operated Rats after Acute Exposure to the Antidepressant Venlafaxine

Patients with chronic liver impairment often display symptoms of affective psychiatric nature where the choice for antidepressant treatment is rational. Since caution is recommended when these drugs are used in such patients, a dose reduction is usually performed. We have previously reported that a dose reduction to liver-impaired portacaval shunted rats has resulted in similar brain concentrations of venlafaxine as compared to sham-operated control rats that received a two times higher dose. The main aim of the present study was therefore to investigate if this "normalisation" in pharmacokinetics of the portacaval-shunted rats also was true for the pharmacodynamic response in terms of drug effect on spontaneous open-field behaviour. Thus, portacaval-shunted rats received a single reduced dose (5 mg/kg) of venlafaxine or saline, whereas sham-operated rats received either 10 mg/kg or saline. Thereafter, central and peripheral arena locomotor and rearing activities were recorded during 60 min. The venlafaxine-treated portacaval-shunted and sham rats displayed reduced and unchanged overall behavioural activities compared with corresponding controls, respectively. However, the ratios between centrally and peripherally performed behavioural activities were higher in the venlafaxine-treated sham rats, indicating an increase in central arena activity as compared to the sham-saline and portacaval-shunted rats. The present study indicates that, despite a 50% dose reduction, caution still is necessary when antidepressants are used in liver insufficient subjects. This study also shows the importance of detailed open-field behavioural studies in which both central and peripheral activities are recorded for measurement of open-field behavioural drug effects.

Deficits in cortico-striatal synaptic plasticity and behavioral habituation in rats with portacaval anastomosis

Hepatic encephalopathy is characterized by disturbances of motor and cognitive functions involving the basal ganglia. So far no standards for assessment of neuropsychiatric abnormalities (disorders of sleep, mood, anxiety and personality) in subclinical hepatic encephalopathy have been defined. Using an animal model of mild (subclinical) hepatic encephalopathy we investigated now striatum-related behaviors and cortico-striatal synaptic plasticity in rats 2 months after introduction of a portacaval shunt and sham-operated matched controls. In a novel open field portacaval shunt rats displayed less locomotor activity; unlike controls they also showed no habituation to the field and no recall of the field environment after 24 h, indicative of cognitive deficit. The elevated-plus maze test indicated no differences in fear/anxiety in the portacaval shunt animals. Tetanic stimulation of cortical afferents in magnesium-free solution evoked an N-methyl- d-aspartate-dependent long-term potentiation in sham-operated animals. In portacaval shunt animals long-term potentiation was significantly impaired. Histamine, a potent modulator of cortico-striatal transmission, induced a larger long-term depression of field potentials in control compared with portacaval shunt rats. In conclusion, a combination of electrophysiological and behavioral approaches has revealed functional changes in cortico-striatal transmission. These data are relevant for understanding the mechanisms of motor and cognitive dysfunctions in hepatic encephalopathy patients and for the development of precise psychometric tests, evaluating cognitive deficits in subclinical hepatic encephalopathy.

Development of bladder urothelial hyperplasia and carcinoma in portacaval shunted rats is not dependent upon urolithiasis

The pathogenesis of bladder tumors is poorly understood, possibly due to the lack of a suitable experimental model that is drug-free. The aim of the present study was to determine whether bladder tumors could be reproduced reliably in portacaval anastomosis (PCS) rats and whether induction is due to urolithiasis from the development of bladder stones. Eighteen male Sprague–Dawley rats were anaesthetised with isoflurane. Twelve were subjected to portacaval anastomosis and allowed to recover for 38 weeks and the remaining 6 underwent sham control procedures. They were then re-anaesthetised, the anastomosis checked for patency and the bladders and livers excised, fixed, block-mounted, sectioned and stained with haematoxylin and eosin staining for histological examination. None of the control rats developed bladder wall abnormalities of any recognisable nature. However, 5 (42%) of the PCS group had urothelial lesions and bladder stones present and a further 5 (42%) had urothelial lesions alone with no recognisable evidence of bladder stone formation. One PCS rat had bladder stones alone and the remaining PCS rat had an apparently normal bladder epithelium and no stones. Thus, 10 (83%) of the 12 PCS rats developed epithelial lesions and half of these did not display evidence of bladder stone formation. This represented a highly significant difference between the development of bladder stones and the occurrence of urothelial lesions in PCS rats ( P > 1.0, χ 2 analysis). Urothelial lesions, therefore, can be reproduced in PCS rats. Their occurrence appears independent of bladder stone formation.

Skeletal muscle atrophy is associated with an increased expression of myostatin and impaired satellite cell function in the portacaval anastamosis rat.

Proliferation and differentiation of satellite cells are critical in the regeneration of atrophied muscle following immobilization and aging. We hypothesized that impaired satellite cell function is responsible for the atrophy of skeletal muscle also seen in cirrhosis. Myostatin and insulin-like growth factor 1 (IGF1) have been identified to be positive and negative regulators, respectively, of satellite cell function. Using a rat model of cirrhosis [portacaval anastamosis (PCA)] and sham-operated controls, we examined the expression of myostatin, its receptor activinR2b, and its downstream messenger cyclin-dependent kinase inhibitor p21 (CDKI p21) as well as IGF1 and its receptor in the gastrocnemius muscle. Expression of PCNA, a marker of proliferation, and myogenic regulatory factors (myoD, myf5, and myogenin), markers of differentiation of satellite cells, were also measured. Real- time PCR for mRNA and Western blot assay for protein quantification were performed. PCA rats had lower body weight and gastrocnemius weight compared with sham animals (P < 0.05). PCNA and myogenic regulatory factors were lower in PCA rats (P < 0.05). Myostatin, activinR2b, and CDKI p21 were higher in the PCA animals (P < 0.05). The expression of IGF1 and its receptor was lower in liver and skeletal muscle of PCA animals (P < 0.05). These data suggest that skeletal muscle atrophy seen in the portacaval shunted rats is a consequence of impaired satellite cell proliferation and differentiation mediated, in part, by higher myostatin and lower IGF1 expression.

Liver atrophy following portacaval shunt in normal rats: A morphologic and ultrastructural study

The aim of the current study was to examine morphological and ultrastructural changes in the rat liver in an experimental model of chronic liver disease (end-to-side portacaval shunt). The surgical procedure providing an end-to-side portacaval shunt (PCS) was performed in Wistar rats. The liver and pancreas weights were determined 8 weeks after the operation, when liver histology and ultrastructural patterns of hepatocytes were examined. Body weights were not significantly different between the groups 8 weeks after the operation. Liver weight was significantly lower in PCS rats than in control and sham operated (SHAM) rats. The same was observed when liver weight was expressed as a percentage of body weight. Pancreas weight was significantly greater in PCS than in control and SHAM rats. Liver histology in rats with PCS showed glycogen depletion and sinusoidal dilatation around the hepatic vein. Kupffer's cells were filled with haemosiderin. The hepatocytes surrounding the portal space exhibited degenerative and microvesicular fatty changes. Multiplication of the biliary ductules in the portal space was present. Atrophy of hepatocytes occurred in other parenchymal zones and apoptopic hepatocytes were seen more frequently in rats with PCS. The ultrastructural characteristics of hepatocyte cell lesions in rats with PCS at the end point of our experiment included reduction and fragmentation of rough endoplasmic reticulum with destroyed or dilated cisternae and few polysomes accompanied by proliferation of smooth endoplasmic reticulum. The present study suggests that end-to-side PCS in rats causes liver atrophy and that the morphological and ultrastructural changes in the hepatocytes partially explain the metabolic and endocrine abnormalities.

811 Hyperglycemia and brain edema in portacaval-shunted rats receiving an ammonia infusion

811 Hyperglycemia and brain edema in portacaval-shunted rats receiving an ammonia infusion

Treatment of liver failure in rats with end-stage cirrhosis by transplantation of immortalized hepatocytes

The shortage of organ donors has impeded the development of human hepatocyte transplantation. Immortalized hepatocytes could provide an unlimited supply of transplantable cells. To determine whether immortalized hepatocytes could provide global metabolic support in end-stage liver disease, 35 immortalized rat hepatocyte clones were developed by transduction with the gene encoding the simian virus 40 T antigen (SV40Tag). The SV40Tag sequence and a suicide gene, herpes simplex virus thymidine kinase (HSV-tk), were flanked by loxP sequences so that they could be excised by Cre/ lox recombination. When transplanted into the spleens of portacaval-shunted rats, 3 of the 35 immortalized hepatocyte clones prevented the development of hyperammonemia-induced hepatic encephalopathy. The protection was reversed by treatment with ganciclovir, which kills HSV-tk–expressing cells. Transplantation of alginate-encapsulated, immortalized hepatocytes into the spleens of cirrhotic rats resulted in significant improvement in prothrombin time, serum albumin and bilirubin levels, hepatic encephalopathy score, and duration of survival. The metabolic support provided by the immortalized cells equaled that observed after transplantation of primary rat hepatocytes. In conclusion, immortalized hepatocytes can function as well as primary hepatocytes following transplantation and can be engineered to contain safeguards that could make them clinically useful. Further investigation is warranted regarding the mechanisms of loss of mass or function of the transplanted hepatocytes over time and how the relatively few engrafted hepatocytes can ameliorate liver decompensation in cirrhosis. (H EPATOLOGY 2002;36:386-394.)

Effects on drug disposition, brain monoamines and behavior after chronic treatment with the antidepressant venlafaxine in rats with experimental hepatic encephalopathy

Patients with chronic hepatic encephalopathy (HE) may present affective symptoms and antidepressant drug treatment in this condition is not uncommon. The present microdialysis study investigated treatment with the chronic antidepressant venlafaxine (VEN) in experimental HE with regard to tentative changes in pharmacokinetic and/or pharmacodynamic parameters. Three weeks after portacaval shunt (PCS) or sham operation in rats, VEN (10 mg/kg daily) was administered by implanted osmotic minipumps. VEN treatment for 14 days resulted in higher concentrations of VEN in PCS rats than in sham controls in serum and brain compartments, and the VEN levels in serum and brain were strongly inter-correlated. The serum N-desmethylvenlafaxine concentration did not differ between the groups, but correlated with the serum VEN levels. The other VEN metabolites were below the quantification limits. VEN treatment for 9–12 days significantly stimulated locomotion and rearing in the open field in sham controls, but failed to do so in the PCS rats. The concentrations of noradrenaline, dopamine, 5-HT, and 5-HIAA in neocortical dialysates were higher in PCS than in sham rats after 14 days of VEN treatment, but the elevations reached statistical significance only in the case of dopamine and 5-HIAA. In summary, there were significant pharmacokinetic and pharmacodynamic alterations in rats with experimental HE as compared to controls. The described experimental HE model may be useful for continued pharmacokinetic/pharmacodynamic interaction studies to unravel the pathophysiological consequences of HE on the CNS.

GeneChip analysis shows altered mRNA expression of transcripts of neurotransmitter and signal transduction pathways in the cerebral cortex of portacaval shunted rats.

Identifying the gene expression changes induced by hepatic encephalopathy (HE) leads to a better understanding of the molecular mechanisms of HE-induced neurological dysfunction. Using GeneChip and real-time PCR, the present study evaluated the gene expression profile of rat cerebral cortex at 4 weeks after portacaval shunting. Among 1,263 transcripts represented on the chip, mRNA levels of 31 transcripts were altered (greater than twofold; 16 increased and 15 decreased) in the portacaval shunted (PCS) rat compared to sham control. Changes observed by GeneChip analysis were confirmed for 20 transcripts (8 increased, 7 decreased, and 5 unchanged in PCS rat brain) by real-time PCR. Neurotransmitter receptors, transporters, and members of the second messenger signal transduction are the major groups of genes altered in PCS rat brain. Of importance was that the increased heme oxygenase-1 and decreased Cu,Zn-superoxide dismutase expression observed raise the possibility of oxidative stress playing a pathogenic role in chronic HE.

Disposition of venlafaxine enantiomers in rats with hepatic encephalopathy after chronic drug treatment.

Portacaval shunted (PCS) rats, a model of hepatic encephalopathy, and control animals were administered racemic venlafaxine for 14 days (10 mg/kg). The levels of the S- and R-enantiomers and the S/R-enantiomer ratios of venlafaxine and its metabolites were assessed by an enantiomer-selective chromatographic assay in serum, brain parenchyma, and brain dialysate of both groups. Higher levels of the S- and R-enantiomers of venlafaxine were found in serum and brain of PCS vs. normal rats (median values of S- and R-venlafaxine in serum: 290 and 201 nM in PCS; 97 and 66 nM in normal rats; median values of S- and R-venlafaxine in cortex: 956 and 939 nM in PCS; 357 and 318 nM in normal rats). Interestingly, similar S/R-venlafaxine ratios were observed in PCS and normal rats both in serum (S/R = 1.4) and brain compartments (S/R = l.0-1.1). These findings may have clinical relevance for the safety of venlafaxine in chronic hepatic encephalopathy.