Ursodeoxycholic acid and in vitro vasoactivity of hydrophobic bile acids.

Lipophilic bile acids, such as deoxycholic acid (DCA), are nonspecific endothelium-independent vasorelaxants whose underlying basis is complex, involving membrane calcium channels blockade and receptor antagonism. The vasorelaxant action of these acids has also been linked to the generation of reactive oxygen species and an increased extent of lipid peroxidation. Ursodeoxycholic acid (UDCA) is a naturally occurring tertiary dihydroxy hydrophilic acid whose mechanism of action has been attributed to minimizing the effects of lipophilic bile acids. Hence, we considered UDCA might be a useful pharmacological tool to delineate the role of enhanced lipid peroxidation in lipophilic bile acid-induced vasorelaxation. UDCA abrogates in vitro DCA-induced vasorelaxation in rat aortic rings and can suppress DCA-initiated lipid peroxidation in vascular smooth muscle microsomal membrane fractions prepared from the rat aortae. Three different studies were performed. In study 1, the ability of UDCA to restore the DCA-blunted contractile response to the alpha1-adrenoceptor, phenylephrine in rat aortic rings, was evaluated. In study 2, the ability of UDCA to restore DCA-induced vasorelaxation in precontracted rat aortic rings was assessed. In study 3, the ability of UDCA to suppress the increased extent of lipid peroxidation effected by DCA in vascular smooth muscle microsomal membrane fractions prepared from rat aortae was measured using the thiobarbituric acid reactive substance (TBARS) assay. UDCA, at a concentration equivalent to that seen in the plasma of patients with cholestatic liver disease treated with the bile acid, partially restored DCA-induced impaired contractility, prevented DCA-induced vasorelaxation, and abolished DCA-induced increases in the extent of lipid peroxidation. In conclusion, these data suggest that DCA-induced vasorelaxation is mediated by increasing the extent of lipid peroxidation in vascular tissue.

Vascular smooth muscle cell signaling in cirrhosis and portal hypertension.

Abnormal vascular responsiveness to ligands has been frequently observed in cirrhosis and portal hypertension, but its existence is not proven. The signaling pathways in vascular smooth muscle cells (VSMCs) have been studied only in animal models of cirrhosis and portal hypertension. Emerging evidence suggests that active relaxation, expressed as augmented content or activity of effectors within the cyclic AMP signaling pathway and suppressed content or activity of effectors in the inositol 1,4,5-trisphosphate/1,2-diacylglycerol signaling pathway, may be occurring in VSMCs of the splanchnic circulation in portal hypertension. The evidence supporting the existence of this phenomenon in the VSMCs of extrasplanchnic circulations in portal hypertension, as well as in the splanchnic circulation when chronic cellular damage is present, is very limited. The status of the other signaling pathways associated with contractile functions of the VSMCs, viz., cyclic GMP and tyrosine kinase-linked pathways, is unknown. The status of all the signaling pathways in non-contractile functions of VSMCs, such as growth and remodeling, has not been studied. As our overall understanding on the signaling pathways in VSMCs is only emerging, it is premature to implicate altered activity of the signaling pathways as the underlying basis of vascular hyporesponsiveness in cirrhosis and portal hypertension, and to extrapolate these limited observations to the human condition.

Oxidative stress and vascular smooth muscle cell function in liver disease.

Reactive oxygen species and reactive nitroxy species are now being recognized as regulatory molecules in signaling pathways influencing contractile and noncontractile functions of healthy vascular smooth muscle cells. In liver disease, oxidative stress is a systemic phenomenon, whose extent correlates with the severity of disease. A role for oxidative stress in the development of the hyperdynamic circulation in portal hypertension has been proposed. Evaluation of the limited available data indicates that it is premature to conclude that oxidative stress per se impacts on vascular smooth muscle cell function in liver disease.

Ursodeoxycholic acid suppresses extent of lipid peroxidation in diseased liver in experimental cholestatic liver disease.

The therapeutic benefit of ursodeoxycholic acid (UDCA) in treating cholestatic liver disease is globally recognized. It is generally accepted that the mechanism of action of UDCA can be attributed to several diverse processes that appear to be uniformly targeted towards minimizing the deleterious actions of accumulated hydrophobic bile acids in the cholestatic liver. Since hydrophobic bile acids are prooxidants, emerging in vitro evidence suggests that UDCA may have an antioxidant mechanism of action. We hypothesize that UDCA suppresses the extent of lipid peroxidation in the cholestatic liver. This hypothesis was tested by assessing the extent of lipid peroxidation in livers harvested from chronic bile duct ligated (CBDL) rats dosed daily for 24 days with 5, 10, or 15 mg/kg UDCA. The extent of lipid peroxidation was evaluated by determining the hepatic content of conjugated dienes, lipid peroxides, and malondialdehyde. The data were compared with identical data collected from unoperated control and 24-day bile duct manipulated (SO) rats. In the two groups of control rats, UDCA has no effect on the serum indices of liver function. In CBDL rats, UDCA suppressed the increased extent of lipid peroxidation in the liver in a dose-dependent manner in the absence of improvement of laboratory parameters of liver function and hepatic architecture. In conclusion, UDCA suppresses the augmented extent of lipid peroxidation in the diseased liver of CBDL rats.

Evidence of a systemic phenomenon for oxidative stress in cholestatic liver disease.

BACKGROUND: There is considerable evidence indicating that the severity of hepatic damage in individuals with cholestatic liver disease is causally associated with the extent of intrahepatic oxidative stress. Increased levels or accelerated generation of reactive oxygen species and toxic degradative products of lipid peroxidation have been reported in the plasma of individuals with chronic liver disease and animal models of liver disease. Hence, by virtue of their increased presence in the circulation, it is not unreasonable to suppose that they may account for extrahepatic tissue damage in chronic liver disease. MATERIALS AND METHODS: This hypothesis was tested by determining plasma levels of the ubiquitous antioxidant glutathione (GSH) and lipid peroxides (LP), together with assessment of the extent of lipid peroxidation in the kidney, brain, and heart, in 24 day chronically bile duct ligated (CBDL) rats. The extent of lipid peroxidation in tissues was based on measurement of conjugated dienes, lipid peroxides, and malondialdehyde (MDA) content. Data were compared with identical data collected from unoperated control, pair fed, 24 day bile duct manipulated (sham operated), and pair fed sham operated rats. RESULTS: In CBDL rats, total and reduced plasma GSH levels were almost half those determined in all control rats. Plasma, kidney, and heart LP levels were significantly increased in CBDL rats compared with controls. MDA levels were significantly higher in the kidney, brain, and heart homogenates prepared from CBDL rats compared with MDA content measured in tissue homogenates prepared from the four groups of control rats. CONCLUSIONS: Our data show that experimental cholestatic liver disease is associated with increased lipid peroxidation in the kidney, brain, and heart. Hence we have concluded that the oxidative stress in cholestatic liver disease is a systemic phenomenon probably encompassing all tissues and organs, even those separated by the blood-brain barrier.

On the in vitro vasoactivity of bile acids.

We compared the vasorelaxant action of nine different bile acids and correlated their vasorelaxant activity with their individual indices for hydrophobicity or lipophilicity. Vasorelaxant activity correlated with the relative lipid solubility of bile acids with lipophilic bile acids exhibiting the greatest vasorelaxant activity with modest to no vasorelaxant activity exhibited by hydrophilic bile acids. We also investigated whether bile acid-induced vasorelaxation is mediated by antagonism of a prototypal contractile receptor, the alpha(1)-adrenoceptor, by stimulation of a bile acid surface membrane receptor, by the release of endothelium-derived relaxant factors, by promoting the generation of reactive oxygen species and increasing the extent of lipid peroxidation, or by modifying membrane fluidity. Lipophilic bile acids induce vasorelaxation possibly by antagonizing alpha(1)-adrenoceptors, a phenomenon that manifests itself as a lowering of the affinity of vascular alpha(1)-adrenoceptors. Bile acid-induced vasorelaxation was not dependent upon stimulation of a bile acid surface membrane receptor or the release of endothelium-derived relaxant factors. Lipophilic bile acids can also increase the extent of lipid peroxidation with a subtle reduction in the fluidity of rat vascular smooth muscle membranes not associated with loss of membrane cholesterol or phospholipid. We have concluded that lipophilic bile acids are non-selective vasorelaxants whose mechanism of action is a multifaceted process involving antagonism of contractile surface membrane receptors possibly effected by an increased extent of lipid peroxidation and/or membrane fluidity but occurs independent of the release of endothelial-derived relaxant factors or stimulation of a surface membrane bile acid binding site.

The effects of bile acids on beta-adrenoceptors, fluidity, and the extent of lipid peroxidation in rat cardiac membranes.

Bile acids have been proposed as a causative factor for the cardiomyopathy of cholestatic liver disease, since they cause negative inotropism and chronotropism and attenuate cardiac responsiveness to sympathetic stimulation. Bile acids can also modify membrane fluidity and generate reactive oxygen species (ROS). The effects of 10(-6)-10(-3) M deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) and their taurine conjugates, TDCA and TCDCA, on (1) the binding characteristics of beta-adrenoceptors, (2) membrane fluidity, and (3) the extent of lipid peroxidation in rat cardiac membranes were assessed. The results were compared to the effects of the oxidant, 10(-4)-10(-3) M hydrogen peroxide (H(2)O(2)), and the membrane-fluidizing compound, 5 x 10(-5) M 2-(2-methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl)octanoate (A(2)C). Cardiac beta-adrenoceptor density alone was reduced at 10(-4) M bile acid concentration while, at 10(-3) M bile acids, reductions in both receptor density and affinity were seen. At 10(-4) M H(2)O(2), receptor number and affinity were reduced, whereas A(2)C increased receptor affinity without affecting receptor density. Bile acids (10(-3) M) and 10(-4) M H(2)O(2) reduced membrane fluidity. H(2)O(2) caused a concentration-dependent increase in the extent of lipid peroxidation, whereas the bile acids and A(2)C had no effect. Bile acids (10(-4) M) reduced beta-adrenoceptor density in the absence of variations in membrane fluidity and in the extent of membrane lipid peroxidation. This result suggests that bile acids, at concentrations equivalent to the plasma/serum total or estimated free bile acid concentration, may have a possible role in the etiology of cardiomyopathy of cholestatic liver disease. At 10(-3) M bile acid concentration, beta-adrenoceptor number and affinity were adversely affected, accompanied by a decrease in membrane fluidity but without any significant increase in the extent of membrane lipid peroxidation. Although cardiac beta-adrenoceptor density and affinity and membrane fluidity were adversely affected by bile acids, the relevance of these findings to our understanding of the etiological basis of hepatic cardiomyopathy is questionable, since such concentrations exceeded the highest concentrations seen in the plasma and/or tissues of patients with cholestatic liver disease.

A pilot study on the hemodynamic effect of short-term ursodeoxycholic acid therapy in patients with stable liver cirrhosis.

OBJECTIVE: Total serum bile acid concentrations are elevated in individuals with liver disease. Ursodeoxycholic acid (UDCA) therapy in such patients results in a further significant rise in plasma levels to the extent that it becomes the major circulating bile acid. In laboratory animals, bile acids, such as taurocholic acid, have also been shown to possess a diuretic-like action, as they can promote diuresis, natriuresis, and kaliuresis by inhibiting tubular sodium reabsorption. The aim of the present study was to assess the effect of 1 month's UDCA therapy on cardiovascular function in cirrhotic patients. METHODS: Two groups of patients with cirrhosis were studied, six with primary biliary cirrhosis (PBC) and six with postnecrotic liver cirrhosis (PNC). Cardiovascular function was assessed by determination of blood pressure, heart rate, and by two-dimensional and pulsed Doppler echocardiography. RESULTS: In PBC patients, 1 month's treatment with UDCA significantly reduced diastolic volume without changing systolic, diastolic, and mean blood pressures, heart rate, systolic and stroke volumes, ejection fraction, cardiac output, and systemic vascular resistance. In PNC patients, UDCA significantly reduced cardiac output, with a tendency to reduce left ventricular volumes, without any changes in systolic, diastolic, and mean blood pressures. CONCLUSIONS: UDCA caused reductions in diastolic volume in the PBC patients and cardiac output in the PNC patients. Such reductions are not unlike that seen in individuals treated with diuretics. This diuretic-like action deserves further study, particularly in cirrhotic patients who are also being treated with diuretics or show evidence of cardiac myopathy.

Role of cardiac structural and functional abnormalities in the pathogenesis of hyperdynamic circulation and renal sodium retention in cirrhosis.

The aim of this study was to assess the relationship between subtle cardiovascular abnormalities and abnormal sodium handling in cirrhosis. A total of 35 biopsy-proven patients with cirrhosis with or without ascites and 14 age-matched controls underwent two-dimensional echocardiography and radionuclide angiography for assessment of cardiac volumes, structural changes and systolic and diastolic functions under strict metabolic conditions of a sodium intake of 22 mmol/day. Cardiac output, systemic vascular resistance and pressure/volume relationship (an index of cardiac contractility) were calculated. Eight controls and 14 patients with non-ascitic cirrhosis underwent repeat volume measurements and the pressure/volume relationship was re-evaluated after consuming a diet containing 200 mmol of sodium/day for 7 days. Ascitic cirrhotic patients had significant reductions in (i) cardiac pre-load (end diastolic volume 106+/-9 ml; P<0.05 compared with controls), due to relatively thicker left ventricular wall and septum (P<0.05); (ii) afterload (systemic vascular resistance 992+/-84 dyn.s.cm(-5); P<0. 05 compared with controls) due to systemic arterial vasodilatation; and (iii) reversal of the pressure/volume relationship, indicating contractility dysfunction. Increased cardiac output (6.12+/-0.45 litres/min; P<0.05 compared with controls) was due to a significantly increased heart rate. Pre-ascitic cirrhotic patients had contractile dysfunction, which was accentuated when challenged with a dietary sodium load, associated with renal sodium retention (urinary sodium excretion 162+/-12 mmol/day, compared with 197+/-12 mmol/day in controls; P<0.05). Cardiac output was maintained, since the pre-load was normal or increased, despite a mild degree of ventricular thickening, indicating some diastolic dysfunction. We conclude that: (i) contractile dysfunction is present in cirrhosis and is aggravated by a sodium load; (ii) an increased pre-load in the pre-ascitic patients compensates for the cardiac dysfunction; and (iii) in ascitic patients, a reduced afterload, manifested as systemic arterial vasodilatation, compensates for a reduced pre-load and contractile dysfunction. Cirrhotic cardiomyopathy may well play a pathogenic role in the complications of cirrhosis.

Down-regulation of vascular alpha1-adrenoceptors does not account for the loss of vascular responsiveness to catecholamines in experimental cholestasis.

AIMS/BACKGROUND: Vascular hyporesponsiveness to sympathomimetic stimulation occurs in jaundice. Recently, we reported that this vascular adrenergic hyporesponsiveness was associated with the loss of reactivity of vascular alpha1-adrenoceptors. This study examines the possibility that the vascular adrenergic hyporesponsiveness is due to down-regulation of vascular alpha1-adrenoceptors. METHODS: This question was addressed by measuring the changes in the plasma norepinephrine (NE) and epinephrine (E) concentrations, determined by high performance liquid chromatography, and the affinity and number of alpha1-adrenoceptors determined by a competitive antagonist radioligand binding assay in vascular smooth muscle membranes prepared from 3-day bile duct ligated (BDL) rats. The results were compared to data obtained from 3-day bile duct manipulated (sham-operated; SO) and control (C) rats. RESULTS: Compared to C and SO rats, the plasma concentrations of NE and E in the BDL rats were significantly elevated reflecting increased sympathetic nervous system activity. BDL did not change either the affinity or the number of vascular alpha1-adrenoceptors. CONCLUSIONS: Since the affinity and number of vascular alpha1-adrenoceptors were unchanged in the face of elevated plasma concentrations of catecholamines in the BDL rats, we have concluded that down-regulation of vascular alpha1-adrenoceptors does not account for the vascular adrenergic hyporesponsiveness in experimental cholestasis.

Effects of ursodeoxycholic acid on systemic, renal and forearm haemodynamics and sodium homoeostasis in cirrhotic patients with refractory ascites.

Systemic arterial vasodilatation has been implicated in the pathogenesis of sodium retention in cirrhosis. Hydrophobic bile acids, which have vasodilatory actions, may be involved. Ursodeoxycholic acid, a hydrophilic bile acid, could potentially decrease systemic arterial vasodilatation, possibly due to its antioxidant effects, and improve sodium handling in cirrhosis. The effects of ursodeoxycholic acid on systemic, renal and forearm haemodynamics, liver function and renal sodium handling were assessed in vasodilated cirrhotic patients with refractory ascites treated with a transjugular intrahepatic porto-systemic shunt (TIPS). Eight cirrhotic patients with refractory ascites without TIPS placement served as controls for the sodium handling effects of ursodeoxycholic acid. From 1 month post TIPS, seven patients were studied before, after 1 month of treatment with ursodeoxycholic acid (15 mg.day-1.kg-1) and at 1 month follow-up. Lipid peroxidation products were used as indices of its antioxidant effects. Ursodeoxycholic acid caused a significant reduction in sodium excretion in both groups (P<0.05). This, in the post-TIPS patients (urinary sodium excretion: 35+/-8 mmol/day at 1 month versus 93+/-21 mmol/day at baseline, P<0.05), was due to a significant increase in sodium reabsorption proximal to the distal tubule (P<0.05), without any significant changes in systemic, renal or forearm haemodynamics, or in liver function. No significant change in lipid peroxidation products was observed. We conclude that: (i) in cirrhotic patients with refractory ascites, ursodeoxycholic acid causes sodium retention, (ii) the abnormality in sodium handling in the post-TIPS cirrhotic patients appears to be the result of a direct effect on the proximal nephron, suggesting that factors other than systemic vasodilatation also contribute to sodium retention in cirrhosis, (iii) caution should be exercised in administering ursodeoxycholic acid in cirrhotic patients with ascites.

The effect of bile duct manipulation on cardiovascular responsiveness: in vivo studies.

Cholestasis depresses cardiovascular function and responsiveness. In a previous study, the 3-day bile duct manipulated (BDM) rat was validated as the appropriate control for studying in vitro vascular neuroeffector mechanisms in cholestasis. The present study reports the findings on the effect of BDM on cardiovascular function and responsiveness in conscious rats. Cardiovascular responsiveness was assessed by measuring the in vivo pressor responses to a 90 degrees head-up vertical tilt, a controlled hemorrhage, and to intravenously infused norepinephrine, tyramine, the indirectly acting sympathomimetic drug, isoproterenol, the nonselective beta-adrenoceptor agonist, angiotensin I, and angiotensin II. The concentrations of catecholamines and plasma renin activity measured in plasma samples obtained from conscious chronically arterial catheterized BDM rats were compared to identical data obtained from rats in which the bile duct was not manipulated. There were no differences in cardiovascular responsiveness to any of these procedures or drug infusions between the two groups of rats. Plasma catecholamine concentrations and renin activities in the BDM rats were not significantly different from control rats. Although no differences in cardiovascular responsiveness between BDM and control rats were observed, these data confirm the choice of the BDM as the control group for experiments assessing the effects of cholestasis on cardiovascular responsiveness.

Bile acids, oxidative stress, and renal function in biliary obstruction.

Renal dysfunction occurs in patients with biliary obstruction. Plasma accumulation of bile acids and oxidative stress have been proposed as contributory factors. Bile acids can alter the renal handling of electrolytes and water by blocking the Na(+)-H+ antiport in the tubule. Oxidative stress, defined as an imbalance between radical generating systems and radical scavenging systems giving rise to free radical induced tissue damage, occurs in patients with liver disease. Bile acids cause oxidative damage to tubular cell membranes by stimulating the generation of oxygen free radicals from mitochondria, as well as promoting their release from neutrophils and macrophages. Oxidative stress can promote the formation of a variety of vasoactive mediators including endothelin-1, cysteinyl leukotrienes, as well as the F2-isoprostanes, endogenous products of lipid peroxidation. These mediators can each affect renal function directly by causing renal vasoconstriction or decreasing the glomerular capillary ultrafiltration coefficient, and thus reduce glomerular filtration rate. Collectively, these factors contribute to the onset of renal failure in patients with biliary obstruction.

Experimental study in bile duct-ligated rats of vasopressin and preoperative volume loading to prevent hypotensive crises.

BACKGROUND: Systemic hypotension may result in postoperative renal failure in jaundiced patients. Attenuated responsiveness to catecholamines and hypovolaemia has been reported in jaundiced animals and may be a mechanism contributing to the increased susceptibility of jaundiced patients to haemorrhagic shock. This suggests that an alternative to vasoactive amines to control perioperative hypotension could be desirable. METHODS: This study evaluated the pressor response to vasopressin in normovolaemic 3-day bile duct-ligated rats and in 3-day bile duct-ligated rats after an acute controlled haemorrhage. It also evaluated the response after volume loading with 0.9 per cent saline, 7.5 per cent saline, colloid and mannitol before controlled haemorrhage. In addition, blood volume was measured using radiolabelled albumin. All the data obtained from bile duct-ligated rats were compared with data from sham-operated animals. RESULTS: Attenuated pressor responses to vasopressin were not observed in either normotensive bile duct-ligated rats or in the bile duct-ligated rats subjected to controlled haemorrhage. Volume loading with the four fluids over the dosing range 2.5-7.5 microliters per g body-weight in bile duct-ligated rats reversed the susceptibility to haemorrhagic hypotension. CONCLUSION: Although no reduction in blood volume was demonstrated, bile duct-ligated rats may have a reduced effective blood volume manifesting itself as a latent hypovolaemia and/or tendency to hypotension. Preoperative fluid loading could be beneficial because it corrects hypovolaemia and improves cardiovascular function, as well as improving the cardiovascular response to haemorrhage.

The effects of Bile Acids on Freshly Isolated Rat Glomeruli and Proximal Tubular Fragments.

The role of bile acids in post-surgical acute renal failure in jaundiced patients is obscure. In this study the effects of 11 bile acids were assessed on freshly isolated rat glomeruli and proximal tubular fragments using de novo protein synthesis and lactate dehydrogenase (LDH) leakage as markers of cytotoxicity. Lithocholic acid inhibited protein synthesis from 5mum, chenodeoxycholic and deoxycholic acid from 50mum (P<0.05). The concentration of hydrophobic bile acids that inhibited protein synthesis by 50% (IC(50)) was 10mum, 75mum and 80mum for lithocholic, chenodeoxycholic and deoxycholic acids, respectively. The glycine and taurine conjugates of these bile acids had no significant effect on de novo protein synthesis up to 200mum. Lithocholic acid (50mum), chenodeoxycholic (200mum) and deoxycholic acids (200mum) caused a significant increase (P<0.05) in LDH leakage. Lithocholic acid also directly inhibited LDH activity above 50mum (P<0.05), whereas chenodeoxycholic acid and deoxycholic acid had no effect on LDH below 500mum, at which concentration they caused a slight increase in activity. The cytotoxic bile acids had no effect on the level of reactive oxygen species in kidney fragments. Hydrophobic bile acids inhibit protein synthesis and increase membrane permeability. Hydrophobic bile acids also directly alter LDH activity. Kidney cells are susceptible to the hydrophobic bile acids at concentration significantly below their critical micellar concentration. These results suggest that both glomeruli and tubules are highly sensitive to hydrophobic bile acids.

Effect of deoxycholic acid and ursodeoxycholic acid on lipid peroxidation in cultured macrophages.

BACKGROUND: Kupffer cells are essential for normal hepatic homeostasis and when stimulated, they secrete reactive oxygen species, nitric oxide, eicosanoids, and cytokines. Some of these products are cytotoxic and attack nucleic acids, thiol proteins, or membrane lipids causing lipid peroxidation. Hydrophobic bile acids, such as deoxycholic acid (DCA), can damage hepatocytes by solubilising membranes and impairing mitochondrial function, as well as increasing the generation of reactive oxygen species. OBJECTIVES: The hypothesis that hydrophobic bile acids could stimulate Kupffer cells to increase their capacity to generate reactive oxygen species by measuring cellular lipid peroxidation was tested. Because the hydrophilic bile acid, ursodeoxycholic acid (UDCA) can block hydrophobic bile acid induced cellular phenomena, it was also hypothesised that UDCA could antagonise macrophage activation by hydrophobic bile acids to blunt their capacity to generate reactive oxygen species. METHODS: J-774A.1 murine macrophages were incubated for 24 hours with either 10(-5) M and 10(-4) M (final concentration) DCA alone, or 10(-4) M UDCA alone, or a mixture of 10(-4) M 1:1 molar ratio of DCA and UDCA. At the end of the incubation period, the culture medium was collected for determination of cellular lipid peroxidation by measuring the malondialdehyde (MDA) content in the medium with the thiobarbituric acid reactive substances assay. RESULTS: 10(-5) M and 10(-4) M DCA increased MDA generation by cultured macrophages. 10(-4) M UDCA alone did not increase MDA generation but blocked the peroxidative actions of DCA. CONCLUSIONS: Hydrophobic bile acids, after their hepatic retention, can oxidatively activate Kupffer cells to generate reactive oxygen species. Because UDCA can block this action, the beneficial effect of UDCA is, in part, related to its ability to act as an antioxidant.

Epinephrine dose-response of the isolated working heart in O2-exposed rats.

BACKGROUND: Heart energy efficiency, which is affected by catecholamines, has previously been shown to decline in rats with prolonged normobaric O2 exposure. HYPOTHESIS: Oxygen exposure affects dose response of the heart to catecholamines. METHODS: Epinephrine dose-response (10(-10) - 5 x 10(-6) mol.L-1) was measured in the isolated working heart excised from control rats breathing air, and rats exposed to normobaric 100% oxygen for either 24 h or 49 h. The variables measured were input (oxygen consumption (VO2) and output power, cardiac contractility (Emax and maximal dP/dT), coronary resistance, heart frequency (fH) and left ventricular pressure. Variable (Y*) dose response to epinephrine concentration (C) was fitted to the equation: Y* = Ymax/(1 + (C/C50)n), Ymax--maximal Y*, C50--C for half Ymax and n--an empirical power. RESULTS: Oxygen exposure of the intact rat had little influence on baseline cardiac variables, but did affect sensitivity to catecholamines. A general effect of the O2 exposure was a left shift of the dose-response curve for example, C50 was reduced by 72, 41 and 43 x 10-8 mol.L-1 for VO2, fH and Emax, respectively, after the 24 h exposure. CONCLUSIONS: There was a pronounced change in the dose-response in hearts from 24 h O2-exposed rats, a change partially reversed in hearts from 49 h O2-exposed rats. The high dose, which had a stimulatory effect on hearts from control rats, failed to stimulate hearts from hyperoxic rats.

Vasodilatory responses of isolated arteries of cirrhotic rats.

1. There is currently considerable interest in the role of locally produced vasodilators such as nitric oxide and adenosine in the pathogenesis of the peripheral vasodilatation of cirrhosis. However, the signal transduction pathways involving guanylate cyclase and adenylate cyclase have not been clearly delineated in the isolated blood vessel. 2. We therefore aimed to examine the in vitro vasorelaxant effects of the endothelium-dependent dilator bethanechol, the endothelium-independent dilator sodium nitroprusside and adenosine, as drugs that work via activation of guanylate and adenylate cyclases, in isolated aortic and superior mesenteric arterial rings from cirrhotic and control rats. 3. Cirrhosis was induced by chronic bile duct ligation and section of 24-28 days' duration, while controls underwent sham operation. The vessels were precontracted with the alpha 1-adrenoceptor agonist phenylephrine, then relaxed by incremental doses of the three drugs. 4. Marked attenuation of vasoconstriction induced by phenylephrine in isolated aortic and mesenteric arterial rings from cirrhotic rats compared with the control vessels was observed. 5. There were no significant differences in relaxation between the cirrhotic and control vessels to the three drugs. We conclude that in vitro vasodilatory responses mediated through signal transduction pathways involving guanylate cyclase and adenylate cyclase remain unchanged in a rat model of biliary cirrhosis.