THE EFFECT OF VASOPRESSIN ON HEPATIC ARTERY FLOW IN THE RAT

The effects of vasopressin infusion on hepatic artery flow was studied in rats. Hepatic artery ligation followed by the infusion of vasopressin (0.08 microU/g body weight per min) decreases portal venous flow and liver blood flow. Vasopressin infusion results in an increase in hepatic artery flow and liver blood flow both of which are abolished by subsequent hepatic artery ligation. The increase in hepatic artery flow and the decrease in portal venous flow following the infusion of vasopressin is discussed in relation to the management of patients presenting with bleeding oesophageal varices.     

THE HEPATIC TRANSPORT OF SODIUM TAUROCHOLATE IN THE RAT: EFFECT OF PHENOBARBITONE

SUMMARY 1. The effect of pretreatment with phenobarbitone on the hepatic transport of sodium ¹⁴C-taurocholate was studied in the Sprague Dawley rat. Taurocholate solutions were injected into the portal vein in a volume of 0.2 ml in 2 s.
2. Biliary secretion of taurocholate injected into the portal vein in a concentration of 25 μM was not altered by pretreatment with phenobarbitone. This concentration of taurocholate corresponds to that occurring normally in portal venous blood.
3. When taurocholate was injected in a much larger concentration (13 mM), biliary secretion of taurocholate was significantly slower in phenobarbitone-pretreated rats than in control rats.
4. Changes in hepatic bile salt transport do not appear to contribute to the choleresis that occurs with phenobarbitone.     

1-methyl-4-phenylpyridinium-induced alterations of glutathione status in immortalized rat dopaminergic neurons

Decreased glutathione levels associated with increased oxidative stress are a hallmark of numerous neurodegenerative diseases, including Parkinson's disease. GSH is an important molecule that serves as an anti-oxidant and is also a major determinant of cellular redox environment. Previous studies have demonstrated that neurotoxins can cause changes in reduced and oxidized GSH levels; however, information regarding steady state levels remains unexplored. The goal of this study was to characterize changes in cellular GSH levels and its regulatory enzymes in a dopaminergic cell line (N27) following treatment with the Parkinsonian toxin, 1-methyl-4-phenylpyridinium (MPP(+)). Cellular GSH levels were initially significantly decreased 12 h after treatment, but subsequently recovered to values greater than controls by 24 h. However, oxidized glutathione (GSSG) levels were increased 24 h following treatment, concomitant with a decrease in GSH/GSSG ratio prior to cell death. In accordance with these changes, ROS levels were also increased, confirming the presence of oxidative stress. Decreased enzymatic activities of glutathione reductase and glutamate-cysteine ligase by 20-25% were observed at early time points and partly account for changes in GSH levels after MPP(+) exposure. Additionally, glutathione peroxidase activity was increased 24 h following treatment. MPP(+) treatment was not associated with increased efflux of glutathione to the medium. These data further elucidate the mechanisms underlying GSH depletion in response to the Parkinsonian toxin, MPP(+).     

EFFECTS OF GENERAL ANAESTHETICS ON THE ACTIVITY OF THE Na,K-ATPASE OF CANINE RENAL MEDULLA

Several previous studies have reported inhibition of Na,K-ATPase activity by chlorpromazine, phenobarbital and pentobarbital, thiopental, and monoketones. The purpose of this study is to investigate the influences of other general anaesthetics on Na,K-ATPase activity. The ATPase activity of Na,K-ATPase-enriched membranes from canine renal medulla was determined at 37 degrees C in the absence and in the presence of hexanol, diethylether, halothane, and propofol. The influence of hexanol on stimulation of Na,K-ATPase activity by Na+ and K+ was investigated. Hexanol, diethylether, halothane, and propofol inhibited the activity at 37 degrees C of the Na,K-ATPase of canine renal medulla. The IC50 values at 37 degrees C were: hexanol, 12.3 mM; diethylether, 170 mM; halothane, 7.35 mM; propofol, 0.127 mM. Hexanol increased the K0.5 of the Na,K-ATPase for K+ at 37 degrees C, but did not affect the K0.5 for Na+. At lower [K+] hexanol was a more potent inhibitor than at higher [K+].     

EFFECT OF INCREASED BILE FLOW AND BILE ACID SECRETION ON THE HEPATIC ELIMINATION OF SODIUM VALPROATE IN THE CAT

The effect of increased bile flow and hepatic bile acid flux on the systemic clearance and hepatic elimination of intravenously administered sodium valproate was studied in the bile fistula cat. Taurochenodeoxycholic acid (TCDC), tauro-3 alpha, 7 beta-dihydroxy-12-keto-5 beta-cholanoic acid (T12K), SC-2644, and secretin were infused intravenously to vary bile flow and biliary bile acid secretion. Control animals were infused with 0.15 mol/l NaCl. Less than 1% of the drug administered to controls appeared as unchanged valproate in the bile over 6 h. Although SC-2644, T12K, and secretin significantly increased biliary excretion of valproate, it did not exceed 2% of the intravenous dose. Biliary clearance was directly related to the rate of bile flow, but not to the bile acid flux. By contrast, 18-19% of the dose appeared in bile as metabolite in controls, and none of the choleretic agents significantly increased this percentage. As a result, systemic clearance of valproate was unaltered. We conclude that the movement of unchanged valproate into bile is consistent with a process of simple diffusion. The fact that choleretic agents do not increase metabolite excretion into bile suggests that metabolite formation may be the rate-limiting step in the hepatic elimination of valproate, rather than transport and excretion of metabolites into bile.     

THE EFFECT OF ADRENALECTOMY ON WATER PERMEABILITY IN RAT PAPILLARY COLLECTING DUCT

1. Chronic adrenal insufficiency impairs maximal urine concentration, probably in part due to reduced medullary tonicity but also possibly by inhibition of distal nephron water transport. This latter defect has been demonstrated in rabbit but not in rat. 2. Since the time between adrenalectomy and experiment was different in rabbit and rat studies, diffusional water permeability was evaluated in the papillary collecting duct in the absence and presence of submaximal (20 μU/mL) and supramaximal (200 μU/mL) arginine vasopressin (AVP) in adrenalectomized rats at 7, 14 and 21 days. 3. Experimentation 7 days after adrenalectomy failed to demonstrate significantly altered basal or AVP-induced water permeability which increased by 23 and 78% with submaximal and supramaximal concentrations, respectively. Submaximal AVP concentrations also induced a comparable change in water permeability in adrenalectomized rats at 14 days; however, 21 days after adrenalectomy, diffusional water permeability was not increased by 20 μU/mL AVP (3.31 ±.22 to 3.31 ±.24 μm/s). Nevertheless, the effect of a supramaximal AVP concentration (200 μU/mL) was not altered by adrenalectomy (4.54 ±.39 to 8.08 ±.96; P<0.01). Incubation of collecting ducts in aldosterone for 2 h did not reverse the inhibitory effect of chronic adrenalectomy on AVP-stimulated water transport. 4. These studies suggest that mineralocorticoid withdrawal does impair the hydro-osmotic action of AVP in the rat papillary collecting duct but that this effect takes between 14 and 21 days to occur.     

THE HEPATIC TRANSPORT OF TAUROCHOLIC ACID IN THE RAT: DEVELOPMENT OF A MATHEMATICAL MODEL

1. The transport of taurocholic acid from portal blood to bile was studied in the anaesthetized rat by injecting a radiolabeled pulse of bile acid. 2. The transport process was very rapid, 50% of the dose being secreted within 5 min, and the total dose within 15 min. 3. The transport process had a large capacity. The secretory profile was little modified by a 500-fold increase in the injected dose. 4. The transport process was modelled with both analogue and digital computers. The simplest model which fitted the data comprised rapid uptake from portal blood, slow transport across the cell and rapid secretion into bile. The digital computer simulation suggested that this model is not unique, but will require further testing.     

CYCLOSPORINE A HEPATOTOXICITY: EFFECT OF PROLONGED TREATMENT WITH CYCLOSPORINE ON BILIARY LIPID SECRETION IN THE RAT

1. The effects of cyclosporine A (CyA) treatment on liver morphology, bile flow and biliary secretion of bile acid, cholesterol and phospholipid and some plasma biochemical indicators of liver function were examined. 2. Wistar rats were treated i.p. with 10 or 20 mg of CyA/kg per day for 1, 2, 3 or 4 weeks. 3. Treatment increased bile acid and bilirubin plasma concentration. Bile flow and biliary secretion of bile acid, cholesterol and phospholipid were reduced in CyA-treated animals. 4. All these effecs of the drug appeared at 1 week after the start of treatment and were enhanced during prolonged treatment. Cyclosporine A-induced cholestasis was due to a decrease in both the bile acid-dependent and -independent fractions of bile flow. 5. The reduction in cholesterol and phospholipid biliary output may be secondary to the inhibition of the hepatobiliary flux of bile acid; however, perturbations in the removal of lipids from the canalicular membrane as well as intracanalicular interaction between CyA and lipid vesicles/micelles could also be involved.     

EFFECTS OF TOTAL AND SELECTIVE PORTASYSTEMIC SHUNTING ON HEPATIC HAEMODYNAMICS AND SOME ASPECTS OF LIVER FUNCTION IN THE CIRRHOTIC RAT

The effects of total and selective portasystemic shunting on hepatic haemodynamics and some aspects of liver function were studied in rats with dimethylnitrosamine-induced cirrhosis. Immediately following end-to-side portacaval shunting there were significant reductions in wedged hepatic venous pressure (WHVP) and liver blood flow. After side-to-side mesocaval shunting liver blood flow and wedged hepatic venous flow fell by approximately the same magnitude. Selective shunting (mesocaval 'H'-grafts and splenopancreaticocaval) preserved liver blood flow to a greater extent than total portasystemic shunting but had a less marked effect on WHVP. Furthermore, selective portasystemic shunting prevented liver atrophy and deterioration in liver function which was observed in rats following total portasystemic shunting. These results suggest that in the cirrhotic rat, selective portasystemic shunts which preserve functional liver blood flow and prevent liver atrophy and a deterioration in liver function do not produce such a marked decrease in WHVP as total shunts. Further studies in man are required to evaluate the relative advantages of total and selective portasystemic shunts.     

NORADRENALINE RELEASE FROM THE RAT HEART DURING ANOXIA: EFFECTS OF CHANGES IN EXTRACELLULAR SODIUM CONCENTRATION AND INHIBITION OF SODIUM UPTAKE MECHANISMS

1. Anoxic perfusion of the isolated rat heart releases noradrenaline in the absence of sympathetic nerve fibre stimulation. 2. Anoxic noradrenaline release is enhanced by reducing the extracellular Na+ concentration, consistent with the proposal that such release occurs by carrier-mediated efflux. 3. Release is also enhanced by lignocaine but inhibited by amiloride and ethylisopropylamiloride, suggesting that sodium entry into adrenergic nerve terminals during anoxia occurs by Na+/H+ (and possibly Na+/Ca2+) exchange.     

EFFECT OF CATIONIC DRUGS ON THE RENAL SECRETION OF RANITIDINE IN THE RAT ISOLATED PERFUSED KIDNEY

1. The rat isolated perfused kidney (IPK) was used to determine whether the renal tubular secretion of ranitidine is influenced by clinically relevant concentrations of other organic cationic drugs (amantadine, pseudoephedrine, triamterene and trimethoprim) that also undergo tubular secretion. 2. Ranitidine and [³H]-ranitidine were administered to the recirculating perfusion medium as a loading dose followed by a constant infusion to maintain clinically relevant perfusate ranitidine concentrations in the range 400–700 ng/mL. The renal clearance of ranitidine (CL_R) was calculated, as was glomerular filtration rate (GFR), from the renal clearance of [¹⁴C]-inulin. 3. A total of 20 perfusions were performed and, in each case, ranitidine was administered for 80 min. In four control IPK, no drug other than ranitidine was administered. In the remaining IPK, amantadine, pseudoephedrine, triamterene or trimethoprim (n= 4 in each case) were administered to achieve low, medium and high concentrations during the 20–40, 40–60 and 60–80 min periods, respectively. 4. The mean (± SD) unbound fraction of ranitidine in the perfusion medium was 0.889±0.046 and was not altered (P>0.05) by the presence of the other drugs. 5. The CL_R/GFR ratio for ranitidine in all kidneys was substantially greater than unity and had a mean value of 10.65 or greater in control kidneys, indicating extensive net tubular secretion. 6. The CL_R/GFR was not affected (P>0.05) by amantadine, pseudoephedrine or triamterene at any concentration or by trimethoprim at the low concentration. However, medium (2000 ng/mL) and high (5000 ng/mL) concentrations of trimethoprim caused significant reductions in CL_R/GFR of 20 and 28%, respectively (P<0.05). 7. The results indicate that at clinically relevant concentrations the renal tubular secretion of ranitidine is inhibited by trimethoprim, but not by amantadine, pseudoephedrine or triamterene.     

LACK OF EFFECT OF BROMOCRIPTINE ON SERUM LEVELS OF CALCIUM IN THE RAT

1. The effect of bromocriptine (a prolactin suppressant drug) on the serum levels of calcium was studied in the male rat. The drug was administered subcutaneously at a dosage of 100μg per 100 g body weight three times per day. 2. Chronic treatment with bromocriptine had no significant effect on the serum calcium levels. It appears that neither bromocriptine per se nor normal circulating prolactin levels exert any significant influence on blood calcium homeostasis.     

EFFECT OF CIMETIDEME ON THE HEALING OF RESTRAINT-INDUCED GASTRIC EROSIONS IN THE RAT

1. Rats after a 24 h restraint developed acute gastric erosions. Cimetidine in a dose of 100 mg/kg body weight was given subcutaneously every 8 h to a group of 150 rats after restraint. A second group received saline subcutaneously (placebo group). 2. Erosions in the placebo group required up to 45 days to heal (median healing time approximately 24 days). Cimetidine treatment reduced the median healing time to approximately 12 days. 3. Cimetidine in this dose promotes healing of acute gastric erosions in the rat induced by restraint.     

HEPATIC SINUSOIDAL RESPONSES TO INTRAPORTAL INJECTIONS OF PHENYLEPHRINE AND ISOPRENALINE IN THE RAT

1. Specific α- and β-adrenoreceptor agonists, phenylephrine and isoprenaline, were injected intraportally into the intact rat liver under direct microscopic observation by an in viva transillumination technique. 2. The diameter of a hepatic sinusoid and the intra-sinusoidal erythrocyte velocity were quantitatively measured, and the sinusoidal volume flow was calculated from these two parameters. 3. Results show that phenylephrine causes a sinusoidal constriction and an increased sinusoidal blood flow, whereas isoprenaline causes the opposite effects on the sinusoids. 4. All the sinusoidal responses to phenylephrine and isoprenaline were dose-dependent and were possibly related to the direct effect of these drugs on the sinusoids.     

THE SPECIFICITY OF BILE SALTS IN THE INTESTINAL ABSORPTION OF MICELLAR CHOLESTEROL IN THE RAT

1. Two aspects of cholesterol absorption; (a) the importance of solubilization and (b) the effects of different bile salts on the mucosal metabolism and lymphatic output of cholesterol, have been investigated using two different in vivo techniques. 2. Bile diverted lymph fistula rats were infused intraduodenally at a steady rate with a constant lipid mixture containing labelled cholesterol, labelled oleic acid and mono-olein. The lipids were completely solubilized in either bile salts or a non-toxic non-ionic detergent, Pluronic F68. Labelled fatty acid was efficiently absorbed from either micellar infusate but virtually no labelled cholesterol appeared in the lymph in the absence of bile salts. 3. Short-term perfusions of the intestine of anaesthetized rats with the same micellar perfusates as above showed approximately 20% of the labelled cholesterol in the mucosa after 30 min perfusion with the bile salt micellar solutions. When the non-ionic micelles were used virtually no isotopic cholesterol left the lumen. 4. Mucosal uptake of labelled cholesterol was linearly dependent on the concentration of solubilized cholesterol in the perfusate and was not dependent on the bile salt concentration. 5. After 30 min the total amount of perfused isotopic cholesterol was recovered from either the lumen or the mucosa, but some fatty acid appeared to have been transported away from the mucosa by this time. 6. The initial rate of mucosal uptake of labelled cholesterol was similar from micellar perfusates using either taurocholate, taurodeoxycholate or taurofusidate. In contrast, after 8 h of infusion, lymphatic output of labelled cholesterol was markedly greater with taurocholate. 7. The increased lymph output with taurocholate was associated with an increase in the esterified fraction of both labelled and unlabelled cholesterol. Fatty acid was absorbed and esterified equally from all three types of perfusate. 8. These results suggested that for the first step in cholesterol absorption, viz. uptake from the lumen, solubilization by a planar detergent was essential. After up take, the more rapid transfer of cholesterol to lymph in the presence of trihydroxy bile acids appeared to be related to a more efficient esterification of cholesterol, but not to a more efficient resynthesis of triglyceride, the other major component of lymph chylomicrons.     

EFFECT OF cGMP INHIBITORS ON THE ACTIONS OF NITRODILATORS IN RAT AORTA

1. The involvement of cGMP in vasodilatation produced by a range of nitrodilators was investigated using two different protein kinase G inhibitors, r_(p) 8-bromoguanosine-3′5′-cyclic monophosphothioate (RBrcGMPS) and KT5823. 2. The nitric oxide donors sodium nitroprusside (SNP), glyceryltrinitrate (GTN) and s-nitroso-acetylpenicillamine (SNAP), the endothelium-dependent vasodilator acetylcholine (ACh) as well as the cGMP analogues 8-(4-chlorophenylthio)-cGMP (CPTcGMP) and β-phenyl-1-N²-etheno-8-bromo-cGMP (PETcGMP) all relaxed rat aortic rings preconstricted with phenylephrine (0.1 μmol/L). 3. The protein kinase G inhibitor KT 5823 (10 μmol/L) produced a very small inhibition of the vasodilatation produced by GTN, but had no effect against vasodilatation produced by SNP, CPTcGMP or PETcGMP, which suggests that KT 5823 is not a useful tool in this system. 4. In contrast, RBrcGMPS (0.5 mmol/L) produced a rightward shift of the concentration-response curves to SNP, CPTcGMP and PETcGMP. RBrcGMPS (0.5 mmol/L) also completely abolished vasodilatation to ACh and GTN but, surprisingly, had no effect on vasodilatation produced by SNAP. 5. The guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 1 and 10 μmol/L) completely inhibited the relaxation produced by GTN, whereas SNAP still had an appreciable relaxant effect after ODQ (1 μmol/L). 6. The differential effect of RBrcGMPS and ODQ on the nitrodilators suggests that there are differences in the mechanism of dilatation between the nitrodilators.     

ACUTE EFFECT OF ETHANOL ON RENAL ELECTROLYTE TRANSPORT IN THE RAT

1. Despite human and animal studies, the direct effect of ethanol on renal water and electrolyte transport is poorly understood. The acute effect of increasing plasma concentrations of ethanol was evaluated in a water diuretic anaesthetized rat model which inhibits endogenous arginine vaso-pressin (AVP) release. 2. Ethanol at a plasma concentration of 1.69 ±0.28 mmol/L produced an immediate increase in urine flow (174 ± 11 μL/min pre-ethanol and 189 ± 13 and then 206 ± 12 μL/min during the ethanol infusion; P<0.001) as well as an increase in fractional sodium excretion (0.17 ± 0.04 to 0.28 ± 0.05 and 0.27 ± 0.05%; P<0.001). There was also a brief phosphaturia. These increases in electrolyte excretion had returned to control values by 20 min despite a further increase in the plasma ethanol concentration. 3. The urinary excretion of potassium, calcium and magnesium was not altered nor was glomerular filtration rate or renal plasma flow. 4. Ethanol at a mean concentration of 1.60 mmol/L did not alter the action of a maximal concentration of AVP (75 ng/kg) on water or electrolyte transport. However, the antidiuretic effect of a submaximal concentration of AVP (7.5 ng/kg) was augmented by ethanol at concentrations of 1.63 and 0.98 mmol/L. 5. These studies suggest that the ethanol induced diuresis commonly ascribed to inhibition of AVP secretion may also be due to other intrarenal effects of ethanol, possibly acting within the proximal tubule. These results also confirm recent in vitro findings that while ethanol does not inhibit the action of a maximal concentration of AVP, it does modulate the effects of lower AVP concentrations.     

Allopurinol suppresses 2-bromoethylamine and 1-methyl-4-phenylpyridinium ion (MPP(+))-induced hydroxyl radical generation in rat striatum

The present study was examined whether or not 2-bromoethyamine, a semicarbazide-sensitive amine oxidase (SSAO, EC; 1.4.3.6) inhibitor, would increase an active dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP(+))-induced hydroxyl radical ((*)OH) generation in the rat striatum. Rats were anesthetized, and sodium salicylate (0.5 mM or 0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of (*)OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Infusion of 2-bromoethylamine (100 microM or 100 pmol/microl/min) into the striatum drastically increased the formation of (*)OH products, trapped as DHBA by the action of MPP(+). Further, I studied the effect of allopurinol, a xanthine oxidase inhibitor, an 2-bromoethylamine and MPP(+)-induced (*)OH generation. Allopurinol (10 microM or 10 pmol/microl/min) significantly suppressed 2-bromoethyamine and MPP(+)-induced (*)OH. These results suggest that a definite mechanism is not clear at the moment, after inhibition of tissue-bound and/or blood plasma SSAO activity, with consequent increases in bioactive amine levels, enhances the formation of (*)OH products of efflux/oxidation due to MPP(+).