ALTERED LIPID PEROXIDATION/GLUTATHIONE RATIO IN EXPERIMENTAL EXTRAHEPATIC CHOLESTASIS

1. Lipid peroxidation can occur in the presence of a cellular antioxidant-oxidant imbalance, but the role of lipid peroxides in cholestasis is not well understood. 2. This study was undertaken in order to: (i) evaluate the behaviour of a product of lipid peroxidation (thiobarbituric acid-reactive species), and of an important antioxidant tripeptide, reduced glutathione, in the course of experimental extrahepatic cholestasis; and (ii) ascertain whether there was a link between this aspect and the alterations in liver morphology. 3. Forty-five male Sprague-Dawley rats (250–300 g) were double bile duct ligated and followed from 1 to 28 days. At the end of each experimental period, blood and liver samples were collected for thiobarbituric acid-reactive species and glutathione determinations. 4. Bile duct ligated rats showed a marked increase in liver weight which was related to cholestasis duration and to some anatomical alterations such as bile duct proliferation and dilation and liver fibrosis (periportal, perivenular, perineoductular and parenchymal). 5. An increase in serum lipid peroxidation was also observed but this was not linked to hepatic thiobarbiturie acid-reactive species. Erythrocyte and hepatic glutathione decreased in relation to cholestasis duration. Serum lipid peroxides and erythrocyte glutathione were correlated with liver cell necrosis. 6. In conclusion, experimental extrahepatic cholestasis determines bile duct proliferation and fibrosis, the degree of which is directly related to the duration of cholestasis itself and to liver cell necrotic phenomena. Furthermore, extrahepatic cholestasis is associated with increased lipid peroxide formation and with a depletion of reduced glutathione both in the liver and in the erythrocytes. The alteration in the oxidative balance may be a contributory factor in necrotic liver cell phenomena.     

INCREASED BILIARY EXCRETION OF OUABAIN INDUCED BY BUCOLOME IN THE RAT

1. Following the intravenous injection of ³H-ouabain (0.4 or 0.6 mg/100 g body weight) the plasma concentration and biliary excretion of ouabain were compared for control male Wistar rats and rats given bucolome (BC, l-cyclohexyl-5-n-butyl-2,4,6,-trioxoperhydroxypyrimidine, 20 mg/100 g) 40 min before the ouabain injection. In bucolome treated rats, the bile flow rate was 80–90% higher than in control rats and the biliary excretion rate of ouabain for the 40 min post-injection period was significantly higher in bucolome treated rat groups. The increase was due to an approximately two-fold increase in the excretion rate in the first 10 min period. On the other hand, plasma concentration of ouabain was significantly higher in bucolome treated rats compared with control rats at corresponding time intervals. Plasma volume as determined by ¹³¹I-labelled albumin dilution was not decreased in bucolome treated rats. 2. The results indicated that the significant increase in biliary excretion of ouabain administration was due to the enhancement of the hepatic transport and/or biliary excretion process and not due to an increase in hepatic uptake.     

INFLUENCE OF BILE ACIDS ON THE BILIARY TRANSPORT MAXIMUM OF PHENOLSULPHONPHTHALEIN IN THE RAT

1. The effect of changes in bile acid secretion induced by cholestyramine treatment or taurocholate infusion on the biliary transport maximum (Tm) of phenolsulfonphthalein (PSP) was studied in Wistar rats. 2. Five hours after oral administration of cholestyramine (1.5 g/kg bodyweight) the biliary output of bile acids decreased to 51% and bile flow to 76% of control values. The percentage of conjugated and unconjugated PSP excreted into bile and the Tm of the dye were not significantly modified by cholestyramine pretreatment. 3. Administration of sodium taurocholate at increasing rates (60-480 nmol/100 g bodyweight per min) enhanced bile flow and the biliary output of bile acids in a linear dose-related fashion. The Tm of PSP increased progressively until a maximum of 29% above the control values was reached at a taurocholate dose of 240 nmol/100 g bodyweight per min). The enhancement corresponded mainly to the unconjugated dye, the excretion of conjugated PSP not being significantly modified by the infusion of the bile acid. 4. The results indicate that bile acids can influence to some extent biliary excretion of PSP in the rat, although this component is of minor importance at low bile acid secretory rates.     

ETHANOL IMPAIRS BILIARY LYSOSOMAL ENZYME RELEASE IN RATS

The effects of ethanol on hepatic lysosomes are poorly documented. This study examined the biliary release of lysosomal enzymes, a marker of the hepatocyte-to-bile excretory pathway, after ethanol administration in the isolated perfused rat liver model. At concentrations similar to those reached in human plasma during social drinking, ethanol markedly decreased biliary lysosomal enzyme output and bile flow in the rat. Ethanol did not affect hepatic activities or the release into perfusate of lysosomal and other subcellular marker enzymes. Hence, ethanol may potentially inhibit hepatocyte-to-bile excretion of other compounds processed through lysosomes.     

EFFECTS OF OPIATES ON SODIUM EXCRETION IN THE ISOLATED PERFUSED RAT KIDNEY

1. A rat isolated perfused kidney preparation was utilized to define clearly a renal site of action. The variables measured were perfusate pressure and flow, glomerular filtration rate, urine volume, sodium excretion and potassium excretion. 2. Dextromethorphan (3 nmol/L) and dextrorphan (10 nmol/L) reduced sodium excretion in kidneys from rats on either control or high K+ diet, in the absence of any other measured renal effects. Dextromethorphan (10 nmol/L) produced a decrease in glomerular filtration rate as well as a decrease in sodium excretion. Naloxone (1 mumol/L) inhibited the effect of dextromethorphan on sodium excretion but had no effect when administered alone. 3. The levorotatory opiates levorphanol and levomethorphan, the kappa agonist ketocyclazocine and a range of other opiates had no effect on sodium excretion. 4. The results suggest a renal action specific for dextrorotatory opiates. This renal action is consistent with earlier binding studies suggesting preferential recognition of dextrorotatory opiates.     

PIRETANIDE AND URINARY EXCRETION OF IONS IN RAT. EFFECT OF INDOMETHACIN

1. Piretanide is a new loop diuretic resembling furosemide. The effects of this diuretic on various parameters of renal function and on the excretion of the major ions were studied on anaesthetized, hydrated rats. 2. Piretanide induced a marked diuresis and increased sodium, potassium, chloride and calcium excretion. Calcium excretion increased more than that of sodium. Urinary osmolality and water reabsorption decreased. 3. Inulin clearance and phosphate excretion were significantly altered by piretanide. 4. Pretreatment of rats with indomethacin did not suppress the effects of piretanide on diuresis nor its effects on urinary excretion of sodium, chloride and potassium, since these parameters increased in the same proportion in the presence or in the absence of indomethacin. 5. Pretreatment with indomethacin abolished piretanide-induced dissociation of sodium and calcium excretions.     

RENAL SODIUM EXCRETION FOLLOWING SYSTEMIC INFUSION OF VASOACTIVE INTESTINAL PEPTIDE IN THE RAT

1. The aim of this clearance study was to examine the renal effects of systemic infusion of vasoactive intestinal peptide (VIP) in the intact rat. 2. Mean arterial blood pressure (MAP), plasma electrolytes and haematocrit, glomerular filtration rate (GFR), and urinary sodium and potassium excretion were measured in a baseline period and following VIP infusion (0.1-1.2 nmol/h per 200 g), as well as during a time control study. 3. During infusion of low doses of VIP (0.1 and 0.4 nmol/h per 200 g), a small increase in fractional and absolute excretion of sodium occurred but this did not differ from that occurring in the time control group. In the high dose VIP group (1.2 nmol/h per 200 g), significant falls occurred in MAP and GFR, and absolute sodium excretion fell (though not significantly) from its baseline level. 4. These findings suggest that systemic VIP has no net natriuretic effect in the rat, but produces haemodynamic changes associated with reduced sodium excretion at high doses. This study does not exclude the possibility of direct effects on tubular sodium transport of VIP released from renal nerves.     

CHOLIC ACID AND THE HEART: IN VITRO STUDIES OF THE EFFECT ON HEART RATE AND MYOCARDIAL CONTRACTILITY IN THE RAT

1. Cholic acid has a dose-dependent negative chronotropic effect on isolated atria ofWistar rats. 2. The positive inotropic effect of cholic acid is the result of a negative chronotropic effect and can be eliminated by electrical pacing. 3. Cholic acid does not appear to exert its negative chronotropic effect through cholinoceptors and alterations in bath concentrations of calcium and potassium does not influence this effect significantly. 4. Cholic acid is a functional antagonist of isoprenaline. 5. It is suggested that cholic acid exerts its negative chronotropic effect by forming a monolayer on the surface of the cell membrane, thereby mechanically interfering with membrane function.     

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.     

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.