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.     

Acute effects of pentobarbital-anaesthesia on bile secretion

Male Wistar rats were equipped with permanent catheters in the bile duct and the duodenum under ether anaesthesia, at least seven days before the experiments. By this technique, the enterohepatic circulation can be interrupted for bile collection without direct surgical intervention. 14C-Pentobarbital (26.6 mumole/100 g body wt) was injected intraperitoneally immediately before interruption of the enterohepatic circulation (NBD, Non-Bile Diverted) or after eight days of bile diversion (BD, Bile Diverted). In NBD rats, bile flow and biliary bile acid excretion were significantly reduced during the first hour after pentobarbital administration when compared to unanaesthetized controls, but markedly increased thereafter. Pentobarbital treatment slightly decreased biliary bile acid excretion in BD rats, but caused a 60% increase in bile flow. Within four hours 22.3 +/- 0.4% and 26.0 +/- 2.7% of the injected radioactivity was excreted into bile in NBD and BD rats, respectively. The calculated osmotic activity of pentobarbital and its metabolites was 47.8 +/- 5.2 microliter/mumole in NBD rats and 37.8 +/- 1.3 microliter/mumole in BD rats. Consequently, pentobarbital treatment affected the bile acid independent fraction of bile flow (BAIF). The calculated BAIF was 2.68 microliter/min/100 g body wt in unanaesthetized animals, but 4.27 microliter/min/100 g body wt in pentobarbital treated NBD rats. Corresponding values for BD rats were 1.70 and 2.38 microliter/min/100 g body wt. It is concluded that pentobarbital anaesthesia affects bile production in the rat by direct and indirect means. Firstly, pentobarbital and its metabolites are rapidly excreted into bile and exert a significant choleretic effect, thereby increasing the BAIF. Secondly, pentobarbital anaesthesia retards the exhaustion of the intestinal bile acid pool, which leads to secondary changes in the biliary excretion process.     

The effect of felodipine on bile flow in pentobarbital anaesthetized rats and conscious rats receiving bile salt supplementation.

Felodipine, a vasoselective dihydropyridine calcium antagonist, has been given i.v. (0.2 mumol/kg) to anaesthetized and conscious male rats. There was no effect of pentobarbital anaesthesia on bile flow over a 6 h observation period. Felodipine increased the 6 h recovery of bile by approximately 25% in the conscious rat but in the anaesthetized rat there was a 20% decrease in bile flow following i.v. felodipine. A positive effect of Na-taurocholate infusion (1 mumol/min/100 g body weight) on bile flow in conscious rats was reinforced by concomitant felodipine dosing. Accumulated 6 h recoveries were 2.32 +/- 0.80 g/100 g body weight (control), 3.09 +/- 0.91 g/100 g body weight (taurocholate) and 5.00 +/- 0.80 g/100 g body weight. (taurocholate plus felodipine). The excretion of felodipine in the bile was significantly reduced during anaesthesia and during infusion of 2% bovine serum albumin (0.01 ml/min/100 g body weight) to conscious rats.     

Effect of lysosomotropic agents on the taurocholate-stimulated biliary excretion of horseradish peroxidase.

The effects of the lysosomotropic agents chloroquine and leupeptin on the taurocholate-stimulated biliary excretion of horseradish peroxidase (HRP) was studied in bile fistula rats. HRP (0.5 mg/100 g body wt) was injected into the portal vein during taurocholate (0.4 mumol/min/100 g body wt) or saline infusion. HRP appeared in bile showing both an early (approx. 5 min) and a late (approx. 25 min) excretion peak. The late peak, which represented about 95% of the total HRP excreted, is due to transcellular vesicular transport. The early peak is mainly due to paracellular leakage although a rapid vesicular transport also contributes. Taurocholate infusion significantly increased the biliary output of HRP (both peaks) and of the endogenous lysosomal enzyme acid phosphatase. Pretreatment with chloroquine or leupeptin inhibited the taurocholate-stimulated late excretion of HRP into bile, without affecting its early excretion. The lysosomotropic agents did not affect the biliary excretion of bile salts but significantly inhibited the taurocholate-stimulated biliary excretion of acid phosphatase. The results are consistent with a role of lysosomes in the taurocholate-stimulated major transcellular vesicular transport of HRP into bile.     

Toxic effect of streptozotocin on the biliary secretion of nicotinamide-treated rats

The effect of streptozotocin (SZ) on bile flow (BF) and on protein and lipid biliary outputs were studied in rats with bile fistula. SZ was given i.v. as a single dose (50 mg/kg body wt.). Nicotinamide was administrated (500 mg/kg body wt., i.p.) 10 min prior to SZ. Decreases in BF and in biliary outputs of bile acids, proteins and acid phosphatase were observed in SZ-treated rats; conversely, the biliary excretion of cholesterol and phospholipids was increased. Nicotinamide pretreatment prevented the hyperglycemia induced by SZ and also suppressed the SZ-mediated increase of cholesterol and phospholipid biliary outputs, suggesting that they could be related to the diabetic state. The results also demonstrated a direct effect of SZ on BF and on the biliary excretion of bile acids and proteins. Since SZ is used clinically, and in experimental diabetes, the effects produced by this drug on the rat liver should be considered.     

Effects of butylated hydroxytoluene (BHT) on biliary excretion of xenobiotics and bile flow in rats

A significant enhancement in the biliary excretion of iv injected sulfobromophthalein (BSP), phenol- 3,6 -dibromphthalein disulfonate (DBSP), procaine amide ethobromide (PAEB) and ouabain was observed in rats maintained on diets containing 0.25% BHT for periods of 10 days. The enhanced biliary excretion of these drugs in BHT treated rats appears to be correlated with the increase in bile flow produced by BHT. The increased bile flow was due to an increase in canalicular bile production rather than a change in net ductular secretion or reabsorption of fluid since bile to plasma concentration ratios of erythritol were unchanged and no permeability change in the biliary tree was observed when mannitol was administered by retrograde intrabiliary injection. The increase in bile flow was not due to an enhanced excretion of bile salts into bile, because both the biliary bile acid concentration and total biliary excretion of bile acids were lower in BHT-treated rats than in control rats. It appears that the increase in bile flow produced by BHT is due to the osmotic choleresis related to the secretion of BHT and its metabolites into bile.     

The influence of cholic acid and dehydrocholic acid on the biliary excretion of unconjugated and conjugated sulfobromophthalein in rats.

Urethane anesthetized Wistar rats with biliary fistulas were infused during 100 min with sulfobromophthalein (BSP), the glutathione conjugate of sulfobromophthalein (BSP-GSH), cholic acid (CA) and dehydrocholic acid (DCA). The dyes (594 nmol/100 g/min) and the bile acids (1200 nmol/100 g/min) were infused separately, and in combination as well. When BSP was infused, CA and DCA increased the maximal excretion of total BSP (conjugated plus unconjugated) from 1400 to 4100 and 3300 nmol/100 g/10 min. The bile flow observed with BSP plus CA was not significantly different from that with BSP plus DCA. The biliary excretion of total BSP was higher throughout with CA than with DCA because CA increased the biliary concentration of PSP while DCA did not. The bile flow attained with CA alone was significantly lower than that with BSP plus CA. The current data provide arguments for abandoning the view that choleresis per se is the crucial determinant for BSP excretion. When BSP-GSH was infused instead of BSP, the excretion rate of the dye was not altered by the additional infusion of CA whereas it was significantly reduced by DCA. The maximal biliary concentration of BSP-GSH fell from 25.9 nmol/mul to 15.3 and 9.4 nmol/mul with CA and DCA, respectively. Both CA and DCA impaired the hepatic uptake of BSP and BSP-GSH. During the infusion with CA, BSP plus CA and BSP-GSH plus CA the biliary excretion rates of bile acids did not differ significantly from each other. This favours the view that the transfer for CA from the liver to bile is different from that for BSP and BSP-GSH. A fraction of bile fluid "independent of choleretics" (viz. of bile salts, BSP and BSP-GSH) is estimated and discussed in view of the different types of infusion.     

Effect of gomisin A (TJN-101), a lignan compound isolated from Schisandra fruits, on liver function in rats

TJN-101 [+)-(6S, 7S, R-biar)-5,6,7,8-tetrahydro-1,2,3,12-tetramethoxy- 6,7-dimethyl-10,11-methylenedioxy-6-dibenzo [a, c] cyclooctenol) is one of the lignan compounds isolated from Schisandra fruits. When TJN-101 was administered orally at the doses of 3-100 mg/kg/day for 4 days, bile secretion, hepatic excretion of dye or hepatic hemodynamics 24 hr after the last dose was investigated in comparison with the phenobarbital (100 mg/kg/day)-treated group. Bile flow was dose-dependently increased; in contrast, biliary concentration of bile acids was decreased in TJN-101 (30 and 100 mg/kg/day)-treated groups. Similar changes were also observed in the phenobarbital-treated group. These results suggested that the enhancement of bile secretion caused by TJN-101 or phenobarbital was due to an increase of a bile acid-independent fraction. In the bromosulfophthalein (BSP) clearance test for liver function, both TJN-101 (30 and 100 mg/kg/day) and phenobarbital accelerated the disappearance from the blood and biliary excretion of BSP. Hepatic hemodynamics was examined by the hydrogen clearance method and measurement of liver wet and dry weight. Liver blood flow tended to increase in the TJN-101 (10-100 mg/kg/day) or phenobarbital-treated group. On the other hand, TJN-101 (3-100 mg/kg/day) or phenobarbital hardly altered the water content of the liver. These results suggested that the liver enlargement caused by both compounds was not accompanied with hepatic edema and that the enhancement of bile secretion or hepatic excretion of BSP might be related to an increase of liver blood flow.     

Mirex inhibits bile acid secretory function in vivo and in the isolated perfused rat liver.

The insecticides mirex and chlordecone suppress the biliary excretion of a wide variety of non-bile acid organic anions in vivo in the rat, and mirex inhibits the uptake of taurocholate (TC), a common bile acid, in isolated rat hepatocytes. We have therefore investigated the effects of mirex and chlordecone on bile acid secretory function (bile flow, bile acid concentration, bile acid secretory rate) in vivo and in the single-pass isolated perfused liver. Male Sprague-Dawley rats were orally dosed with corn oil, mirex (50 mg/kg), or chlordecone (18.75 mg/kg; in vivo studies only) for 3 consecutive days and experiments performed on Day 6. Mirex significantly increased liver weight from 12.2 +/- 0.8 to 20.8 +/- 1.3 g with no change in body weight whereas chlordecone had no significant effect on liver weight (11.9 +/- 0.7 g) or body weight. Mirex significantly decreased while chlordecone increased bile flow per gram liver in vivo; both compounds, however, increased bile flow when expressed per kilogram of body weight. Mirex and chlordecone significantly decreased the bile acid concentration in bile and the bile acid secretory rate (nmol/min/g liver and mumol/min/kg body weight). Studies in the isolated perfused liver were designed to determine the effect of mirex on the ability of the liver to extract increasing concentrations of [3H]TC from the perfusate and excrete it in the bile. Mirex treatment significantly decreased the TC extraction ratio by 40-89% and the hepatic intrinsic clearance by 85-95%. Mirex also significantly decreased the TC-induced choleresis, the concentration of TC in the bile, and the TC secretory rate. The data indicate that mirex treatment markedly inhibits the ability of the liver to extract TC from the blood/perfusate and concentrate it in the bile.     

Bile formation and biliary lipid composition under the influence of clofibrate and phenobarbital pretreatment in the rat

Summary The effect of the two enzyme inducing agents, clofibrate and phenobarbital, on bile formation and biliary lipid composition was compared in male rats. Clofibrate (100 mg per kg body weight per day for 14 days) and phenobarbital (at first 60 mg per kg body weight per day for 3 days, then 100 mg per kg body weight per day for 11 days) increase the spontanous bile flow, the ¹⁴C-erythritol clearance but do not alter the bile salt excretion, indicating a stimulation of the bile acid independent fraction of bile. The bile of rats pretreated with clofibrate contains less cholesterol than the bile of saline treated control animals, whereas the concentrations of bile acids, phospholipids and cholesterol are reduced in the bile of the rats of the phenobarbital group. Both drugs diminish the cholesterol saturation of bile. If the biliary bile acid concentration and excretion are augmented by an infusion of sodium taurocholate (1000 nmol per min per 100 g body weight), the biliary concentration of cholesterol remains unchanged in the clofibrate group but increases in the phenobarbital group as compared with the saline control animals. The biliary phospholipid concentration is enhanced after clofibrate as well as after phenobarbital pretreatment. These studies indicate that the biliary excretion of cholesterol and phospholipids is at least to some extent regulated by the bile acid excretion. The importance of the synthesis of cholesterol and phospholipids for their biliary excretion, however, seems to be limited: a reduced cholesterol synthesis by clofibrate results in a reduced biliary cholesterol elimination. By contrast, an increased synthesis of cholesterol by phenobarbital and of the phospholipids by both drugs, however, may enlarge the intrahepatic lipid pools and may place more lipids available for biliary secretion.     

Effect of Bile Acids on Hepatobiliary Transport of Cisplatin by Perfused Rat Liver

Abstract: The liver and kidney collaborate in the excretion of the cytostatic drug, cis-diamminedichloroplatinum(II) (cisplatin) from the body. Enhancement of this procces is envisaged as a way of reducing cisplatin toxicity, thus allowing increases in the doses administered. In this sense, using different compounds, several attempts have been made to enhance cisplatin biliary excretion. In this study, the ability of endogenous compounds belonging to the bile acid family to improve cisplatin excretion by the isolated perfused rat liver was investigated. A highly choleretic bile acid (ursodeoxycholic acid) and two others bile acids with marked micelle-forming properties (glycocholic acid and chenodeoxycholic acid) were chosen for study. When these drugs were given at concentrations (1 μM) that did not affect the viability of liver preparations, a correlation between the biliary excretion of platinum and bile acid output was found. This was not due to the incorporation of cisplatin into mixed micelles because no correlation between the biliary output of lecithin or cholesterol and platinum was observed. Moreover, a wash-out effect of bile acids was probably not the cause of bile acid-induced platinum output into bile because no correlation between this and bile flow was found. An enhancement in cisplatin transport processes by the hepatocyte or by direct binding of cisplatin to bile acid monomers or aggregates cannot be ruled out. In spite of the biliary induction of cisplatin output, the net excretion of platinum was reduced under bile acid administration. This was related to lower platinum contents in the liver tissue, probably due to an inhibition of the ability of the hepatocyte to take up and/or retain cisplatin while subject to bile acid infusion. In summary, our results indicate that bile acids reduce the net excretion of cisplatin by the liver even though they induce an enhancement in the transport of this compound from the hepatocyte into bile.     

The effects of thiamine and EDTA on biliary and urinary lead excretion in sheep.

Relative efficacy of thiamine (B1) and/or calcium disodium ethylinediaminetetraacetate (EDTA) administration on lead (Pb) excretion via bile and urine was studied in Pb-loaded sheep. The sheep were administered B1 s.c., 75 mg/kg body wt., EDTA i.v., 110 mg/kg body wt., and a combination of B1-EDTA at rates as above. Each treatment was followed by 69 h sampling of blood, bile, and urine. Urinary Pb excretion increased following B1-EDTA greater than EDTA greater than B1 administration. Thiamine and B1-EDTA treatments increased biliary Pb excretion. Overall, B1, EDTA and B1-EDTA administration increased Pb excretion via bile and urine by 72%, 595%, and 842% respectively over basal level (mean +/- SE: 20.1 +/- 2.9 micrograms Pb/h). It has been concluded that thiamine enhances elimination of Pb from the body and this feature may be beneficial in chelation therapy.     

Choleresis and inhibition of biliary lipid secretion induced by piperacillin in the rat

1. The effects of the administration piperacillin on bile flow and biliary lipid secretion were studied in male Wistar rats. 2. Intravenous injection of piperacillin at doses ranging from 0.3 to 3.0 mmol/kg bodyweight led to an increase in its biliary concentration and excretion rate. Maximal biliary excretion was reached at a dose of 2.0 mmol/kg piperacillin. 3. Excretion of the antibiotic into bile was associated with a marked choleresis. A linear relationship was observed between bile flow and piperacillin excretion, 5.7 micro L bile being produced per micro mol piperacillin excreted into the bile. 4. Continuous i.v. infusion of piperacillin at 2.0 mmol/100 g per min did not result in significant changes in bile acid or cholesterol secretion, but biliary phospholipid secretion was markedly reduced. The inhibitory effect on phospholipid secretion was also present when biliary lipid output had been previously increased by an infusion of taurocholate (200 nmol/100 g per min). Addition of taurocholate did not reverse the impairment of phospholipid secretion induced by piperacillin. 5. These results indicate that acute administration of piperacillin in the rat induces a marked choleresis by stimulating bile acid-independent bile flow. The significant impairment in phospholipid secretion suggests a specific effect on intracellular supply and/or translocation across the canalicular membrane.     

The effect of cisapride on defaecation in normal human subjects—lack of effect on faecal excretion of water, fat, and bile acids

In order to elucidate whether or not the increased stool frequency that occurs during cisapride treatment is a result of malabsorption of water, fat, and bile acids, 12 healthy volunteers were dosed with either tablets of placebo q.d.s. or tablets of 10 mg cisapride q.d.s. during two periods of 5 days in a double-blind, crossover study. Stool frequency, stool consistency, and side-effects were recorded each day. Total faecal mass, faecal water content, and faecal excretion of fat and bile acids were determined during the last 72 h of each study period. Mean daily stool frequency was 18.8% higher during cisapride [1.68 +/- 0.12 (S.E.M.)] administration than during placebo (1.42 +/- 0.12); P = 0.038. The stool consistency score increased by 11.8% towards softer stools during cisapride dosing (N.S.). There were no significant differences in total faecal mass (placebo 399.4 g/72 h; cisapride; 414.5 g/72 h), faecal water content (placebo; 75.6%: cisapride 76.2%), or faecal excretion of fat (placebo; 12.7 g/72 h: cisapride; 11.6 g/72 h) and total bile acids (placebo; 2212 mumol/72 h: cisapride; 2261 mumol/72 h). The side-effects reported during placebo were constipation (n = 3), and during cisapride meteorism (n = 4) and increased appetite (n = 2). The increased stool frequency during cisapride treatment is not caused by malabsorption of water, fat, or bile acids, but seems to be the consequence of a direct motor effect.     

Biliary excretion of polyethylene glycol molecular weight 900. Evidence for a bile salt-stimulated vesicular transport mechanism

Polyethylene glycol molecular weight 900 (PEG-900) has been used as a marker of vectorial water transport into bile canaliculus. However, the mechanisms by which this compound is excreted have not been clarified. To gain more information on this process, we studied the biliary excretion of [3H]PEG-900 in rats during choleresis induced by canalicular choleretics. In addition, the effects of the microtubule inhibitors colchicine and vinblastine, and of the acidotropic agent chloroquine, on PEG-900 excretion were studied to determine whether a vesicular pathway is involved. Continuous i.v. infusion of either dehydrocholate (DHC, a non-micelle forming bile salt choleretic) or 4-methylumbelliferone (4-MU, a non-bile salt canalicular choleretic) at stepwise-increasing rates [0.7, 1.0 and 1.2 mumol.min-1.(100 g body wt)-1] induced a gradual increment in bile flow, whereas a transient increment of [3H]PEG-900 excretion was observed only during DHC-induced choleresis. Furthermore, studies in which two consecutive i.v. injections of DHC (10 mumol/100 g body wt) were administered showed that [3H]PEG-900 excretion induced by a second administration of DHC was 54% lower than that induced by the first one, despite a similar excretion in bile flow. Finally, colchicine (0.5 mumol/100 g body wt), vinblastine (0.5 mumol/100 g body wt) and chloroquine (50 mg/kg body wt) pretreatments inhibited the DHC-induced increment in biliary [3H]PEG-900 output, while DHC-induced choleresis was almost unaffected. Conversely, excretion of [14C]sucrose, when coadministered with [3H]PEG-900, was not impaired by the treatments. These results suggest that, unlike sucrose, PEG-900 excretion is not associated with canalicular water movements. Instead, it may be related to a vesicular transport process followed by a bile acid-stimulated discharge of secretory vesicles into bile through the lysosomal compartment.     

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.     

Effect of the glutathione-depleting agents diethylmaleate, phorone and buthionine sulfoximine on biliary copper excretion in rats

The involvement of glutathione (GSH) in the biliary excretion of Cu was investigated in bile-cannulated inbred WAG/Rij and BN rats, pretreated with diethylmaleate (DEM), phorone or buthionine sulfoximine (BSO) and injected with Cu doses of 10 or 30 micrograms/100 g body wt. DEM reduced liver GSH to 27-56% and biliary GSH excretion to 18-38%; phorone reduced GSH in the liver to 55% and increased it in the bile (113%) followed by a slight decrease (79%); BSO reduced liver GSH to 50% and bile GSH to 20%. After injection of Cu to control rats a profile of biliary Cu excretion was found, composed of a slowly (SCuE) and a rapidly (RCuE) disappearing component, the latter only present after the dose of 30 micrograms Cu. DEM had no effect on SCuE after a 10 micrograms dose and a temporary effect on SCuE after a 30 micrograms dose in both WAG/Rij and BN rats. Phorone reduced SCuE after both Cu doses to 50%. Both agents abolished RCuE and reduced endogenous biliary Cu excretion to less than 50%. Release of injected Cu from plasma and uptake by the liver was inhibited by DEM and phorone in both rat strains; in BN rats basal plasma Cu level of DEM-treated rats was increased as well. BSO reduced SCuE after both Cu doses but had no influence on RCuE. Endogenous Cu excretion was reduced by BSO in BN rats but not in WAG/Rij rats. The results show that biliary Cu excretion proceeds by a pattern, the components of which can be affected differently by the various drugs. They also indicate that GSH is not directly involved in biliary Cu excretion but suggest that it may play a role in the metabolism of Cu in the liver.     

A possible mechanism of choleretic action of 3-(2,4,5-triethoxybenzoyl)-propionic acid (AA-149) in dogs

The choleretic action of 3-(2,4,5-triethoxybenzoyl)propionic acid (AA-149) was studied in anesthetized dogs. AA-149 produced a dose-dependent increase of the bile flow with both i.v. and intrajejunal administration of doses 1 mg/kg and higher. Biliary clearance of 14C-erythritol showed that AA-149 stimulated canalicular bile formation without enhancement of water secretion and/or inhibition of bile reabsorption in the biliary ductules and ducts. AA-149 did not increase the excretion of bile acids into the bile, but enhanced the excretion of the biliary electrolytes, in particular sodium ion, in proportion to an increase of the bile flow. About 3--4% of AA-149 administered i.v. was excreted into the bile during the first 1 h period, so that biliary AA-149 was insufficient to increase the bile flow via its osmotic effect. These results strongly suggest that the choleretic action of AA-149 is attributable to stimulation of a bile acid-independent bile formation in the canaliculi coupled with an active sodium transport system.     

Polarity of hepatic glutathione and glutathione S-conjugate efflux, and intraorgan mercapturic acid formation in the skate

Mechanisms of hepatic glutathione and glutathione S-conjugate efflux were investigated in isolated hepatocytes and perfused liver of the little skate (Raja erinacea). Glutathione was released by isolated skate hepatocytes at a rate of 0.12 +/- 0.03 nmol.hr-1.(mg protein)-1. In the perfused liver, glutathione concentrations in bile were high (approximately 0.7 mM) compared to hepatic tissue levels (0.61 +/- 0.11 mumol.g-1). During the first hour of perfusion, the biliary glutathione excretion rate was 3 nmol.hr-1.(g liver)-1, whereas glutathione accumulated in the recirculating perfusate at a rate of only 1.5 nmol.hr-1.(g liver)-1. Release of glutathione by isolated hepatocytes and perfused liver was not affected by the addition of acivicin, an inhibitor of gamma-glutamyltransferase (EC 2.3.2.2), to cell suspension medium or liver perfusate. 1-Chloro-2,4-dinitrobenzene (CDNB) was taken up by isolated hepatocytes, conjugated to glutathione, and released as S-(2,4-dinitrophenyl) (DNP)-glutathione. After infusion of 0.5 mumol CDNB in perfused liver, S-DNP-glutathione was concentrated in bile (0.5 mM) and was associated with choleresis. S-DNP-Conjugates of cysteinylglycine, cysteine and N-acetylcysteine, were also found in bile, suggesting intrahepatic breakdown of S-DNP-glutathione and subsequent acetylation of the resulting cysteine conjugate to form the mercapturic acid, S-DNP-N-acetylcysteine. This mercapturic acid accounted for 31% of the total S-DNP-conjugates collected in bile. In contrast, neither S-DNP-glutathione nor other S-DNP-conjugates were detected in the perfusate (less than 0.5 microM). These findings demonstrate that biliary excretion is the predominant route for efflux of glutathione and a glutathione S-conjugate from skate liver. The results also identify an intrahepatic pathway for mercapturic acid biosynthesis facilitated by biliary glutathione S-conjugate excretion.     

Effects of F2833 on cholesterol metabolism in the genetically hyperlipidemic rat

The effects of the new hypolipidemic agent, F2833 or (chloro 2' (1-1') biphenyl-4)-2 propanol-2, on cholesterol metabolism were studied in genetically hyperlipidemic rats (RICO). Cholesterolemia decreased after 2 days of treatment to 60% of its initial value (1.20+/-0.10 g/l vs. 1.99+/-0.08, P < 0.001) and then stabilised within 10 days. This hypocholesterolemic action was effective for as long as 3 months. Concerning the different classes of lipoproteins, a significant drop was observed in HDL (high density lipoproteins) (25%, 0.49 +/- 0.02 g/l vs. 0.66 +/- 0.007, P < 0.01) and particularly in LDL (low density lipoproteins) (70%, 0.30 +/- 0.04 g/l vs. 0.92 +/- 0.05, P < 0.001). Whole body cholesterol showed a higher fractional catabolic rate (0.25 +/- 0.02 vs. 0.17 +/- 0.005 day(-1), P < 0.01) together with an increased cholesterol synthesis (60 +/- 5 vs. 36 +/- 4 mg/day, P < 0.01). LDL kinetics showed that the decrease in these lipoproteins is essentially caused by an increase in the fractional catabolic rate (10.6 +/-0.1%/h vs. 5.2 +/- 0.1%/h, P < 0.001) and by a lesser decrease in the LDL production rate. This cholesterol metabolic profile created by treatment suggests an effect through stimulation of cholesterol output (biliary cholesterol elimination or cholesterol transformation into bile acids).