Effect of diethyl ether on the biliary excretion of acetaminophen

The biliary and renal excretion of acetaminophen and its metabolites over 8 hr was determined in rats exposed to diethyl ether by inhalation for 1 hr. Additional rats were anesthetized with urethane (1 g/kg ip) while control animals were conscious throughout the experiment (surgery was performed under hexobarbital narcosis: 150 mg/kg ip; 30-min duration). The concentration of UDP-glucuronic acid was decreased 80% in livers from ether-anesthetized rats but was not reduced in urethane-treated animals when compared to that in control rats. The concentration of reduced glutathione was not affected by either urethane or diethyl ether. Basal bile flow was not altered by the anesthetic agents. Bile flow rate after acetaminophen injection (100 mg/kg iv) was increased slightly over basal levels for 2 hr in hexobarbital-treated control rats, was unaltered in urethane-anesthetized animals, and was decreased throughout the 8-hr experiment in rats exposed to diethyl ether for 1 hr. In control and urethane-anesthetized animals, approximately 30-35% of the total acetaminophen dose (100 mg/kg iv) was excreted into bile in 8 hr, while only 16% was excreted in rats anesthetized with diethyl ether. Urinary elimination (60-70% of the dose) was not altered by exposure to ether. Separation of metabolites by reverse-phase high-pressure liquid chromatography showed that ether decreased the biliary elimination of unchanged acetaminophen and its glucuronide, sulfate, and glutathione conjugates by 47, 40, 49, and 73%, respectively, as compared to control rats. Excretion of unchanged acetaminophen and the glutathione conjugate into bile was depressed in urethane-anesthetized animals by 45 and 66%, respectively, whereas elimination of the glucuronide and sulfate conjugates was increased by 27 and 50%, respectively. These results indicate that biliary excretion is influenced by the anesthetic agent and that diethyl ether depresses conjugation with sulfate and glutathione as well as glucuronic acid.     

Multiple hepatic excretory mechanisms for organic anions. A study with succinylsulfathiazole and taurocholate in the rat.

A study was done to investigate interactions in the biliary excretion of [14-C]succinylsulfathiazole and [3-H]taurocholate after intravenous administration of the two compounds to anesthetized rats. Either compound administered alone increased bile flow and was excreted in the bile. The simultaneous infusion of both significantly increased bile flow above the values seen when either was given alone. However, the biliary-excretion rates of both compounds and their concentrations in bile were reduced when they were administered concomitantly. The simultaneous injection of radioactive taurocholate and succinylsulfathiazole did not alter significantly the plasma concentrations of either compound or their binding to plasma proteins from the values obtained when each was given alone. These results are consistent with a concept of competition between these compounds for the same liver-to-bile transport system. They contrast with previous observations that indicated that the concomitant administration of taurocholate increased the biliary excretion of acidic compounds. In the light of this work, it might be suggested that there are more than one transport system for the biliary excretion of organic anions.     

Cardiovascular effects of cocaine in anesthetized and conscious rats

This study examined the cardiovascular and respiratory effects of cocaine and procaine in anesthetized and conscious rats. Intravenous cocaine (0.16-5 mg/Kg) elicited a rapid, dose dependent increase in mean arterial pressure of relatively short duration. In pentobarbital anesthetized (65 mg/Kg, i.p.) animals, the pressor phase was generally followed by a more prolonged depressor phase. These effects on arterial pressure were generally accompanied by a significant tachypnea and at larger doses (2.5 and 5 mg/Kg, i.v.), bradycardia. Procaine (0.31 and 1.25 mg/Kg, i.v.) produced similar cardiovascular and respiratory effects (depressor phase, tachypnea) in pentobarbital anesthetized animals. In conscious-restrained animals, both cocaine and procaine (1.25 mg/kg, i.v.) produced pressor responses. The subsequent depressor response was, however, absent in both cases. The cardiovascular effects of cocaine (0.25-1 mg/Kg, i.v.) in urethane anesthetized (1.25 g/Kg, i.p.) animals were essentially similar to those observed in conscious animals. Procaine (1mg/Kg) did not produce any significant cardiovascular effects in urethane anesthetized animals, but did elicit tachypnea. Reserpine pretreatment (10 mg/Kg, i.p.) did not significantly attenuate the pressor response in urethane anesthetized animals. Phentolamine pretreatment (3 mg/Kg, i.v.) did significantly antagonize the pressor effect in urethane anesthetized animals. These results suggest that: the depressor phase is likely due to a interaction between local anesthetic activity (cocaine and procaine) and barbiturate anesthesia, the cardiovascular effects of cocaine in conscious animals are more similar to those observed in urethane anesthetized rats than in pentobarbital anesthetized rats and the pressor effect in urethane anesthetized rats is apparently due to a reserpine resistant catecholaminergic mechanism.     

Measurement of bile acid synthesis by 14CO2: the metabolism of propionyl CoA.

The relationship between 14CO2 evolution from the catabolism of [26 or 2714C] cholesterol to bile acids was studied in rats with biliary fistulae. When equal quantities of [26 or 2714C] cholesterol and [414C] cholesterol were administered, there was a significant linear relationship between 14CO2 expiration in the breath and [414C] bile acid excreted in the bile. Bile acid synthesis calculated as the ratio of 14CO2: molar specific activity of biliary cholesterol correlated highly with biliary bile acid excretion in the bile acid depleted rat. Phenobarbital, a known inducer of gamma-amino levulenic acid formation from succinyl CoA did not alter the relationship between the 14CO2 estimation of bile acid synthesis and biliary bile acid excretion, indicating that the relationship between [26 or 2714C] cholesterol side chain cleavage and 14CO2 formation was not altered. Phenobarbital, however, did cause a reduction in bile acid synthesis measured by 14CO2 evolution and by biliary bile acid excretion. The 14CO2 method underestimated bile acid excretion. 8.7% in untreated and phenobarbital treated rats respectively. Since 11% of the radioactivity which was expired as 14CO2 was isolated as bile acids, radioactivity cleaved as [1 or 314C] propionyl CoA may enter cholesterol-bile acid biosynthesis resulting in the underestimation of bile acid synthesis. To test whether radioactivity from propionyl CoA enters steroid biosynthesis [114C] propionate and [214C] propionate were given to untreated biliary fistula rats and the biliary lipids excreted in 60 hours were analyzed. Incorporation of radioactivity into cholesterol and bile acids was greater after the administration of [214C] propionate than after [114C] propionate than after [114C] propionate, suggesting that radioactivity from propionyl CoA may enter steroid biosynthesis by metabolic events in which the methylene and carboxyl carbon atoms are differentiated. Although the use of 14CO2 expiration from [26 or 2714C] cholesterol catabolism underestimates the rate of bile acid synthesis, it should have many applications because of the constant relationship between 14CO2 formation and cholesterol side chain cleavage.     

Excretion of cholate glucuronide

[3-3H]Cholic acid glucuronide [7 alpha,12 alpha-dihydroxy-3 alpha-O-(beta-D-glucopyranosyluronate)-5 beta- cholan-24-oate] was synthesized and administered to rats prepared with either an external biliary fistula or a ligated bile duct. When bile fistula animals were given either microgram or milligram amounts of the glucuronide, biliary secretion of label was rapid and efficient: greater than 90% of the administered label was secreted within 60 min and total recovery of label in bile was 98.6 +/- 1.2%. Studies in which [14C]taurocholate was included in the dose indicated that this bile acid was secreted into bile significantly more rapidly than was the glucuronide. In animals with ligated bile ducts, urinary excretion was the major route of elimination: after 20 hr, 83.4 +/- 9.3% of the administered dose had been excreted in urine. Urinary excretion of cholate glucuronide was significantly more rapid than that of taurocholate. Gas-liquid chromatographic analysis of the methyl ester acetate derivatives of labeled compounds isolated from bile and urine by chromatography established that the bulk (greater than 70%) of the administered material was secreted in bile or excreted in urine as the intact cholate glucuronide. From these results, we conclude that the glucuronidation of cholic acid produces a derivative which is rapidly and effectively cleared from the circulation and excreted.     

Mutagenic activity of biliary metabolites of 6-hydroxymethylbenzo[a]pyrene

The biliary excretion of the carcinogen 6-hydroxy-methylbenzo[a]pyrene was investigated in rats after i.p. administration. Mutagenicity of the parent compound and its biliary metabolites was tested in Ames Salmonella/microsome mutagenicity assay. Approximately 40% of the dose administered (0.25-0.5 mg/kg) to the rats was excreted in the bile within 6 h. 6-Hydroxymethylbenzo[a]pyrene was excreted primarily as water-soluble metabolites, including glucuronide and sulfate conjugates. Negligible quantities of unchanged 6-hydroxymethylbenzo[a]pyrene were excreted in the bile. In the presence of Aroclor-induced S9, 6-hydroxymethylbenzo[a]pyrene was a potent mutagen. The mutagenicity of bile from rats treated with 6-hydroxymethylbenzo[a]pyrene was variable in the absence of an activation system. However, the same bile samples were mutagenic in the presence of beta-glucuronidase and/or S9. These results indicate that biliary metabolites of 6-hydroxymethylbenzo[a]pyrene can be metabolically activated to mutagenic species.     

Molecular weight as a factor in the excretion of monoquaternary ammonium cations in the bile of the rat, rabbit and guinea pig

1. The excretion in the bile and urine of intraperitoneally injected (14)C-labelled monoquaternary ammonium or pyridinium cations was measured in bile-duct-cannulated rats (ten compounds) and in guinea pigs and rabbits (six compounds). 2. Seven of these, namely N-methylpyridinium, tetraethylammonium, trimethylphenylammonium, diethylmethylphenylammonium, methylphenyldipropylammonium, dibenzyldimethylammonium and tribenzylmethylammonium, were excreted largely unchanged in the bile and urine. 3. 3-Hydroxyphenyltrimethylammonium, 3-bromo-N-methylpyridinium and cetyltrimethylammonium were metabolized to an appreciable extent in the rat. 4. In intact rats intraperitoneally injected trimethylphenylammonium (mol.wt. 136) was excreted mainly in the urine, dibenzyldimethylammonium (mol.wt. 226) was excreted in roughly equal amounts in the urine and faeces, and tribenzylmethylammonium (mol.wt. 302) was excreted mainly in the faeces. The faecal excretion of these compounds corresponded to their biliary excretion in bile-duct-cannulated rats. About 3-4% of tribenzyl[(14)C]methylammonium was eliminated as (14)CO(2). 5. In rats the extent of biliary excretion of four cations with molecular weights in the range 94-164 was less than 10% of the dose, whereas that of five cations with molecular weights 173-302 was greater than 10%. These results and other data from the literature suggested that the molecular weight needed for the biliary excretion of such cations to an extent of 10% or more of the dose was about 200+/-50. Studies with six cations in guinea pigs and rabbits suggest that this value applies also to these species. 6. The results suggest that the threshold molecular weight for the appreciable (>10%) biliary excretion of monoquaternary cations is different from that for anions (Millburn et al., 1967a; Hirom et al., 1972b). With rats, guinea pigs and rabbits, no significant species difference was noted, whereas with anions there is a marked species difference.     

Age dependence of hepatic transport in control and phenobarbital-pretreated rats.

Eosine is excreted in rat bile unchanged, which makes it suitable for the study of age dependent changes in hepatic uptake and excretion. Bile flow was approximately 40 μl/kg/min in 20-day-old rats and twice as high in 30-day-old animals. In 60- and 120-day-old rats the bile volume was decreased, moreover in 220-day-old ones it fell to the level of 20-day-old rats. The biliary excretion of eosine (150 μmol/kg i.v.) was highest in 60-day-old rats, however, the biliary flow reached its peak in 30-day-old rats. After phenobarbital (PB) pretreatment (75 mg/kg i.p. daily for five days) each age group showed enhancement in liver weight and bile volume. On the other hand, the hepatic concentration of eosine did not change after PB pretreatment caused an increase in the biliary excretion of eosine in 30-, 60-, 120- and 220-day-old rats but no significant change in 20-day-old animals. Our results indicate that the hepatic transport in young rats was immature and was not induced by PB. However, PB can increase the low excretion rate in old rats.     

Biliary excretion of barium in the rat

Biliary excretion of barium was studied in Sprague-Dawley bile-duct-cannulated rats injected intravenously with 1.8 micrograms Ba/rat as 133Ba-labeled barium chloride. Approximately 0.5% of the barium dose was excreted into bile within 2 h. The time-course profile of biliary excretion of the radiotracer closely reflected that of plasma concentrations. Biliary barium levels reached their peak in the first 15-min period after administration and rapidly declined thereafter. The plasma-to-bile barium-concentration ratio was approx 1 at 2 h after injection. There was no tendency of barium to concentrate in liver, and the 133Ba levels in stomach and small intestine largely exceeded hepatic levels. There is evidence indicating that barium is predominantly excreted with feces following parenteral administration in rats and humans. The results of this study suggest that biliary excretion is of little quantitative importance and that physiological routes other than bile contribute to elimination of barium by the digestive tract.     

The influence of (3H)taurocholate on the biliary excretion of (14C)acetylprocaine amide ethobromide.

The biliary excretion rates of [14C]acetylprocaine amide ethobromide (acetyl-PAEB) and [3H]taurocholate, either administered alone or in combination to adult male Wistar rats, were studied. Their renal pedicles were ligated, and the common bile duct and one jugular vein cannulated. Acetyl-PAEB, 20 mg/kg, and sodium taurocholate, 70 mg/kg, were infused over a 5-min period. Blood and bile samples were collected every 10 min for 60 min. Liver samples were taken at 10 and 20 min. Approximately 100% of the administered taurocholate was excreted within 50 min. The simultaneous administration of acetyl-PAEB did not significantly alter the taurocholate excretion. The amount of the acetyl-PAEB dose excreted in 1 h was 9.4%. This was increased significantly to 16.5% when taurocholate was given concomitantly. The concentration of acetyl-PAEB in the bile increased significantly when taurocholate was given, and the ratios of its concentrations in bile-liver and bile-plasma were also increased. Taurocholate did not alter the liver-plasma concentration ratio of acetyl-PAEB. It is suggested that the concomitant administration of taurocholate increased the biliary excretion of acetyl-PAEB by facilitating its secretion by the liver into the bile.     

Role of the hepatocyte microtubular system in the excretion of bile salts and biliary lipid: implications for intracellular vesicular transport

The role of the hepatocyte microtubular system in the transport and excretion of bile salts and biliary lipid has not been defined. In this study the effects of microtubule inhibition on biliary excretion of micelle- and non-micelle-forming bile salts and associated lipid were examined in rats. Low-dose colchicine pretreatment had no effect on the baseline excretion of biliary bile salts and phospholipid in animals studied 1 hr after surgery (basal animals), but slightly retarded the excretion of tracer [14C]taurocholate relative to that of lumicolchicine-pretreated (control) rats. However, colchicine pretreatment resulted in a marked reduction in the excretion of 2 mumol/100 g doses of a series of four micelle-forming bile salts of differing hydrophilicity, but had no significant effect on the excretion of the non-micelle-forming bile salt, taurodehydrocholate. Continuous infusion of 0.2 mumol of taurocholate/(100 g.min) following 24 hr of biliary drainage (depleted/reinfused animals) resulted in physiologic bile flow with biliary excretion rates of bile salts, phospholipid, and cholesterol that were markedly inhibited (mean 33, 39, and 42%, respectively) by colchicine or vinblastine pretreatment. Excretion of tracer [14C]taurocholate also was markedly delayed by colchicine in these bile salt-depleted/reinfused animals. In contrast, colchicine did not inhibit bile salt excretion in response to reinfusion of taurodehydrocholate. Thus, under basal conditions, the microtubular system appears to play a minor role in hepatic transport and excretion of bile salts and biliary lipid. However, biliary excretion of micelle-forming bile salts and associated phospholipid and cholesterol becomes increasingly dependent on microtubular integrity as the transcellular flux and biliary excretion of bile salts increases, in both bile salt-depleted and basal animals. We postulate that cotransport of micelle-forming bile salts and lipids destined for biliary excretion, via an intracellular vesicular pathway, forms the basis for this microtubule dependence.     

Species variations in the threshold molecular-weight factor for the biliary excretion of organic anions

1. The excretion in the bile and urine after intravenous injection of 16 organic anions having molecular weights between 355 and 752 was studied in female rats, guinea pigs and rabbits. 2. These compounds were mostly excreted unchanged, except for three of them, which were metabolized to a slight extent (<7% of dose). 3. The rat excreted all the compounds extensively (22-90% of dose) in the bile. 4. In guinea pigs four of the compounds with mol.wt. 355-403 were excreted in the bile to the extent of 7-16% of the dose, four with mol.wt. 407-465 to the extent of 25-44% and eight compounds with mol.wt. 479-752 to the extent of 44-100%. 5. In rabbits four compounds with mol.wt. 355-465 were excreted in the bile to the extent of 1-8% of the dose, two compounds with mol.wt. 479 and 495 to the extent of 24 and 22%, and six compounds with mol.wt. 505-752 to the extent of 31-94%. 6. These results, together with those of other investigations from this laboratory, are discussed and the conclusion is reached that there is a threshold molecular weight for appreciable biliary excretion (i.e. more than 10% of dose) of anions, which varies with species: about 325+/-50 for the rat, 400+/-50 for the guinea pig and 475+/-50 for the rabbit. 7. Anions with molecular weights greater than about 500 are extensively excreted in the bile of all three species. 8. That proportion of the dose of these compounds which is not excreted in the bile is excreted in the urine, and in the three species, bile and urine are complementary excretory pathways, urinary excretion being greatest for the compounds of lowest molecular weight and tending to decrease with increasing molecular weight. 9. Some implications of this interspecies variation in the molecular-weight requirement for extensive biliary excretion are discussed.     

Differences between the biliary excretion of tri[14C]methyl-1-(3-hydroxyphenyl)ammonium iodide in Wistar and Gunn rats

1. The biliary excretion of [¹⁴C]trimophonium iodide [tri[¹⁴C]methyl(3-hydroxyphenyl)ammonium iodide] was studied in normal Wistar animals and in jaundiced homozygous Gunn rats. 2. In normal Wistar rats small amounts of radioactivity (approx. 3% of the dose in 4h) were excreted in bile as two glucuronide conjugates, i.e. [¹⁴C]trimophonium glucuronide [tri[¹⁴C]methyl-(3-oxyphenyl)ammonium glucuronide] (85%) and 3-di[¹⁴C]methylaminophenyl glucuronide (10–15%). Only minor amounts of the unchanged drug were detected in bile. 3. In the homozygous jaundiced Gunn rat large amounts of radioactivity (26% of the dose in 4h) were eliminated in bile as [¹⁴C]trimophonium glucuronide alone. The quantitative excretion of this metabolite in Gunn rat bile was about ten times that in normal animals. 4. It is proposed that the biochemical lesion in the homozygous Gunn rat may indirectly affect the biliary transport of exogenous glucuronides across the canalicular membrane.     

Biliary excretion of foreign compounds. Biphenyl, stilboestrol and phenolphthalein in the rat: molecular weight, polarity and metabolism as factors in biliary excretion

1. The extent of biliary excretion of biphenyl, tetralin, stilboestrol and phenolphthalein was studied in the rat. 2. Biphenyl and its 4-hydroxy and 4,4′-dihydroxy derivatives are extensively excreted in the bile as glucuronides in amounts increasing in order of molecular weight. 3. Stilboestrol and its glucuronide are excreted almost quantitatively in the bile mainly as the monoglucuronide, as are also phenolphthalein and its glucuronide. 4. Tetralin is excreted to the extent of about 13% of the dose, mainly as ac-tetralyl glucuronides. 5. The results and those of Abou-El-Makarem, Millburn, Smith & Williams (1967) are discussed and it is concluded that the extent of biliary excretion of foreign compounds in rats depends on their molecular weight and their possessing a strongly polar anionic group. There appears to be a minimum value of this molecular weight below which little biliary excretion (i.e. not more than 5–10% of the dose) occurs. There is some latitude in the choice of this molecular weight, which is about 325±50. The necessary molecular weight and polar group can be acquired by metabolism. Above this minimum value biliary excretion increases with molecular weight. It is suggested that the mechanism of the biliary excretion of foreign compounds may be similar to that of conjugated bile acids, which are highly polar and whose molecular weights exceed 400.     

Biliary excretion of foreign compounds. Benzene and its derivatives in the rat

1. The extent of the excretion in the bile of the rat of benzene and 21 of its simple derivatives was studied. 2. Some 16 compounds of molecular weight less than 200, and including neutral molecules (benzene and toluene), aromatic acids, aromatic amines and phenols, were injected in solution intraperitoneally into biliary-cannulated rats. Metabolites in the bile were identified and estimated. The extent of biliary excretion of these compounds was low, i.e. 0–10% of the dose in 24hr., and most appeared in the bile mainly as conjugates. 3. The biliary excretion of six conjugates of molecular weight less than 300, including three glycine conjugates, one sulphate conjugate, one glucuronic acid conjugate and two acetyl derivatives, was low (less than 3% of the dose). 4. It is concluded that simple benzene derivatives of molecular weight less than about 300 are poorly excreted in rat bile.     

Effects of ether and pentobarbital anesthesia on thyroid function in the rat.

Studies were performed to examine the effect of two anesthetic agents, ether and pentobarbital, on the hypothalamic-pituitary-thyroid function in vivo. In non-anesthetized animals, plasma thyrotropin (TSH) increased rapidly from basal values of 0.1, a peak of 0.49 microng/ml, 25 min after exposure to the cold. Anesthesia with ether during exposure to the cold completely prevented the rise in TSH. During pentobarbital anesthesia, the rise in TSH after exposure to cold was reduced by more than 90%. Even a three minute period of ether anesthesia prior to cold exposure reduced the peak response to cold as well as delayed this response when compared to the untreated group. During two hours of anesthesia with ether, the TSH concentration declined in animals which were fed a low iodine diet at essentially the same rate as in animals on the same diet given an injection of 3 microng of triiodothyronine. Pentobarbital did not suppress TSH at room temperature. The release of thyrotropin after injection of synthetic thyrotropin-releasing hormone (TRH) was greater in animals anesthetized with pentobarbital than in controls and was slightly reduced in ether-anesthetized animals. This difference was observed when thyrotropin was given intraperitoneally or intravenously and the slope of the dose-response curves to TRH showed a flattening of the curve of rats treated with ether and a steeper slope of response in animals anesthetized with pentobarbital. We conclude that pentobarbital inhibited TSH response to cold but did not reduce the resting levels. Ether inhibited the rise of TSH in the cold and lowered the basal levels of TSH in animlas at room temperature. Pentobarbital increased the response to TRH and ether may have reduced the response to TRH.     

Studies on flavonoid metabolism. Biliary and urinary excretion of metabolites of (+)-[U-14C]catechin

1. The biliary and urinary excretion of (+)-[U-(14)C]catechin was studied in normal male rats after a single injection of the flavonoid. 2. In rats large amounts of radioactivity (33.6-44.3% of the dose in 24h) were excreted in the bile as two glucuronide conjugates [one of which was a (+)-catechin conjugate] and three other unconjugated metabolites. 3. Excretion of radioactivity in the urine when the bile duct was not cannulated amounted to 44.5% of the dose. 4. In both the urine and bile the new metabolites showed maximum excretion in the (1/2)-1(1/2)h after intravenous injection of [(14)C]catechin. 5. The metabolites m-hydroxyphenylpropionic acid, p-hydroxyphenylpropionic acid, delta-(3-hydroxyphenyl)-gamma-valerolactone and delta-(3,4-dihydroxyphenyl)-gamma-valerolactione originate from the action of the intestinal micro-organisms on the biliary-excreted metabolites of (+)-catechin. These phenolic acid and lactone metabolites are then reabsorped and excreted in the urine. 6. It is proposed that, depending on the route of administration of (+)-catechin, there exists an alternative pathway, involving biliary excretion, for the metabolism of (+)-catechin.     

Biliary excretion of [C]succinylsulphathiazole in the rat and rabbit

1. After intravenous injection about 30% of the dose (20mg./kg.) of succinylsulphathiazole is excreted unchanged in the bile in 3hr. by the rat, whereas only about 1% is excreted by the rabbit. When the renal pedicles are ligated the biliary excretion of succinylsulphathiazole in the rat increases to about 80% of the dose, but in the rabbit under these conditions the biliary excretion is only 2% of the dose. 2. In the rat, the sulphonamide readily enters the liver and biliary excretion occurs against a concentration gradient from liver to bile; further, the excretory process can be saturated, and can be depressed by the simultaneous administration of phenolphthalein glucuronide or bile salts. 3. In the rabbit, these conditions have not been found; succinylsulphathiazole does not readily enter the liver from the plasma, there is no transfer of the drug from the liver cells to the bile against a concentration gradient, and no saturation or depression of the biliary excretion of succinylsulphathiazole is found. 4. It is suggested that two factors responsible, at least partly, for the low biliary excretion of succinylsulphathiazole in the rabbit are the poor entry of the sulphonamide into the liver in this species and a deficiency of the concentrative mechanism for its excretion in the bile.     

In vivo relevance of Mrp2-mediated biliary excretion of the Amanita mushroom toxin demethylphalloin

To determine which efflux carriers are involved in hepatic phalloidin elimination, hepatobiliary [(3)H]-demethylphalloin (DMP) excretion was studied in normal Wistar rats and in Mrp2 deficient TR(-) Wistar rats as well as in normal wild-type FVB mice, Mdr1a,b(-/-) knockout mice, and Bcrp1(-/-) knockout mice by in situ bile duct/gallbladder cannulation. A subtoxic dose of 0.03 mg DMP/kg b.w. was used, which did not induce cholestasis in any tested animal. Excretion of DMP into bile was not altered in Mdr1a,b(-/-) mice or in Bcrp1(-/-) mice compared with wild-type FVB mice. Whereas 17.6% of the applied dose was excreted into bile of normal Wistar rats, hepatobiliary excretion decreased to 7.9% in TR(-) rats within 2 h after intravenous application. This decrease was not due to reduced cellular DMP uptake, as shown by normal expression of Oatp1b2 in livers of TR(-) rats and functional DMP uptake into isolated TR(-) rat hepatocytes. Tissue concentrations of phalloidin were also not altered in any of the transgenic mice. Interestingly, the decrease of biliary DMP excretion in the TR(-) rats was not followed by any increase of phalloidin accumulation in the liver but yielded a compensatory excretion of the toxin into urine, indicating that hepatocytes of TR(-) rats expelled phalloidin back into blood circulation.     

Gastrointestinal absorption of estrone sulfate in germfree and conventional rats

Steroids are extensively excreted in the bile of rats. There was no significant difference in biliary excretion of steroid following administration of [3H]-estrone sulfate into the proximal small intestine (PSI) of conventional (CVL; 17.8 +/- 62%; mean +/- SD) or germfree (GF; 28.2 +/- 5.3) rats. A similar finding resulted from administration into the distal small intestine (DSI)-CVL, 22.3 +/- 11.8%; GF, 11.4 +/- 3.7%. However, when the drug was given into the caecum, excretion in the bile of CVL rats after 5 h was 59.1% whereas in GF rats it was only 1.7%. When estrone was injected into the PSI and DSI of CVL and GF rats, absorption (as judged by excretion in bile) was more rapid than that seen with estrone sulfate. Five hours after injection into the PSI, biliary excretion was, in CVL 88.2% and in GF 81.7% and after injection into the DSI excretion was, in CVL 84.7% and in GF 83.6%. Absorption of estrone from the caeca of GF rats was apparently reduced (49.0% and 25.3% excreted in the bile of CVL and GF rats respectively). There was no significant difference in bile flow rate between CVL and GF rats. These results give unequivocal evidence of intact absorption of estrone sulfate from the small intestine of the rat. The rate of absorption is however very much reduced compared to the non-sulphated steroid. Estrone sulfate is not absorbed intact in the caecum but is hydrolysed by the gut microflora prior to absorption.