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

Toxicokinetics and Biliary Excretion of N-Nitrosodiethylamine in Rat Supplemented with Low and High Dietary Proteins

Although biliary excretion is one of the biological elimination processes for foreign compounds, intake of high-protein diets was hypothesized to enhance their detoxification rates. Hence, this study investigates the effect of differential dietary protein intake on toxicokinetics and biliary excretion in rats following exposure to N-nitrosodiethylamine (NDEA) and aflatoxin B1 (AFB1). The animals were divided into five groups. Groups I and II were exposed to low and high dietary proteins following a single intraperitoneal dose of 43 µg NDEA/kg body weight, respectively. Groups III and IV were equally treated after a combined single intraperitoneal dose of 43 µg NDEA plus 0.022µg AFB_I/kg body weight, respectively. Group V was fed with low-protein diets following a single intraperitoneal dose of 0.022µg AFB1/kg body weight. The experiment lasted 35 days. The bile excreted higher amounts of unchanged NDEA than nitrite. The groups placed on high-protein diets (HPD = 64%) eliminated higher amounts of the unchanged NDEA and nitrite than the lower-protein diet (LPD = 8%) groups. Furthermore, the animals fed with high dietary protein (HPD = 64%) depicted short half-life with corresponding increase in elimination rate constant. The presence of AFB₁ heightened the excretion of bound NDEA with AFB₁ than NDEA only. Generally, this study advocates that N-nitrosodiethylamine and the corresponding metabolites follow hepatobiliary system potentiated by high intake of dietary proteins.

Estimation of biliary excretion of foreign compounds using properties of molecular structure

Biliary excretion is one of the main elimination pathways for drugs and/or their metabolites. Therefore, an insight into the structural profile of cholephilic compounds through accurate modelling of the biliary excretion is important for the estimation of clinical pharmacokinetics in early stages of drug discovery. The aim of this study was to develop quantitative structure-activity relationships as computational tools for the estimation of biliary excretion and identification of the molecular properties controlling this process. The study used percentage of dose excreted intact into bile measured in vivo in rat for a diverse dataset of 217 compounds. Statistical techniques were multiple linear regression analysis, regression trees, random forest and boosted trees. A simple regression tree model generated using the CART algorithm was the most accurate in the estimation of the percentage of bile excretion of compounds, and this outperformed the more sophisticated boosted trees and random forest techniques. Analysis of the outliers indicated that the models perform best when lipophilicity is not too extreme (log P < 5.35) and for compounds with molecular weight above 280 Da. Molecular descriptors selected by all these models including the top ten incorporated in boosted trees and random forest indicated a higher biliary excretion for relatively hydrophilic compounds especially if they are anionic or cationic, and have a large molecular size. A statistically validated molecular weight threshold for potentially significant biliary excretion was above 348 Da.

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 in foreign compounds. Sulphonamide drugs in the rat

1. The extent of biliary excretion in the rat of 15 sulphonamide compounds was studied. 2. Most of the sulphonamides studied, with molecular weights from 172 (sulphanilamide) to 352 (N(4)-acetylsulphadimethoxine) are poorly excreted in the bile (0-4% of the dose), except sulphapyridine, sulphamethoxypyridazine and sulphadimethoxine. The last three are partly metabolized to glucuronides, whose molecular weights and polarities are such as to allow them to be excreted in the bile in appreciable amounts. 3. Succinylsulphathiazole and phthalylsulphathiazole are polar and have molecular weights (355 and 403) of an appropriate order, and are excreted unchanged in the bile in appreciable amounts. 4. Sulphadimethoxine N(1)-glucuronide (mol.wt. 487) is extensively excreted in the bile unchanged. 5. The results are examined in the light of the hypotheses put forward in the preceding paper (Millburn, Smith & Williams, 1967).

Biliary excretion in foreign compounds. Species difference in biliary excretion

1. The biliary excretion of injected [(14)C]aniline, [(14)C]benzoic acid, 4-amino-hippuric acid and 4-acetamidohippuric acid in six or eight species of animal (rat, dog, hen, cat, rabbit, guinea pig, rhesus monkey and sheep) was studied. 2. These compounds, with molecular weights in the range 93-236, are poorly excreted in the bile in all the species examined and, in effect, there is little significant species difference in the extent of their biliary excretion. 3. Compounds of higher molecular weight (355-495) were also studied, namely succinylsulphathiazole, [(14)C]stilboestrol glucuronide, sulphadimethoxine N(1)-glucuronide and phenolphthalein glucuronide. 4. With these compounds a clear species difference in the extent of biliary excretion was found, the rat, dog and hen being good excretors, the rabbit, guinea pig and monkey poor excretors, and the cat and sheep taking an intermediary position. 5. There was a general trend for biliary excretion to be higher in all species when the compounds were of higher molecular weight. 6. These results are discussed in their relation to species differences in drug metabolism.

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.

The fate of ethyltin and diethyltin derivatives in the rat

1. Ethyltin trichloride does not appear to be metabolized by the rat. When given orally excretion occurs almost entirely in the faeces, and when given intraperitoneally it occurs exclusively in the urine. Biliary excretion is almost negligible. 2. Di[1-(14)C]ethyltin dichloride has been synthesized. When given intraperitoneally it is excreted in the urine and faeces in the ratio about 1:2. Both the urine and faeces contain ethyltin(3+) and diethyltin(2+). Diethyltin is also excreted extensively in the bile. Di[(14)C]ethyltin is not converted into (14)CO(2) in the rat. 3. About 50% of the injected diethyltin dichloride is de-ethylated to ethyltin(3+). Since ethyltin and diethyltin are found in the urine and faeces after intraperitoneal injection of diethyltin dichloride and since only diethyltin is excreted in the bile, then the de-ethylation of diethyltin occurs in the body tissues and the gut. 4. The conversion of diethyltin into ethyltin has been demonstrated in a preparation of rat caecal contents, but not in liver homogenates. 5. The dealkylation of diethyltin(2+) to ethyltin(3+) in the rat is discussed and it is suggested that the ethyl group is lost as ethane.

In silico prediction of biliary excretion of drugs in rats based on physicochemical properties

Evaluating biliary excretion, a major elimination pathway for many compounds, is important in drug discovery. The bile duct-cannulated (BDC) rat model is commonly used to determine the percentage of dose excreted as intact parent into bile. However, a study using BDC rats is time-consuming and cost-ineffective. The present report describes a computational model that has been established to predict biliary excretion of intact parent in rats as a percentage of dose. The model was based on biliary excretion data of 50 Bristol-Myers Squibb Co. compounds with diverse chemical structures. The compounds were given intravenously at <10 mg/kg to BDC rats, and bile was collected for at least 8 h after dosing. Recoveries of intact parents in bile were determined by liquid chromatography with tandem mass spectrometry. Biliary excretion was found to have a fairly good correlation with polar surface area (r = 0.76) and with free energy of aqueous solvation (DeltaG(solv aq)) (r = -0.67). In addition, biliary excretion was also highly corrected with the presence of a carboxylic acid moiety in the test compounds (r = 0.87). An equation to calculate biliary excretion in rats was then established based on physiochemical properties via a multiple linear regression. This model successfully predicted rat biliary excretion for 50 BMS compounds (r = 0.94) and for 25 previously reported compounds (r = 0.86) whose structures are markedly different from those of the 50 BMS compounds. Additional calculations were conducted to verify the reliability of this computation model.

Prediction of biliary excretion in rats and humans using molecular weight and quantitative structure-pharmacokinetic relationships

The aims were (1) to evaluate the molecular weight (MW) dependence of biliary excretion and (2) to develop quantitative structure-pharmacokinetic relationships (QSPKR) to predict biliary clearance (CL(b)) and percentage of administered dose excreted in bile as parent drug (PD(b)) in rats and humans. CL(b) and PD(b) data were collected from the literature for rats and humans. Receiver operating characteristic curve analysis was utilized to determine whether a MW threshold exists for PD(b). Stepwise multiple linear regression (MLR) was used to derive QSPKR models. The predictive performance of the models was evaluated by internal validation using the leave-one-out method and external test groups. A MW threshold of 400 Da was determined for PD(b) for anions in rats, while 475 Da was the cutoff for anions in humans. MW thresholds were not present for cations or cations/neutral compounds in either rats or humans. The QSPKR model for human CL(b) showed a significant correlation (R (2) = 0.819) with good prediction performance (Q (2) = 0.722). The model was further assessed using a test group, yielding a geometric mean fold-error of 2.68. QSPKR models with significant correlation and good predictability were also developed for CL(b) in rats and PD(b) data for anions or cation/neutral compounds in rats and humans. Both CL(b) and PD(b) data were further evaluated for subsets of MRP2 or P-glycoprotein substrates, and significant relationships were derived. QSPKR models were successfully developed for biliary excretion of non-congeneric compounds in rats and humans, providing a quantitative prediction of biliary clearance of compounds.

Effects of feeding and short-term fasting on water and electrolyte turnover in female mink (Mustela vison)

Daily (24 h) rates of water and electrolyte turnover were measured in a conventional balance study in ten adult female pastel mink (Mustela vison) given free access to a standard mink feed for a 1-week conditioning period, followed by a 4 d experimental period and a 2 d fasting period. Drinking water was available throughout. In addition, the completeness of urine collection and the fraction of urine collected with the faeces were determined using a new experimental technique based on 24 h recoveries of specific urinary markers such as tritiated p-aminohippuric acid ([3H]PAH) or 14C-labelled inulin ([14C]IN) continuously delivered by small Alzet osmotic pumps implanted intraperitoneally. During feeding the mean individual percentage recovery in urine of [3H]PAH released from the osmotic pumps ranged from 68 to 88% (median 78%). The mean percentage of urinary [3H]PAH recovered from faecal collections was 6% (range 3-12%). In response to fasting the mean individual percentage recovery of [3H]PAH in urine ranged from 62 to 78% (median 68%). For urinary [14C]IN the mean percentage recoveries in fed and fasted animals were 79 and 63% respectively. Furthermore, during fasting, withdrawal of the supplies of dietary water caused a slight but insignificant (P = 0.17) increase in the daily intake of drinking water and, hence, the animals maintained their normal water balance by a dramatic reduction in urine excretion (P < 0.001). At the same time urinary solute excretion declined significantly (P < 0.001), due in part to the cessation of dietary electrolyte intake and in part to reduced formation of urea, whereas urinary osmolality decreased only moderately. The mean 24 h balances of Na, K, Ca, Mg, Cl and P were close to zero and only minor differences between the feeding and fasting periods were observed. When corrected for the measured inaccuracies in urine collection the balance data obtained in the present study represent useful reference standards for normally fed and fasted non-growing mink and, to some extent, useful guidelines for future studies in experimental animals.

Intestinal metabolism of mephentermine and its biliary metabolites in male Wistar rats

1. Intestinal metabolites produced in the incubation (0-24 h) of mephentermine (MP), phentermine (Ph), N-hydroxymephentermine (N-hydroxy-MP), N-hydroxyphentermine (N-hydroxy-Ph), p-hydroxymephentermine (p-hydroxy-MP) and p-hydroxyphentermine (p-hydroxy-Ph) with male Wistar rat intestinal contents under N2 were examined by g.l.c. and g.l.c.-electron impact (EI) mass spectrometry. Metabolites produced in the anaerobic incubation of bile from rats given MP, with the intestinal contents were also examined. In addition, urinary and biliary metabolites of p-hydroxy-MP and p-hydroxy-Ph dosed orally to rat were examined. 2. Metabolites in the anaerobic incubation of N-hydroxy-MP and N-hydroxy-Ph were MP and Ph, and Ph, respectively. No metabolites were detected in the incubation of MP, Ph, p-hydroxy-MP and p-hydroxy-Ph. 3. p-Hydroxy-MP and p-hydroxy-Ph (major), and MP and Ph (minor) were detected when bile from rats given MP was incubated with intestinal contents. 4. Unchanged p-hydroxy-MP, and conjugates of p-hydroxy-MP and p-hydroxy-Ph, were detected in the 24-h urine of rats dosed with p-hydroxy-MP, which accounted for about 3, 72 and 1% dose, respectively. Unchanged p-hydroxy-Ph and conjugated p-hydroxy-Ph were detected in the 24-h urine of rats dosed with p-hydroxy-Ph, which accounted for about 4 and 68% dose, respectively. 5. Conjugated p-hydroxy-MP and conjugated p-hydroxy-Ph, which accounted for about 3% doses, were detected in the 24-h bile of rats dosed with p-hydroxy-MP and p-hydroxy-Ph.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephrotoxicity of 4-aminophenol glutathione conjugate

4-Aminophenol (p-aminophenol, PAP) causes selective necrosis to the pars recta of the proximal tubule in Fischer 344 rats. The basis for this selective toxicity is not known, but PAP can undergo oxidation in a variety of systems to form the 4-aminophenoxy free radical. Oxidation or disproportionation of this radical will form 1,4-benzoquinoneimine which can covalently bind to tissue macromolecules. Recent studies have shown that certain benzoquinol-glutathione conjugates can cause renal necrosis in rats. We have synthesized a putative glutathione conjugate of PAP. The effect on the kidney of this conjugate and the sulphate and N-acetyl conjugates, known metabolites of PAP, have been examined in Fischer 344 rats. 4-Amino-3-S-glutathionylphenol produced a dose-dependent (92-920 mumol kg-1) necrosis of the proximal tubular epithelium and altered renal excretory function. The lesion at the low dose was restricted to the pars recta of the proximal tubule in the medullary rays, while at the higher doses it affected the pars recta region of all nephrons. In contrast, PAP-O-sulphate and N-acetyl-4-aminophenol (paracetamol) caused no histological or functional alteration to the kidney at 920 mumol kg-1. The renal necrosis produced by 4-amino-3-S-glutathionylphenol was very similar to that produced by PAP (367-920 mumol kg-1), both functionally and histologically, except that smaller doses of the glutathione conjugate were required. These studies indicate that glutathione conjugation of PAP generates a metabolite that is more toxic to the kidney than the parent compound. A possible mechanism of toxicity (analogous to that reported for glutathione conjugates of certain quinones) involving oxidation to form a 1,4-benzoquinoneimine thioether that could redox cycle is discussed.

Pharmacokinetics of biliary excretion of N-nitrosodiphenylamine (NDPA) in animals of different species

Pharmacokinetic investigations into the biliary excretion of N-nitrosodiphenylamine given as an i.p. dose of 50 mg/kg were conducted and results compared in three animal species; rat, guinea pig and rabbit following bile duct cannulation and collection of bile in vitro. The guinea pig excreted NDPA into bile fastest while the rabbit, which excreted it slowest, eliminated it fastest. Both appearance and disappearance of the nitrosamine were comparatively slow in the rat. NDPA elimination half-life values in the animal species were 510, 240 and 95 min respectively, while cumulative excretions amounted to 12, 3 and 0.3 percent. The toxicological implications of these species differences are highlighted.

Metabolism of 2,6-dinitrotoluene in male Wistar rat

1. Unchanged 2,6-dinitrotoluene (2,6-DNT), 2-amino-6-nitrotoluene, 2,6-dinitrobenzyl alcohol, 2-amino-6-nitrobenzyl alcohol, conjugated 2,6-dinitrobenzyl alcohol and conjugated 2-amino-6-nitrobenzyl alcohol were detected in urine of male Wistar rats dosed with 2,6-DNT. The major metabolite was conjugated 2,6-dinitrobenzyl alcohol, which accounted for about 1.5% of the dose. 2. Unchanged 2,6-DNT, 2-amino-6-nitrotoluene, 2,6-dinitrobenzyl alcohol, and conjugates of 2,6-dinitrobenzyl alcohol, 2-amino-6-nitrotoluene and 2,6-dinitrobenzaldehyde were detected in the bile of rats dosed with 2,6-DNT. The major metabolite was conjugated 2,6-dinitrobenzyl alcohol, which accounted for 30% of the dose. Conjugates of 2,6-dinitrobenzyl alcohol (major) and 2,6-dinitrobenzaldehyde (minor) were common biliary metabolites in rats dosed with 2,6-dinitrobenzyl alcohol or 2,6-dinitrobenzaldehyde. 3. 2,6-Dinitrobenzyl alcohol and 2,6-dinitrobenzaldehyde were detected by incubating bile from rats given 2,6-DNT with rat intestinal contents under N2. 4. Incubation of 2,6-DNT with hepatic microsomal preparations gave 2,6-dinitrobenzyl alcohol. Incubation of 2,6-dinitrobenzyl alcohol with microsomal plus cytosol preparations gave 2,6-dinitrobenzaldehyde. Incubation of 2,6-dinitrobenzaldehyde with cytosol preparations gave 2,6-dinitrobenzyl alcohol and 2,6-dinitrobenzoic acid. The activities of 2,6-DNT oxidation to 2,6-dinitrobenzyl alcohol, 2,6-dinitrobenzyl alcohol oxidation to 2,6-dinitrobenzaldehyde, 2,6-dinitrobenzaldehyde oxidation to 2,6-dinitrobenzoic acid, and 2,6-dinitrobenzaldehyde reduction to 2,6-dinitrobenzyl alcohol were 22.0, 4.7, 1.3, and 23.3 nmol formed/g liver per min, respectively. 5. These results indicate that 2,6-dinitrobenzaldehyde, an intermediary metabolite of 2,6-DNT in male Wistar rats, is produced either by oxidation of 2,6-DNT in the liver, or by oxidation of 2,6-dinitrobenzyl alcohol formed by hydrolysis of 2,6-dinitrobenzyl alcohol conjugates excreted in the bile, and further indicate that enterohepatic circulation of 2,6-dinitrobenzyl alcohol and 2,6-dinitrobenzaldehyde occurs. This result, together with previous findings, shows that there are metabolic differences, including the biliary excretion of a diol glucuronide of 2,6-dinitrobenzaldehyde and the lack of urinary excretion of 2,6-dinitrobenzoic acid, between 2,4-DNT and 2,6-DNT in male Wistar rat.

Urinary and biliary metabolites of mephentermine in male Wistar rats

1. Excretion of urinary and biliary radioactivity, and metabolites of [3H]mephentermine (MP), after i.p. or subcutaneous administration of [3H]MP to male Wistar rats, were determined by preparative t.l.c.-liquid scintillation counting. 2. About 45% of the radioactivity administered i.p. was excreted in the 24 h urine. The major urinary metabolite was conjugated p-hydroxymephentermine (p-hydroxy-MP), which accounted for about 18% of the administered radioactivity in the 24 h urine. 3. About 4.2% of the radioactivity administered subcutaneously was excreted in bile during 24 h. The major biliary metabolite was conjugated p-hydroxy-MP, which accounted for about 39% of the radioactivity excreted in the bile in 24 h. 4. Urinary and biliary minor metabolites detected were phentermine (Ph), p-hydroxyphentermine (p-hydroxy-Ph), N-hydroxyphentermine (N-hydroxy-Ph), N-hydroxymephentermine (N-hydroxy-MP) and their conjugates, and conjugated MP. 5. The conjugates were considered to be glucuronides from the inhibitory effect of saccharic acid 1,4-lactone on their hydrolysis with beta-glucuronidase. 6. Biliary excretion rates of conjugated p-hydroxy-Ph and p-hydroxy-MP reached maxima at 3 to 4 h, and non-conjugated metabolites were maximal at 1 to 2 h, after administration. 50% of the biliary metabolites was excreted within 5 h.

Enterohepatic circulation of 2,4-dinitrobenzaldehyde, a mutagenic metabolite of 2,4-dinitrotoluene, in male Wistar rat

1. The major biliary metabolite of 2,4-dinitrotoluene (2,4-DNT) in male Wistar rat was 2,4-dinitrobenzyl alcohol glucuronide and the minor metabolites were 2,4-dinitrobenzyl alcohol, 2,4-dinitrobenzaldehyde, 2-acetylamino-4-nitrotoluene, 4-amino-2-nitro(2-amino-4-nitro)benzyl alcohol sulphate, 2,4-dinitrobenzoic acid, 2,4-diacetylaminobenzoic acid and 2-amino-4-nitrobenzoic acid. 2. 2,4-Dinitrobenzyl alcohol, 2,4-dinitrobenzaldehyde, 2,4-dinitrobenzyl alcohol glucuronide and 4-amino-2-nitro(2-amino-4-nitro)benzyl sulphate were excreted in the bile of male Wistar rat dosed with 2,4-dinitrobenzyl alcohol. 3. 2,4-Dinitrobenzaldehyde, 2,4-dinitrobenzyl alcohol, 2,4-dinitrobenzyl glucuronide, 4-amino-2-nitro(2-amino-4-nitro)benzyl alcohol sulphate and 2,4-diacetylaminobenzoic acid were excreted in the bile of male Wistar rat dosed with 2,4-dinitrobenzaldehyde. 4. These results indicate that the common biliary metabolites of 2,4-DNT, 2,4-dinitrobenzyl alcohol and 2,4-dinitrobenzaldehyde are 2,4-dinitrobenzyl alcohol and its glucuronide, and 2,4-dinitrobenzaldehyde, and suggest the enterohepatic circulation of 2,4-dinitrobenzaldehyde in the metabolism of 2,4-DNT.

Health effects of the alkylbenzenes. I. Toluene

The alkylbenzenes, toluene being the most common example, represent a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points and are used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are also integral components of gasoline, distillate fuels and other petroleum products. These substituted aromatics are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, xylene, ethylbenzene, styrene and cumene are toxicologically important since they are produced, used or disposed of in the largest quantities and therefore might pose significant and potential health risks to man and the environment. In general, the toxicity of alkylbenzenes has been found to be relatively low. Also, for the most part, human and environmental risks are low; however, there may be a few operations where the potential for high exposure could exist. These exposures are minimized by workplace controls or personal protective equipment. Furthermore, health risks for humans are minimized by guidelines for maximum allowable exposure concentrations which have been established for the workplace. This present paper reviews the toxicology and disposition of toluene in animals and humans.

The effect of molecular size on the nasal absorption of water-soluble compounds in the albino rat

The nasal absorption of a range of water-soluble compounds with different molecular weights, 4-oxo-4H-1-benzopyran-2-carboxylic acid (mol. wt 190), p-aminohippuric acid (mol. wt 194), inulin (mol. wt 5200) and dextran (mol. wt 70,000), has been investigated in the male Wistar rat. Compounds were instilled into the nasal cavities of anaesthetized animals, and for comparison, similar doses were administered intravenously. Serial samples of bile and urine were collected for up to 6 h. Nasal absorption, estimated by comparison of the extent of excretion in bile and urine following intranasal and intravenous administration, was 100% for 4-oxo-4H-1-benzopyran-2-carboxylic acid (1 mg kg-1), 75% for p-aminohippuric acid (1 mg kg-1), 15% for inulin (0.1 mg kg-1) and 2.8% for dextran (0.25 mg kg-1). The log molecular weight gave a good linear correlation with the log per cent intranasally absorbed (correlation coefficient of -0.996). From the molecular weight relationship, these data infer aqueous channel mechanisms for the nasal absorption of water-soluble compounds.

Chemical of current interest--benzene

Benzene is one of the world's major commodity chemicals. It is derived from petroleum and coal and is used both as a solvent and as a starting material in chemical syntheses. The numerous industrial uses of benzene over the last century need not be recounted here, but the most recent addition to the list of uses of benzene is as a component in a mixture of aromatic compounds added to gasoline for the purpose of replacing lead compounds as anti-knock ingredients. The best known and longest recognized toxic effect of benzene is the depression of bone marrow function seen in occupationally exposed individuals. These people have been found to display anemia, leucopenia, and/or thrombocytopenia. When pancytopenia, i.e., the simultaneous depression of all three cell types, occurs and is accompanied by bone marrow necrosis, the syndrome is called aplastic anemia. In addition to observing this decrease in humans and relating it to benzene exposure, it has been possible to establish animal models which mimic the human disease. The result has been considerable scientific investigation into the mechanism of benzene toxicity. Although the association between benzene exposure and aplastic anemia has been recognized and accepted throughout most of this century, it is only recently that leukemia, particularly of the acute myelogenous type, has been related to benzene. The acceptance of benzene as an etiological agent in aplastic anemia in large measure derives from our ability to reproduce the disease in most animals treated with sufficiently high doses of benzene over the necessary time period. Unfortunately, despite extensive efforts in several laboratories, it has not been possible to establish a reproducible, reliable model for the study of benzene-induced leukemia. The recent demonstration that several animals exposed to benzene either by inhalation or in the drinking water during studies by Drs. B. Goldstein and C. Maltoni suggests that such a model may be forthcoming. Nevertheless, at this time it is not clear whether bone marrow damage of the type that leads to aplastic anemia is required for the development of leukemia. Most studies of benzene toxicity have involved dosing animals with benzene either by inhalation or by injection, using high doses to ensure a toxic response. Very few studies have concentrated on the oral route of administration and none have concentrated on administering benzene by mouth at the low doses occasionally detected in drinking water.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of dose on the absorption and excretion of [14C]benzene administered orally or by inhalation in rats and mice

The effect of dose on the absorption and excretion of [14C]benzene was studied using 13-week old male F344/N rats, Sprague-Dawley rats, and B6C3F1 mice. Gastrointestinal absorption of benzene administered by gavage was greater than 97% in these species for doses between 0.5 and 150 mg benzene/kg body wt. At oral doses below 15 mg/kg, greater than 90% of the 14C excreted was in the urine as nonethylacetate extractable material. Above 15 mg/kg, in both rats and mice, an increasing percentage of the administered benzene was exhaled unmetabolized, suggesting saturation of metabolic pathways. Above 50 mg/kg, total metabolites (as determined by 14C in the urine, feces, and carcass after 2 days) were not linearly related to administered dose. Total metabolites per unit body weight was equal in F344/N rats and B6C3F1 mice at gavage doses up to 50 mg/kg; however, total metabolites in mice did not increase at higher doses. For inhalation exposures, the percentage of inhaled benzene that was absorbed and retained during a 6-hr exposure decreased from 33 +/- 6% (mean +/- standard deviation) to 15 +/- 9% in rats, and from 50 +/- 15 to 10 +/- 2% in mice as the exposure concentration was increased from approximately 26 to 2600 micrograms/liter (10 to 1000 ppm at 615 Torr, 23 degrees C). Total metabolite formation was exponentially related to the benzene exposure concentration with one-half the maximal amount of metabolite formation occurring at 220 micrograms/liter (84 ppm) for B6C3F1 mice and 650 micrograms/liter (250 ppm) for F344/N rats. Total metabolites were higher in mice than in rats at any of the vapor concentrations used due mainly to the higher amount inhaled by mice. Saturation of overall metabolism in mice but not in rats at high doses by both routes of administration indicates species differences in metabolism of benzene.

Relation between renal and hepatic excretion of drugs: I. Phenol red in comparison with p-aminohippurate and indocyanine green

Phenol red is a suitable compound for the simultaneous assay of renal and hepatic excretion in the rat. Its elimination has been compared with those of p-aminohippurate (PAH) and indocyanine green (ICG) which are eliminated nearly exclusively via kidneys or liver, respectively. The interruption of one elimination route one day before the experiment, that means bile duct ligation (DL) in the case of ICG or bilateral nephrectomy (NX) in the case of PAH are followed by a slight increase in the elimination via the alternative pathway, but no effective compensation occurs. On the other hand, the renal excretion of phenol red is significantly increased after DL only following administration of high doses. This intensification is caused by an increase in the unbound amount of phenol red depending on the plasma concentration and reflects an enhanced glomerular filtration fraction. The biliary excretion increases significantly after NX, but only after infusion of low doses. The maximal biliary secretion capacity cannot be exceeded following NX, either. The competitive inhibition of phenol red excretion by probenecid supports the findings of NX or DL experiments. An influence of the three test substances on arterial blood pressure has been excluded. The most important factors influencing the switch over from one to the other elimination route seem to be at least in the case of phenol red the amount of unbound substance, the influence of the administered dose on the glomerular filtration, and disturbances in the volume of distribution, e.g. the possible reduction of hepatic uptake after DL.

Influence of the gut microflora on the metabolism of 4-nitrobenzoic acid in the marmoset

1. 4-Nitrobenzoic acid was metabolized by the marmoset to amino derivatives to the extent of 18.8% (p.o.) and 11.4% (i.p.) of the dose. 2 Reduction of 4-nitrobenzoic acid was significantly decreased by antibiotic pretreatment; the mean decrease in reduction was 81% for animals doses orally and 73% for intraperitoneally dosed marmosets. 3. 4-Nitrohippuric acid was the major metabolite of 4-nitrobenzoic acid, accounting for 30.6% and 49.6% of p.o. and i.p. doses respectively. 4. Antibiotic pretreatment affected the marmosets' normal capacity to reduce 4-nitrobenzoic acid for many weeks after the initial administration. 5. Maximum radioactivity in the blood, after an oral dose, was reached in 30-40 min; the average half-life for the elimination of 4-nitro[carboxy-14C]benzoic acid and its metabolites was 30.4 +/- 3 min after an intramuscular dose. 6. Radioactivity of 4-nitro[carboxy-14C]benzoic acid representing 3.4% of the dose was excreted in rat bile in 24 h.

Enterohepatic recycling of phenolphthalein, morphine, lysergic acid diethylamide (LSD) and diphenylacetic acid in the rat. Hydrolysis of glucuronic acid conjugates in the gut lumen

1. Biliary elimination in female Wistar albino rats 3 h after i.p. injection of [3H]phenolphthalein, [3H]morphine, 14C-LSD and [14C]diphenylacetic acid was 90%, 45%, 75% and 57% respectively, predominantly as glucuronides. 2. Infusion of 3 h bile from the previous experiments into the duodena of bile-duct-cannulated animals demonstrated enterohepatic circulation, amounting in 24 h to 85%, 41%, 28% and 66% of the infused doses of the conjugates of phenolphthalein, morphine, LSD and diphenylacetic acid respectively. 3. Pretreatment with antibiotics to suppress intestinal microflora decreased this enterohepatic recirculation to 22%, 8.6% and 21% in 24 h for phenolphthalein, morphine and diphenylacetic acid glucuronides respectively. Antibiotic pretreatment did not influence the absorption and re-excretion of infused doses of the free aglycones, thus demonstrating the importance of bacterial beta-glucuronidase hydrolysis of the biliary conjugates. 4. The extent of intestinal absorption of the aglycones after bacterial beta-glucuronidase hydrolysis of the conjugates is related to their lipid-solubility as estimated by octan-1-ol:0.1 M phosphate buffer partition ratios (P-values). 5. The persistence of compounds in the enterohepatic circulation is determined by the faecal and urinary elimination of the circulating compounds. Faecal elimination is governed by the extent of intestinal absorption of the circulating compounds, which is influenced by the efficacy of intestinal hydrolysis of the conjugates and the relative lipophilicity of the aglycones released.

Colorimetric determination of glycine conjugates of bile acids

A simple assay was developed for the determination of glycine-conjugated bile acids. Samples containing the glycine-conjugated bile acids in the range from 15 to 250 nmol were acidified with HCl, and extracted with ethyl acetate containing ethanol (50 ml/l). An aliquot of the organic phase was evaporated to dryness, and the dried residue was treated to develop the color by the addition of acetic anhydride, pyridine and a trace amount of phosphoric acid. the absorbance was measured at 429 or 456 nm after the reaction at 50 degrees C for 2 h. Color development did not occur with unconjugated and taurine-conjugated bile acid. Beer's law was obeyed from 12.5 to 200 nmol in a cuvette. The recovery of the conjugates from the rabbit gall bladder bile and liver homogenate was satisfactory. This method requires no hydrolysis step and is applicable to the determination of glycine-conjugated bile acids in bile, duodenal aspirate and liver homogenate.

Studies of metabolic fate of a new antiallergic agent, azelastine (4-(p-chlorobenzyl)-2-[N-methylperhydroazepinyl-(4)]-1-(2H)-phthalazinone hydrochloride)

The metabolic fate of a new antiallergic agent, azelastine (4-(p-chlorobenzyl)-2-[N-methylperhydroazepinyl-(4)]-1-(2H)-phthalazinone hydrochloride) in rats and guinea pigs was investigated using its 14C-labelled compound. The blood level of radioactivity reached the maximum at 1-1.5 hr after oral administration, indicating the rapid absorption of the drug from gastrointestinal tract. A high concentration of radioactivity was detected in the lung of both species following either oral or intravenous administration. The major pathway of excretion of radioactivity was by way into feces, in both species. The radioactivity excreted in feces was attributable to that which was excreted in bile and exsorbed into gastrointegtinal tract. When the drug was given to pregnant rats, the concentration of radioactivity in the fetus was significantly lower than those in placenta and uterus, indicating the limited placental transfer of the drug. The successive oral administration of the drug in lower doses exerted no effect on the activity of microsomal drug-metabolizing enzymes of rat liver, while in higher doses, had a slight effect.

Metabolic oxidation of the ethynyl group in 4-ethynylbiphenyl

1. 4-Ethynylbiphenyl undergoes extensive metabolism in the rat and the rabbit, involving aromatic hydroxylation and oxidation of the ethynyl group. No metabolites containing the intact ethynyl group were detected. 2. In the rat unchanged 4-ethynylbiphenyl was concentrated initially in the adipose tissue. No other tissues accumulated significant amounts of radioactivity. 3. The major metabolites were the same in both the rat and the rabbit, namely 4'-hydroxybiphenyl-4-ylacetic acid (90-95% of dose) and biphenyl-4-ylacetic acid (2-10% of dose). 4. Excretion was slower in the rat than in the rabbit, probably because of greater biliary and faecal excretion in the rat. Biliary excretion and enterohepatic circulation of biphenyl-4-ylacetic acid and 4'-hydroxybiphenyl-4-ylacetic acid were demonstrated in the rat.

Metabolism of phenformin in the rat and guinea-pig

1. Following administration of [2'-14C]phenformin to rat and guinea pig, the guinea-pig showed a slower rate of excretion of radioactivity than the rat, together with a slower rate of metabolism, which may partly explain the increased pharmacological response of the guinea-pig to the drug. 2. The rat eliminated 26% of an intraduodenal dose of [2'-14C]phenformin (20 mg/kg) in the bile in 6 h compared to 6% in the guinea-pig. 3. The rat excreted large amounts of 4-hydroxyphenformin (free and conjugated with glucuronic acid) and also some unchanged phenformin, but the extent of metabolism varied with dose and route of administration. 4. The guinea-pig excreted no 4-hydroxyphenformin after an oral dose (25 mg/kg) and only a small amount after i.p. administration (12.5 mg/kg). After oral administration, guinea-pig urine contained an unidentified metabolite, and its glucuronide, which may be a product of aliphatic C- or N-hydroxylation and which accounted for 47% of the 24 h urinary radioactivity (17% of the dose). Guinea-pig faeces contained an unidentified metabolite which had similar chromatographic properties to the novel urinary metabolite.

Metabolism of arylacetic acids. 3. The metabolic fate of diphenylacetic acid and its variation with species and dose

1. [carboxy-14C]Diphenylacetic acid has been administered to seven primate species including man, and four other mammals and the qualitative and quantitative aspects of its elimination determined. 2. In most species, 50-100 percent of the administered 14C was excreted in the urine in 48 h; 2-30 percent of the dose was recovered unchanged in the 24 h urine. 3. In all species the only urinary metabolite detected by radiochromatogram scanning was diphenylacetylglucuronide (10-70 percent of dose). Reverse isotope dilution additionally revealed the formation of trace amounts (less than 1 percent of dose) of the glycine conjugate by four species and of the taurine conjugate by the cat. No evidence was found for the formation of a glutamine conjugate. 4. The influence of dose on the pattern of metabolism and excretion of diphenylacetic acid has been studied in the rat. In this species diphenylacetic acid undergoes extensive elimination and enterohepatic circulation.

Metabolism of arylacetic acids. 1. The fate of 1-naphthylacetic acid and its variation with species and dose

1. [Carboxy-14C]-1-Naphthylacetic acid has been administered to man, 6 primate species and 4 other mammalian species and the urinary metabolites examined by radiochromatogram scanning and reverse isotope dilution. Animals all received a dose of 100 mg/kg and man received 5 mg, orally. 2. Most species excreted at least 60% of the 14C in the urine in 48 h. Unchanged acid was a minor (0-17% dose) excretion product in all species except the cynomolgus monkey (35%). 3. In man, in 24 h 95% of 14C was excreted as 1-naphthylacetyl-glucuronide and 5% as 1-naphthylacetyltaurine. 4. 1-Naphthylacetylglucuronide was the major excretion product in all species except the bushbaby (21% dose) and the cat, which did not form this conjugate. 5. 1-Naphthylacetylglutamine was formed only by the cynomolgus, squirrel and capuchin monkeys and marmoset, and in no case accounted for more than 3% dose. 6. 1-Naphthylacetylglycine was found in the urines of 4 primate and 3 non-primate species, and was the major metabolite in the squirrel monkey, bushbaby and cat. 7. 1-Naphthylacetyltaurine was excreted by all species except the rabbit and the fruit bat. It was a major excretion product in the squirrel and capuchin monkeys, the marmoset and the cat. 8. The influence of dose on the pattern of metabolism and excretion of 1-naphthylacetic acid has been investigated in the rat.

Metabolism of arylacetic acids. 2. The fate of [14C]hydratropic acid and its variation with species

1. (+/-)-[methyl-14C]-Hydratropic acid was administered to man, rhesus monkey, cat, rabbit and fruit bat. 2. All species excreted 60-100% of administered 14C in the urine in 24 h, and unchanged hydratropic acid accounted for 0-17% of the dose. 3. In man, the urinary 14C consisted of a very small quantity (1%) of unchanged hydratropic acid with the remainder as hydratropylglucuronide. 4. Hydratropylglucuronide was the major urinary excretion product in the 4 animal species, while the glycine conjugate was present in the urine of cat and rat. Additionally, cats excreted the taurine conjugate of hydratropic acid. 5. Bile-duct cannulated rats excreted 20-30% of an injected dose of [14C] hydratropic acid in the bile in 3 h mainly as hydratropylglucuronide.

Bile and urine as complementary pathways for the excretion of foreign organic compounds

1. The urinary and biliary excretion in the rat of 30 aromatic compounds with mol. wt. of 100-850, and largely excreted unchanged, has been studied. 2. These compounds fall into three groups as regards their pattern of elimination, which is related to mol. wt: group 1, with mol. wt. less than 350 and the major route of elimination the urine. When urinary excretion is prevented by ligating the renal pedicles the biliary excretion remains low. group 2, with mol, wt. of 450-850 which are excreted predominantly in bile. Even when the bile duct is obstructed, only small amounts of these compounds are found in urine. group 3, with mol. wt. of 350-450, which are eliminated extensively in both urine and bile. When one of these routes is blocked excretion by the other increases. 3. These studies emphasize the interrelationship of urine and bile as excretory routes for organic compounds. Urine and bile are complementary pathways; the extent of urinary excretion is greatest for the compounds of lowest mol. wt. and tends to decrease as mol. wt. increases and biliary excretion becomes more extensive.

Biliary excretion of xenobiotics

The biliary route is very important for the elimination of some foreign compounds from the body. For many of these compounds, an increase in the rate at which they are excreted into the bile will decrease their toxicity and vice versa. A number of factors which are known to alter the biliary excretion of xenobiotics, as well as the current concepts of the physiological mechanisms responsible for the excretion of foreign compounds, have been enumerated. However, much remains still to be understood; essentially nothing is known at the subcellular level about the biliary excretion of foreign compounds. It has recently been concluded that our knowledge of the biliary excretion of compounds is about 40 years behind that of the renal excretion mechanism.