Metabolism and excretion of 2,4-[14C]dinitrotoluene in conventional and axenic Fischer-344 rats

Comparisons of in vitro reduction of 2,4-dinitrotoluene (2,4-DNT) by cecal microflora and liver have indicated that microflora may play a large role in the in vivo metabolism of 2,4-DNT to reduced metabolites. Furthermore, reduction of 2,4-DNT by cecal microflora produces nitroso and, presumably, hydroxylamino intermediates which may account for the toxic actions of 2,4-DNT, including hepatocarcinogenesis. This study examines the metabolism, excretion, and hepatic covalent binding of 2,4-DNT in conventional, DNT-fed, and axenic Fischer-344 rats in order to define more precisely the role of DNT pretreatment and intestinal microflora in the disposition and toxicity of 2,4-DNT. No differences in 2,4-DNT disposition were produced by 30 days of feeding DNT (35 mg/kg/day) in the diet of male or female rats. Axenic males and females excreted less of a dose of 2,4-DNT in the urine than did conventional animals, and half-times for excretion of 4-(N-acetyl)amino-2-nitrobenzoic acid (4NAC2NBA), 2,4-dinitrobenzoic acid, 2-amino-4-nitrobenzoic acid (2A4NBA), and 2,4-dinitrobenzyl alcohol glucuronide were longer in axenic males than in conventional males. In axenic females half-times for excretion of only 4NAC2NBA and 2A4NBA were longer than in conventional females. Amounts of 4NAC2NBA and 2A4NBA excreted by axenic animals were 1/10th to 1/5th those excreted by conventional animals. Hepatic covalent binding was decreased by half in axenic animals. These data suggest that intestinal microflora play a major role in the appearance of reduced urinary metabolites and of covalently bound material after 2,4-DNT administration.     

Metabolism and excretion of 2,4-dinitrotoluene in male and female Fischer 344 rats after different doses

Female Fischer 344 rats are less susceptible to the hepatocarcinogenic effects of 2,4-dinitrotoluene (2,4-DNT) than males. This study is a comparison of the metabolism and excretion of 2,4-DNT in male and female rats after oral doses of 10, 35, or 100 mg of 14C-2,4-DNT per kg. The major route of elimination of 14C after all doses was the urine. 4-(N-Acetyl)amino-2-nitrobenzoic acid (4Ac2NBAcid), 2,4-dinitrobenzoic acid (2,4-DNMBAcid), 2-amino-4-nitrobenzoic acid (2A4NBAcid), and 2,4-dinitrobenzyl alcohol glucuronide (2,4-DNBAlcG) were identified in urine of rats. These four compounds accounted for greater than 85% of the radioactivity excreted in urine. Female rats excreted a significantly greater percentage of the dose in the urine as 2,4-DNBAlcG at doses of 10 or 35 mg/kg when compared to males. Both sexes showed dose-dependent changes in urinary excretion of 2,4-DNT metabolites. Males excreted a smaller percentage of the dose as 2,4-DNBAcid at 100 mg/kg than at 10 or 35 mg/kg. Females excreted less of the dose as 2,4-DNBAcid and 2,4-DNBAlcG at 100 mg/kg than at 10 or 35 mg/kg. The only sex difference in 2,4-DNT metabolism or excretion of sufficient magnitude to account for the sex difference in susceptibility to the hepatocarcinogenic effects of 2,4-DNT was the greater percentage of 2,4-DNT excreted as 2,4-DNBAlcG by female rats at 10 or 35 mg/kg.     

Identification and quantification of urinary metabolites of dinitrotoluenes in occupationally exposed humans

Rats exposed to technical grade dinitrotoluene (DNT) develop hepatocellular carcinomas. Humans may be exposed to DNT during its manufacture and use. To permit comparisons of human excretion patterns of DNT metabolites with those previously observed in rats, urine specimens were collected over a 72-hr period from workers at a DNT manufacturing plant. Samples were analyzed for 2,4- and 2,6-DNT and putative metabolites by gas chromatography-mass spectrometry. Urine from workers exposed to DNT contained 2,4- and 2,6-DNT, 2,4- and 2,6-dinitrobenzoic acid, 2,4- and 2,6-dinitrobenzyl glucuronide, 2-amino-4-nitrobenzoic acid, and 2-(N-acetyl)amino-4-nitrobenzoic acid. Excretion of these metabolites peaked near the end of the workshift, but declined to either very low or undetectable concentrations by the start of work the following day. The calculated half-times for elimination of total DNT-related material detected in urine ranged from 1.0 to 2.7 hr, and those of individual metabolites from 0.8 to 4.5 hr. The most abundant metabolites were 2,4-dinitrobenzoic acid and 2-amino-4-nitrobenzoic acid, collectively accounting for 74 to 86% of the DNT metabolites detected. The data indicate that urinary metabolites of DNT in humans are qualitatively similar to those found in rats, but quantitative differences exist in the relative amounts of each metabolite excreted.     

Hepatic microsomal metabolism and covalent binding of 2,4-dinitrotoluene

The effects of 2,4-dinitrotoluene (2,4-DNT) on xenobiotic metabolizing enzymes and the hepatic metabolism and covalent binding of this compound to microsomal proteins in vitro were studied. Male Fischer-344 rats received po doses of DNT daily for 5 days at 14, 35, and 70 mg/kg/day. Hepatic oxygen-insensitive cytosolic azoreductase activity was increased and microsomal nitroreductase was decreased by DNT treatments. A small but significant increase in liver/body weight ratio and in hepatic cytochromes P-450 and b₅ occurred in the absence of changes in microsomal biphenyl hydroxylase or aryl hydrocarbon hydroxylase activities. The patterns of in vitro microsomal metabolism of DNT were dependent on oxygen tension: under aerobic conditions, 2,4-dinitrobenzyl alcohol (DNBAlc) was the major metabolite whereas under anaerobic conditions no DNBAlc was detected; 2-amino-4-nitrotoluene (2A4NT) and 4-amino-2-nitrotoluene (4A2NT) were the major metabolites. Pretreatment of rats with phenobarbital or Aroclor 1254 increased the metabolism of 2,4-DNT to DNBAlc by six- to sevenfold. Metabolism to the alcohol was inhibited by SKF-525A. These data suggested that oxidative metabolism of 2,4-DNT to DNBAlc was mediated by cytochrome P-450-dependent mixed-function oxidases. Covalent binding studies showed that a maximum of only 7 pmol of 2,4-DNT-derived radioactivity was bound per milligram of microsomal protein per hour; this binding was increased to 1.0 nmol bound/mg protein/hr in microsomes from phenobarbital of Aroclor 1254-pretreated rats. It is concluded that 2,4-DNT treatment had little effect on the activity of some hepatic xenobiotic metabolizing enzymes and was readily metabolized by liver preparations in vitro. The pathways of in vitro metabolism were dependent on oxygen tension. This in vitro metabolism produced mostly polar metabolites which did not bind appreciably to microsomal macromolecules.     

Administration of L-3,4-dihydroxyphenylalanine to rats after complete hepatectomy-II. Excretion of metabolites

The excretion of metabolites of l-[3-¹⁴C]dihydroxyphenylalanine (l-[3-¹⁴C]DOPA) was studied after its injection into rats with complete hepatectomies and into control rats. Approximately 60 per cent of the dose (11 mg/kg; 20 μCi) of injected [¹⁴C]DOPA was excreted in urine in 24 hr by the control rats, and 11 per cent in bile. Although a similar percentage of the dose (69.4 per cent) was excreted by the hepatectomized rats into urine, excretion was at a slower rate. Decarboxylation of injected [¹⁴C]DOPA within 24 hr appeared to be as great in the hepatectomized rats as in the controls, but metabolism of 3,4-dihydroxyphenylethylamine (dopamine, DA) to norepinephrine was less. In the operated animals most of the DA was metabolized to 3,4-dihydroxyphenylacetic acid or to homovanillic acid. Little radioactivity was present in tissues at 24 hr after injection of l-DOPA into control rats or into hepatectomized rats; however, some radioactivity appeared to be bound to protein in some tissues in both groups of rats.     

The Disposition and Metabolism of Amodiaquine in Small Mammals

1. 7-Chloro-4-(3′-diethylamino-4′-hydroxyanilino)quinoline (amodiaquine) labelled with ¹⁴C has been synthesized and administered in single doses to rats including bile-duct-cannulated rats, to guinea-pigs and to mice, by oral or parenteral routes.

2. Amodiaquine was extensively and rapidly absorbed from the rat intestinal tract. Excretion of total radioactivity from rats and guinea pigs was slow and prolonged and was <50% dose in 9 days. Excretion of ¹⁴C was predominantly in faeces of rats after oral and i.p. dosage, and guinea-pigs after i.p. dosage. Radioactivity in rat and guinea-pig urine was <11% dose.

3. Biliary excretion of ¹⁴C following oral or i.v. dosage to rats was 21% dose in 24?h.

4. Amodiaquine was extensively metabolized and conjugated with <10% dose excreted unchanged in urine or bile. Two major basic metabolites in rat urine were tentatively identified as the mono- and bis-desethyl amines.

5. 7-Chloro-4-(4′-diethyl-1′-methylbutylamino)quinoline (chloroquine) was excreted largely unchanged in urine of rats after oral or parenteral administration of single doses, with <5% dose excreted in rat bile in 24?h.     

Studies on the Biliary Excretion and Metabolites of the Antioxidant Ethoxyquin, 6-Ethoxy-2,2,4-Trimethyl-1,2-Dihydroquinoline in the Rat

1. Biliary excretion and metabolites of ethoxyquin, and gastro-intestinal absorption of ethoxyquin were studied in rat.

2. An average of 28 and 36% of the dose of¹⁴C following intragastric administration of [¹⁴C]ethoxyquin was recovered in the bile of bile-duct cannulated rats in 12 and 24?h, respectively.

3. By g.l.c.-mass spectrometry, 75 to 85% of the ¹⁴C excreted in the 12?h bile was identified as unchanged ethoxyquin, and the following metabolites were isolated and identified: 8-hydroxy-ethoxyquin, hydroxylated 8-hydroxy-ethoxyquin, 6-ethoxy-2,2,4-trimethyl-8-quinolone, hydroxylated 6-ethoxy-2,2,4-trimethyl-8-quinolone, 6-ethoxy-2,4-dimethylquinoline and 2,2,4-trimethyl-6-quinolone.

4. Three groups of rats were used in the biliary excretion experiments, and the effect of standardization of experimental conditions was demonstrated. Infusion of sodium tauro-cholate following bile-duct cannulation did not affect the biliary excretion kinetics of ethoxyquin.

5. Only about 3% of the radioactivity administered was absorbed from the gastrointestinal tract via the lymphatic pathway in thoracic-duct cannulated rats within 24?h. It was concluded that ethoxyquin was absorbed primarily by the portal route.     

Sex differences in excretion of zenarestat in rat

1. Rat shows a marked sex difference in the excretion of ¹⁴C-zenarestat: only 1% of the dose was excreted in the urine of males, about 45% of the dose was excreted in the urine of females. ¹⁴C in the urine of female rats was almost entirely unchanged drug.

2. Plasma protein binding was similar in both sexes: 99.3–99.5% in males and 99.4–99.6% in females.

3. The type and ratio of metabolites in the faeces and bile were not significantly different between males and females.

4. Renal clearance experiments, and inhibition of urinary excretion by probenecid, indicated that female rats may possess an active secretory mechanism which is lacking or relatively inactive in male rats.     

Biliary excretion and microfloral transformation of major conjugated metabolites of 2,4-dinitrotoluene and 2,6-dinitrotoluene in the male Wistar rat

1. Major biliary conjugates of the male Wistar rat dosed orally with 2,4-dinitrotoluene (2,4-DNT) or 2,6-dinitrotoluene(2,6-DNT) were examined by hplc using potassium 2,4- dinitrobenzyl glucuronide (potassium 2,4-DNB- G), potassium 2,6-dinitrobenzyl glucuronide (potassium 2,6-DNB- G), pyridinium 2,4-dinitrobenzyl sulphate (pyridinium 2,4- DNB- S) and pyridinium2,6-dinitrobenzylsulphate (pyridinium2,6-DNB- S) as authentic compounds. Other metabolites were also examined by hplc. In addition, metabolites formed by incubation of potassium 2,4-DNB- G and potassium 2,6-DNB- G with rat intestinal microflora under nitrogen were examined by hplc. 2. Conjugates detected directly from bile following administration of 2,4-DNT and 2,6-DNT were 2,4-DNB- G and 2,6-DNB- G, which accounted for 35 0 and 51 5 % of the administered dose respectively. No peaks corresponding to pyridinium 2,4-DNB- S and pyridinium 2,6-DNB- S were detected in bile samples. 3. 2-Amino- 4-nitrotoluene,4-amino- 2-nitrotoluene,2,4-diaminotolueneand 4-acetylamino- 2-nitrobenzoic acid (0 02-0 12 % of the dose excreted in 24?h), in addition to the known metabolites 2,4-dinitrobenzyl alcohol (2,4-DNB), 2,4-dinitrobenzalde hyde and 2,4-dinitrobenzoic acid (0 09-0 14 %), were detected in ether extracts of bile of rat given 2,4-DNT. 2,6-Dinitrobenzylalcohol (2,6-DNB), 2-amino- 6-nitrotolueneand 2,6-dinitrobenzaldehyde(0 02-0 03 %), which are known metabolites, were detected in ether extracts of bile from rat given 2,6-DNT. 4. Potassium 2,4-DNB- G was transformed by the anaerobic incubationof rat intestinal microflora into 2,4-DNB, 4-amino- 2-nitrobenzyl alcohol and 2-amino- 4-nitrobenzyl alcohol. Potassium 2,6-DNB- G was transformed into 2,6-DNB and 2-amino- 6-nitrobenzyl alcohol by the anaerobic incubation. Time-course studies showed that 2,4-DNB, 4-amino- 2-nitrobenzyl alcohol, 2-amino- 4-nitrobenzyl alcohol and 2,6-DNB, 2-amino- 6- nitrobenzyl alcohol peaked at 30, 75, 120 and 10, 50?min respectively. 5. These results, together with previous findings, show that 2,4-dinitrobenzalde hyde and 2,6-dinitrobenzalde hyde, which are potent mutagens, are formed either by the hepatic metabolism of 2,4-DNB and 2,6-DNB formed by the intestinal metabolism of 2,4-DNBG and 2,6-DNB- G excreted in bile or by the direct hepatic metabolism of 2,4-DNT and 2,6-DNT.     

In vivo biotransformation and biliary excretion of 1-14C-acrylonitrile in rats

1-¹⁴C-Acrylonitrile (VCN) was given orally to rats, 27% of the given dose was excreted in bile in 6 h. When 1-¹⁴C-VCN was given to overnight fasted or cobaltous chloride treated rats, a significant increase in the biliary excretion occurred. Pretreatment of rats with phenobarbital produced no change, while diethyl maleate pretreatment significantly decreased the portion of the dose excreted in bile in 6 h. Four metabolites of 1-¹⁴C-VCN have been isolated from the collected bile, and characterized. The two major biliary metabolites were found to be glutathione (GSH) conjugates of VCN, indicating the importance of GSH in VCN biotransformation.This research was supported by NIH Grant No. ES 01871. A preliminary report of this work was presented at the annual meeting of the Society of Toxicology, March 1981, San Diego CA, USA.     

Intestinal absorption, intestinal distribution, and excretion of (14C) labelled hyoscine N-butylbromide (butylscopolamine) in the rat

Butylscopolamine was labelled with ¹⁴C and its gastrointestinal absorption, biliary and urinary excretion, enterohepatic circulation and gastrointestinal distribution were examined in anaesthetized rats. Biliary excretion was the main elimination route of intra-portally administered [¹⁴C]butylscopolamine, with 42% of the dose recovered in the bile during 12 h. About 6% of the radioactivity administered orally as [¹⁴C]butylscopolamine was excreted in the bile and 1.2 % in the urine during 24 h, which indicates poor gastrointestinal absorption of butylscopolamine in the rat. When collected radioactive bile was readministered intrajejunally, only about 7% of the radioactivity was recovered in bile and urine during 12 h, which suggests that only a small fraction of butylscopolamine and its metabolites engage in an enterohepatic circulation. After oral administration of [¹⁴C]butylscopolamine, radioactivity was found to accumulate in the wall of the distal small intestine, and about 20% of the dose was found in this tissue 24 h after drug administration. As a result, local anti-acetylcholine effects of butylscopolamine might be expected.     

Metabolism and excretion of CP-122,721, a non-peptide antagonist of the neurokinin NK1 receptor,in dogs: Identification of the novel cleaved product 5-trifluoromethoxy salicylic acid in plasma

The metabolism and excretion of a potent and selective substance P receptor antagonist, CP-122,721, have been studied in beagle dogs following oral administration of a single 5?mg?kg^?1 dose of [¹⁴C]CP-122,721. Total recovery of the administered dose was on average 89% for male dogs and 95% for female dogs. Approximately 94% of the radioactivity recovered in urine and feces was excreted in the first 72?h. Male bile duct-cannulated dogs excreted a mean of ～56% of the dose in bile, ～11% in feces, and ～25% in urine. The sum of radioactivity in bile and urine indicates >80% of the [¹⁴C]CP-122,721-derived radioactivity was absorbed by the gastrointestinal tract. CP-122,721 was extensively metabolized in dogs, and only a small amount of parent CP-122,721 was excreted as unchanged drug. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or feces. The major metabolic pathways of CP-122,721 were O-demethylation, aromatic hydroxylation, and indirect glucuronidation. The minor metabolic pathways included: Aliphatic oxidation at the piperidine moiety, O-dealkylation of the trifluoromethoxy group, and N-dealkylation with subsequent sulfation and/or oxidative deamination. In addition, the novel cleaved product 5-trifluoromethoxy salicylic acid (TFMSA) was identified in plasma. These results suggest that dog is the most relevant animal species in which the metabolism of CP-122,721 can be studied for extrapolating the results to humans.     

Tissue distribution of 2,4-dinitrotoluene and its metabolites in male and female Fischer-344 rats

The hepatocarcinogen, dinitrotoluene (DNT), produces a lower incidence of hepatocellular carcinoma in female rats than in male rats. This study compares the elimination of radiolabeled 2,4-DNT in male rats at three dosages and the elimination of 2,4-DNT in male and female rats at a dose of 100 mg/kg. Terminal half-lives of total radioactivity in various tissues were similar after doses of 10 or 35 mg/kg in male rats, but were shorter after a dose of 100 mg/kg in plasma, red blood cells, liver, and kidney. Although terminal half-lives for total radioactivity were similar in male and female rats after a dose of 100 mg/kg, female liver contained concentrations of radioactivity which were one-half those found in males. The tissues of both sexes contained parent compound, 2,4-dinitrobenzoic acid, and 2-amino-4-nitrobenzoic acid. No evidence for the presence of the hepatocarcinogen, 2,4-diaminotoluene, was found. The difference between nanomole equivalents of 2,4-DNT and its metabolites found by specific assay and nanomole equivalents found by radioactivity measurements was two to five times larger in female rats than in males. The data suggest that dose-dependent changes occur in the elimination and distribution of 2,4-DNT at high doses and that female rats metabolize 2,4-DNT to unidentified metabolites to a greater extent than males. Furthermore, the lack of evidence for the formation of 2,4-diaminotoluene from 2,4-DNT suggests that the hepatocarcinogenicity of 2,4-DNT is not due to its conversion to 2,4-diaminotoluene.     

The excretion of 3H-papaverine in the rat

The excretion of ³H-papaverine has been studied in the rat. After per oral as well as parenteral administration about 85 per cent of the administered radioactivity is excreted in faeces and urine in 4 days, and only negligible amounts of this radioactivity consist of unchanged ³H-papaverine; most of the radioactivity is recovered in the faeces in the first 24 hr.After an intravenous dose of ³H-papaverine, about 70 per cent of the tritium is excreted in the bile in 6 hr. All this radioactivity is due to conjugated metabolites, which after hydrolysis with glusulase, give five peaks on thin layer chromatograms. After intraduodenal administration of these conjugated metabolites, a very small absorption occurs, while after administration of the hydrolysed metabolites about 60 per cent of the dose is excreted in the bile. After intramuscular injection of ³H-papaverine radioactivity in the intestine follows quite good the time pattern of excretion of tritium in the bile. No significant difference was observed between control and bile cannulated rats with regard to the blood levels of radioactivity and ³H-papaverine. These results suggest that the bile is the main route of excretion of papaverine metabolites and that enterohepatic circulation of these metabolites is not important.     

Disposition of 3,3′-dichlorobenzidine in the rat

The disposition of the carcinogen 3,3′-dichlorobenzidine (DCB) was studied in the male rat following oral administration. [¹⁴C]DCB was well absorbed by the rat with the maximum plasma radioactivity levels being found within 8 hr after dosing. The radioactivity was well distributed in the tissues 24 hr after administration with the highest levels found in the liver, followed by kidney, lung, and spleen. Repeated administration (six doses) of [¹⁴C]DCB to animals did not result in a substantial accumulation of ¹⁴C in the tissues. The elimination of radioactivity from the plasma, liver, kidney, and lung was biphasic showing an initial rapid decline (half-lives 1.68, 5.78, 7.14, and 3.85 hr, respectively) followed by a slower disappearance phase (half-lives 33.0, 77.0, 138.6, and 43.3 hr, respectively). Approximately half of the total ¹⁴C in the liver and kidney was covalently bound to cellular macromolecules 72 hr after dosing. [¹⁴C]DCB-derived radioactivity was extensively excreted by rats, mainly via the feces. Approximately 23–33% of the administered dose was recovered in the urine and 58–72% in the feces of rats within 96 hr. More than 65% of the administered ¹⁴C was eliminated in the bile of bile duct-cannulated rats within 24 hr after dosing. The radioactivity excreted in the urine and bile was primarily in the form of free (urine 71.2%, bile 25.5%) and conjugated (urine 19.6%, bile 57.9%) metabolites of DCB. Thus DCB is readily absorbed following oral administration, and then metabolized and excreted mainly via the feces.     

The in vivo biotransformation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the rat

This study presents evidence for the in vivo biotransformation of TCDD in the rat. Three male rats with indwelling bile loop cannulas were given repeated daily po doses of 15 μg [¹⁴C]TCDD/kg body weight. After either two, four, or six doses, the total output of bile from one rat was collected for 24 hr following the last dose. Biliary ¹⁴C activity was excreted at a rate similar to the excretion of ¹⁴C activity in the feces of normal (noncannulated) rats given po doses of [¹⁴C]TCDD. Therefore it is not likely that enterohepatic recycling plays a significant role in the retention of ¹⁴C activity following a dose of [¹⁴C]TCDD. High-pressure liquid chromatography of the bile from these rats showed the presence of at least eight radioactive peaks and very little, if any, unchanged TCDD. These metabolites were all more polar than TCDD, and the chromatographic profile was altered following incubation of the bile with β-glucuronidase. These data, in conjunction with previous studies, indicate that the metabolic transformation of TCDD in the liver may be the rate-limiting step in the elimination of TCDD from the body.     

The biliary excretion and enterohepatic circulation of benzo(a)pyrene and its metabolites in the rat

The enterohepatic circulation of benzo(a)pyrene (BP) has been investigated in the rat with a view to determining the availability of potentially toxic metabolities to tissues within this cycle. Some 60% of the dose of [¹⁴C]-BP (3 μmoles kg^?1, i.v.) is excreted in bile in 6 hr, with less than 3% in urine. The biliary metabolities are mainly polar conjugates; only 8% of the ¹⁴C in 2 hr bile samples can be directly extracted into ethyl acetate. However, following hydrolysis by β-glucuronidase some 40% of the ¹⁴C is extractable at pH 7. The extract consisted of polar metabolites (polyhydroxylated and/or conjugated; 37.5%), BP 4,5-diol (16.8%), BP 3,6-quinone (5.9%). 9-hydroxy BP (5.4%) and 3-hydroxy BP (5.3%) as indicated by co-chromatography with authentic standards on reversed phase HPLC, together with several unidentified metabolites. The proximate carcinogen BP 7, 8-diol was not detected. Biliary metabolites of [¹⁴C]-BP undergo enterohepatic recirculation in the rat; following the intraduodenal infusion of bile containing metabolites of [¹⁴C]-BP into bile duct cannulated rats, approximately 20% of the dose is absorbed and excreted in bile in 30 hr, with only 1% in urine. The pattern of metabolites in this bile is very similar to that in bile from rats administered [¹⁴C]-BP i.v. Following a single i.v. dose of [¹⁴C]-BP (3 μmoles kg^?1) to rats with re-entrant bile duct cannulae, which allowed intermittent collection of bile over a period of several days with minimal interference to the enterohepatic circulation, the proximate carcinogen BP 7, 8-diol was detected in recirculating bile. Biliary metabolites of BP, which have recently been shown to be mutagenic, can thus traverse the intestine to undergo enterohepatic circulation in the rat.     

Sex differences in the metabolism and excretion of nilvadipine,a new dihydropyridine calcium antagonist,in rats

1. The metabolic profiles of nilvadipine in the urine and bile of male and female rats were studied after i.v. dosing with 1?mg/kg of the ¹⁴C-labelled compound.

2. Excretion rates of the dosed radioactivity in male and female rats, respectively, in the first 48?h were 8.41% and 59.1% in bile, 12.0% and 36.9% in urine, and 2.5% and 3.6% in faeces.

3. Comparison of biliary and urinary excretion for each radioactive metabolite after dosing with ¹⁴C-nilvadipine, showed marked sex-related differences in the excretion routes of several metabolites. In male rats, metabolite M3, having a free 3-carboxyl group on the pyridine ring, was not excreted in urine, but in female rats urinary excretion of M3 accounted for 4.7% of the dose. One reason for the lower urinary excretion of radioactivity by males than by females was that the main metabolite, M3, was not excreted in the urine of the male rats.

4. To clarify the sex difference in the route of excretion of M3, this metabolite (M3) was given i.v. to rats. No excretion of the metabolite was observed in urine of male rats within 24?h but, in marked contrast, 41.5% of the dose was excreted in urine of females in the same period.     

Metabolism and disposition of ferbam in the rat.

Approximately 40–70% of an oral dose of ferric [³⁵S]dimethyldithiocarbamate ([³⁵S]ferbam) or ferric [¹⁴C]dimethyldithiocarbamate ([¹⁴C]ferbam) was absorbed through the gastrointestinal tract of the rat during a 24-hr period. In rats receiving [³⁵S]ferbam, 22.7, 18.1, and 1.0% of the radioactivity was found in urine, expired air, and bile, respectively. Only small amounts of ³⁵S were found in the various tissues, including blood, kidneys, muscle, and brain. In rats receiving [¹⁴C]ferbam 42.9 and 1.4% of the ¹⁴C was found in the urine and bile, respectively; whereas only 0.6% of the radioactivity was recovered in the expired air. The other tissues contained only small amounts of ¹⁴C. Analysis of expired air indicated that the only expired ferbam metabolite was carbon disulfide. Major metabolites in the urine included inorganic sulfate, a salt of dimethylamine and a glucuronide conjugate of dimethyldithiocarbamate. Unchanged ferbam was not excreted in the urine. In pregnant rats given [¹⁴C]ferbam a small but significant amount of radioactivity readily crossed the placenta into the fetus. In lactating rats given [¹⁴C]ferbam, radioactivity was secreted into milk, absorbed by the pups and excreted in the pups' urine.     

Absorption,distribution, metabolism and excretion of an isocitrate dehydrogenase-2 inhibitor enasidenib in rats and humans

1. The absorption, distribution, metabolism and excretion of enasidenib were studied following a single oral dose of [¹⁴C]enasidenib to rats (10?mg/kg; 100 μCi/kg) and healthy volunteers (100?mg; 318 nCi).

2. Enasidenib was readily absorbed, extensively metabolized and primarily eliminated via the hepatobiliary pathway. Enasidenib-derived radioactivity was widely distributed in rats. Excretion of radioactivity was approximately 95–99% of the dose from rats in 168?h post-dose and 82.4% from human volunteers in 504?h post-dose. In rat bile, approximately 35–42% of the administered dose was recovered, with less than 5% of the dose excreted as the parent drug. Renal elimination was a minor pathway, with <12% of the dose excreted in rat urine and <10% of the dose excreted in human urine.

3. Enasidenib was the prominent radioactive component in rat and human systemic circulation. Enasidenib was extensively metabolized in rats and human volunteers through N-dealkylation, oxidation, direct glucuronidation and combinations of these pathways. Glucuronidation was the major metabolic pathway in rats while N-dealkylation was the prominent metabolic pathway in human volunteers. All human metabolites were detected in rats.