Species differences in the metabolism of sulphadimethoxine

1. The fate of sulphadimethoxine (2,4-dimethoxy-6-sulphanilamidopyrimidine) was studied in man, rhesus monkey, dog, rat, guinea pig and rabbit. 2. About 20–46% of the dose (0·1g./kg.) of the drug is excreted in the urine in 24hr. in these species, except the rat, in which only 13% is excreted. 3. In man and the monkey sulphadimethoxine N¹-glucuronide is the major metabolite in the urine. In the rabbit and guinea pig N⁴-acetylsulphadimethoxine is the main metabolite. In the dog the drug is excreted mainly unchanged. In the rat equal amounts of the unchanged drug and its N⁴-acetyl derivative are the main products. 4. Small amounts of sulphadimethoxine N⁴-glucuronide are found in the urine of all the species. Sulphadimethoxine N¹-glucuronide occurs in small amounts in the urine of rat, dog and guinea pig; none is found in rabbit urine. 5. Sulphadimethoxine N⁴-sulphate was synthesized and found to occur in small amounts in rat urine. 6. Monkey liver homogenates fortified with UDP-glucuronic acid are able to synthesize sulphadimethoxine N¹-glucuronide with the drug as substrate. Rat liver has also this ability to a slight extent, but rabbit liver is unable to do so. 7. Sulphadimethoxine N⁴-glucuronide is formed spontaneously when the drug is added to human urine. 8. The biliary excretion of the drug and its metabolites was examined in rats. The drug is excreted in rat bile mainly as the N¹-glucuronide. The N¹- and N⁴-glucuronides administered as such are extensively excreted in the bile by rats.     

The metabolism of arylazoisoxazolones by rats and dogs

1. When rats were given a single oral dose of the lipid-soluble fungicide 4-(2-chlorophenylhydrazono)-3-methyl[4-(14)C]isoxazol-5-one ([(14)C]drazoxolon), about 75% of the label was excreted in the urine and 13% in the faeces in 96hr. An additional 7% of the radioactivity was recovered as (14)CO(2) in 48hr. 2. About 8% of the label was excreted by rats in the bile in 0-24hr. and an additional 6% was excreted by the same route in 24-48hr. 3. When dogs were given a single oral dose of [(14)C]drazoxolon about 35% of the label was excreted in the urine and a similar amount was excreted in the faeces in 96hr. 4. The major metabolites in the urine of the rat and the dog were identified as 2-(2-chloro-4-hydroxyphenylhydrazono)acetoacetic acid (dog, 14%), the corresponding ether glucosiduronic acid (dog, 12%; rat, 13%) and ester sulphate (rat, 65%). 5. When rats were given a single oral dose of 3-methyl-4-([U-(14)C]phenylhydrazono)isoxazol-5-one about 75% of the label was excreted in the urine and 15% in the faeces in 96hr. The major metabolite in the urine was identified as the ester sulphate conjugate of 2-(4-hydroxyphenylhydrazono)-acetoacetic acid. 6. Reduction of the azo link was of minor quantitative significance. 7. These results are discussed in their relation to species differences in the toxicity of these compounds.     

Species differences in the aromatization of quinic acid in vivo and the role of gut bacteria

1. The fate of (−)-quinic acid has been investigated in 22 species of animals including man. 2. In man and three species of Old World monkeys, i.e. rhesus monkey, baboon and green monkey, oral quinic acid was extensively aromatized (20–60%) and excreted in the urine as hippuric acid, which was determined fluorimetrically. 3. In three species of New World monkeys, i.e. squirrel monkey, spider monkey and capuchin, in three species of lemurs, i.e. bushbaby, slow loris and tree shrew, in the dog, cat, ferret, rabbit, rat, mouse, guinea pig, hamster, lemming, fruit bat, hedgehog and pigeon, oral quinic acid was not extensively aromatized (0–5%). 4. In the rhesus monkey, injected quinic acid was not aromatized, but largely excreted unchanged. 5. In rhesus monkeys pretreated with neomycin to suppress gut flora, the aromatization of oral quinic acid was considerably suppressed. 6. In rats and rhesus monkeys [¹⁴C]quinic acid was used and this confirmed its low aromatization in rats and its high aromatization in the monkeys. 7. Shikimic acid given orally was excreted as hippuric acid (26–56%) in rhesus monkeys, but not in rats. 8. The results support the view that quinic acid and shikimic acid are aromatized by the gut flora in man and the Old World monkeys.     

Metabolism of propranolol in rat: the fate of the N-isopropyl group

The metabolic fate of the side-chain of propranolol has been studied in the rat $\text{in vivo}$ and with liver preparations $\text{in vitro}$ using drug labelled with ¹⁴C in the isopropyl group. Oxidative N-dealkylation to yield acetone was the major route of metabolism $\text{in vitro}$. Direct deamination to form isopropylamine was a very minor pathway of metabolism of propranolol by rat liver. In the intact rat only 1.4% of an intra-peritoneal dose of propranolol was excreted as isopropylamine in urine. In addition, isopropylamine administered to a rat was rapidly excreted unchanged in urine. Thus, if a similar metabolic pattern obtains in man, it seems unlikely that part of the pharmacological effects of propranolol can be attributed to this active metabolite.     

The metabolism of labelled hexadecyl sulphate salts in the rat, dog and human.

The metabolic fate of [1-14-C]hexadecylsulphate and hexadecyl[35-S]sulphate, administered intravenously as the sodium and trimethylammonium salt to dogs and orally as the erythromycin salt to dogs, rats and humans, was studied. Studies with rats indicated that the compounds were well absorbed and rapidly excreted in the urine. However, after oral administration of the 14-C-and 35-S-labelled hexadecyl sulphate erythromycin salt to dogs, considerable amounts of radioactivity were excreted in the faeces as unmetabolized hexadecyl sulphate. Studies with two humans showed that orally administered erythromycin salt of [1-14C]hexadecyl sulphate was well absorbed in one person but poorly absorbed in the other. Radioactive metabolites in urine were separated by t.l.c. in two solvent systems. The main metabolite of hexadecyl sulphate in the dog, rat and human was identified as the sulphate ester of 4-hydroxybutyric acid. In addition, psi-[14-C]butyrolactone as a minor metabolic product of [1-14-C]hexadecyl sulphate was also isolated from the urine of rat, dog and man. However, there was still another metabolite in dog urine, which comprised about 20% of the total urinary radioactivity and carried both 14-C and 35-S labels. This metabolite was absent from rat urine. The metabolite in dog urine was isolated and subsequently identified by t.l.c. and g.l.c. and by isotope-dilution experiments as the sulphate ester of glycollic acid. Small amounts (about 5% of the total recovered radioactivity in excreta) of labelled glycollic acid sulphate were also found in human urine after ingestion of erythromycin [1-14-C]hexadecyl sulphate.     

Separation and identification of phase I and phase II [14C]antipyrine metabolites in rat and dog urine

A simple and accurate HPLC procedure was developed to quantify, in a single run, all phase I and phase II [¹⁴C]antipyrine metabolites that occur in rat and dog urine. All metabolites were subjected to thermospray-LC-MS and EI-MS in order to establish their structure. The rat metabolizes antipyrine to eight major metabolites, six of which are conjugated; 1.4% of the dose was excreted unchanged, 18.9% in a free form, 30.6% as sulfates and 21.1% as glucoronides. The dog metabolizes antipyrine to four metabolites, all as sulfate (61.0% of the dose) or glucoronide conjugates (16.2% of the dose).     

Urinary metabolites of cannabidiol in dog, rat and man and their identification by gas chromatography—mass spectrometry

Urinary metabolites of cannabidiol (CBD), a non-psychoactive cannabinoid of potential therapeutic interest, were extracted from dog, rat and human urine, concentrated by chromatography on Sephadex LH-20 and examined by gas chromatography—mass spectrometry as trimethylsilyl (TMS), [²H₉]TMS, methyl ester—TMS and methyloxime—TMS derivatives. Fragmentation of the metabolites under electron-impact gave structurally informative fragment ions; computer-generated single-ion plots of these diagnostic ions were used extensively to aid metabolite identification. Over fifty metabolites were identified with considerable species variation. CBD was excreted in substantial concentration in human urine, both in the free state and as its glucuronide. In dog, unusual glucoside conjugates of three metabolites (4″- and 5″-hydroxy- and 6-oxo-CBD), not excreted in the unconjugated state, were found as the major metabolites at early times after drug administration. Other metabolites in all three species were mainly acids. Side-chain hydroxylated derivatives of CBD-7-oic acid were particularly abundant in human urine but much less so in dog. In the latter species the major oxidized metabolites were the products of β-oxidation with further hydroxylation at C-6. A related, but undefined pathway resulted in loss of three carbon atoms from the side-chain of CBD in man with production of 2″-hydroxy-tris,nor-CBD-7-oic acid. Metabolism by the epoxide-diol pathway, resulting in dihydro-diol formation from the Δ-8 double bond, gave metabolites in both dog and human urine. It was concluded that CBD could be used as a probe of the mechanism of several types of biotransformation; particularly those related to carboxylic acid metabolism as intermediates of the type not usually seen with endogenous compounds were excreted in substantial concentration.     

The fate of benzoic acid in various species

1. The urinary excretion of orally administered [¹⁴C]benzoic acid in man and 20 other species of animal was examined. 2. At a dose of 50mg/kg, benzoic acid was excreted by the rodents (rat, mouse, guinea pig, golden hamster, steppe lemming and gerbil), the rabbit, the cat and the capuchin monkey almost entirely as hippuric acid (95–100% of 24h excretion). 3. In man at a dose of 1mg/kg and the rhesus monkey at 20mg/kg benzoic acid was excreted entirely as hippuric acid. 4. At 50mg/kg benzoic acid was excreted as hippuric acid to the extent of about 80% of the 24h excretion in the squirrel monkey, pig, dog, ferret, hedgehog and pigeon, the other 20% being found as benzoyl glucuronide and benzoic acid, the latter possibly arising by decomposition of the former. 5. On increasing the dose of benzoic acid to 200mg/kg in the ferret, the proportion of benzoyl glucuronide excreted increased and that of hippuric acid decreased. This did not occur in the rabbit, which excreted 200mg/kg almost entirely as hippuric acid. It appears that the hedgehog and ferret are like the dog in respect to their metabolism of benzoic acid. 6. The Indian fruit bat produced only traces of hippuric acid and possibly has a defect in the glycine conjugation of benzoic acid. The main metabolite in this animal (dose 50mg/kg) was benzoyl glucuronide. 7. The chicken, side-necked turtle and gecko converted benzoic acid mainly into ornithuric acid, but all three species also excreted smaller amounts of hippuric acid.     

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[1-¹⁴C]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 ethyltin³⁺ and diethyltin²⁺. Diethyltin is also excreted extensively in the bile. Di[¹⁴C]ethyltin is not converted into ¹⁴CO₂ in the rat. 3. About 50% of the injected diethyltin dichloride is de-ethylated to ethyltin³⁺. 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 diethyltin²⁺ to ethyltin³⁺ in the rat is discussed and it is suggested that the ethyl group is lost as ethane.     

The metabolic fate of amphetamine in man and other species

1. The fate of [(14)C]amphetamine in man, rhesus monkey, greyhound, rat, rabbit, mouse and guinea pig has been studied. 2. In three men receiving orally 5mg each (about 0.07mg/kg), about 90% of the (14)C was excreted in the urine in 3-4 days. About 60-65% of the (14)C was excreted in 1 day, 30% as unchanged drug, 21% as total benzoic acid and 3% as 4-hydroxyamphetamine. 3. In two rhesus monkeys (dose 0.66mg/kg), the metabolites excreted in 24h were similar to those in man except that there was little 4-hydroxyamphetamine. 4. In greyhounds receiving 5mg/kg intraperitoneally the metabolites were similar in amount to those in man. 5. Rabbits receiving 10mg/kg orally differed from all other species. They excreted little unchanged amphetamine (4% of dose) and 4-hydroxyamphetamine (6%). They excreted in 24h mainly benzoic acid (total 25%), an acid-labile precursor of 1-phenylpropan-2-one (benzyl methyl ketone) (22%) and conjugated 1-phenylpropan-2-ol (benzylmethylcarbinol) (7%). 6. Rats receiving 10mg/kg orally also differed from other species. The main metabolite (60% of dose) was conjugated 4-hydroxyamphetamine. Minor metabolites were amphetamine (13%), N-acetylamphetamine (2%), norephedrine (0.3%) and 4-hydroxynorephedrine (0.3%). 7. The guinea pig receiving 5mg/kg excreted only benzoic acid and its conjugates (62%) and amphetamine (22%). 8. The mouse receiving 10mg/kg excreted amphetamine (33%), 4-hydroxyamphetamine (14%) and benzoic acid and its conjugates (31%). 9. Experiments on the precursor of 1-phenylpropan-2-one occurring in rabbit urine suggest that it might be the enol sulphate of the ketone. A very small amount of the ketone (1-3%) was also found in human and greyhound urine after acid hydrolysis.     

The fate of sulphadimethoxine in primates compared with other species

1. The metabolism of sulphadimethoxine (2,4-dimethoxy-6-sulphanilamidopyrimidine) was examined in nine species of primates and nine species of non-primates. 2. The main metabolite of the drug in the urine in man, rhesus monkey, baboon, squirrel monkey, capuchin, bushbaby, slow loris and tree shrew was sulphadimethoxine N(1)-glucuronide. In the green monkey, although the main metabolite was N(4)-acetylsulphadimethoxine, the N(1)-glucuronide was also a major metabolite. 3. In the dog, rat, mouse, guinea pig, Indian fruit bat and hen the N(1)-glucuronide was a minor metabolite in the urine, whereas in the cat, ferret and rabbit this glucuronide was not found in the urine. 4. All the species examined except the dog excreted some N(4)-acetylsulphadimethoxine, which was the major metabolite in the green monkey, rabbit and guinea pig. 5. In the tree shrew, a doubtful primate, N(1)-glucuronide formation was similar to that in the other primates. 6. It is suggested that the slow excretion of the drug by the rat may be due partly to strong binding of the drug to tissue proteins and that the strength of binding may vary with species. 7. In the rat the amount of N(1)-glucuronide found in the urine is not a true indication of the extent of this conjugation since much more of the conjugate was found in the bile (7% of the dose) than in the urine (1%). In the rabbit, no N(1)-glucuronide was found in the bile or urine, but a small amount of sulphadimethoxine N(4)-glucuronide was found in the bile of the rat (0.5% of dose) and rabbit (0.8%).     

The metabolism of methoxyethylmercury salts

The metabolism of methoxy[(14)C]ethylmercury chloride in the rat has been investigated. After a single subcutaneous dose a small proportion is excreted unchanged in urine and a larger amount in bile with some resorption from the gut. The greater part of the dose is rapidly broken down in the tissues with a half-time of about 1 day to yield ethylene and inorganic mercury. Ethylene is exhaled in the breath and the mercury migrates to the kidney and is excreted in urine. A small proportion of the dose appears as carbon dioxide in the breath and about 12% in urine as a mercury-free metabolite. It is possible that the breakdown of methoxyethylmercurychloride to ethylene and inorganic mercury is not catalysed by an enzyme system.     

The metabolites of cyclohexylamine in man and certain animals

1. [1-(14)C]Cyclohexylamine hydrochloride was synthesized and given orally or intraperitoneally to rats, rabbits and guinea pigs (dose 50-500mg/kg) and orally to humans (dose 25 or 200mg/person). The (14)C is excreted mainly in the urine, most of the excretion occurring in the first day after dosing. Only small amounts (1-7%) are found in the faeces. 2. In the rat, guinea pig and man, the amine is largely excreted unchanged, only 4-5% of the dose being metabolized in 24h in the rat and guinea pig and 1-2% in man. In the rabbit about two-thirds of the dose is excreted unchanged and about 30% is metabolized. 3. In the rat, five minor metabolites were found, namely cyclohexanol (0.05%), trans-3- (2.2%), cis-4- (1.7%), trans-4- (0.5%) and cis-3-aminocyclohexanol (0.1% of the dose in 24h). 4. In the rabbit, eight metabolites were identified, namely cyclohexanol (9.3%), trans-cyclohexane-1,2-diol (4.7%), cyclohexanone (0.2%), cyclohexylhydroxylamine (0.2%) and trans-3- (11.3%), cis-3- (0.6%), trans-4- (0.4%) and cis-4-aminocyclohexanol (0.2%). 5. In the guinea pig, six minor metabolites were found, namely cyclohexanol (0.5%), trans-cyclohexane-1,2-diol (2.5%) and trans-3- (1.2%), cis-3- (0.2%), trans-4- (0.2%) and cis-4-aminocyclohexanol (0.2%). 6. In man only two metabolites were definitely identified, namely cyclohexanol (0.2%) and trans-cyclohexane-1,2-diol (1.4% of the dose), but man had been given a smaller dose (3mg/kg) than the other species (50mg/kg). 7. The hydroxylated metabolites of cyclohexylamine were excreted in the urine in both free and conjugated forms. 8. Although cyclohexylamine is metabolized to only a minor extent, in rats the metabolism was mainly through hydroxylation of the cyclohexane ring, in man by deamination and in guinea pigs and rabbits by ring hydroxylation and deamination.     

Glutaminase II Pathway in Human Kidney

THE principal mechanism whereby excess hydrogen ions are excreted in man is by renal production of ammonia and subsequent urinary excretion as ammonium. The major and direct source of this renal ammoniagenesis is glutamine¹. Two distinct metabolic pathways of glutamine metabolism have been demonstrated in rat, guinea-pig and dog. The intramitochondrial glutaminase I isoenzymes which hydrolyse glutamine to ammonia and glutamic acid and its subsequent deamidation to ammonia and 2-oxo-glutarate constitute the major metabolic route in the rat². The extramitochondrial glutamine-aminotransferase-ω-amidase pathway (glutaminase II), however, has been shown to be important in the dog³. In man, whereas the glutaminase I pathway has been demonstrated⁴ there is no direct evidence for the latter metabolic pathway. We investigated this metabolic pathway using the alkyl substituted glutamine, L-γ-glutamylmethylamide. In contrast to glutamine, this substituted compound on deamidation yields methylamine⁵.     

N G,N G -Dimethyl-l-arginine,a dominant precursor of endogenous dimethylamine in rats

Summary The metabolic significance ofN ^G ,N ^G -dimethyl-l-arginine (DMA) as a precursor of endogenous dimethylamine (DMN) in rats was examined in connection with the wide distribution and active operation of dimethylargininase (EC3.5.3.18) in rat tissues (Kimoto et al., 1993). When [methyl-¹⁴C]DMA was administered intraperitoneally to rats, the radioactive DMN was detected in various tissues as a major radioactive metabolite one hour after injection, and about 65% of the radioactivity administered was recovered in the first 12-h urine as DMN. In the case of the [¹⁴C] DMN-injected rats, almost all the radioactivity was excreted in the 12-h urine as DMN, except for a negligible amount of radioactivity found in urea. The time-dependent decrease in the specific radioactivity of DMA and DMN in urine showed that dimethylargininase was significantly involved in thein vivo formation of DMN by the hydrolytic cleavage of DMA released from methylated proteins and that DMA is a dominant precursor of endogenous DMN in rats.     

Metabolic Fate of Sarcosyl-14C-glycine in Normal Young Rats

The metabolic fate of the non-physiological synthetic dipeptide, sarcosyl-[2-¹⁴C]glycine, was investigated in normal young rats in vivo and in vitro compared to that of seryl-[2-¹⁴C]glycine as a typical example of common physiological dipeptides. The radioactive dipeptides were synthesized from sarcosine or L-serine and [2-¹⁴C]glycine in our laboratory. When radioactive sarcosylglycine was given intraperitoneally, about 30% of the dose was excreted in the urine, and more than 90% of the urinary radioactivity was present in the sarcosylglycine fraction. The recovery of radioactivity in the the expired carbon dioxide and body protein was 8 and 50% of the dose, respectively, during a 24-h period. When the labeled serylglycine was given, the recovery of radioactivity in the urine was 8% of the dose, and 15% in the expired carbon dioxide. In slices of the kidney, liver and small intestine from normal rats, serylglycine was rapidly and almost completely hydrolyzed, and a large amount of free glycine was released. However, sarcosylglycine was hardly hydrolyzed to the corresponding amino acids in the liver and small intestine, and only slightly in the kidney. These results suggest that a considerable amount of sarcosylglycine given intraperitoneally was rapidly excreted into the urine of normal young rats, reflecting less sensitivity to hydrolysis by tissue peptidase(s) when compared to serylglycine.     

The metabolism of benzyl isothiocyanate and its cysteine conjugate.

1. The corresponding cysteine conjugate was formed when the GSH (reduced glutathione) or cysteinylglycine conjugates of benzyl isothiocyanate were incubated with rat liver or kidney homogenates. When the cysteine conjugate of benzyl isothiocyanate was similarly incubated in the presence of acetyl-CoA, the corresponding N-acetylcysteine conjugate (mercapturic acid) was formed. 2. The non-enzymic reaction of GSH with benzyl isothiocyanate was rapid and was catalysed by rat liver cytosol. 3. The mercapturic acid was excreted in the urine of rats dosed with benzyl isothiocyanate or its GSH, cysteinyl-glycine or cysteine conjugate, and was isolated as the dicyclohexylamine salt. 4. An oral dose of the cysteine conjugate of [14C]benzyl isothiocyanate was rapidly absorbed and excreted by rats and dogs. After 3 days, rats had excreted a mean of 92.4 and 5.6% of the dose in the urine and faeces respectively, and dogs had excreted a mean of 86.3 and 13.2% respectively. 5. After an oral dose of the cystein conjugate of [C]benzyl isothiocyanate, the major 14C-labelled metabolite in rat urine was the corresponding mercapturic acid (62% of the dose), whereas in dog urine it was hippuric acid (40% of the dose). 5. Mercapturic acid biosynthesis may be an important route of metabolism of certain isothiocyanates in some mammalian species.     

Some metabolites of 1-bromobutane in the rabbit and the rat

1. Rabbits and rats dosed with 1-bromobutane excrete in urine, in addition to butylmercapturic acid, (2-hydroxybutyl)mercapturic acid, (3-hydroxybutyl)mercapturic acid and 3-(butylthio)lactic acid. 2. Although both species excrete both the hydroxybutylmercapturic acids, only traces of the 2-isomer are excreted by the rabbit. The 3-isomer has been isolated from rabbit urine as the dicyclohexylammonium salt. 3. 3-(Butylthio)lactic acid is formed more readily in the rabbit; only traces are excreted by the rat. 4. Traces of the sulphoxide of butylmercapturic acid have been found in rat urine but not in rabbit urine. 5. In the rabbit about 14% and in the rat about 22% of the dose of 1-bromobutane is excreted in the form of the hydroxymercapturic acids. 6. Slices of rat liver incubated with S-butylcysteine or butylmercapturic acid form both (2-hydroxybutyl)mercapturic acid and (3-hydroxybutyl)mercapturic acid, but only the 3-hydroxy acid is formed by slices of rabbit liver. 7. S-Butylglutathione, S-butylcysteinylglycine and S-butylcysteine are excreted in bile by rats dosed with 1-bromobutane. 8. Rabbits and rats dosed with 1,2-epoxybutane excrete (2-hydroxybutyl)mercapturic acid to the extent of about 4% and 11% of the dose respectively. 9. The following have been synthesized: N-acetyl-S-(2-hydroxybutyl)-l-cysteine [(2-hydroxybutyl)mercapturic acid] and N-acetyl-S-(3-hydroxybutyl)-l-cysteine [(3-hydroxybutyl)mercapturic acid] isolated as dicyclohexylammonium salts, N-toluene-p-sulphonyl-S-(2-hydroxybutyl)-l-cysteine, S-butylglutathione and N-acetyl-S-butylcysteinyl-glycine ethyl ester.     

The metabolism of dipotassium 2-hydroxy-5-nitrophenyl [S]sulphate, a substrate for lysosomal arylsulphatases A and B

The metabolic fate of dipotassium 2-hydroxy-5-nitrophenyl [³⁵S]sulphate ([³⁵S]NCS), a chromogenic substrate for lysosomal arylsulphatases A and B, has been studied in rats. Intraperitoneal injection of [³⁵S]NCS into free-ranging animals is followed by excretion of the bulk of the radioactivity in the urine within 24hr., less than 13% being eliminated as inorganic [³⁵S]sulphate. Most of the urinary radioactivity can be accounted for as [³⁵S]NCS, but small amounts of a labelled metabolite are also present. Experiments in which [³⁵S]NCS was injected intravenously into anaesthetized rats with bile-duct and bladder cannulae confirm that the ester is rapidly excreted in the urine. However, small amounts of radioactivity appear in bile, mainly in the form of the metabolite detected in urine. When [³⁵S]NCS is perfused through the isolated rat liver, about 35% of the dose is hydrolysed within 3hr. Similar results are obtained if [³⁵S]NCS is injected into anaesthetized rats in which kidney function has been eliminated by ligature of the renal pedicles. The labelled metabolite has been isolated from bile obtained by perfusing several rat livers with blood containing a total of 100mg. of [³⁵S]NCS. It has been identified as 2-β-glucuronosido-5-nitrophenyl [³⁵S]sulphate. The implications of the various findings are discussed. The Appendix describes the preparation of [³⁵S]NCS.     

Metabolism of [14C]methamphetamine in man, the guinea pig and the rat

1. The metabolites of (+/-)-2-methylamino-1-phenyl[1-(14)C]propane ([(14)C]methamphetamine) in urine were examined in man, rat and guinea pig. 2. In two male human subjects receiving the drug orally (20mg per person) about 90% of the (14)C was excreted in the urine in 4 days. The urine of the first day was examined for metabolites, and the main metabolites were the unchanged drug (22% of the dose) and 4-hydroxymethamphetamine (15%). Minor metabolites were hippuric acid, norephedrine, 4-hydroxyamphetamine, 4-hydroxynorephedrine and an acid-labile precursor of benzyl methyl ketone. 3. In the rat some 82% of the dose of (14)C (45mg/kg) was excreted in the urine and 2-3% in the faeces in 3-4 days. In 2 days the main metabolites in the urine were 4-hydroxymethamphetamine (31% of dose), 4-hydroxynorephedrine (16%) and unchanged drug (11%). Minor metabolites were amphetamine, 4-hydroxyamphetamine and benzoic acid. 4. The guinea pig was injected intraperitoneally with the drug at two doses, 10 and 45mg/kg. In both cases nearly 90% of the (14)C was excreted, mainly in the urine after the lower dose, but in the urine (69%) and faeces (18%) after the higher dose. The main metabolites in the guinea pig were benzoic acid and its conjugates. Minor metabolites were unchanged drug, amphetamine, norephedrine, an acid-labile precursor of benzyl methyl ketone and an unknown weakly acidic metabolite. The output of norephedrine was dose-dependent, being about 19% on the higher dose and about 1% on the lower dose. 5. Marked species differences in the metabolism of methamphetamine were observed. The main reaction in the rat was aromatic hydroxylation, in the guinea pig demethylation and deamination, whereas in man much of the drug, possibly one-half, was excreted unchanged.