Effect of cyclic AMP-dependent phosphorylation on the reactivity of sulphydryl groups in cardiac sarcoplasmic reticulum.

1. The metabolism of 4-ethynylbiphenyl has been studied in vitro with subcellular fractions of normal and induced rat liver, and rat intestinal microflora (caecal contents). 2. Oxidation was NADPH-dependent, was inhibited by CO and stimulated by pretreatment with phenobarbitone or 3-methylcholanthrene. 3. Oxidation of the ethynyl group occurred in washed microsomal preparations, but not significantly in soluble fractions. Oxidation of the ethynyl group by a microsomal fraction preceded aromatic hydroxylation and no metabolites containing the intact ethynyl group were detected. 4. The major metabolite in liver fractions was biphenyl-4-ylacetic acid. This was the only product produced by a modified Udenfriend system. 5. Metabolism of 4-ethynylbiphenyl by rat caecal contents under anaerobic conditions produced very small amounts of 4-vinylbiphenyl. 6. In a modified Ames test with Salmonella typhimurium TA98, 4-ethynylbiphenyl gave a weak positive result that was doubled after 'activation' with an induced rat S9 fraction.     

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.     

Structure and species as factors affecting the metabolism of some methoxy-6-sulphanilamidopyrimidines

1. A comparative study was made in man, rhesus monkey, rat and rabbit of the urinary excretion of 2-, 4- and 5-methoxy- and 2,4-, 2,5- and 4,5-dimethoxy-6-sulphanilamidopyrimidines given orally. 2. In the rabbit, 70-80% of the dose of each drug was excreted in 2 days, mainly as N(4)-acetyl derivatives, except 2,5-dimethoxy-6-sulphanilamidopyrimidine, which was mainly excreted unchanged. 3. In the rat, 50-70% of the dose of each drug was excreted in 2 days, except the 2-methoxy and 2,4-dimethoxy compounds, whose excretion was about 30%. The N(4)-acetyl derivatives accounted for 20-70% of the drugs excreted, except the 2,5-dimethoxy derivative, which was excreted unchanged. 4. In the rhesus monkey, some 40-60% of the dose of the 2-methoxy, 2,4-dimethoxy and 2,5-dimethoxy compounds was excreted in 2 days, but the 4-methoxy, 5-methoxy and 4,5-dimethoxy compounds were excreted at less than half this rate. The 4-methoxy, 5-methoxy and 4,5-dimethoxy compounds were highly acetylated (80-90%) whereas the 2-methoxy compound was poorly acetylated (17%) and the 2,5-dimethoxy compound hardly at all. The major metabolite of the 2,4-dimethoxy compound in the monkey was the N(1)-glucuronide. 5. In man, 30% of the dose of the 4-methoxy and 2,4-dimethoxy compounds was excreted in 24 hr., whereas the 4,5-dimethoxy compound (Fanasil) was very slowly excreted (12% in 2 days). The 4-methoxy compound was well acetylated (65%), but the 2,4- and 4,5-dimethoxy compounds were not (20-30%). The main metabolite of the 2,4-dimethoxy compound in man was the N(1)-glucuronide. 6. N(1)-Glucuronide formation occurred extensively only with the 2,4-dimethoxy compound and only in man and the rhesus monkey. It did not occur in the rabbit and only to a minor extent in the rat. 7. The 2,5-dimethoxy compound was not significantly acetylated in vivo in the rabbit, rat or monkey, but acetylation occurred in vitro in rabbit or monkey liver homogenates. 8. These findings are discussed.     

Species differences in the metabolism of norephedrine in man, rabbit and rat

1. (+/-)-2-Amino-1-phenyl[1-(14)C]propan-1-ol ([(14)C]norephedrine) was administered orally to man, rat and rabbit and the metabolites excreted in the urine were identified and measured. Pronounced species differences in the metabolism of the drug were found. 2. Three male human subjects, receiving 25mg each of [(14)C]norephedrine hydrochloride, excreted over 90% of the (14)C in the first day. The main metabolite was the unchanged drug (86% of the dose) and minor metabolites were hippuric acid and 4-hydroxynorephedrine. 3. In rats given 12mg of the drug/kg almost 80% of the (14)C administered was excreted in the first day. The major metabolites in the urine were the unchanged drug (48% of the dose), 4-hydroxynorephedrine (28%) and trace amounts of side-chain degradation products. 4. Rabbits given 12mg of the drug/kg excreted 85-95% of the dose of (14)C in the urine in the first 24h after dosing. The major metabolites in the urine were conjugates of 1,2-dihydroxy-1-phenylpropane (31% of the dose) and of 1-hydroxy-1-phenylpropan-2-one (27%) and hippuric acid (20%). The unchanged drug was excreted in relatively small amounts (8%).     

Demonstration of a new mammalian isoleucine catabolic pathway yielding an Rseries of metabolites.

1. Normal human urine contains small amounts (less than 4 mg/g of creatinine) of 2-ethylhydracrylic acid, formed, we believe, by a previously undisclosed endogenous catabolic pathway for the oxidation of a newly described series of R metabolites of isoleucine. 2. Urinary excretion of 2-ethylhydracrylic acid is variably increased in defects of isoleucine oxidation at distal steps in the catabolic pathway (3-oxoacyl-CoA thiolase deficiency and methylmalonyl-CoA mutase deficiency) and is diminished when proximal steps of the oxidative pathway are blocked as in branched-chain oxo acid decarboxylase deficiency ('maple-syrup-urine' disease). 3. Precursors of R-pathway metabolites [R(-)-2-methylbutyrate and 2-ethylacrylate ] lead to increased 2-ethylhydracrylate excretion in the mammal(rat, rabbit and dog); the corresponding S metabolites [S(+)-2-methylbutyric acid and tiglic acid ], when given in equimolar amounts, have little effect on its excretion, suggesting that little or no interconversion between S and R metabolites occurs in vivo. 4. Studies with 2H-labelled precursors indicate that conversion of R 2-methylbutyrate into 2-ethylhydracrylic acid occurs by a direct pathway (apparently via 2-ethylacrylic acid). 5. The further oxidation of 2-ethylhydracrylic acid to ethylmalonic acid was demonstrated, and may be analogous to S-metabolite oxidation via methyl malonate. 6. Valine metabolites do not interact with the R=isoleucine pathway under the conditions of these experiments in vivo.     

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.     

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.     

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

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

Studies on anabolic steroids--8. GC/MS characterization of unusual seco acidic metabolites of oxymetholone in human urine.

One of the biotransformation routes of oxymetholone (17 beta-hydroxy-2-hydroxymethylene-17 alpha-methyl-5 alpha-androstan-3-one) in man leads to the formation of 17 beta-hydroxy-17 alpha-methyl-5 alpha-androstan-3-one (mestanolone). To demonstrate that this latter steroid may be formed by decarboxylation of an intermediate metabolite of oxymetholone bearing a 2-carboxylic group, we studied the urinary excretion of oxymetholone acidic metabolites. Five new acidic metabolites are reported here for the first time, among which four are unusual seco steroids resulting from the oxidative cleavage of the A-ring. The most abundant compound is 17 beta-hydroxy-17 alpha-methyl-2,3-seco-5 alpha-androstane-2,3-dioic acid 1, the cumulative excretion of which accounted for 1.52% of the dose. Three other seco diacids were produced in smaller amounts, namely 17 beta-hydroxy-17 alpha-methyl-2,3-seco-5 alpha-androstane-2,4- dicarboxylic acid 3, 17 beta-hydroxy-17 alpha-methyl-1,3-seco-5 alpha-androstane-1,3-dioic acid 4 and 17 beta-hydroxy-17 alpha-methyl-2,4-seco-5 alpha-androstane-2,4-dioic acid 5. The fifth acidic metabolite was identified as 3 alpha, 17 beta-dihydroxy-17 alpha-methyl-5 alpha-androstane-2 beta-carboxylic acid 2. The excretion in urine of these acidic metabolites suggests that the 2-hydroxymethylene group in oxymetholone is readily oxidized to yield the corresponding beta-keto acid which can be (1) decarboxylated to form mestanolone; (2) reduced at C-3 to give compound 2; and (3) further oxidized to afford the unexpected seco diacids 1, 3, 4 and 5. The identity of compounds 1 and 2 was ascertained by GC/MS and 1H and 13C-NMR analysis of reference compounds. The other metabolites were characterized by GC/MS analysis.     

The metabolism of 3,5-di-tert.-butyl-4-hydroxytoluene in the rat and in man

1. The major metabolites of 3,5-di-tert.-butyl-4-hydroxytoluene (BHT) in the rat are 3,5-di-tert.-butyl-4-hydroxybenzoic acid (BHT-acid), both free (9% of the dose) and as a glucuronide (15%), and S-(3,5-di-tert.-butyl-4-hydroxybenzyl)-N-acetylcysteine. 2. The mercapturic acid does not appear to derive from the usually accepted enzyme mechanism, and may involve a non-enzymic reaction between BHT free radical and cysteine. 3. The ester glucuronide and mercapturic acid found in rat urine are also the major metabolites in rat bile and must be responsible for the enterohepatic circulation. 4. Free BHT-acid is the main component in rat faeces. 5. In man, BHT-acid, free and conjugated, is a minor component in urine, and the mercapturic acid is virtually absent. The bulk of the radioactivity is excreted as the ether-insoluble glucuronide of a metabolite in which the ring methyl group and one tert.-butyl methyl group are oxidized to carboxyl groups, and a methyl group on the other tert.-butyl group is also oxidized, probably to an aldehyde group. 6. These differences in metabolism by the rat and by man are sufficient to account for the difference in excretion by the two species.     

Biliary excretion of some diquaternary ammonium cations in the rat, guinea pig and rabbit

1. The extent of the excretion in the bile and urine of the (14)C-labelled dications, diquat, paraquat, morfamquat, decamethonium and dimethyltubocurarine in bile-duct-cannulated rats, guinea pigs and rabbits was examined. 2. These compounds were excreted unchanged in bile and urine, except diquat, which was metabolized to a significant extent (18% of the dose) in the rabbit only. 3. The extent of the biliary excretion of diquat (mol wt. of ion 184), paraquat (186), decamethonium (258) and morfamquat (469) was less than 10% of the dose in the three species, whereas that of dimethlytubocurarine (653) was greater than 10% in the rat and rabbit but not in the guinea pig. 4. These results together with data from the literature suggest that the molecular weight at which the excretion of dications in the bile exceeds 10% of the dose is in the region of 500-600, which differs from the values for monocations (Hughes et al., 1973) and anions (Millburn et al., 1967; Hirom et al., 1972).     

Metabolism of [6]-gingerol in rats

The metabolic fate of [6]-gingerol, one of the active constituents of Zingiber officinale Roscoe, was investigated using rats. The bile of rats orally administered [6]-gingerol was shown to contain a major metabolite (1) by HPLC analysis. Although the metabolites derived from [6]-gingerol were not detected in the urine, the ethyl acetate extract of the urine after enzymatic hydrolysis was shown to contain six minor metabolites (2-7). Their structures were determined to be (S)-[6]-gingerol-4'-O-beta-glucuronide (1), vanillic acid (2), ferulic acid (3), (S)-(+)-4-hydroxy-6-oxo-8-(4-hydroxy-3-methoxyphenyl) octanoic acid (4), 4-(4-hydroxy-3-methoxyphenyl)butanoic acid (5), 9-hydroxy [6]-gingerol (6) and (S)-(+)-[6]-gingerol (7) based on spectroscopic and chemical data. The total cumulative amount of 1 excreted in the bile and 2-7 in the urine during 60 h after the oral administration of [6]-gingerol were approximately 48% and 16% of the dose, respectively. The excretion of 2-7 in the urine decreased after gut sterilization. On the other hand, the incubations of [6]-gingerol with rat liver showed the presence of 9-hydroxy [6]-gingerol, gingerdiol (8), and (S)-[6]-gingerol-4'-O-beta-glucuronide (1). These findings suggest that the gut flora and enzymes in the liver play an important part in the metabolism of [6]-gingerol.     

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.     

Metabolic profiles of endogenous and ethynyl steroids in plasma and urine from women during administration of oral contraceptives

Conjugated ethynyl and endogenous steroids in plasma and urine from two women taking an oral contraceptive (Conlumin) containing 1 mg norethindrone and 50 micrograms mestranol have been analyzed by methods based on anion and ligand exchange chromatography and gas chromatography-mass spectrometry. Conjugated norethindrone and its reduced metabolites with 3 alpha,5 alpha, 3 alpha,5 beta, 3 beta,5 beta and 3 beta,5 alpha configurations were identified in the fluids. The quantitatively major metabolites in plasma were a disulphate of the 3 alpha,5 alpha isomer and a monosulphate of the 3 alpha,5 beta isomer. The renal clearance of the former compound was low. The major urinary metabolite of norethindrone was the 3 alpha,5 beta isomer conjugated with glucuronic or sulphuric acid. Disulphates constituted only a small portion of urinary ethynyl steroids. Metabolic profiles of endogenous neutral steroids in plasma and urine during the contraceptive cycle were compared with profiles during a physiological menstrual cycle. The concentrations of steroids in plasma during contraception were similar to those during the follicular and mid phases of the menstrual cycle, whereas levels of progesterone metabolites were higher in the luteal phase. The urinary excretion of steroids was 15-30% lower during the contraceptive cycle, due to a decrease in excretion of C21O5 steroids, 11-oxygenated androgens and etiocholanolone. The increase of urinary progesterone metabolites seen during the luteal phase was not observed during contraception, but the excretion of 5 beta-pregnane-3 alpha,20 alpha-diol glucuronide was higher than during the follicular and mid phases of the menstrual cycle.     

Metabolism of N-(3′,5′-Dichlorophenyl)succinimide in Rats and Dogs

When N-(3′,5′-dichlorophenyl)succinimide (DSI)-carbonyI-¹⁴C and –pheny-³H were each orally administered to rats, regardless of the label site, most of the dose was readily eliminated. There was no difference in the excretion rate between male and female rats. No radioactive residues were detected in tissues and organs 24 hr after dosing. Urinary metabolites consisted of N-(3′,5′-dichlorophenyl) succinamic acid (DSA), N-(3′,5′-dichlorophe-nyl) malonamic acid (DMA), N-(3′5’-dichlorophenyl)-2-hydroxysuccinamic acid (2-OH-DSA) and 2-OH-DSA derivatives. In dogs, most of the administered dose was excreted in equal amounts in urine and feces. 2-OH-DSA derivatives were main urinary metabolites and most of fecal radiocarbon was due to intact DSL. The results of this study indicate that DSI is a biodegradable compound which is unlikely to leave any persistent residues in animals.

The degradation of DSI to DSA was mediated by an arylamidase-type hydrolase, which was present in the microsomal fraction of rabbit liver. The enzyme activity was found in livers and kidneys of four animal species tested. Depending on the animal species, the enzyme appears to be important for the metabolism of DSI.     

Metabolism of myricetin and related compounds in the rat. Metabolite formation in vivo and by the intestinal microflora in vitro

1. The metabolism of a group of polyphenols related in structure to myricetin (3,5,7,3',4',5'-hexahydroxyflavone), including myricetin, myricitrin, 3,4,5-trihydroxyphenylacetic acid, delphinidin, robinetin, tricetin, tricin, malvin and 5,7-dihydroxy-3',4',5'-trimethoxyflavone, has been studied both in vivo after oral administration to the rat and in vitro in cultures of micro-organisms derived from the intestine of the rat. 2. It was shown that the rat intestinal microflora are able to degrade compounds of this group to the ring-fission products observed in urine after oral administration of the specific flavonoid. 3. All flavones and flavonols possessing free 5- and 7-hydroxyl groups in the A ring and a free 4'-hydroxyl group in the B ring gave rise to ring-fission products that included 3',5'-dihydroxyphenylacyl derivatives. 4. The metabolites 3,5-dihydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, 3,5-dihydroxyphenylpropionic acid and 3-hydroxyphenylpropionic acid were isolated and identified by chromatographic and spectral methods. 5. On anaerobic incubation in a thioglycollate medium it was shown that intestinal micro-organisms can effect cleavage of glycosidic bonds, ring fission of certain flavonoid molecules showing 3',4',5'-trihydroxyphenyl substitution and dehydroxylation of certain flavonoid metabolites. 6. The urinary excretion of the metabolites 3,5-dihydroxyphenylacetic acid and 3-hydroxyphenylacetic acid was completely abolished when neomycin-treated rats were used.     

Inhibition of rat liver tryptophan pyrrolase activity and elevation of brain tryptophan concentration by administration of DL-alpha-amino-beta-pyridinepropanoic acid (pyridylalanine) analogs

Single doses of DL-alpha-amino-beta-(2-pyridine)propanoic acid (2-PA, 100 mg/kg) significantly decreased the holoenzyme and apoenzyme activities of rat liver tryptophan pyrrolase (TP) and increased brain tryptophan, serotonin (5-HT) and 5-hydroxyindole-3-ylacetic acid concentrations. 2-PA had no inhibitory effect on either of the enzyme activities in vitro, but its expected metabolites were effective. Single doses of DL-alpha-amino-beta-(3-pyridine)propanoic acid (3-PA, 100 mg/kg) decreased only the holoenzyme activity and elevated brain tryptophan and its metabolites levels in rats. 3-PA and its metabolite, 3-pyridylpyruvate, inhibited only the holoenzyme activity in vitro. DL-alpha-Amino-beta-(4-pyridine)propanoic acid (4-PA) caused significant changes in liver TP (holo- and apoenzyme forms) activity and brain tryptophan concentration only after repeated administration (100 mg/kg/day). 4-PA was a weak inhibitor of the holoenzyme, but its metabolites apparently inhibited the holo- and apoenzyme activities in vitro. These findings suggest that PA analogs (and/or their metabolites) increased brain tryptophan (and hence 5-HT synthesis) by directly inhibiting liver TP activity.     

Urinary excretion of hydroxycinnamates and flavonoids after oral and intravenous administration.

The urinary recoveries of the hydroxycinnamates, ferulic acid (3-methoxy, 4-hydroxy cinnamic acid), and chlorogenic acid (the quinic acid ester of 3,4-dihydroxycinnamic acid), and three structurally related flavonoids were studied in the rat. For the latter, the aglycone quercetin was compared with its 3-glucoside (isoquercitrin) and 3-rhamnoglucoside (rutin). Doses of 50 mg/kg were administered via the oral and intravenous routes and urine collected over the subsequent 24-h period. Reverse phase HPLC with photo-diode array detection was used to analyze the unchanged compound and their metabolites excreted in the urine. Ferulic acid and isoquercitrin were orally absorbed (5.4 and 0.48% of administered dose, respectively) and are therefore bioavailable. In contrast, neither unchanged chlorogenic acid, rutin, quercetin, nor the conjugated metabolites in the form of glucuronide or sulphate were detected in the urine after oral dosing. All the flavonoids studied produced low total urinary recoveries after intravenous administration, 9.2% for quercetin-3-rhamnoglucoside, 6.7% for the 3-glucoside, and 2.4% for the aglycone, indicating that extensive metabolism to low molecular weight compounds or excretion via other routes may be occurring. Overall it can be stated that renal excretion is not a major pathway of elimination for intact flavonoids and hydroxycinnamates in the rat.     

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.     

In vivo metabolism of 4'-deoxypyridoxine in rat and man.

In rats 80 to 95% of 4'-deoxypyridoxine administered intraperitoneally, intravenously, intramuscularly, or subcutaneously was excreted in the urine within 7.5 hours. Orally administered deoxypyridoxine was also rapidly eliminated. Over one-half of the excreted material appeared as deoxypyridoxine-3-(hydrogen sulfate) and the remainder as unchanged deoxypyridoxine. Tissue concentrations of deoxypyridoxine 5'phosphate were comparable to those of pyridoxal 5'phosphate. In normal men about 50% of a single oral dose (3 to 7.5 mg/kg of body weight) appeared in the urine within 6 hours. 4'Deoxy-5-pyridoxic acid accounted for 50 to 100% of the excreted material. The remainder was unchanged deoxypyridoxine. No deoxypyridoxine-3-(hydrogen sulfate) was detected in human urine and no 4'-deoxy-5-pyridoxic acid was found in rat urine. Deoxypyridoxine 5'-phosphate was not detected in the urine of either species. The complexity of deoxypyridoxine metabolism indicated by these data suggests the use of caution in extrapolating data obtained with deoxypyridoxine to B6 metabolism in the absence of deoxypyridoxine, and particularly in extrapolating results from the rat to man. Synthesis for 4'-deoxypyridoxine-3-(ethyl carbonate), 4'-deoxypyridoxine 5'-acetate, 4'-deoxy-3-0-(2-sulfoethyl)-pyridoxine, and the metabolites are presented. These synthesis were facilitated by using ethylchloroformate conjugates and N-methylpiperazine hydrolysis to block and unblock the phenol group.