In vivo metabolism of leukotriene C4 in germ-free and conventional rats. Fecal excretion of N-acetylleukotriene E4

[5,6,8,9,11,12,14,15-3H8]Leukotriene C4 was subcutaneously injected into rats. Substantial amounts of the administered radioactivity were excreted in feces of germ-free and conventional animals during a 72-h period (78 and 64%, respectively). Analyses of fecal extracts by high performance liquid chromatography showed eight radioactive components for each type of animal. One metabolite amounted to 4.6% of the injected radioactivity in germ-free and 0.6% in conventional rats. Its chemical structure, 5-hydoxy-6-S-(2-acetamido-3-thiopropionyl)-7,9-trans-11,14-c is-eicosatetraenoi c acid (N-acetylleukotriene E4) was determined by ultraviolet spectroscopy, fast atom bombardment mass spectrometry, chemical and enzymatic transformations, and confirmed by chemical synthesis. Another metabolite (2.7% of the administered radioactivity in germ-free and 0.5% in conventional rats) was characterized as the 11-trans isomer of the former metabolite. The pathway of formation of these compounds appears to be analogous to the pathway of mercapturic acid biosynthesis.     

The metabolism of tetralin

1. [1-(14)C]Tetralin was synthesized and fed to rabbits. 2. Of the radioactivity, 87-90% was excreted in the urine within two days and 0.5-3.7% on the third day. The faeces contained 0.6-1.8%. No radioactivity was found in the breath and negligible amounts were retained in the tissues. About 90-99% of an administered dose was accounted for. 3. The main metabolite in the urine was the glucuronide of alpha-tetralol (52.4%). Other conjugated metabolites were beta-tetralol (25.3%), 4-hydroxy-alpha-tetralone (6.1%), cis-tetralin-1,2-diol (0.4%) and trans-tetralin-1,2-diol (0.6%). 4. beta-Tetralone, alpha-naphthol, 1,2-dihydronaphthalene and naphthalene, previously reported as metabolites, are artifacts, and tetralin, alpha-tetralone, beta-naphthol, 5-hydroxytetralin, and 6-hydroxytetralin are not metabolites. 5. The major metabolite of tetralin, alpha-tetralol and alpha-tetralone is the glucuronide of alpha-tetralol, which was isolated as methyl (1,2,3,4-tetrahydro-1-naphthyl tri-O-acetyl-beta-d-glucosid)uronate; the major metabolite of beta-tetralol and beta-tetralone is the glucuronide of beta-tetralol, which was characterized as methyl (1,2,3,4-tetrahydro-2-naphthyl tri-O-acetyl-beta-d-glucosid)uronate. 5-Hydroxytetralin is conjugated with glucuronic acid, and was characterized as methyl (5,6,7,8-tetrahydro-1-naphthyl tri-O-acetyl-beta-d-glucosid)uronate. 6-Hydroxytetralin is conjugated with glucuronic acid, and was characterized as methyl (5,6,7,8-tetrahydro-2-naphthyl tri-O-acetyl-beta-d-glucosid)uronate. 6. A metabolic sequence accounting for the observed biological transformation products is proposed.     

Analysis of the metabolites of the sodium salt of 6-hydroxy-5-(phenylazo)-2-naphthalenesulfonic acid in Sprague–Dawley rat urine

The sodium salt of 6-hydroxy-5-(phenylazo)-2-naphthalenesulfonic acid (SS-AN), which is a subsidiary color present in Food Yellow No. 5 [Sunset Yellow FCF, disodium salt of 6-hydroxy-5-(4-sulfophenylazo)-2-naphthalenesulfonic acid], was orally administered to Sprague–Dawley rats. Metabolite A, metabolite B, and unaltered SS-AN were detected as colored metabolites in the rat urine. Analysis of the chemical structures showed that metabolite A (major peak) was 6-hydroxy-5-(4-sulfooxyphenylazo)-2-naphthalenesulfonic acid, the sulfuric acid conjugate of SS-AN, and metabolite B (minor peak) was 6-hydroxy-5-(4-hydroxyphenylazo)-2-naphthalenesulfonic acid (SS-PAP), which is a derivative of metabolite A without the sulfuric acid. The colorless metabolites p-aminophenol, o-aminophenol, and aniline present in the urine were analyzed by liquid chromatography–mass spectrometry. The orally administered SS-AN had been metabolized to the colorless metabolites (p-aminophenol 45.3%, o-aminophenol 9.4%, aniline 0.4%) in the 24-h urine samples. Analysis of the colored metabolites by high-performance liquid chromatography with detection at 482 nm indicated the presence of metabolite A (0.29%), SS-PAP (0.01%), and SS-AN (0.02%) were detected in the 24-h urine samples. Approximately 56% of SS-AN was excreted into the urine and the rest is probably excreted into feces.     

Studies on the positional integrity of glyceride fatty acids during digestion and absorption in rats

1. Rats previously starved for 24hr. were separately given by intraduodenal injections 0.5ml. of a dispersion containing 10mg. of sodium taurocholate, with 50mg. of glycerol 1,3-dioleate 2[1-(14)C]-palmitate, glycerol 1,2-dioleate 3[1-(14)C]-palmitate, a mixture of [1-(14)C]palmitic acid and triolein, or a mixture of [1-(14)C]-palmitic acid and oleic acid. 2. At the end of 30min., the net amounts, and the radioactivity, of the neutral-lipid components recovered from the intestinal lumen and mucosa, and the position of the labelled palmitic acid in the mucosal triglycerides, were determined. 3. When glycerol 1,3-dioleate 2[1-(14)C]-palmitate was administered, most of the labelled acid was retained in the di- and monoglycerides of the lumen; the triglycerides were the major components containing the radioactivity in the mucosa and 75-80% of the labelled acid was located at the beta-position of these triglycerides. 4. When glycerol 1,2-dioleate 3[1-(14)C]-palmitate was administered, the labelled acid was readily split off in the lumen and virtually no radioactivity could be traced in the monoglyceride fraction; in the intestinal mucosa, triglycerides were again the chief components containing most of the radioactivity, and 80-85% of the labelled acid was esterified at the outer positions of the glycerol. 5. When [1-(14)C]palmitic acid mixed with triolein was administered, the concentrations of free fatty acids increased markedly in the intestinal lumen and mucosa, and 80-88% of the radioactivity of the mucosal triglycerides was located at the outer positions of the glycerol. 6. When [1-(14)C]palmitic acid mixed with oleic acid was administered, the labelled acid accumulated in the lumen as well as in the cell, and it was randomly incorporated into all three positions of the mucosal triglycerides.     

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.     

The differential tissue distribution of the citrus flavanone naringenin following gastric instillation

Citrus flavonoids have been investigated for their biological activity, with both anti-inflammatory and -carcinogenic effects being reported. However, little information is known on the bioavailability of these compounds in vivo. The objectives of this study were to determine the tissue distribution of naringenin after gastric gavage of [³H]-naringenin to rats. Unlabelled naringenin was also used to quantify the levels of naringenin and its major metabolites in tissues and eliminated in the urine and faeces. Significant radioactivity was detected in the plasma as well as all tissues examined 2 h post-gavage. After 18 h, higher levels of radioactivity were retained in plasma and tissues (55% of the administered radioactivity). Investigation of the nature of metabolites, using unlabelled naringenin, revealed that the glucuronides were the major components in plasma, tissues and urine, in addition to the colonic metabolite 3-(4-hydroxyphenyl) propionic acid, detected in the urine. The aglycone was the form extensively retained in tissues after 18 h post-gavage. Total identified metabolites detected after 18 h in most tissues were only 1-5% of the levels detected after 2 h. However, the brain, lungs and heart retained 27, 20 and 11%, respectively, relative to the total metabolites detected at 2 h. While radioactive detection suggests increased levels of breakdown products of naringenin after 18 h versus 2 h, the products identified using unlabelled naringenin are not consistent with this, suggesting that a predominant proportion of the naringenin breakdown products at 18 h are retained as smaller decomposition molecules which cannot yet be identified.     

Metabolism of coenzyme Q10: biliary and urinary excretion study in guinea pigs.

Biliary and urinary metabolites were examined after intravenous administration of 14C-coenzyme Q10 (14C-CoQ) to guinea pigs. Cumulative recovery of administered radioactivity for up to 8 hours by bile drainage was 4.8%. The greater part of radioactivity was detected in conjugate form. After hydrolyzing with beta-glucuronidase, aglycone fragments were subjected to methylation and reductive acetylation. The main metabolite was demonstrated to be Q acid-1 1,4-hydroquinone diacetate methyl ester (M-1) on HPLC. Then, the main metabolite was assumed to be glucuronide of 2,3-dimethoxy-5-methyl-6-(3'-methyl-5'-carboxy-2'-pentenyl)-1, 4-benzohydroquinone [Q acid-I hydroquinone]. The cumulative urinary recovery of the administered radioactivity over 48 hours was 8.3%. The labeled samples were treated similarly to bile. The urinary metabolites of CoQ10 consisted of unconjugated and conjugated forms. Lyophilized urine was treated as a bile sample and analyzed. The two major metabolites were assigned to be M-1 and Q acid-II 1,4-hydroquinone diacetate methyl ester (M-2). Then, the two metabolites were assumed to be composed of Q acid-I and 2,3-dimethoxy-5-methyl-6-(3'-carboxypropyl)-1,4-benzoquinone (Q acid-II) in free and corresponding hydroquinone conjugate forms. To investigate the effect of exogenous labeled CoQ10 on unlabeled CoQ10 (endogenous) metabolites in urine, simultaneous quantitative determination was performed using deuterium labeled CoQ10 (CoQ10-d5). Urine collected over a 72-hour period after intravenous administration of CoQ10-d5 was processed similarly to that described above and two derivatized metabolites (M-1 and M-2) were quantified by gas chromatography-mass fragmentography with the multi-ion detection method. The analytical results showed that the addition of exogenous labeled CoQ10 did not influence the metabolism (or breakdown) of unlabeled (endogenous) CoQ10.     

Bile acids. XXXV. Metabolism of 5 -cholestan-3 -ol in the Mongolian gerbil

The principal bile acid of Mongolian gerbil bile is cholic acid, although small amounts of chenodeoxycholic and lesser amounts of deoxycholic acids are identified. Muricholic acids were not found in gerbil bile. The ratio of trihydroxy to dihydroxy bile acids in gerbil bile is approximately 11:1. After administration of [4-(14)C]5alpha-cholestan-3beta-ol to gerbils with bile fistulas, 4-7% of the administered (14)C was recovered in bile and 16% in urine on the first 6 days. Alkaline hydrolysis of the bile afforded the biliary acids which were separated by partition chromatography. The (14)C ratio of trihydroxy to dihydroxy bile acids was 11:1. Allocholic acid was identified as the major acidic biliary metabolite. From analysis of (14)C retained in selected tissues, the adrenal gland appears to be an important site for retention of cholestanol or its metabolites.     

Intestinal absorption and metabolism of retinoyl beta-glucuronide in humans, and of 15-[14C]-retinoyl beta-glucuronide in rats of different vitamin A status

In order to prove the hypothesis that humans and animals with adequate vitamin A status do not absorb and metabolize orally administered all-trans retinoyl β-glucuronide, unlabeled retinoyl glucuronide (0.1 mmol) was orally dosed to fasting well-nourished young men. Neither retinoyl glucuronide nor retinoic acid, a possible metabolite, appeared in the blood within 12 h after ingestion. Next, radiolabeled all-trans 15-[¹⁴C]-retinoyl β-glucuronide was chemically synthesized by a new procedure, and fed orally to rats of different vitamin A status. Analysis of blood and other tissues 5 or 24 h after the dose, showed the presence of radioactivity ( 0.5%) in the blood of vitamin A deficient rats, but not in sufficient rats. Livers of all rats contained small, but detectable amounts (0.3 to 1.1% of the dose) of radioactivity. The accumulation of radioactivity in the liver was highest in deficient rats. Analysis of the retinoids showed that the radioactivity in serum and liver was due to retinoic acid formed from retinoyl glucuronide. Within 24 h after the dose, 31 to 40% of the administered radioactivity was excreted in the feces, and 2 to 4.7% of the dose was excreted in the urine. Results of the present studies show that oral administration of retinoyl β-glucuronide did not give rise to detectable changes in blood retinoyl glucuronide and/or retinoic acid concentrations in humans or rats with adequate vitamin A status.     

The Metabolism of [18F]6-Fluoro-l-3,4-Dihydroxyphenylalanine in the Hooded Rat

The metabolism of the positron-emitting compound [18F]6-fluoro-L-3,4-dihydroxyphenylalanine (*F-DOPA) was studied in carbidopa-pretreated male hooded rats. Thirty minutes following carbidopa administration (5 mg/kg i.p.), animals received *F-DOPA (500 micrograms/kg; specific activity, 175-230 Ci/mol) as an intrajugular bolus. Blood samples were taken at various times between 5 and 90 min, and the plasma was analyzed by HPLC with gamma counting of fractions. *F-DOPA disappeared rapidly from plasma in concert with the formation of the 3-O-methylated metabolite, Me-*F-DOPA. Animals were killed from 5 to 120 min after injection, and the brains were rapidly dissected. The disappearance of *F-DOPA from both vermis and striatal samples was rapid. Me-*F-DOPA, the sole metabolite observed in the vermis, was the major labeled material in the striatum at greater than or equal to 20 min after injection. Fluorodopamine was an important metabolite in the striatum, making up 25% of total radioactivity at early intervals. Striatal samples also contained fluoro-3,4-dihydroxyphenylacetic acid, which constituted approximately 10% of the total radioactivity, and traces of two radiolabeled compounds, tentatively identified as fluorohomovanillic acid and fluoro-3-methoxytyramine.     

Steroid metabolism in the rabbit. Biliary and urinary excretion of metabolites of [4-14C]progesterone

1. [4-(14)C]Progesterone was administered intravenously to anaesthetized male and female New Zealand White rabbits as a single injection or as a 45-60min. infusion. 2. After a single dose about 60% of the radioactivity was recovered in 6hr., and twice as much radioactivity was present in bile as in urine. After infusion total recovery of radioactivity was only about 40% in 6hr., but the relative proportions of metabolites in bile and urine were about the same as after a single dose. 3. Bile and urine samples were hydrolysed successively by beta-glucuronidase, cold acid and hot acid. 4. In bile the major proportion of metabolites appeared in the glucuronide fraction; in urine beta-glucuronidase hydrolysis yielded the greatest amounts of ether-extractable radioactivity, but the greatest proportion of radioactivity could not be extracted by ether from an alkaline solution of the hydrolysed urine. 5. There was no apparent difference in the quantity or distribution of metabolites excreted by male and female animals.     

Hepatic metabolism of short-chain bile acids. Inversion of the 3-hydroxyl group of isoetianic acid (3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acid) by the adult rat

The stereospecificity of mechanisms for hepatic transport of short-chain bile acids has been examined by following the hepatic metabolism and biliary secretion of 3 beta-hydroxy-5 beta-androstane-17 beta-carboxylic acid (isoetianic acid) administered in two different labeled forms to rats prepared with an external biliary fistula. While 93% of the administered [2,2,4,4-3H]isoetianic acid was recovered in bile after 20 h, only 18% of a similar dose of [3 alpha-3H]isoetianic acid was secreted in bile over the same time period. The recovered radioactivity of the latter compound was mainly associated with bile water. With the [2,2,4,4-3H]isoetianic acid, the bulk of the biliary isotope was determined to be in the form of two glucuronide conjugates. Spectral analysis identified these metabolites as the hydroxyl-linked (major) and carboxyl-linked (minor) beta-glucuronides, not of the 3 beta-hydroxy compound administered, but of 3 alpha-hydroxy-5 beta-androstane-17 beta-carboxylic acid (etianic acid), i.e., the products of hydroxyl group inversion. It is concluded that isoetianic acid is efficiently cleared from plasma and conjugated with glucuronic acid after its epimerization to etianic acid. The prevalent, but not complete, loss of the 3-tritium atom and the retention of the 2- and 4-tritium atoms probably indicates a 3-oxo-5 beta-androstane-17 beta-carboxylic acid intermediate with partial return of the label via a limited labeled pool of reduced nicotinamide cofactor.     

In vitro and in vivo synthesis of long-chain fatty acids from (1-14C) acetate in the renal papillae of rats.

1. The relationship between the rate of [1-14C] acetate incorporation into the fatty acids of renal papillary lipids and the acetate concentration in the medium has been measured. 2. [1-14C] acetate was incorporated mainly into fatty acids of phospholipids and triacylglycerols. Only a few per cent of the radioactivity was found in the free fatty acid fraction. 3. The major part of the [1-14C] acetate was found to be incorporated by a chain elongation of prevalent fatty acids. The major component of the poly-unsaturated fatty acids in triacylglycerols and the major product of fatty acid synthesis from [1-14C] acetate in vitro was demonstrated by mass spectrometry to be docosa-7,10,13,16-tetraenoic acid. 4. The radioactivity of docosa-7,10,13,16-tetraenoic acid accounted for 40% of total radioactivity in triacylglycerol fatty acids (lipid droplet fraction) and 20% of total radioactivity in membrane phospholipid fatty acids.     

The Differential Tissue Distribution of the Citrus Flavanone Naringenin Following Gastric Instillation

Citrus flavonoids have been investigated for their biological activity, with both anti-inflammatory and -carcinogenic effects being reported. However, little information is known on the bioavailability of these compounds in vivo. The objectives of this study were to determine the tissue distribution of naringenin after gastric gavage of [³H]-naringenin to rats. Unlabelled naringenin was also used to quantify the levels of naringenin and its major metabolites in tissues and eliminated in the urine and faeces. Significant radioactivity was detected in the plasma as well as all tissues examined 2?h post-gavage. After 18?h, higher levels of radioactivity were retained in plasma and tissues (55% of the administered radioactivity). Investigation of the nature of metabolites, using unlabelled naringenin, revealed that the glucuronides were the major components in plasma, tissues and urine, in addition to the colonic metabolite 3-(4-hydroxyphenyl) propionic acid, detected in the urine. The aglycone was the form extensively retained in tissues after 18?h post-gavage. Total identified metabolites detected after 18?h in most tissues were only 1–5% of the levels detected after 2?h. However, the brain, lungs and heart retained 27, 20 and 11%, respectively, relative to the total metabolites detected at 2?h. While radioactive detection suggests increased levels of breakdown products of naringenin after 18?h versus 2?h, the products identified using unlabelled naringenin are not consistent with this, suggesting that a predominant proportion of the naringenin breakdown products at 18?h are retained as smaller decomposition molecules which cannot yet be identified.     

The metabolism and disposition of 3-methylindole in goats

The metabolism and disposition of 3-methylindole (3MI), a ruminal metabolite of L-tryptophan which causes acute pulmonary edema and emphysema (APE) when administered to cattle, goats, and sheep was investigated. Goats given jugular infusions of [¹⁴C] 3MI excreted 87 to 92% of the infused radioactivity in the urine, 0.4 to 0.9% in expired air, and negligible amounts in the feces over a period of three days. Composite urine samples were fractionated into 10 peaks by ion exchange chromatography, which represented 80% of the urinary radioactivity. A major route of metabolism involved formation of 3-methyloxindole and suggests that a mixed function oxidase (MFO), pyrrolooxygenase, may be the major metabolic system involved. A minor route of metabolism involved oxidation of the methyl carbon of 3MI.     

Release and degradation of neurotensin during perfusion of rat small intestine with lipid

The levels of neurotensin (NT) and its metabolite, the N-terminal octapeptide (NT1-8), identified by HPLC and measured by RIA, were increased in the hepatic-portal circulation of the anesthetized rat during perfusion of the small intestine with a lipid solution, while levels of both peptides remained unchanged in the general circulation. There was no significant arteriovenous difference for NT or NT1-8 during saline perfusion of the small intestine. Plasma collected from the superior mesenteric vein during the infusion of [3H]NT into the superior mesenteric artery showed major peaks of radioactivity with the retention times of NT1-8 and NT1-11 on HPLC. Only 12% of the radioactivity recovered from plasma was intact NT. These studies demonstrate that chromatographically identified NT and its metabolite, NT1-8, are elevated in the portal circulation but not systemic circulation during lipid perfusion and that the small intestine may be both the site of release and metabolism of NT.     

Metabolism of intravenously administered 7 alpha-hydroxycholesterol-3 beta-stearate in the hamster.

In order to investigate the metabolic fate of serum esterified 7 alpha-hydroxycholesterol, [4-14C]7 alpha-hydroxycholesterol-3 beta-stearate was synthesized from labeled cholesterol and administered to bile fistula hamsters intravenously. Bile samples were collected at every 20 min for 7 h. Radioactivity was detected in bile 40 min after the beginning of the infusion of the labeled compound and 56.5 +/- 5.7% (48.7-66.0%) of the administered radioactivity was recovered in bile during 7 h. The liver contained appreciable radioactivity (19.5 +/- 7.6% of the administered dose) at the time of sacrifice. Only a trace amount of radioactivity was detected in urine and blood. Cumulative recovery of the radioactivity was 76.3 +/- 8.6% (63.3-90.4%). Major radioactive metabolites in the bile samples were identified to be taurine- and glycine-conjugated cholic acid and chenodeoxycholic acid by radioactive thin-layer chromatographic analysis of the bile samples before and after enzymatic hydrolysis and 3 alpha-hydroxysteroid dehydrogenase treatment. The conversion was nearly complete and we could not detect neutral metabolites, such as the mother compound, free 7 alpha-hydroxycholesterol and bile alcohols, as well as glucuronidated or sulfated bile acids. It is concluded that serum esterified 7 alpha-hydroxycholesterol could be effectively taken up by the liver, hydrolyzed by cholesterol esterase and metabolized via the normal biosynthetic pathway to taurine- or glycine-conjugated primary bile acids to be excreted into bile.     

Differential Metabolism of Hydroxyeicosatetraenoic Acid Isomers by Mouse Cerebromicrovascular Endothelium

Hydroxyeicosatetraenoic acid (HETE) derivatives of arachidonic acid are produced in the brain and have been implicated as pathologic mediators in various types of brain injury. To understand better their fate in the brain, particularly in cerebral microvessels, several HETEs were incubated with cultured mouse cerebromicrovascular endothelium for 1, 2, and 4 h, followed by HPLC analysis of medium and cellular lipids. 5(S)-, 8(RS)-, and 9(RS)-HETE were not metabolized by the cells, but were extensively incorporated, unmodified, into cell lipids. On the other hand, 11(RS)-, 12(S)-, and 15(S)-HETE were extensively metabolized and only minimally incorporated into cell lipids. Previously, the major 12-HETE metabolite was identified as 8-hydroxyhexadecatrienoic acid. In the present study, we identified the major 11-HETE metabolite as 7-hydroxyhexadecatrienoic acid and the major 15-HETE metabolite as 11-hydroxyhexadecatrienoic acid. omega-3 compounds, 15(S)- and 12(S)-hydroxyeicosapentaenoic acids (HEPE), were also metabolized to more polar compounds, but to a lesser extent than their tetraenoic acid, omega-6 counterparts. Comparison of 5-, 12-, and 15-HETE enantiomers revealed no differences in metabolism or incorporation between the R and S stereoisomers. These data suggest that many isomers of HETE and HEPE can be incorporated into cell lipids or metabolized by pathways that do not distinguish between enantiomers. These pathways, however, are sensitive to the position or number of double bonds and are selective based on the position of the hydroxyl group.     

The urinary excretion of orally administered pteroyl-l-glutamic acid by the rat

1. The urinary excretion of folates after oral administration of [2-(14)C]pteroyl-l-glutamic acid was studied by assaying the radioactivity in the urine and in materials purified and characterized by t.l.c. 2. Radioactivity excreted was 6.8, 5.9 and 30.7% of the oral dose in the first 24h after doses of 3.1, 32 and 320mug/kg respectively. 3. Extensive decomposition of urinary folates to pteroyl-l-glutamic acid was prevented by antioxidants or collection of urine frozen. 4. At the three dosages, two major and one minor radioactive compounds were isolated. One of the major metabolites was 5-methyltetrahydropteroylglutamic acid. The others were unidentified but were not pteroylglutamic acid, 7,8-dihydro-, 5,6,7,8-tetrahydro-, 5- or 10-formyl-tetrahydro-, 5,10-methylidyne-tetrahydro-, 5-formimidoyl-tetrahydro-, 5,10-methylene-tetrahydro-, 5-methyltetrahydro-pteroylglutamic acid, nor any decomposition products of these compounds formed during isolation. Labelled unconjugated pteridines were absent. 5. Labelled pteroyl-l-glutamic acid was displaced by oral administration of unlabelled pteroyl-l-glutamic acid (1.6mg/kg) when given 3.5h after, but not when given 24h after the labelled dose. 6. The results show that orally administered [2-(14)C]pteroyl-l-glutamic acid is absorbed without metabolism and is then metabolized into naturally occurring tetrahydro-folates. 7. These findings are discussed with reference to previous work.     

Metabolic fate of radiolabeled prostaglandin D2 in a normal human male volunteer

50 microCi of [3H]prostaglandin D2 tracer (100 Ci/mmol) was infused intravenously into a normal human male volunteer. 75% of the infused radioactivity was excreted into the urine within 5 h. This urine was added to urine obtained from two mastocytosis patients with marked overproduction of prostaglandin D2. Radiolabeled prostaglandin D2 urinary metabolites were chromatographically isolated and purified and subsequently identified by gas chromatography-mass spectrometry. 25 metabolites were identified. 23 of these compounds comprising 37% of the recovered radioactivity had prostaglandin F-ring structures, and only two metabolites comprising 2.7% of the recovered radioactivity retained the prostaglandin D-ring structure. The single most abundant metabolite identified was 9,11-dihydroxy-15-oxo-2,3,18,19-tetranorprost-5-ene-1,20-dioic acid which was isolated in a tricyclic form as a result of formation of a lower side chain hemiketal followed by lactonization of the terminal carboxyl and the hemiketal hydroxyl. Different isomeric forms of several prostaglandin F-ring metabolites were identified. An isomer of prostaglandin F2 alpha was also excreted intact into the urine as a metabolite of prostaglandin D2. 15 PGF-ring compounds were treated with n-butylboronic acid and 13 failed to form a boronate derivative, suggesting that the orientation of the hydroxyl group at C-11 in these 13 metabolites is beta. This study documents that prostaglandin D2 is metabolized to prostaglandin F-ring metabolites in vivo in humans. These results also bring into question the accuracy of quantifying prostaglandin F2 alpha metabolites as a specific index of endogenous prostaglandin F2 alpha biosynthesis, as well as quantifying urinary prostaglandin F2 alpha as an accurate index of renal production of prostaglandin F2 alpha.