Isomers In Rats Research Articles

The influence of OATP2B1 and atorvastatin on coproporphyrin isomers in rats

Coproporphyrin I (CPI) and III (CPIII) are discussed as biomarkers for organic anion transporting polypeptides (OATPs). We report on CPI and CPIII levels in wildtype, rSlco2b1-knockout, and SLCO2B1-humanized rats at baseline and after administration of atorvastatin, an inhibitor of the CPIII-specific rOATP2B1/hOATP2B1 and the CPI/CPIII-transporting rOATP1B2. OATP-inhibition by atorvastatin leads to significantly increased CPI and CPIII serum levels. However, basal CP serum levels in rSlco2b1-knockout animals were significantly lower (CPI), or unaffected (CPIII). In the presence of atorvastatin, this genotype effect was abolished. In conclusion, our results indicate an unexpected impact of OATP2B1 on CP serum levels in rats.

Determination and pharmacokinetic analysis of ticarcillin disodium-clavulanate potassium for injection in rat plasma by UPLC-ESI-MS/MS.

ObjectiveTo establish a specific and rapid ultra-high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (UPLC-ESI-MS/MS) method for measuring ticarcillin and clavulanate levels in rat plasma.MethodsA Waters ACQUITY BEH C18 column (50 mm × 2.1 mm, 1.7 μm) and SCIEX QTRAP® LC-MS/MS System were used. Analyses were conducted to optimize the chromatographic and MS conditions, and the pharmacokinetic parameters of ticarcillin and clavulanate were assessed.ResultsLinear relationships were observed in the ranges of 10 to 10,000 ng/mL for ticarcillin R (r2 = 0.9967) 30 to 10,000 ng/mL for ticarcillin S (r2 = 0.9961), and 30 to 10,000 ng/mL for clavulanate (r2 = 0.9981). The average extraction recoveries of all compounds ranged from 86.9% to 96.4%. The pharmacokinetic parameters of the ticarcillin R and S isomers in rats were distinctive. The ticarcillin R and S isomers and clavulanate were rapidly absorbed in vivo. Ticarcillin S and clavulanate had similar elimination rates, whereas that of ticarcillin R was slower.ConclusionA UPLC-ESI-MS/MS method was developed and validated for the determination of ticarcillin and clavulanate in rat plasma.

P.458 Acute antidepressant effects of different ketamine isomers in rats submitted to maternal separation animal model: A pilot study

P.458 Acute antidepressant effects of different ketamine isomers in rats submitted to maternal separation animal model: A pilot study

Comparative inhalation toxicity of ethyltoluene isomers in rats and mice

The C9 alkylbenzenes, composed mostly of ethyltoluenes and trimethylbenzenes, comprise 75–90% of the naphtha fraction of crude oil. Occupational and environmental exposure to C9 alkylbenzenes occur via inhalation. We conducted short-term inhalation studies on the ethyltoluene isomers (2-, 3- or 4-) to select one isomer for more comprehensive studies. Male Hsd:Sprague Dawley rats and female B6C3F1/N mice (n = 10) were exposed by nose-only inhalation to 2-, 3- or 4-ethyltoluene (0, 1000 or 2000 ppm) or cumene (a reference compound: 0, 500 or 1000 ppm) 3 h/day, 5 days/week, for 2 weeks. Clinical observations included abnormal gait and delayed righting reflex. Rats and mice exposed to 2000 ppm 2-ethyltoluene and mice exposed to 2000 ppm 4-ethyltoluene were euthanized early in moribund condition; no exposure-related deaths were observed with 3-ethyltoluene or cumene. Histopathology of selected tissues revealed that the nose and liver (rats and mice) and lung (mice only) to be toxicity targets. In the mouse lung, all compounds except 4-ethyltoluene produced bronchial and bronchiolar hyperplasia. In rats and mice, 2-ethyltoluene was the only compound to produce lesions in the nose and liver: in mice, squamous metaplasia and neutrophilic inflammation of the respiratory epithelium and atrophy and degeneration of the olfactory epithelium were observed in the nose and centrilobular hypertrophy and necrosis were observed in the liver. In rats, 2-ethyltoluene exposure produced atrophy of the olfactory epithelium in the nose and centrilobular necrosis in the liver. Based on mortality, body weight effects and histopathology, the 2-ethyltoluene isomer was the most potent isomer.

Enantioselective pharmacokinetics of doxazosin and pharmacokinetic interaction between the isomers in rats.

In this study, the stereoselective pharmacokinetics of doxazosin enantiomers and their pharmacokinetic interaction were studied in rats. Enantiomer concentrations in plasma were measured using chiral high-pressure liquid chromatography (HPLC) with fluorescence detection after oral or intravenous administration of (-)-(R)-doxazosin 3.0 mg/kg, (+)-(S)-doxazosin 3.0 mg/kg, and rac-doxazosin 6.0 mg/kg. AUC values of (+)-(S)-doxazosin were always larger than those of (-)-(R)-doxazosin, regardless of oral or intravenous administration. The maximum plasma concentration (Cmax ) value of (-)-(R)-doxazosin after oral administration was significantly higher when given alone (110.5 ± 46.4 ng/mL) versus in racemate (53.2 ± 19.7 ng/mL), whereas the Cmax value of (+)-(S)-doxazosin did not change significantly. The area under the curve (AUC) and Cmax values for (+)-(S)-doxazosin after intravenous administration were significantly lower, and its Cl value significantly higher, when given alone versus in racemate. We speculate that (-)-(R)-doxazosin increases (+)-(S)-doxazosin exposure probably by inhibiting the elimination of (+)-(S)-doxazosin, and the enantiomers may be competitively absorbed from the gastrointestinal tract. In conclusion, doxazosin pharmacokinetics are substantially stereospecific and enantiomer-enantiomer interaction occurs after rac-administration.

Determination of Pharmacokinetics Differences of Ammuxetine Isomers in Rat Plasma Using On-Line Solid Phase Extraction Coupled with Liquid Chromatography-Tandem Mass Spectrometry

Abstract An on-line solid phase extraction (SPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to determine the novel chiral antidepressant, S / R -ammuxetine in rat plasma. The plasma sample pretreatment consisted of the following steps: protein precipitation using methanol and acetonitrile (50:50, V/V ), an on-line SPE process to remove proteins and most matrices in plasma, and a separation step using a C 18 analytical column after elution of ammuxetine isomers enriched on SPE column. Then S/R -ammuxetine were determined by tandem mass spectrometry. The SPE column was a Retain PEP Javelin column (10 mm × 2.1 mm, 5 μm), while the chromatographic separation was achieved on a ZORBAX SB-C 18 (50 mm × 2.1 mm, 3.5 μm) analytical column. The multiple reaction monitoring mode of the positive ion was adopted in MS detection, and the precursors to the product ion transitions of m/z 292.1/154.0 and m/z 260.4/116.2 were used to measure S / R -ammuxetine and internal standard (propranolol). The method was linear over S/R -ammuxetine concentration range from 0.2 μg L −1 to 1000 μg L −1 with the correlation coefficients ( R ) of 0.9903 and 0.9951, respectively. The average intra-day precision values (RSD) were 1.2%−12% for S -ammuxetine and 0.4%−11.2% for R -ammuxetine, respectively. The average recovery values were 94.2%−101.6% for S -ammuxetine and 94.3%−109.4% for R -ammuxetine. This method exhibited a dramatically increased sensitivity compared to previous reports, thus could be used in the pharmacokinetic study of ammuxetine isomers in rat after intragastric administration.

Differential pharmacokinetics and the brain distribution of morphine and ephedrine constitutional isomers in rats after oral administration with Keke capsule using rapid‐resolution LC–MS/MS

Opioid and ephedra alkaloids known as the active ingredients for Keke capsule, which is used to treat coughs and bronchial asthma, could have potential adverse effects on the central nervous system. Therefore, an efficient, sensitive rapid-resolution LC-MS/MS method for the simultaneous determination of morphine, ephedrine, and pseudoephedrine in rat plasma and brain tissue homogenate has been developed. The method was validated in the plasma and brain tissue samples, showed good linearity over a wide concentration range (r(2) > 0.99). The intra- and interday assay variability was less than 15% for all analytes, and the accuracy was between -8.8 and 5.7%. The study provided the pharmacokinetics profiles and the brain regional distribution of the three active alkaloids after oral administration of Keke capsule. The results also indicated that significant difference in pharmacokinetics parameters of the epimers was observed between ephedrine and pseudoephedrine.

Studies on the in vivo contribution of human cytochrome P450s to the hepatic metabolism of glaucine, a new drug of abuse

Glaucine ((S)-5,6,6a,7-tetrahydro-1,2,9,10-tetramethoxy-6-methyl-4H-dibenzo [de,g]quinoline), main isoquinoline alkaloid of Glaucium flavum (Papaveraceae), is used as antitussive, but also as recreational drug of abuse. Glaucine was mainly metabolized by O- and N-demethylation to four isomers in rats. So far, only scarce pharmacokinetic data were available. Therefore, the aim of the presented study was to assess the involvement of the ten most important cytochrome P450 (P450) isoforms in the main metabolic steps and determination of their kinetic parameters using the metabolite formation approach. Reference standards of investigated metabolites were synthesized for quantification. In addition, the impact of isomeric standards was tested for calibration and the use of simple peak area ratios on the kinetic constants and resulting contribution of P450 isoforms on estimated hepatic clearance. Kinetic profiles of all metabolite formations followed classic Michaelis–Menten behavior. Km values were between 25 and 140μM, Vmax between 0.10 and 1.92pmol/min/pmol. Using the relative activity factor approach, the hepatic clearance was calculated to be 27 and 73% for 2-O-demethylation by CYP1A2 and CYP3A4, 82, 3, and 15% for 9-O-demethylation by CYP1A2, CYP2C19, and CYP2D6, and finally <1 and 99% for N-demethylation by CYP2D6 and CYP3A4. These data were confirmed by inhibition tests. The calibration mode for determination of the metabolite concentrations had no relevant impact on the estimation of in vivo hepatic clearance of glaucine. As glaucine was metabolized via three initial steps and different P450 isoforms were involved in the hepatic clearance of glaucine, a clinically relevant interaction with single inhibitors should not be expected.

Relaxation of tracheal smooth muscle independent on functional epithelium cells induced by lidocaine, bupivacaine and isomers in rats

Lidocaine is a local anesthetic which has been used to protect spasm reaction during tracheal intubation and bronchoscopy. We compared the potency of lidocaine, bupivacaine (RS(±)-bupivacaine) and isomers (S(−)-bupivacaine and R(+)-bupivacaine) to promote relaxation of tracheal smooth muscle. Relaxation of airways smooth muscle can be dependent on the release of relaxing factors by epithelium such as prostanoids and nitric oxide (NO). Possible mechanisms involved in the tracheal smooth muscle relaxation induced by these local anesthetics were evaluated in preparation in which the epithelium layer was intact or denuded. Bupivacaine and its isomers were approximately six to eleven-fold more potent than lidocaine to promote relaxation on acetylcholine-induced contraction in tracheal rings. The concentration of lidocaine, RS(±)-bupivacaine, S(−)-bupivacaine and R(+)-bupivacaine necessary to produce a 50% reduction of maximal contraction to acetylcholine (IC 50) in tracheal rings with intact epithelium was 1.25 ± 0.01, 0.11 ± 0.01, 0.15 ±0.01, 0.19 ± 0.01 mM, respectively. Removal of epithelium or exposure to N G-nitro-L-arginine methyl ester, indomethacin did not alter the IC 50. However, calcium influx of depolarized tracheal smooth muscle was inhibited by lidocaine, bupivacaine and isomers. S(−)-bupivacaine reduced by 78.8 ± 7.4% the calcium influx followed by RS(±)-bupivacaine (41.8 ± 6.7%) and R(+)-bupivacaine (25.6 ± 9.5%). In conclusion, local anesthetic action was stereoselective and partially dependent on blockade of Ca 2+ influx to muscular cells. The isomer S(−)-bupivacaine is more potent and less toxic which could represent a valuable clinical advantage to use as broncholitic agent.

Comparative Oral Toxicity of Coenzyme Q10 and Its (2Z)-Isomer in Rats: Single and Four-Week Repeated Dose Toxicity Studies

It has been reported that coenzyme Q10 (CoQ10) functions as an electron transfer carrier in mitochondria, and can produce an improvement in heart diseases such as congestive heart failure. Its (2Z)-isomer contains a cis-double bond at the 2-position of the decaprenyl side chain. As the original organic industrial synthesis of CoQ10 resulted in a product that contained a small amount of this isomer, the efficacy and safety of CoQ10 was determined using CoQ10 containing this isomer; however, no toxicity data have been reported for the (2Z)-isomer itself. Thus, we conducted single (2,000 mg/kg) and 4-wk repeated (1,000 mg/kg) oral dose toxicity studies in rats to compare the toxicological profiles of CoQ10 and its (2Z)-isomer. The two compounds displayed similar toxicological profiles, and it was concluded that neither CoQ10 nor its (2Z)-isomer produce toxic effects in rats in single or repeated doses.

Metabolic effects of dietary conjugated linoleic acid (CLA) isomers in rats

To know the effect of individual conjugated linoleic acid (CLA) isomers on lipid metabolism, male rats were fed diets containing either linoleic acid (LA, a control fatty acid), CLA containing mainly 9 c,11 t-isomer, 10 t,12 c-isomer (at the 0.8% level) or an equivalent mixture of these isomers (at the 0.4% level) for 26 days. Although there were no differences in food intake and body weight gain among the groups, the food efficiency was low in rats fed the CLA containing 10 t,12 c-isomer in comparison with those fed 9 c,11 t-CLA. The weight of white (epididymal and perirenal) adipose tissues decreased in all CLA groups, while that of brown adipose tissue increased in rats fed 10 t,12 c-CLA, the difference between 9 c,11 t- and 10 t,12 c-isomers being significant. The concentration of serum total cholesterol, triacylglycerol and phospholipid tended to be lower in rats fed CLA preparations containing 10 t,12 c-CLA, while there was a trend toward an increasing concentration of serum HDL-cholesterol in all CLA groups. The rate of fatty acid β-oxidation in the liver peroxisomes was slightly higher in rats fed CLA than in those fed LA, and the activity of mitchondrial carnitine parmitoyltranceferase (CPT) in the CLA-mix group significantly increased compared to the LA group. The effect of CLA on the concentration of spleen and serum IgE, IgG and IgA level was variable. No CLA effect was observed on the concentration of serum leptin and TNF-α. Thus, individual isomers of CLA may have different effects on some metabolic parameters in rats. The results also suggested a probable interaction of different isomers on lipid metabolism.

Analysis of heme oxygenase isomers in rat.

To purify and identify heme oxygenase (HO) isomers which exist in rat liver, spleen and brain treated with hematin and phenylhydrazine and in untreated rat liver and to investigate the characteristics of HO isomers, to isolate and confirm the rat HO-1 cDNA that actually encodes HO-1 by expressing cDNA in monkey kidney cells (COS-1 cells), to prepare the rat heme oxygenase-1 (HO-1) mutant and to detect inhibition of HO-1 mutated enzyme. First, rat liver, spleen and brain microsomal fractions were purified by DEAE-Sephacel and hydroxylapatite. The characteristics including activity, immunity and inducibility of two isomers (HO-1 and HO-2), and their apparent molecular weight were measured by detecting enzymatic activities, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting analysis, respectively. Second, plasmid pcDNA3HO1 containing native rat HO-1 cDNA and pcDNA3HO1D25 carrying mutated rat HO-1 cDNA (His25Ala) were constructed by site-directed mutagenesis. COS-1 cells transfected with pcDNA3HO1 and pcDNA3HO1D25 were collected and disrupted by sonication, the microsomes were prepared by ultracentrifugation. Third, the inhibition of rat HO-1 mutant was analyzed. Two isomers were purified and identified in treated rat liver, spleen, brain and untreated rat liver. HO-1 was the predominant form with a ratio of 2.0:1 and 3.2:1 of HO-1 and HO-2 in liver and spleen, respectively, but only the activity of HO-2 in the brain and untreated liver could be detected. The apparent molecular weights of HO-1 and HO-2 were about M(r)30 000 and M(r) 36 000 under reducing conditions, respectively. The antiserum against liver HO-2 was employed in Western blotting analysis, the reactivity of HO-1 in the liver was not observed. The plasmid pcDNA3HO1 was highly expressed in endoplasmic reticulum of transfected COS-1 cells. The specific activity was -5-fold higher than that of the control. However, the enzyme activity of mutated HO-1 declined. While an equal amount of mutant was added to the enzyme reaction system, the levels of bilirubin decreased 42 %. The studies suggest that HO-1 and HO-2 exist in the hematin and phenylhydrazine treated rat liver and spleen, but only HO-2 in the brain and untreated liver. Two constitutive forms are different in molecular weight, inducibility and immunochemical properties. The activity of expressed HO-1 in COS-1 cells is higher than that of purified enzyme from rat spleen tissue. It suggests that this clone has an insert of 1030 base-pairs encodes HO-1. His25Ala mutant reduced the formation of bilirubin and it suggests that the mutant could completely bind the heme with native enzyme.

Pharmacokinetics and metabolism of a vitamin D analogue (Seocalcitol) in rat and minipig

1. Seocalcitol (EB 1089), a vitamin D analogue with strong antiproliferative effects in vitro and in vivo, is presently under clinical evaluation for the systemic treatment of various solid tumours. 2. The aim was to investigate the pharmacokinetics of Seocalcitol after single and multiple oral administration to rat and minipig. Furthermore, the hepatic metabolism of Seocalcitol was studied both in vitro and in vivo. In vitro metabolism was also investigated in human. 3. In rat, the pharmacokinetic profile of Seocalcitol (Cmax, AUC, Tmax, T½) was the same after single and oral administration. Pharmacokinetics were also demonstrated as doseindependent. The same was more difficult to evaluate in the minipig due to a great variation among individual animals. 4. In the male rat, the serum T½ was 3 h, but in the female rat and minipig (both genders) T½ = 8 h. 5. At T max the concentration of Seocalcitol in the liver (both species) was 10-fold higher than the concentration in serum. The major metabolites in the liver were various isomers of 26-hydroxy Seocalcitol, although the concentration of the individual isomers in rat and minipig were not the same. 6. The same metabolites were formed in vitro following incubations with rat, minipig and human S9 fractions.

Optical Isomer Analysis of 3,4-Methylenedioxyamphetamine Analogues and their Stereoselective Disposition in Rats

Identification of the optical activity and simultaneous analysis of racemates (+/-) of three hallucinogens, 3,4-methylenedioxy-amphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDEA), and the urinary excretion of their optical isomers in rats was performed by high-performance liquid chromatographic analysis. Analysis of optical enantiomers of three N-alkyl MDA derivatives was performed within 50 min using two different detectors, polarimetry (OR) and ultraviolet spectroscopy (UV). The OR detector proved suitable for identification of the optically active forms, whereas the UV detector was suitable for simultaneous analysis of the enantiomers in urine. After the administration of each of the three N-alkylated derivatives, rat urine specimens were collected over four intervals, 0-4, 4-12, 12-20, and 20-24 h. After the administration of 30 mg/kg of racemic MDA and MDMA, somewhat less of the S(+)-forms of unchanged MDA and MDMA than of the R(-)-forms in each urine specimen were detected, which gave R/S ratios greater than 1.00 (p < 0.01). Conversely, after the administration of 30 mg/kg of racemic MDEA, more of the S(+)-form than the R(-)-form was found in the urine, thus giving R/S ratios less than 1.00 (p < 0.01). The percentage of the dose excreted up to 24 h was approximately 29.4% of the administered dose for MDA [S(+) 13.40% and R(-) 15.98%], 5.8% for MDMA [S(+) 1.96% and R(-) 3.79%], and 7.3% for MDEA [S(+) 3.89% and R(-) 3.43%]. Urinary excretion of optical isomers of N-dealkylated MDA from MDMA and MDEA origin were the opposite of those of the unchanged forms, and their R/S ratios up to 24 h were 0.48 to 0.72 (p < 0.01) and 1.31 to 1.50 (p < 0.01), respectively. The urinary excretion rates up to 24 h were approximately 4.3% for N-dealkylated MDA from MDMA origin [S(+) 2.72% and R(-) 1.63%] and 0.8% for N-dealkylated MDA from MDEA origin [S(+) 0.36% and R(-) 0.47%]. The total percent of unchanged forms and N-dealkylated MDA was approximately 10.1% for MDMA [S(+) 4.68% and R(-) 5.42%] and 8.2% for MDEA [S(+) 4.25% and R(-) 3.91%]. The total R/S ratio of MDMA was found to be 1.95 (p < 0.01), whereas that of MDEA was 0.88 (p < 0.01). The total R/S ratio of MDA was 1.20 (p < 0.01 ), which was comparable with that of MDMA. These three R/S ratios did not conform to the theoretical values for three N-alkyl derivatives used and neither did the R/S ratios of urine specimens collected at the four interval. These results suggested the stereoselective disposition of three N-alkyl MDA analogues in rat. The method would be suitable for the forensic chemistry and toxicology analysis of specimens obtained from hallucinogen abusers.

Cocaine—Stimulus Generalization to MDA Optical Isomers: A Reevaluation

It has already been demonstrated that the psychoactive agent 1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDA) produces effects that are both hallucinogen-like and amphetamine- or stimulant-like in animals. Hallucinogenic activity is associated primarily with the R(−)-isomer of MDA whereas stimulant activity is primarily associated with the S(+)-isomer. Because a previous report indicates that S(+)MDA fails to substitute for cocaine in rats trained to discriminate cocaine from vehicle, and because these findings are inconsistent with the purported stimulant nature of S(+)MDA, we reinvestigated the effect of both MDA isomers in rats. In this investigation, S(+)MDA doses of 1.25 and 1.5 mg/kg were found to produce > 80% cocaine-appropriate responding in rats trained to discriminate 8 mg/kg of cocaine from saline. However, consistent with a previous report, R(−)MDA resulted only in partial generalization. These new results support the hypothesis that the optical isomers of MDA produce distinguishable stimulus effects in rats, and that S(+)MDA is the more stmulant isomer of MDA.

Metabolism of tetramethrin isomers in rat: IV. Tissues responsible for formation of reduced and hydrated metabolites

1. To identify the sites of formation of the reduced metabolites, 3-hydroxycyclohexane-1,2-dicarboximide (3-OH-HPI-1 and-2), 1,2-cyclohexanedicarboxylic acid (TCDA) and 1-hydroxy-1,2-cyclohexanedicarboxylic acid (1-OH-HPA), in rat treated with 14C-labelled (1 RS, trans)-tetramethrin, [3,4,5,6-tetrahydrophthalimidomethyl (1 RS, trans)-chrysanthemate], bile-duct cannulated animals were orally or intravenously administered 14C-labelled 3,4,5,6-tetrahydrophthalimide (TPI) or 3,4,5,6-tetrahydrophthalic acid (THPA), precursors of these metabolites, and bile, urine and faeces were collected for analysis. 2. 3-OH-HPI-1 and 3-OH-HPI-2, which are cis-form reduced metabolites, and 1- OH-HPA were detected in bile and urine samples of the bile-cannulated rat treated intravenously and orally with 14C-labelled TPI, indicating their formation in tissues or blood. TCDA, a trans-form reduced metabolite, was not detected in bile, urine or faeces of the bile-cannulated rat treated intravenously with 14C-THPA, but was found in the faeces after oral application, indicating formation in the gastrointestinal tract. 3. To clarify whether 1-OH-HPA is produced from THPA via TCDA (hydroxylation via reduction) or by direct addition of H2O to its double bond (hydration), rats were orally administered 14C-labelled TCDA, and metabolites in urine and faeces were analysed. The observed lack of 1-OH-HPA indicated formation by direct addition of H2O to the doublebond of THPA. 4. To specify whichtissues form reduced and hydratedmetabolites, in vitro metabolism studies were carried out. Reduction to the cis-form was found to take place in blood cells, reduction to the trans-form took place in the gastrointestinal tract contents, and hydration took place in the liver and the intestinal tract contents.

Metabolism of tetramethrin isomers in rat. III. Stereochemistry of reduced metabolites.

1. Three main urinary metabolites, two isomers of 3-hydroxycyclohexane-1,2-dicarboximide (3-OH-HPI-1 and 2) and 1,2-tetrahydrodicarboxylic acid (TCDA) were purified from rat treated with (1RS, trans)-tetramethrin [3,4,5,6-tetrahydrophthalimidomethyl (1RS, trans)-chrysanthemate]. 2. To elucidate the mechanism of formation of these reduced metabolites, the stereochemistry of 3-OH-HPI-1, 3-OH-HPI-2 and TCDA was clarified by chemical reactions, spectroanalysis (nmr) and X-ray analysis. 3. The sole difference in configuration between 3-OH-HPI-1 and 3-OH-HPI-2 was found to be the orientation of the hydroxyl group to the cyclohexane ring, and both of these reduced metabolites showed cis-addition of two hydrogens. In contrast, reduction resulted in the trans form with TCDA. 4. These findings indicate the existence of two different reduction reaction mechanisms in the rat.

Metabolism of tetramethrin isomers in rat. I. Identification of a sulphonic acid type of conjugate and reduced metabolites.

1. Urinary and faecal metabolites in rat treated with 14C-labelled (1RS, trans)-tetramethrin [3,4,5,6-tetrahydrophthalimidomethyl (1RS, trans)-chrysanthemate] were identified using chromatographic techniques and spectroanalyses (nmr and ms). 2. 3-Hydroxy-cyclohexane-1,2-dicarboximide was found to be a major and unique urinary metabolite, reduced at the 1,2-double bond of the 3,4,5,6-tetrahydrophthalimide moiety. 3. The major faecal metabolites were sulphonic acid conjugates, having a sulphonic acid group incorporated into the double bond of the 3,4,5,6-tetrahydrophthalimide moiety. 4. On the basis of the metabolites identified here, the major biotransformation reactions of trans-tetramethrin in rats are: (1) cleavage of the ester linkage; (2) cleavage of the imide linkage; (3) hydroxylation of the cyclohexene or cyclohexane ring of the 3,4,5,6-tetrahydrophthalimide moiety; (4) oxidation at the methyl group of the isobutenyl moiety; (5) reduction at the 1,2-double bond of the 3,4,5,6-tetrahydrophthalimide moiety; and (6) incorporation of a sulphonic acid group into the 1,2-double bond of the 3,4,5,6-tetrahydrophthalimide moiety.

Gas chromatographic analysis of isomeric organic mononitrates in plasma

A specific, sensitive and precise capillary gas chromatographic method using electron-capture detection was developed for the determination of four isomeric vasodilating organic mononitrates, viz. l-isoidide mononitrate (L-IIMN), isosorbide-2-mononitrate (IS-2-MN), isomannide mononitrate (IMMN) and isosorbide-5-mononitrate (IS-5-MN), in rat plasma. With a sample size of 100 μl of rat plasma, the detection limits were found to be between 0.5 and 2 ng/ml for these mononitrates, and the absolute recovery was found to range from 83 to 90%. The within-day coefficients of variation for the assay of the four isomers were less than 5%, while the between-day coefficients of variation were less than 10%. Because of the short retention times of these isomers in this assay, routine analyses of about sixty plasma samples per day can be carried out. The possibility of in vivo interconversion among these four isomers in rats was investigated after individual administration of each isomer. No interconversion was found based on examination of plasma samples. The gas chromatographic method was applied to the pharmacokinetic studies of these four isomers in rats; at an intravenous dose of 2 mg/kg, the biological half-lives of L-IIMN, IMMN, IS-2-MN and IS-5-MN were found to be 13.2, 25.2, 54.6 and 112 min, respectively.

Lack of self-administration of different fenfluramine isomers in rats

Twelve rats were tested in an animal model for self-administration of dl-, d-, and l-fenfluramine. Amphetamine and saline were used as reference substances. In addition to being tested on the reference substances amphetamine and saline, each rat was only tested on one drug and dose. Analyses of variance were performed to assert that high rates of self-administration were maintained on amphetamine whereas saline gave low rates of responding. The results showed that all three forms of fenfluramine (dl-fenfluramine 0.1, 0.5, 2.0 mg/kg; d-fenfluramine 0.05, 0.1, 0.25, 1.0 mg/kg; l-fenfluramine 0.1, 0.5, 1.0, 2.0 mg/kg) differed significantly from amphetamine, but not from saline. As d-fenfluramine is both more effective in reducing food intake, and has less sedative action than dl-fenfluramine, it may be an improvement in the pharmacotherapy of obesity.