The metabolic transformations of columbinic acid and the effect of topical application of the major metabolites on rat skin

The metabolism of columbinic acid by various fatty acid oxidizing enzyme systems was studied. A cyclooxygenase product, 9-hydroxy-(5E,10E,12Z)-octadecatrienoic acid, was formed nearly quantitatively by ram seminal vesicle microsomes and in small amounts by washed human platelets. The major lipoxygenase product from washed human platelets, soybean lipoxygenase, and neonatal rat epidermal homogenate was 13-hydroxy-(5E,9Z,11E)-octadecatrienoic acid, although lesser quantities of other isomers differing in the double bond configurations were also identified by ultraviolet spectrophotometry and gas chromatography-mass spectroscopy. Topical application of the major lipoxygenase product to paws of essential fatty acid-deficient rats resulted in nearly as complete resolution of the scaly dermatitis as did the application of columbinic acid itself; the cyclooxygenase product was not at all effective.     

Teratogenicity of dimethoxyethyl phthalate and its metabolites methoxyethanol and methoxyacetic acid in the rat

It is hypothesized that the known teratogen di(2-methoxyethyl) phthalate (DMEP) acts by in vivo hydrolysis to 2-methoxyethanol (2-ME), also a known teratogen, which in turn is metabolized to methoxyacetic acid (MAA), the proximate teratogen. Teratological studies were conducted with Wistar rats, with the administration of these three agents on day 12 of gestation. On an equimolar dosage basis, DMEP, 2-ME, and MAA were equally potent, which is consistent with the hypothesis. There was a striking similarity in the defects produced by these agents, mainly hydronephrosis, heart defects, and short limbs and tails. In particular all three agents produced unusual heart defects (dilated ductus arteriosus and dilated aortic arch) not seen with other agents, as well as ventral polydactyly, a rarely seen defect, suggesting teratogenic action by a common mechanism or component; 4-methylpyrazole, an alcohol dehydrogenase inhibitor, provided significant protection against 2-ME. This combination of effects strongly suggests that following the administration of DMEP, 2-ME, or MAA, MAA is the proximate teratogen.     

The neurotoxic effects of methylenedioxymethamphetamine (MDMA) and its metabolites on rat brain spheroids in culture

Rat whole-brain spheroids were used to assess the intrinsic neurotoxicity of methylenedioxymethamphetamine (MDMA, Ecstasy) and two of its metabolites, dihydroxymethamphetamine (DHMA) and 6-hydroxy-MDMA (6-OH MDMA). Exposure of brain spheroids to MDMA or the metabolite 6-OH MDMA (up to 500 mol/L) for 5 days in culture did not alter intracellular levels of glutathione (GSH), glial fibrillary acidic protein (GFAP) or serotonin (5-HT). In contrast, exposure to the metabolite DHMA, which can deplete intracellular thiols, significantly increased GSH levels (up to 170% of control) following exposure to 50 and 100 mol/L DHMA. There was also a significant reduction in the levels of glial fibrillary acidic protein (GFAP) and GSH by DHMA at the highest concentration tested (500 mol/L) but there was no effect on 5HT. This may constitute a sublethal neurotoxic compensatory response to DHMA in an attempt to replenish depleted intraneural GSH levels following metabolite exposure. Rat whole-brain spheroids may thus be a useful in vitro model to delineate mechanisms and effects of this class of neurotoxin.     

Physiologic regulation of mixtalol in rape senescence and its yield effects

Physiologic and yield effects of mixtalol at various concentrations sprayed on rape at the anthesis stage were examined. Foliar sprays of 4 and 2 ppm mixtalol significantly increased the chlorophyll content of rape leaves and pods, reduced the accumulation of malondialdehyde and ethylene production, and delayed the degradation of superoxide dismutase and catalase activities of the rape plant. Mixtalol also increased root oxidizability. Meanwhile, the number of branches and pods per plant was increased, and a 10.7% and 8.2% increase of seed yield over the controls was observed with treatments of 4 and 2 ppm mixtalol, respectively. No significant effects from mixtalol were observed on the maturation of plants or on the seed oil content or the erucic acid and glucosinolate content. Total rape oil production increased with 4 and 2 ppm mixtalol significantly by 12.4% and 10.5%, respectively, over the controls.Abbreviations MTL mixtalol - MDA malondialdehyde - TBA thiobarbituric acid - SOD Superoxide dismutase - CAT catalase - TTC tetrazolium     

Arachidonic acid metabolites in pregnant rat uterus

Production of prostaglandin E2 (PGE2), F2 alpha (PGF2 alpha) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) by pregnant rat uterus were measured in vitro. At mid-pregnancy, myometrium incubated with decidua attached released more prostanoids into the culture medium than when incubated without. As pregnancy progressed to 21 days more prostanoids were detected in the culture medium. However, no significantly increased conversion of exogenous arachidonic acid (AA) by myometrium was found.     

Biliary metabolites of all-trans-retinoic acid in the rat

Biliary metabolites from physiological doses of all-trans-[10-3H]retinoic acid were examined in normal and vitamin A-deficient rats. The bile from normal and vitamin A-deficient rats contained approximately 60% of the administered dose following a 24-h collection period. However, vitamin A-deficient rats show a 6-h delay in the excretion of radioactivity compared to normal rats. Retinoyl-beta-glucuronide excretion was particularly sensitive to the vitamin A status of the rats. In normal rats, retinoyl-beta-glucuronide reached a maximum concentration of 235 pmol/ml of bile 2 h following the dose and then rapidly declined. Vitamin A-deficient rats show a relatively constant concentration of this metabolite (100-150 pmol/ml of bile) over a 10-h collection period. Retinoic acid excretion was low in both normal and deficient rats. The concentration of retinotaurine, a recently identified biliary metabolite, was approximately equal to retinoyl-beta-glucuronide in normal rats and appeared in the bile 2 h later than the glucuronide.     

Correlation of the effects of citric acid cycle metabolites on succinate oxidation by rat liver mitochondria and submitochondrial particles

1. Succinate dehydrogenase is inhibited by citrate and β-hydroxybutyrate in a complex manner, both in mitochondria and submitochondrial particles. Kinetics of inhibition in the particles points to a competitive component in the mechanism involved.
2. Pyruvate, α-ketoglutarate, malate, and glutamate stimulate oxidation of succinate by mitochondria.
3. Stimulation by α-ketoglutarate and glutamate is not influenced by the presence of rotenone.
4. Stimulation by pyruvate is higher in the absence of rotenone and increases significantly in the presence of K⁺ and valinomycin. Pyruvate supplies in mitochondria reducing equivalents for malate dehydrogenase operating in the reverse direction-reduction of oxaloacetate to malate.
5. Stimulation by malate is higher in the presence of rotenone.

     

Isotopic effects on retention times of caffeine and its metabolites 1,3,7-trimethyluric acid, theophylline, theobromine and paraxanthine

Physicochemical parameters that influence gas chromatographic separation are numerous. Consequently, isotope labelling, because it modifies physicochemical properties, can induce isotopic effects on retention time. Caffeine has been chosen to study this influence because as itself and its metabolites, it allows the preparation of different methylxanthine isotopomers and thus is one of the best models to study isotopic effects induced by stable isotope labelling. Using a caffeine molecule labelled with deuterium at different positions and rat hepatocytes to obtain metabolites, it was possible to study the influence of labelling on retention time [(14% cyanopropylphenyl)methylpolysiloxane] and to point out the role of each labelled site. It appears that isotopic effects induced by the labelling depend not only on the number of labelling atoms but also on whether this labelling is at position 1, 3 or 7 and, consequently, on the role of the labelled site on the function of the molecule.     

Correlation of the effects of citric acid cycle metabolites on succinate oxidation by rat liver mitochondria and submitochondrial particles.

1. Succinate dehydrogenase is inhibited by citrate and beta-hydroxy-butyrate in a complex manner, both in mitochondria and submitochondrial particles. Kinetics of inhibition in the particles points to a competitive component in the mechanism involved. 2. Pyruvate, alpha-ketoglutarate, malate, and glutamate stimulate oxidation of succinate by mitochondria. 3. Stimulation by alpha-ketoglutarate and glutamate is not influenced by the presence of rotenone. 4. Stimulation by pyruvate is higher in the absence of rotenone and increases significantly in the presence of K+ and valinomycin. Pyruvate supplies in mitochondria reducing equivalents for malate dehydrogenase operating in the reverse direction-reduction of oxaloacetate to malate. 5. Stimulation by malate is higher in the presence of rotenone.     

Physiologic effects of caffeine on cross-country runners

This study determined the physiological effects of caffeine on cross-country runners during submaximal exercise. Ten college-age subjects (5 women; 5 men) volunteered to participate in this study. After completing a VO2max test, each subject completed 2 30-minute runs at 70% VO2max on the treadmill, 1 after ingesting caffeine and the other after ingesting a placebo. A caffeine dosage of 7 mg.kg(-1) of body weight was administered. The same dosage of vitamin C was used as a placebo. The order of treatments was randomly assigned, and the trials followed a double-blind format. The physiological data were analyzed using a repeated measures analysis of variance (SPSS). Tidal volume (TV), alveolar ventilation (VA), and rating of perceived exertion (RPE) were significantly different (p < 0.05) between treatment and control groups. The results suggest that the ingestion of caffeine at 7 mg.kg(-1) of body weight prior to submaximal running might provide a modest ergogenic effect via improved respiratory efficiency and a psychological lift.