5-6-epoxyretinoic-acid and Vitamin-A-Deficiency

The major metabolite in the small intestinal mucosa of vitamin A deficient rats dosed intrajugularly with 5,6-epoxy[3H]-retinoic acid has been identified as 5,6-epoxyretinoyl beta-glucuronide. The assignment was based on the metabolite's chemical, spectral, and chromatographic properties. Incubation of the metabolite with beta-glucuronidase released 5,6-epoxyretinoic acid. Incubation of 5,6-epoxyretinoic acid with rat liver microsomes in the presence of uridine-5'-diphospho-1 alpha-D-glucuronic acid produced the metabolite. 5,6-Epoxy[3H]retinoyl beta-glucuronide weas observed in the liver, small intestinal mucosa, and intestinal contents but not in kidney of vitamin a deficient rats. Its concentration was greatly diminished in liver and small intestinal mucosa, and it was not observed in kidney of vitamin A deficient rats dosed orally with retinoic acid for several days before administration of 5,6-epoxy[3H]retinoic acid. Generally, oral retinoic acid treatment accelerated 5,6-epoxyretinoic acid metabolism and enhanced accumulation of highly polar metabolites. Moreover, 5,6-epoxyretinoic acid metabolism was more rapid than that of retinoic acid and did not result in production of retinoic acid.

Topics: Animals; Chromatography, High Pressure Liquid; Intestinal Mucosa; Intestine, Small; Male; Microsomes, Liver; Rats; Rats, Inbred Strains; Tretinoin; Vitamin A Deficiency

A method is described for measuring the relative activities of vitamin A active substances based on their direct effect on the cornified vaginal epithelium of vitamin A-deficient rats. The results obtained agree well with those found in the tracheal organ culture assay. The relative activities found for several test compounds were: all-trans-retinoyl-beta-glucuronide greater than all-trans-retinoic acid greater than all-trans retinol greater than all-trans-5,6-epoxyretinoic acid. The assay is simple and inexpensive to perform, and should find use in laboratories where the equipment and personnel required for the tracheal organ culture assay are not available.

Topics: Animals; Biological Assay; Castration; Dose-Response Relationship, Drug; Epithelium; Female; Glucuronates; Rats; Tretinoin; Vaginal Diseases; Vaginal Smears; Vitamin A; Vitamin A Deficiency

A description of the enzyme that produces 5,6-epoxyretinoic acid from all-trans-retinoic acid has been presented. This enzyme system is found in highest concentrations in the kidney followed by intestine, liver and spleen. The enzyme requires molecular oxygen, magnesium ions, ATP, and NADPH. In the kidney, it is found in the mitochondrial and microsomal fractions and has a Michaelis constant of 3.2 X 10(-6) M and 3.7 X 10(-6) M for 13-cis and all-trans-retinoic acid, respectively. The resultant product, 5,6-epoxyretinoic acid, has minimal activity in supporting growth of vitamin A-deficient rats, its activity estimated to be 0.5% that of retinoic acid. An investigation of the biliary excretion products of tritiated retinoic acid has revealed several unknown metabolites. A glucuronidase sensitive metabolite from these products has been isolated and identified as retinoyl-beta-glucuronide by ultraviolet absorption spectrometry and mass spectrometry. The retinoyl-beta-glucuronide originally discovered by Olson and collaborators accounts for only 12% of the total excreted biliary products of retinoic acid. At least four to six major unknown retinoic acid metabolites, in addition to retinoyl-beta-glucuronide, have been detected and will shortly be identified.

Topics: Animals; Bile; Chromatography, High Pressure Liquid; Epoxy Compounds; Glucuronates; Kidney; Rats; Tretinoin; Vitamin A Deficiency

5,6-Epoxyretinoic acid was detected in small intestine, kidney, liver, testes and serum of vitamin A-deficient rats 3 h after a single physiological dose of [3H]retinoic acid. The maximum concentration of 5,6-epoxide in intestinal mucosa was observed 3 h after intrajugular administration of retinoic acid. However, at 7 h post administration, no 5,6-epoxyretinoic acid was detected in mucosa, demonstrating the rapid intestinal metabolism or excretion of this metabolite. No 5,6-epoxy[3H]retinoic acid was detected in mucosa, liver or serum of retinoic acid-repleted rats 3 h after administration of 2 micrograms of [3H]retinoic acid.

Topics: Animals; Chromatography, High Pressure Liquid; Epoxy Compounds; Kinetics; Male; Rats; Tissue Distribution; Tretinoin; Vitamin A Deficiency

The potential of all-trans-5,6-epoxyretinoic acid to promote growth in vitamin A-deficient rats was evaluated over a 25-fold dose range using single daily intraperitoneal injections. 5,6-Epoxyretinoic acid was found to be 0.5% as active as all-trans-retinoic acid. The discrepancies between the present results and those obtained previously by other workers are discussed.

Topics: Administration, Oral; Animals; Dose-Response Relationship, Drug; Epoxy Compounds; Growth; Injections, Subcutaneous; Male; Rats; Tretinoin; Vitamin A Deficiency