Isolation of 5,8-oxyretinoic acid from rat intestinal mucosa

Demonstration of retinoic acid isomers in human urine under physiological conditions

Untransformed retinoic acid has never been demonstrated in human excreta under normal physiological conditions. We have developed a two-step liquid chromatographic system for the demonstration of subnanogram amounts of this compound in human urine without administration of any precursor.

The biological activity of rat intestinal retinoic acid metabolites in the vaginal smear assay

Vitamin A-deficient rats were given a single intrajugular injection of 1 mg all-trans-[11-3H]retinoic acid and 3 h later the rats were killed. The small intestines were extracted and chromatographed by high-performance liquid chromatography to yield distinct metabolites. These were quantitated using the assumption that the specific activity of the metabolite is equal to that of the parent [3H]retinoic acid. The biological activity of all discernible metabolites was determined in the vitamin A-deficient female rat by vaginal smear assay. Retinoic acid and retinoyl-beta-glucuronide from the preparation had equal activity while no activity was found for any of the other metabolite fractions. Thus, no evidence for an unknown metabolite having potent epithelial differentiating activity could be found in this target tissue of vitamin A action.

Tissue dependence of retinoic acid metabolism in vivo

Metabolites formed in vivo from [3H]retinoic acid dosed intrajugularly to vitamin A-deficient rats and to vitamin A-deficient rats supplemented orally with unlabeled retinoic acid were investigated. Extracts of liver, small intestinal mucosa, kidney, testes and serum were separated into charged uncharged fractions by DEAE-Sephadex. This allowed the direct application of 20-40% of the combined charged extracts from up to six organs to be loaded onto a high-performance liquid chromatography column. The large aliquot size plus the use of relatively high specific activity [3H]retinoic acid resulted in detection of nanomolar metabolite quantities. The substantial resolution achieved with the high-performance liquid chromatography gradient system aided in demonstrating the complexity, extent and variations of retinoic acid metabolism in vivo, The metabolic profiles changed with retinoic acid pretreatment, time after dose and tissue source. Some 3H-labeled metabolites were predominant in vitamin A-deficient animals; others appeared to be predominant in the retinoic acid-supplemented animals. The gross effect of retinoic acid supplementation was to both accelerate retinoic acid metabolism and cause an accumulation of more polar metabolites. It appears that retinoic acid metabolism in vivo is a complex process that occurs through multiple metabolites, which are, at least partially, tissue-specific.

5,6-epoxyretinoic acid is a physiological metabolite of retinoic acid in the rat

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.