METABOLISM INVIVO OF ALL-TRANS-[11-H-3]RETINOIC ACID AFTER AN ORAL DOSE IN RATS - CHARACTERIZATION OF RETINOYL BETA-GLUCURONIDE IN THE BLOOD AND OTHER TISSUES

Soon after [11-H-3]retinoic acid (RA) (1.1 x 10(8) d.p.m.) was administered orally to rats either as a large dose (115-mu-g = 0.38-mu-mol/rat) or mixed with unlabelled RA as a huge dose (22 mg = 73.33-mu-mol/rat), retinoyl beta-glucuronide (RAG) was identified and characterized as a significant metabolite in the serum and small intestine. Of the administered dose, 70% remained unchanged as retinoic acid in the stomach up to 1 h. Significant amounts of 5,6-epoxyretinoic acid, 4-hydroxyretinoic acid, esters of retinoic acid and several polar retinoids, including 4-oxoretinoic acid, were also detected in the stomach. No significant difference was observed in the nature of the retinoids found after a large or a huge dose; however, the ratio of RAG/RA was higher after a huge dose than after a large dose. Thus RAG, which is biologically active in vivo and in vitro, is formed quickly in significant amounts in tissues after a dose of RA.