The nature of the glycosidic conjugates of estriol epimers in rabbits.

After administration of estriol-6,7-3H to rabbits, 37% of the dose was recovered in the urine in 3 days. Estriol conjugates partially identified as glucuronosides were found, but there was no evidence for the conjugation of this steroid with N-acetylglucosamine. After hydrolysis of the radioactive steroid diglycosides with Ketodase, a conjugate was obtained, and identified by infrared and ultraviolet spectroscopy, optical rotation, and isotope dilution as the 17-N-acetylglucosaminide of 17-epiestriol. Indications were found by chromatography and enzyme treatment of the presence of smaller amounts of 16,17-epiestriol-N-acetylglucosaminide. The results confirm that rabbits excrete administered estriol partly as its 17α-epimers, and provide further evidence that the phenolic steroid N-acetylglucosaminyl transferase in this species is highly specific for the 17α-hydroxyl group.