Isolation and identification of 25-hydroxyvitamin D2 25-glucuronide: a biliary metabolite of vitamin D2 in the chick.

The biliary metabolites of vitamin D2 obtained from chickens dosed with 3H-labeled vitamin D2 were investigated. Most of the biliary radioactivity migrated as charged compounds on diethylaminoethyl-Sephadex chromatography, and the charged fraction could be resolved into several components by reversed-phase high pressure liquid chromatography. A major charged metabolite was further purified by reversed-phase high-pressure liquid chromatography. This compound was found to be beta-glucuronidase sensitive and to yield 25-hydroxyvitamin D2 upon mild acid hydrolysis. The metabolite was converted first to the methyl ester and then to silylated and acetylated derivatives, which were subjected to mass spectrometry. The structure of the original metabolite was established as 25-hydroxyvitamin D2 25-beta-D-glucuronic acid. This 25-hydroxyvitamin D2 25-beta-glucuronide is a major biliary metabolite of vitamin D2 in the chick and may play a role in the chick's discrimination against vitamin D2.