Immunochemical and biochemial evidence indicates that an isozyme of cytochrome P-450 in rat liver microsomes catalyzes the formation of a previously unidentified metabolite, 17Beta-hydroxy 4,6-androstadiene-3-one. The identity of the metabolite was confirmed by HPLC, uv spectroscopy and thermospray, mass spectrometry. The metabolite appears to be formed by isozymes of cytochrome P-450 that catalyze the 6Alpha-hydroxylation of testosterone. When animals were treated with various inducers the ratios of 6-hydroxytestosterone over 17Beta-hydroxy 4,6-androstadiene-3-one remained constant. Furthermore, a known 6Beta-hydroxylase inhibitor, 16Alpha-methylprogesterone, inhibited the formation of the metabolite as well as 6Beta-hydroxytestosterone. An antibody raised against a P-450 isozyme isolated from liver microsmes of rats pretreated with dexamethasone also inhibited the formation of both the metabolite and 6Beta-hydroxytestosterone to the same extent.
