The metabolism of C21- and C19-steroids by sheep myometrium in vitro has been investigated. At 134 days of gestation, extensive interconversion of progesterone and 20α-dihydroprogesterone was demonstrated, the reaction favouring the reduced form. Low yields only of 20β-dihydroprogesterone and 17α-hydroxyprogesterone were obtained from either precursor. Saturation of the 4-ene bond resulted mainly in the formation of 5α-reduced compounds whilst evidence was obtained for the presence of both 3α- and 3β-hydroxysteroid dehydrogenase activities as opposed to that of a steroid C17-20 lyase.
Similar incubation studies with [4-14C]androstenedione and [1,2-3H]epitestosterone at term indicated a low metabolizing ability of the tissue for these steroids. The main metabolites isolated were 5α-reduction products whilst no 5β-reductase activity could be demonstrated. Interconversion of the two substrates was also shown and testosterone bearing both labels was isolated in low yield. There was little evidence that sheep myometrium at this stage of gestation utilizes these C19-steroids as precursors for oestrogen formation.