Effects of enclomiphene and zuclomiphene on basal and gonadotrophin-stimulated progesterone secretion by isolated subpopulations of small and large ovine luteal cells

We examined the effects of enclomiphene and zuclomiphene, alone and in combination with oestradiol, on basal and gonadotrophin-stimulated progesterone secretion by isolated subpopulations of both large (granulosa-lutein) and small (theca-lutein) ovine luteal cells. Isolated large and small luteal cells derived from intact, enucleated ovine corpora lutea were incubated for 48-120 h with or without 22R-hydroxycholesterol or pregnenolone (2.5 microM) and a range of enclomiphene, zuclomiphene, and/or oestradiol concentrations (3-100 microM), both with and without ovine luteinizing hormone (100 ng/ml). Spent media were assayed in duplicate for progesterone content by radioimmunoassay. Enclomiphene, zuclomiphene, and oestradiol exhibited equivalent dose-dependent inhibitory effects on basal and gonadotrophin-stimulated small and large ovine luteal cell progesterone secretion under all substrate conditions. Both cell types became more sensitive to clomiphene inhibition with increasing time in culture. In combined treatments, the effects of oestradiol and either enclomiphene or zuclomiphene became additive in longer-term cultures and were never antagonistic. In this model system, (i) clomiphene, like oestradiol, appears to inhibit 3beta-hydroxysteroid dehydrogenase activity, (ii) both stereoisomers act as oestrogen agonists, (iii) neither demonstrates any anti-oestrogenic properties, and (iv) both large and small luteal cells become more sensitive to clomiphene inhibition with increasing duration of exposure.