Insulin-like growth factor-I stimulates the expression of 3 beta-hydroxysteroid dehydrogenase messenger ribonucleic acid in ovarian theca-interstitial cells

Evidence accumulating in the literature supports the hypothesis that insulin-like growth factor-I (IGF-I) may play a role in stimulating differentiation of the ovarian theca-interstitial cells (TIC) during early follicular development. IGF-I has been shown to synergistically enhance the stimulation of androgen biosynthesis and to increase LH binding in TIC. The purpose of the present studies was to examine the role of IGF-I in TIC differentiation by determining the effects of IGF-I on 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) mRNA expression in TIC stimulated to differentiate in vitro. TIC were isolated from the ovaries of hypophysectomized immature rats by Percoll gradient centrifugation and cultured in the presence and absence of LH and IGF-I for up to 6 days. At various times cytoplasmic RNA was extracted from the TIC, and 3 beta-HSD mRNA was measured by specific assay using reverse transcription followed by the polymerase chain reaction. Amplification of 3 beta-HSD mRNA using primers designed to distinguish between the type I and type II 3 beta-HSD gene products revealed that the TIC expressed primarily the type I gene. Increasing concentrations of LH (0-1 microgram/ml) stimulated a dose-related increase in 3 beta-HSD mRNA that was approximately 3-fold at 100 ng/ml of LH. Addition of IGF-I (30 ng/ml) increased 3 beta-HSD mRNA approximately 2-fold over TIC treated with LH alone.