LOCALIZATION OF EPIDERMAL GROWTH-FACTOR (EGF) RECEPTOR IN THE RAT CORPUS-LUTEUM, AND EGF AND TRANSFORMING GROWTH-FACTOR-ALPHA STIMULATION OF LUTEAL CELL STEROIDOGENESIS IN-VITRO

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) have potent mitogenic effects on granulosa and theca cells. However, their effects on steroidogenesis by these cells is controversial, and there is limited information regarding their effects on luteal cell steroidogenesis. The present study investigated the cellular distribution of the EGF receptor (EGF-R) in the rat corpus luteum (CL) by immunocytochemical staining, and the effects of EGF and TGF-alpha on progesterone and 20 alpha-dihydroprogesterone (20 alpha-OH-P) production in cultures of luteal cells. Using a primary antibody directed against the human EGF-R peptide, specific EGF-R staining was obtained in the CL. Both small and large luteal cells had EGF-R staining. In initial cell culture experiments, treatment of freshly isolated luteal cells with EGF or TGF-alpha (0.5-50 ng/ml) for 24 h had no effect on progesterone and 20 alpha-OH-P accumulation. Addition of LH (250 ng/ml) alone caused a 3.5-fold increase in both progestins, but co-treatment with EGF or TGF-alpha produced no further enhancement of progestin accumulation. However, when cells were seeded overnight and the attached cells were washed prior to growth factor treatment for 3 days with media change every 24 h, both EGF and TGF-a caused dose-dependent increases in progesterone accumulation/24 h period (up to 2-fold at 50 ng/ml growth factor) on days 1 and 2 but not day 3 of treatment. 20 alpha-OH-P accumulation was similarly stimulated (up to 2.5-fold) by EGF and TGF-alpha under these conditions. In addition, LH-induced increases in progestin accumulation were further enhanced dose-dependently by TGF-alpha. These data confirm the presence of EGF-R in rat CL, and suggest a physiological role for EGF and TGF-alpha in luteal steroidogenesis.