A polyclonal antibody to murine epidermal growth factor (EGF) was generated in rabbits and characterized by RIA, Western blots, and dot blotting. The antibody detected as little as 0.01 ng of mouse EGF in dot blots at 1:100, 000 dilution and 5 pg of EGF in RIA at 1:50, 000 dilution; it did not cross-react with transforming growth factor-α, insulin-like growth factor, or fibroblast growth factor. Ovarian EGF content peaked (17 ± 2 pg/nonluteal ovary) on Day 1 (estrus as determined by copious vaginal discharge) and declined by Day 3 as measured by RIA of immunoaffinity-purified ovarian extract. Frozen sections of hamster ovaries were stained immunohistochemically for EGF using a Zymed kit. Intense red staining specific for EGF was localized only in granulosa cells of small (1-2 layers of granulosa cells) and medium (3-6 layers of granulosa cells) preantral follicles; moderate staining was observed in the granulosa and theca cells of small antral follicles. Staining intensity faded in granulosa and theca cells of. largeantral follicles, especially on Day 4 (proestrus) and disappeared in pyknoticgranulosa cells of atretic follicles. Follicular EGF staining peaked on Days 1 and 2 and thereafter declined to low levels. On Day 2, oocytes of the primordial follicles showed distinct coloration. Sections of Day 2 ovary incubated with preneutralized antibody or normal rabbit IgG did not show any coloration. For intact hamsters, 10 μg of follicle-stimulating hormone (FSH), twice daily for Days 1 and 2, intensified EGF staining in granulosa cells compared with corresponding untreated Day 3 hamsters, whereas similar treatment with luteinizing hormone for 2 days expanded the interstitium with localized staining of interstitial cells only around follicles with 2 and 3 layers of granulosa cells and lacking theca. Hypophysectomy for 13 days resulted in almost complete absence of EGF-specific staining in the remaining nonatretic follicles; however, exogenous FSH (5 tig, twice daily) for 2 days dramatically increased staining intensity associated with newly developed follicles. Luteinizing hormone (0.4 μg, twice daily) for 2 days, however, induced significant development of only the interstitium with increased staining of small preantral follicles. These results provide strong evidence for the presence of EGF-like activity in hamster ovarian follicles and suggest that its expression is controlled by gonadotropins, especially FSH.
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