In vitroovulation and prostaglandin synthesis by ovarian follicles ofRana dybowskii

Abstract

Changes in the levels of prostaglandin F2α (PGF2α) and E2 (PGE2) in culture medium during in vitro ovulation of Rana dybowskii follicles were examined. The ovulation was induced by frog pituitary homogenate (FPH) or TPA (12‐O‐tetradecanoylphorbol‐13‐acetate, a protein kinase activator) and the levels of PGs were measured by radioimmunoassay. When the ovarian follicles were cultured, only a few oocytes were ovulated by 12 h, but half of them were ovulated by 24 h in response to FPH, whereas around 30% of oocytes were ovulated by 12 h and maximum ovulation (around 50%) occurred by 24 h in response to TPA. Without any stimulation (control), no ovulation occurred. TPA elevated the level of PGF2α to high levels when compared to control (basal levels), but the increase by FPH was less evident. Likewise, the levels of PGE2 increased markedly in response to TPA, but rather decreased by FPH treatment. Interestingly, PGF2α induced ovulation but PGE2 suppressed FPH‐ or PGF2α‐induced oocyte ovulation. Basal levels of PGs increased steadily during culture. When theca/epithelium (THEP) layer and granulosa cell‐enclosed oocytes (GCEOs) were separated by microdissection and cultured independently, higher levels of both PGs were secreted by THEP than by GCEOs. Synthesis of PGs by follicle or follicular components was strongly suppressed by exogenous cAMP or indomethacin. These results suggest that: 1) PGF2α plays an important role in Rana ovulation, 2) protein kinase C is involved in PGs production, and 3) theca/ epithelium layer is responsible for the PGs production in Rana.