Progesterone induces maturation and ovulation of amphibian oocytes and, in the process, binds to the receptors in oocytes and follicle cells. It is still unclear to what extent the progesterone receptors in these cells are similar. We tried to answer this question using RU486, an antagonist of the classical mammalian progesterone receptor. Pretreatment of the ovarian follicles with RU486 (1–20 μM) does not affect the maturation or ovulation of the common frog oocytes stimulated in vitro by pituitary hormones or progesterone and even increases (at low concentrations) the percentage of maturated and ovulated oocytes. In addition, RU486 (5-40 μM) stimulates the oocyte maturation and ovulation in a dose-dependent manner. Pretreatment of the follicles with actinomycin D (5 μg/ml) inhibits both RU486-stimulated processes. An increase in RU486 concentration overcomes the inhibitory effect of actinomycin D on oocyte maturation. On the contrary, the inhibitory AD effect on oocyte ovulation does not depend on the RU486 concentration. RU486 stimulates the maturation of both follicle-enclosed and “denuded” oocytes. However, the sensitivity of the latter to RU486 is much lower and its effect on the denuded oocyte is not inhibited by actinomycin D. The data obtained suggest that in amphibians, unlike in mammals, RU486 is an agonist of progesterone. It stimulates the transcription-independent maturation of denuded oocytes (membrane receptor) and transcription-dependent ovulation (classical receptor). In addition RU486 can stimulate (at certain doses) the transcription-dependent maturation of follicle-enclosed oocytes.
Russian Journal of Developmental Biology – Springer Journals
Published: Oct 13, 2004
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