title: Progesterone and subsequent polar metabolites are essential for completion of the first meiotic division in amphibian oocytes.
abstract: We find that completion of the first meiotic division in Rana pipiens oocytes requires the sequential action of at least two steroids: progesterone and one or more subsequent polar metabolites of progesterone. Progesterone binding in vitro to oocyte surface receptors increases during the first 4-5h of exposure, followed by internalization of plasma membrane together with membrane-bound progesterone over the next hour. The internalized progesterone is metabolized to highly polar polyhydroxylated steroid(s) prior to nuclear membrane disappearance at 8-9h. Polar steroids alone cannot induce meiosis, but do so in oocytes pretreated with progesterone for 1h. Similarly, the non-metabolizable progestin R5020 cannot induce meiosis but does if oocytes are subsequently exposed to polar steroids. An inhibitor of steroid alpha-reductase (4-MA) prevents both progesterone metabolism and progesterone-induced meiosis. However, meiosis does occur if 4-MA is followed by a polar steroid. Thus, progesterone binding at the oocyte surface initiates a process which requires polar progesterone metabolites for completion of the first meiotic division.
authors.affiliation: Department of Physiology & Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Adele B
authors.initials: AB
authors.lastname: Kostellow
authors.forename: Gene A
authors.initials: GA
authors.lastname: Morrill
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D008540:Meiosis / Q000502:physiology*; D015394:Molecular Structure; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D006080:Ovarian Follicle / Q000166:cytology / Q000378:metabolism; D011374:Progesterone / Q000737:chemistry / Q000378:metabolism; D011894:Rana pipiens / Q000502:physiology*
chemical_list: D011374:Progesterone; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase