Steroid membrane receptor. Binds progesterone, progestin and 17-hydroxyprogesterone in vitro. Capable of mediating progestin-induced oocyte maturation (By similarity). Localized to the cell membrane of oocytes and sperm. Strongly expressed in ovary and brain; lower expression in testis and pituitary. Not detected in heart, kidney, spleen, intestine, gill and muscle. Expressed at low expression in fully grown oocytes, highly expressed in maturing oocytes undergoing germinal vesicle breakdown (GVBD) and weakly expressed in ovulated oocytes. By progestin in ovarian tissues and human chorionic gonadotropin (hCG) in oocytes undergoing meiotic maturation. May activate a pertussis toxin-sensitive inhibitory G protein that inhibits adenylate cyclase activity; it may therefore be a G-protein coupled receptor. Belongs to the ADIPOR family.