Plasma 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one levels during sexual maturation of amago salmon (Oncorhynchus rhodurus): correlation with plasma gonadotropin and in vitro production by ovarian follicles.
Plasma gonadotropin (GtH) and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-diOH-prog) levels were assessed by radioimmunoassay during the sexual maturation of female amago salmon (Oncorhynchus rhodurus). Both GtH and 17 alpha, 20 beta-diOHprog levels were low in vitellogenic females (June to September) and in those with full-grown immature oocytes and were elevated in mature and ovulated females to 40 ng/ml for GtH and 50-70 ng/ml for 17 alpha, 20 beta-diOHprog. In vitro production of 17 alpha, 20 beta-diOHprog by ovarian follicles and its stimulation by partially purified chinook salmon gonadotropin (SG-G100) was examined monthly using 18 hr incubations. In June and July, levels were too low to detect (less than 30 pg/ml) in media from all treatment groups. In August and September, SG-G100 at a concentration of 1 microgram/ml stimulated low levels of production (0.2-0.3 ng/ml). Full-grown, immature follicles in October showed a dose-response production of 17 alpha, 20 beta-diOHprog, averaging over 10 ng/ml when incubated with 1 microgram/ml SG-G100. Postovulatory follicles (1-2 days after ovulation) produced large amounts of 17 alpha, 20 beta-diOHprog, averaging over 100 ng/ml with 1 microgram/ml SG-G100. These results are discussed in relation to previous work on amago salmon and other species and together indicate that 17 alpha, 20 beta-diOHprog is the major steroid responsible for oocyte maturation in amago salmon, produced as the follicular mediator of gonadotropin.
D000818:Animals; D005260:Female; D006062:Gonadotropins / Q000097:blood*; D006908:Hydroxyprogesterones / Q000097:blood*; D009865:Oocytes / Q000166:cytology; D006080:Ovarian Follicle / Q000378:metabolism*; D011863:Radioimmunoassay; D012474:Salmon; D012741:Sexual Maturation
D006062:Gonadotropins; D006908:Hydroxyprogesterones; C021012:17 alpha,20 beta-dihydroxypregn-4-en-3-one