Estradiol-17β and 17α,20β-dihydroxy-4-pregnen-3-one production by isolated ovarian follicles of amago salmon ( Oncorhynchus rhodurus) in response to mammalian pituitary and placental hormones and salmon gonadotropin

Abstract

The effects of mammalian pituitary and placental hormones and dibutyryl cyclic AMP (cAMP) on the production of estradiol-17β and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) by amago salmon ( Oncorhynchus rhodurus) ovarian follicles in vitro were compared with partially purified chum salmon ( Oncorhynchus keta) gonadotropin (SGA). Estradiol-17β production was examined using midvitellogenic ovarian follicles; SGA was the most effective hormone tested; at a dose of 1 μg/ml it stimulated the production of approximately 4 ng/ml estradiol-17β. Ovine LH (o-LH) was about 0.5% as effective as SGA. Taking into account the relative purity of the preparations used, ovine FSH (o-FSH) was almost as effective as o-LH. Both HCG and bovine TSH (b-TSH) stimulated estradiol-17β production at high doses. Porcine ACTH (p-ACTH), ovine GH (o-GH), and ovine PRL (o-PRL) induced very modest increases in estradiol-17β; cAMP was highly effective. 17α,20β-DiOHprog production was examined using full-grown immature oocytes which were capable of maturing in vitro in response to 1 μg/ml SGA. o-LH was about 0.5% as effective as SGA. o-FSH, b-TSH, and HCG appeared to be less effective in stimulating 17α,20β-diOHprog production, compared to estradiol-17β. o-GH and o-PRL induced marginal increases in production and p-ACTH had a very modest inverse dose-response effect. Dibutyryl cAMP stimulated the production of approximately 0.9 and 3.8 ng/ml 17α,20β-diOHprog at concentrations of 1 and 10 m M, respectively. These data are discussed in relation to studies on gonadotropin stimulation of gonadal steroidogenesis in other teleosts.