Evidence that 17α,20β,21-trihydroxy-4-pregnen-3-one is a maturation-inducing steroid in spotted seatrout

Abstract

Ovarian steroidogenesis during final oocyte maturation (FOM) in the spotted seatrout (Cynoscion nebulosus) was investigated by incubating ovarian fragments with tritiated pregnenolone, followed by chromatographic separation of the radioactive products. The major tritiated steroid produced during FOM comigrated with 17α,20β,21-trihydroxy-4-pregnen-3-one (20β-dihydro-11-deoxycortisol, 20β-S) on HPLC and TLC. Only minor amounts of radioactive material coeluted with 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-P), 11-deoxycorticosterone (DOC), estradiol-17β and testosterone standards in the HPLC system. Additional chromatography by TLC confirmed the presence of radioactive estradiol-17β and testosterone but not 17α,20β-P and DOC.All the ovarian steroids producedin vitro during FOM were assayed for their ability to induce germinal vesicle breakdown (GVBD) of spotted seatrout oocytes. Twenty grams of ovarian tissue were incubated with human chorionic gonadotropin and exogenous pregnenolone. The steroidal products were purified by HPLC and TLC. Most of the maturation-inducing activity was confined to steroidal material which comigrated in these systems with 20β-S. This material was active at a concentration of 1 ng steroid/ml medium in the GVBD assay. Smaller amounts of material which coeluted with 11-deoxycortisol, DOC, 17α,20β-P and several minor unidentified fractions induced GVBD at concentrations of 10 ng steroid(s)/ml.The structure-activity relationships of authentic steroids in inducing GVBD of spotted seatrout oocytes was investigated. Hydroxylation at the 17α, 20β or 21 positions increased potency to induce GVBD. Steroids with multiple hydroxyl groups at the 17α and 20β positions (17α, 20β-P) and at the 17α, 20β, and 21 positions (20β-S) had maximum biological activity in the GVBD bioassay. The results suggest that 20β-S is a major maturation-inducing steroid in spotted seatrout.

Concentration of four heavy metals (cadmium, lead, mercury, and arsenic) in organs of two cyprinid fish (Cyprinus carpio and Capoeta sp.) from the Kor River (Iran)

“…The deleterious effects of toxicants can be exerted on the hypothalamicpituitary system (see Kime 1995) or they could be directed at gonadal steroid production. For example, plasma estrogen of Atlantic croaker decreased after exposure to lead (Thomas 1990;Thomas and Trant 1989), as it did for Asian swamp eel (Monopterus albus) after exposure to cadmium (Saxena et al 1989), although cadmium contamination has been shown to stimulate both vitellogenesis and plasma levels and in vitro synthesis of estradiol in Atlantic croaker (Thomas and Trant 1989). It has also been shown that cadmium can increase the transcription of the progesterone receptor but decrease that of the estrogen receptor gene in humans (Garcia Morales et al 1994).…”

Particularities of reproduction and oogenesis in teleost fish compared to mammals

“…Then, it was identified in the incubation medium of follicles from another salmonid, stimulated by a salmon gonadotropin [135]. In various marine species, such as the spotted sea-trout Cynoscion nebulosus, another progestin, 17,20β,21-trihydroxy4pregnen-3one, has been identified as a MIS [136]. Moreover, two different MIS receptors have been identified in this species, a membrane receptor [137], and a nuclear receptor [138], exhibiting very different binding affinities for various C21 steroids [139].…”

?Classical? and ?non-classical? reproductive steroids in fish

“…In vitro studies, using exogenous radiolabelled precursors, have recently shown that a number of novel progestogens are synthesized by ovaries of some teleosts. In two species of sciaenid fish, 17,20fl,21P has been identified in in vitro incubations and shown to be potent in inducing GVBD (Trant et al, 1986;Thomas and Trant, 1989). This steroid has also been found in ovarian incubations of 17-hydroxyprogesterone in the tobinumeri dragonet (Repomucenus beniteguri, Perciformes, Callionymidae) by Asahina et al (1991), who showed that it was the major product during final oocyte maturation and greatly exceeded 17,20tiP production, while the related ll-deoxycortisol (17,21P), which was predominant at earlier stages of oocyte maturation, decreased as it was converted to the triol.…”