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Journal ArticleDOI

Relationship between seasonal plasma estradiol-17 beta and testosterone levels and in vitro production by ovarian follicles of amago salmon (Oncorhynchus rhodurus).

01 Sep 1983-Biology of Reproduction (Society for the Study of Reproduction)-Vol. 29, Iss: 2, pp 301-309

TL;DR: The seasonal pattern of plasma testosterone levels lagged behind and followed that of estradiol-17 beta during vitellogenesis, but levels remained high in mature and ovulated fish, and GSI values showed a linear increase, and reached a peak in October.

AbstractPlasma estradiol-17 beta and testosterone levels were assessed by radioimmunoassay during the sexual maturation of female amago salmon (Oncorhynchus rhodurus). Estradiol-17 beta levels gradually increased during vitellogenesis (June to September), reached a peak in September (about 16 ng/ml) and rapidly decreased in mature and ovulated fish (about 3-4 ng/ml) in October. The seasonal pattern of plasma testosterone levels lagged behind and followed that of estradiol-17 beta during vitellogenesis, but levels remained high in mature and ovulated fish (90-110 ng/ml). Estradiol-17 beta levels and the gonadosomatic index (GSI) values correlated well during vitellogenesis: GSI values showed a linear increase, and reached a peak (29.9 +/- 1.4) in October. Values were extremely low in ovulated fish (1.2 +/- 0.2). In vitro production of estradiol-17 beta and testosterone by ovarian follicles in response to partially purified chinook salmon gonadotropin (SG-G100) was examined monthly using 18-h incubations. Throughout the vitellogenic period SG-G100 stimulated both estradiol-17 beta and testosterone production: the steroidogenic response of follicles increased from June (about 2 ng/ml estradiol-17 beta; 0.1 ng/ml testosterone) to September (about 10 and 14 ng/ml, respectively). In October full-grown immature follicles which could be induced to mature in vitro by hormone treatment produced large amounts of testosterone (about 130 ng/ml) but not estradiol-17 beta. Postovulatory follicles also produced testosterone but the values were low (10 ng/ml) compared with full-grown immature follicles. Very low levels of estradiol-17 beta were produced by postovulatory follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Ovarian follicle (51%), Vitellogenesis (50%)

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Journal ArticleDOI
TL;DR: Findings on the identification of steroidal mediators involved in each process of gametogenesis, and the sites and mechanisms of action of the mediators are reviewed.
Abstract: The pituitary-gonadal axis plays an important role in regulating gametogenesis in vertebrates. In most cases, gonadotropins act through the biosynthesis of gonadal steroid hormones which in turn mediate various stages of gametogenesis. A series of studies in our laboratory using several species of teleost fishes as experimental animals has provided new information about the endocrine regulation of gametogenesis, including oocyte growth, oocyte maturation, spermatogenesis and sperm maturation. This article briefly reviews our findings on the identification of steroidal mediators involved in each process of gametogenesis, and the sites and mechanisms of action of the mediators. These observations collectively demonstrate the appropriateness of using teleost fishes as valid models for examining hormonal influences on gametogenesis. Such models could also have applications and validity for vertebrates in general.

704 citations


Journal ArticleDOI
Abstract: A period of oocyte growth is followed by a process called oocyte maturation (the resumption of meiosis) which occurs prior to ovulation and is a prerequisite for successful fertilization. Our studies using fish models have revealed that oocyte maturation is a three-step induction process involving gonadotropin (LH), maturation-inducing hormone (MIH), and maturation-promoting factor (MPF). LH acts on the ovarian follicle layer to produce MIH (17α, 20β-dihydroxy-4-pregnen-3-one, 17α, 20β-DP, in most fishes). The interaction of ovarian thecal and granulosa cell layers (two-cell type model), is required for the synthesis of 17α,20β-DP. The dramatic increase in the capacity of postvitellogenic follicles to produce 17α,20β-DP in response to LH is correlated with decreases in P450c17 (P450c17-I) and P450 aromatase (oP450arom) mRNA and increases in the novel form of P450c17 (P450c17-II) and 20β-hydroxysteroid dehydrogenase (20β-HSD) mRNA. Transcription factors such as Ad4BP/SF-1, Foxl2, and CREB may be involved in the regulation of expression of these steroidogenic enzymes. A distinct family of G-protein-coupled membrane-bound MIH receptors has been shown to mediate non-genomic actions of 17α, 20β-DP. The MIH signal induces the de novo synthesis of cyclin B from the stored mRNA, which activates a preexisting 35 kDa cdc2 kinase via phosphorylation of its threonine 161 by cyclin-dependent kinase activating kinase, thus producing the 34 kDa active cdc2 (active MPF). Upon egg activation, MPF is inactivated by degradation of cyclin B. This process is initiated by the 26S proteasome through the first cut in its NH2 terminus at lysine 57.

603 citations


Book ChapterDOI
TL;DR: Of considerable interest is the finding that MIH, unlike most steroid hormones, acts on its receptors at the surface of oocytes, and the mechanism of MIH-induced MPF activation in fish oocytes differs from that in Xenopus and starfish.
Abstract: Publisher Summary This chapter discusses the current status of the investigations on the hormonal regulation of oocyte growth and maturation in fish. Pituitary gonadotropins are of primary importance in triggering these processes in fish oocytes. In both cases, however, the actions of gonadotropins are not direct but are mediated by the follicular production of steroidal mediators, estradiol-17β (oocyte growth), and 17α,20β-dihydroxy-4-pregnene-3-one (DP) or 4-pregnen-17,20β,21-triol-3-one (20β-S) (oocyte maturation). It has been established that both estradiol- 17β and 17α,20β-DP are biosynthesized by salmonid ovarian follicles through an interaction of two cell layers—namely, the thecal and the granulosa cell layers (two-cell-type model). The granulosa cell layers are the sites of production of these two steroidal mediators, but their production depends on the provision of the precursor steroids by the thecal cell layers.

331 citations


Journal ArticleDOI
Abstract: Maturation-inducing steroid in amago salmon (Oncorhynchus rhodurus) has been identified from media in which immature but fully grown folliculated oocytes of amago salmon had been incubated for 18-24 hr with chum salmon gonadotropin (SGA). The maturation-inducing (MI) activity of residues at various steps of purification was assessed by an in vitro germinal vesicle breakdown (GVBD) assay based on fully grown prophase-arrested folliculated oocytes of amago salmon. Ether extracts of the media from these incubates showed high MI activity. Yolk and oil droplets were removed from the ether extract by partition with equal volumes of 50% methanol and n-hexane. MI activity was found only in the 50% methanol phase. The 50% methanol phase was then fractionated (20 separate fractions) by reversed-phase high-performance liquid chromatography. MI activity was found only in fraction 10 which had a retention time coinciding exactly with 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-diOHprog). The purity and final characterization of the residues of fraction 10 were further confirmed by thin-layer chromatography and mass spectrometry with authentic 17 alpha,20 beta-diOHprog standard. The present study, together with our previous findings that in amago salmon 17 alpha,20 beta-diOHprog is the most potent steroid for the induction of oocyte maturation in vitro and is present at high concentrations in the plasma only around the time of oocyte maturation, indicates that 17 alpha,20 beta-diOHprog is the major naturally occurring maturation-inducing steroid in this species.

241 citations


Journal ArticleDOI
TL;DR: It is indicated that 17 alpha, 20 beta-diOHprog is the major steroid responsible for oocyte maturation in amago salmon, produced as the follicular mediator of gonadotropin.
Abstract: Plasma gonadotropin (GtH) and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOH-prog) levels were assessed by radioimmunoassay during the sexual maturation of female amago salmon (Oncorhynchus rhodurus). Both GtH and 17α,20β-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 17α,20β-diOHprog. In vitro production of 17α,20β-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 μg/ml stimulated low levels of production (0.2–0.3 ng/ml). Full-grown, immature follicles in October showed a dose-response production of 17α,20β-diOHprog, avaraging over 10 ng/ml when incubated with 1 μg/ml SG-G100. Postovulatory follicles (1–2 days after ovulation) produced large amounts of 17α,20β-diOHprog, averaging over 100 ng/ml with 1 μg/ml SG-G100. These results are discussed in relation to previous work on amago salmon and other species and together indicate that 17α,20β-diOHprog is the major steroid responsible for oocyte maturation in amago salmon, produced as the follicular mediator of gonadotropin.

159 citations