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1.
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. 相似文献
2.
综述促性腺素释放激素类似物(GnRH-a)缓释制剂(SRDS),人绒毛膜促性腺激素(HCG)SRDS,类固醇激素SRDS;雄烯二酮(ADSD)和17a-甲基睾丸酮(MT),以及鲤垂体匀浆(CPE)混合SRDS诱导海水养殖鱼类性腺发育成熟和生殖行为的效果,认为采用GnRH-a SRDS处理性腺发育良好的鲈形目鱼类和鲆鲽鱼类,可以显著提高血液促性腺激素(GtH)水平,且持续时间长,诱导排卵成功,HCG乳胶SRDS可诱导日本鳗鲡(Anguila japonicus)血液GtH持续 升高,性成熟系数明显升高并且性腺发育成熟;HCG和CPE水/油/水(W/O/W)复乳SRDS对日本鳗鲡的催熟效果显著,采用ADSD和MT SRDS SRDS可成功诱导日本鳗鲡性腺成熟与排卵。 相似文献
3.
P. Mark Lokman Kataraina A.N. George Graham Young 《Fish physiology and biochemistry》2003,28(1-4):283-285
To investigate the hormonal control of previtellogenic oocyte growth in eel, Anguilla australis, ovarian explants were incubated with or without different doses of steroid (11-ketotestosterone, estradiol-17β) or peptide hormones (ovine growth hormone, human insulin-like growth factor-I, human chorionic gonadotropin, porcine insulin) for 18 days. 11-Ketotestosterone, but not estradiol-17β, significantly increased oocyte diameters at physiological doses (30–100 ng/mL). Similarly, incubation with insulin-like growth factor-I, but not any of the other peptide hormones tested, resulted in increased oocyte diameters at high physiological doses (≥30 ng/mL). These data implicate androgens and hormones from the metabolic axis in mediating growth of previtellogenic oocytes in eel. 相似文献
4.
Michiya Matsuyama Shinji Adachi Yoshitaka Nagahama Katsuhiko Maruyama Shuhei Matsura 《Fish physiology and biochemistry》1990,8(4):329-338
Ovarian developmental stages and serum steroid hormone levels were examined at six different times of day (0100, 0600, 1000,
1300, 1600, 2000 h) in a marine teleost, the Japanese whiting Sillago japonica, which has an asynchronous-type ovary containing oocytes at various stages of development and spawns every day during a period
ranging up to three months. The largest oocytes in the ovaries at the active vitellogenic or post-vitellogenic stages were
found between 0100 and 1300 h. Oocyte maturation indicated by germinal vesicle breakdown (GVBD) occurred at 1600 h, and ovulated
oocytes were observed in the ovaries collected at 2000 h. These processes were accompanied by a significant daily change in
serum steroid hormone levels. The serum level of estradiol-17β showed a peak in fish with mature oocytes sampled at 1600 h.
In these fish, the second-largest oocytes in the ovaries were at the initial stage of vigorous vitellogenesis, the secondary
yolk stage. Therefore the highest level of serum estradiol-17β was considered to be due to the second-largest oocytes. Testosterone
levels remained low and constant throughout the experimental period. The serum levels of 17α,20β-dihydroxy-4-pregnen-3-one
(17α,20β-diOHprog) peaked at 1600 h at which time all fish had mature oocytes. These results indicate that the Japanese whiting
possesses a diurnal rhythm of oocyte development including vitellogenesis, oocyte maturation and ovulation, and further suggest
that daily cycles in oocyte growth and maturation which simultaneously take place in an ovary are regulated by diurnal secretions
of estradiol-17β and the maturation-inducing steroid, 17α,20β-diOHprog. 相似文献
5.
Triploid fish have under-developed gonads due to altered reproductive endocrinology. Triploids of Indian catfish (H. fossilis) showed significantly reduced plasma levels of gonadotropin (GtH-II), testosterone (T) and estradiol-17 (E2) than that of diploids throughout the year, except for the resting phase, irrespective of sex. Plasma levels of GtH-II were significantly different (p<0.001) between diploid and triploid fish during preparatory, prespawning and spawning phase. The plasma testosterone contents in triploids were significantly less (p<0.001) than that of diploids, except during the resting phase. Triploid females showed very low titres of estradiol-17 (<1 ng ml–1) throughout the annual reproductive cycle in contrast to highly fluctuating levels in diploid females. Thus, this study for the first time provides information on reduced levels of GtH-II and sex steroids in plasma of male triploid fish and additional information on species-specific alteration of sex hormones in female triploids. 相似文献
6.
Steroid profiles of cultured and captive red drum (Sciaenops ocellatus L.) were investigated to evaluate the potential use of circulating sex steroid levels as a tool for gender identification in this species. Cultured 18‐month‐old fish were maintained on a 120‐day shortened photothermal cycle to induce precocious maturation. Additionally, wild‐caught fish were maintained in captivity under simulated natural photothermal conditions from late spring to early fall. Circulating 11‐ketotestosterone (11‐KT) levels were significantly higher in males compared with females during the early stages of gonadal growth in both cultured and captive fish. Plasma testosterone (T) levels showed a similar trend; however, the differences were significant only when males were already producing sperm. 17β‐estradiol (E2) concentrations were low in males and females before gonadal recrudescence but increased significantly with the progression of vitellogenesis in females. These results show that a test using a minimum concentration of circulating 11‐KT could be developed to differentiate between sexes in the early stages of gonadal maturation in red drum. Moreover, plasma E2 concentrations could be used to identify vitellogenic females. The two steroids considered together could help avoid possible error in gender identification due to unusually high levels of certain steroids encountered in some individuals. 相似文献
7.
The glutamate agonist, N-methyl-D,L-aspartate (NMA) stimulates the secretion of growth hormone (GH) from pituitary fragments
in vitro and increases plasma GH levels in vivo in rainbow trout, Oncorhynchus mykiss (Flett et al. 1994; Holloway and Leatherland
1997a,b); however gonadal steroid hormones appear to modulate this response in experimental situations. This study examines
whether steroid hormones also modulate the GH-regulatory actions of NMA during the normal reproductive cycle of rainbow trout
by examining the relationship between the stage of sexual maturation and the pituitary release of GH in vitro in response
to an NMA (10-8 M) challenge. NMA had no effect on mean GH release from the pituitary glands of fish that were immature (GSI <1.0), from
males during early development (GSI 1.0-3.0), or from sexually mature males (with free running milt) and females (ovulated).
However, NMA significantly increased GH release from pituitary glands taken from females during the early stages of gonadal
growth (GSI 1.0-9.0) and from males and females sampled during the later stages of gonadal growth (males GSI 3.01-6.0; females
GSI 9.01-15.0). The GH-stimulatory action of NMA in males and females progressed to a maximum effect during the late stages
of gonadal growth, and disappeared in ovulated females and free running males. Moreover, in female fish, the maximal GH release
in response to the NMA challenge is positively correlated with plasma 17β-estradiol levels; no such correlation was evident
for plasma testosterone levels in males. Changes in the GH response to NMA during maturation while gonadal steroid levels
fluctuate provides further evidence to suggest that the effects of NMA on GH secretion are intimately linked to endogenous
gonadal steroid hormone levels.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Hiroaki Chiba Kenji Iwatsuki Kazuo Hayami Akihiko Hara Kohei Yamauchi 《Journal of the World Aquaculture Society》1994,25(4):553-560
Changes in serum concentrations of estradiol-17β, testosterone, 17α,20βdihydroxy-4-pregnen-3-one, and vitellogenin were investigated during ovarian development induced by injection of a salmon pituitary extract in cultured European eel Anguilla anguilla . Vitellogenesis was induced with a weekly dose of 50 mg pituitary extract/kg body weight. In eels receiving that dose, gonadsomatic indices ranged from 20–43% after the 10th–11th weekly injection. Body weights were relatively stable during vitellogenesis, but increased dramatically during final maturation. Serum estradiol-17β levels increased slightly during vitellogenesis and peaked at an average of 6.95 ng/mL at final maturation. The profile of serum vitellogenin followed that of estradiol-17β which increased markedly from an average of 0.36 to 20.72 mg/mL. Control levels of vitellogenin were undetectable throughout the study. Average serum levels of testosterone increased to a peak of 17.74 ng/mL in the early stage of vitellogenesis, followed by a sharp drop to initial levels (3.86 ng/mL) in the late stage of vitellogenesis, and then increased again to an average of 8.84 ng/mL at the final maturation stage. Serum 17α,20β-dihydroxy-4-pregnen-3-one was not detected (<50 pg/mL) throughout the experiment. Profiles of serum estradiol-17β, testosterone, and vitellogenin observed during ovarian development appear different from those found in salmonids and other teleosts. This study indicates, however, that cultured European eels are a useful model for study of gonadal maturation in the eel. 相似文献
9.
Wen-Hung Twan Hua-Fang Wu Jiang-Shiou Hwang Yan-Horn Lee Ching-Fong Chang 《Fish physiology and biochemistry》2005,31(2-3):111-115
Most broadcast spawning scleractinian corals synchronously release gametes during a brief annual spawning period. In southern
Taiwan, the mass spawning of scleractinians occurs in lunar mid-March. Endocrine system has been proposed to play important
roles in this annual phenomenon. A scleractinian coral, Euphyllia ancora has been selected as a model for the hormones and reproduction studies. We detected the presence of estradiol (E2), testosterone
(T), glucuronided E2, glucuronided T, aromatase, immunoreactive (ir)GnRH in coral polyps E. ancora. Annual profiles of sex steroids, aromatase, and irGnRH have also been characterized. We found the parallel increases in
irGnRH concentrations, aromatase activity and free E2 and glucuronided E2 concentrations at the time of coral mass spawning.
The stimulation of mammalian (m)GnRH agonist in the increased aromatase activity and sex steroid concentrations was also observed
in corals. Coral extracts (irGnRH) and mGnRH agonist had a similar dose-dependent effect on luteinizing hormone release in
black porgy fish pituitary cells (in vitro). In conclusion, our data suggest that irGnRH and glucuronided E2 may play important
roles in the control of reproduction and mass spawning in corals. Corals already evolved the vertebrate-type hormone system
in the sexual reproduction. 相似文献
10.
A group of Atlantic salmon (Salmo salar) was followed through their first year of maturation and spawning. At monthly intervals, starting with juvenile fish in December, 5–7 fish of each sex were killed, and liver and plasma were sampled. The last sampling point was of spawning fish in November a year later. Variables in the cytochrome P450 (P450) system were studied in hepatic microsomes, and estradiol 17 was measured in the plasma of females to assess the maturational status. The P450 1A1-mediated 7-ethoxyresorufin O-deethylase (EROD) started at high levels in winter, but decreased to non-detectable activities in pre-spawning females. Decreases, but not to the same extent, were also observed during this period in total cytochrome P450, cytochrome b5, NADPH-cytochrome P450 reductase, and in the content of two immunochemically determined P450 isozymes. At the same time, LSI levels increased in maturing females (starting in July), and GSI levels increased in both sexes (starting in May). Sex specific differences were observed in pre-spawning fish in September and October, with levels of total P450, b5, NADPH-cytochrome P450 reductase, EROD and P450 isozymes significantly lower in females. At the same time, plasma estradiol-17 levels reached peak values in females. The results point to the important role of sex steroids such as estradiol-17 as major factors in the regulation of final sexual maturation. However, this study also indicates that there may be estradiol-17 independent events of equal importance in the early stages of gonadal maturation that may involve the P450 system. The changes observed in the P450 system (as a major drug and steroid metabolizing system) of Atlantic salmon during sexual maturation may be of importance both in the endogenous transduction of hormonal signals, and as a pharmacological basis for designing therapeutic treatment of diseases in the aquaculture industry.Parts of this work were presented at the 5th International Symposium on Responses of Marine Organisms to Pollutants, April 1989 in Plymouth, United Kingdom (Larsen and Goks\/oyr 1989). 相似文献
11.
K. Mol N. Byamungu B. Cuisset Z. Yaron M. Ofir Ch. Mélard M. Castelli E. R. Kühn 《Fish physiology and biochemistry》1994,13(3):209-218
Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower
growth rate of females. When females and males are considered separately, the growth rate is not significantly different in
diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and
17β-estradiol (E2)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological
concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but
the difference is not always significant.
Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months
compared to the triploid females and diploid males. 3,5,3′-triiodo-L-thyronine (T3) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in
4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth
rate of males may be related to the high circulating levels of T3 and 11kT. 相似文献
12.
Anita M. Kelly Christopher C. Kohler E. Gordon Grau 《Journal of the World Aquaculture Society》1996,27(4):384-401
The effects of a mammalian growth hormone-releasing hormone (GHRH), PrebGRF(1–78)OH (bGHRH), on growth and serum growth hormone (GH) levels were investigated in tilapias Oreochromis mossambicus and O. niloticus × O. aureus . Fish were injected intramuscularly or implanted intramuscularly (Silastic or cholesterol implants) with distilled water, 0.1 μg/kg bGHRH, 1.0 μg/kg bGHRH, 10.0 μg/kg bGHRH, or 100.0 μg/kg bGHRH and compared to untreated controls, fish implanted with 60 mg/kg 17α-methyltestosterone (MT), or a combination of bGHRH concentrations plus either MT, 0.01 μg/kg of a thyroid hormone (T3 ), or 0.01 μg/kg of a glucocorticoid (DEX). The bGHRH increased serum GH levels in tilapia maintained at suboptimal temperatures (18 C). Serum GH levels were highest (5.3–0.45 ng/mL) for fish injected with 10.0 μg/kg bGHRH. Fish implanted with a Silastic implant containing 10.0 μg/kg bGHRH had significantly higher (4.35–0.35 ng/mL) serum GH levels than those with an equivalent dosage in a cholesterol implant. The addition of MT, thyroid hormones, and glucocorticoids did not increase serum GH levels above those obtained for fish receiving bGHRH alone. Tilapia reared at suboptimal temperatures and implanted with 10.0 μg/kg and 100.0 μg/kg bGHRH had significantly greater increases in weight and length than control fish. Fish implanted with bGHRH, MT or bGHRH plus MT had significantly higher moisture and protein content, while fat and ash contents were significantly lower than controls or sham-implanted fish. Fish implanted with bGHRH or bGHRH plus MT had significantly higher gonadosomatic indices than fish implanted with MT alone, shams or non-treated controls. This study demonstrates that a mammalian GHRH stimulates release of GH, promotes somatic and gonadal growth and may affect reproductive performance in tilapia. 相似文献
13.
Pham KX Amano M Kurita Y Shimizu A Fujinami Y Amiya N Yamamori K 《Fish physiology and biochemistry》2008,34(4):357-365
The role of gonadotropin (GTH) in the reproduction of the Japanese flounder, Paralichthys olivaceus, was studied by assessing the changes in the apparent activity of follicle-stimulating hormone (FSH) and luteinizing hormone
(LH) in the pituitary gland during gonadal maturation by immunohistochemical analyses. Corresponding changes in plasma levels
of testosterone (T), estradiol-17β (E2), and 17α,20β-dihydroxy-4–pregnen-3-one (DHP) were also studied. Reared fish at the early spawning to termination stages
were sampled from May to August and wild fish at the previtellogenic to termination stages were caught at 3- to 4-week intervals
between April and September offshore from the northern mainland of Japan by gill nets. The gonadosomatic index of the reared
fish decreased from the early spawning stage to the termination stage, while that of the wild fish increased significantly
from the previtellogenic stage to the early spawning stage and decreased thereafter. In the reared fish, the immunostaining
intensities of FSH and LH were high during the spawning period, accompanied by high plasma levels of T, E2, and DHP. In the wild fish, the immunostaining intensities of FSH and LH were low during the previtellogenic stage but increased
during the maturing and spawning stages. These results indicate that both FSH and LH are likely associated with oocyte maturation
in the Japanese flounder. 相似文献
14.
This study investigated the in vivo and in vitro effects of Rhizopus (filamentous fungus) extract (RU) in masu salmon Oncorhynchus masou Brevoort. Underyearling fish were fed with RU for 16 months. Monthly changes in body growth, gonadal maturation and serum levels of sex steroids were monitored. Gonads were also incubated at 0, 1, 10, 100 and 1000 μg RU mL−1 Leibovitz's L‐15 medium for 18 h. The levels of steroids in serum and cultured medium were measured. It was determined that RU‐fed immature and mature males, when compared with control groups, showed significantly higher body growth during spring, summer and the spawning period. Similarly, immature RU‐fed females showed significantly higher fork length and body weight in autumn, spring and summer. Furthermore, RU‐fed males showed significantly higher levels of serum testosterone (T) and 11‐ketotestosterone (11‐KT) levels in the pre‐spawning season, and 17α, 20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) in the spawning season. In vitro RU incubation of gonads showed a dose‐dependent and significant increase in T, 11‐KT, oestradiol‐17β and DHP release in the medium. It appears that the causes of enhanced body growth and increased steroid production herein observed in salmonids are the physiologically active substances that may be present in the mycelium of the fungus. 相似文献
15.
Wild striped bass,Morone saxatilis, were collected from coastal waters and spawning areas to describe the endocrine correlates of oocyte development in non-captive, migratory fish. The fish were classified according to their most advanced oocytes. Serum levels of estradiol (E2), testosterone (T) and 17-20-dihydroxyprogesterone (DHP) were measured by radioimmunoassay (RIA). Females in the primary growth phase and early secondary growth phase (pre-vitellogenic) had low levels of plasma steroids, ovarian lipid content and gonadosomatic indices (GSIs). Significant increases in E2, T, ovarian lipid content and GSIs occurred during the vitellogenic phase. Maximum levels of all reproductive parameters were found in prespawning fish sampled in the Hudson River. Mean levels of E2, T, ovarian lipids and GSIs for these fish were 2.0±0.5 ng/ml, 3.0±0.3 ng/ml, 24±1 mg/g, and 5.6±0.3% (mean±SEM), respectively. In fish induced to spawn with human chorionic gonadotropin (HCG), DHP levels (1.9±0.4 ng/ml) were significantly elevated. Similar levels were found in two fish captured during the spawning season, suggesting that DHP may serve as the maturation-inducing steroid in this species. 相似文献
16.
Ryusuke Sudo Ryota Tosaka Shigeho Ijiri Shinji Adachi Hiroaki Suetake Yuzuru Suzuki Noriyuki Horie Satoru Tanaka Jun Aoyama Katsumi Tsukamoto 《Fisheries Science》2011,77(4):575-582
To improve understanding of the mechanism of early ovarian development in eels, the effects of water temperature decrease
on oocyte development, plasma levels of sex steroids [estradiol 17β (E2), testosterone (T), 11-ketotestosterone (11-KT)],
and gonadotropin β-subunit [follicle-stimulating hormone (FSHβ), luteinizing hormone (LHβ)] messenger RNA (mRNA) expression
levels were investigated. A total of 27 female Japanese eels Anguilla japonica were divided into initial, control, and test (water temperature decrease) groups. Starting on 22 September 2009, eels in
the test group were reared in a tank with gradual temperature decrease from 25°C to 15°C over 39 days, while the control group
was maintained at 25°C. The test group accumulated more oil droplets in their oocytes than did the other groups. Levels of
sex steroids, especially 11-KT, were higher in the test group. In contrast, FSHβ and LHβ mRNA expression levels were lower
in the test group. These results suggest that water temperature decrease only induced an early stage of ovarian development
that was partly affected by an 11-KT increase. For further maturation, other environmental factors related to induction of
gonadotropin increase appear to be needed. 相似文献
17.
Effects of steroid hormones on immunoglobulin M (IgM) in rainbow trout, Oncorhynchus mykiss 总被引:3,自引:0,他引:3
The immunosuppressive effects of steroid hormones were evaluated as the response against implanted steroid hormones, cortisol (F), testosterone (T), estradiol-17 (E2), and 11- ketotestosterone (11-KT), in juvenile rainbow trout. In long term experiments (5 weeks), fish were given a single intraperitoneal implant of F or T. A clear suppressive effect of plasma IgM levels with F and T was not necessarily obtained, although mucus IgM levels were reduced corresponding to the elevated plasma steroid hormone levels. In short term experiments (1 week), intraperitoneal implantation of T, 11-KT and E2 suppressed plasma and mucus IgM levels, although the effects were not dose-dependent. When administered through diet, F and T caused a suppression of plasma IgM levels; F administration at both high and low dosages caused a significant decrease in plasma IgM levels, while only a high dose of T caused the suppression. These results suggest that sex steroid hormones, as well as F, have immunosuppressive functions in rainbow trout. 相似文献
18.
Pituitary gonadotropin (GTH) secreting cells and brain gonadotropin-releasing hormone (GnRH) secreting neurons are known to be subjected to feedback control by gonadal steroid in teleosts. In masu salmon, Oncorhynchus masou, salmon GnRH (sGnRH) neurons in the ventral telencephalon (VT) and the preoptic area (POA) are involved in the control of GTH cells because sGnRH synthesis in these areas is activated with gonadal maturation. In this study, we attempted to clarify mechanisms of feedback control of sGnRH neurons by gonadal steroids. We examined the effects of 17-methyltestosterone (MT) on sGnRH synthesis in yearling and 2-year-old female fish (which were immature during experimentation in May), and the effects of castration on sGnRH synthesis in underyearling precocious male fish in August. sGnRH synthesis in the POA, but not in the VT, was increased by MT administration in 2-year-old females only, indicating higher sensitivity to MT in the preoptic sGnRH neurons. Castration increased sGnRH synthesis in the VT but not in the POA. These results suggest that sGnRH neurons in the VT and those in the POA are differentially regulated by gonadal steroids. 相似文献
19.
Changes in Plasma Concentrations of Sex Steroids in Adult Pacific Halibut, Hippoglossus stenolepis 总被引:1,自引:0,他引:1
Han Wu Liu Robert R. Stickney Walton W. Dickhoff 《Journal of the World Aquaculture Society》1991,22(1):30-35
Blood samples were collected from captive Pacific halibut, Hippoglossus stenolepis , at intervals of about six weeks from early December 1986 to late November 1987. Concentrations of plasma androgen and estradiol-17β were determined by radioimmunoassay. The plasma concentrations of steroid were highest during autumn and winter in halibut that matured during late winter. The concentrations of steroids in samples collected in December were above 2 ng/mL (estradiol) or 1 ng/mL (androgen) in maturing females and below 0.5 ng/mL for both steroids in non-maturing females. The levels of steroids decreased rapidly about one month before spawning. In a mature male, androgen began to rise in August and November, and reached a peak of 7 ng/mL in early December. One month before spawning, the androgen concentration fell to 0.16 ng/mL. Estradiol concentrations were detectable in the male and varied little during the year. In immature fish, neither androgen nor estradiol changed significantly throughout the year. These results suggest that the concentrations of estradiol or androgen measured in blood samples taken during December may be used to determine the sex and state of maturation of Pacific halibut. 相似文献
20.
Makito Kobayashi Peter W. Sorensen Norm E. Stacey 《Fish physiology and biochemistry》2002,26(1):71-84
Species that employ sexual reproduction must synchronize gamete maturity with behavior within and between genders. Teleost
fishes solve this challenge by using reproductive hormones both as endogenous signals to synchronize sexual behavior with
gamete maturation, and as exogenous signals (pheromones) to synchronize spawning interactions between fish. This dual role
of hormonal products is best understood in the goldfish, an external fertilizer with a promiscuous mating system. Female gonadal
growth and vitellogenesis is stimulated by 17β-estradiol (E2) which also evokes release of a recrudescent pheromone. At the
completion of vitellogenesis, ovarian E2 production drops and plasma testosterone increases, sensitizing the female gonadotropin
II (luteinizing hormone; LH) system to environmental cues (temperature, spawning substrate, pheromones). These cues eventually
trigger a LH surge that alters steroidogenesic pathways to favor the production of progestins including 17,20β-dihydroxy-4-pregnen-3-one
(17,20β-P). Plasma 17,20β-P stimulates oocyte maturation but is also released to the water along with sulfated 17,20β-P and
androstenedione to serve as a preovulatory pheromone. This pheromone stimulates male behavior, LH release, and sperm production.
At the time of ovulation, females become sexually active in response to prostaglandin F2α (PGF2α) synthesized in the oviduct.
PGF2α and its metabolites are released as a postovulatory pheromone that induces male spawning behavior which further increases
male LH and sperm production. Androgenic hormones are required for male behavior and LH release. Although goldfish are gonochorists,
hormone treatments can induce heterotypical functions in adults. Similar findings in other fish demonstrate that a sexually
bipotential brain is not restricted to hermaphroditic fishes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献