Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout oogenesis and influence of steroid hormones

Weil, Claudine; Marcuzzi, Odile

doi:10.1016/0016-6480(90)90079-2

Cited by 30 publications

(7 citation statements)

References 31 publications

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“…However, it is not known whether a similar mechanism operates in adult teleosts. On the other hand, it has been shown in early-recrudescing rainbow trout and goldfish that steroids can act directly at the pituitary to potentiate the effect of LHRHa on in vitro GTH II release [20,39]. Therefore, the stimulation of basal and LHRHa-induced GTH II secretion by gonadal steroids could potentially involve two different mechanisms.…”

Section: Discussionmentioning

confidence: 90%

Gonadal Stage-Dependent Effects of Gonadal Steroids on Gonadotropin II Secretion in the Atlantic Croaker (Micropogonias undulatus)1

Khan

Hawkins

Thomas

1999

Biology of Reproduction

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Involvement of gonadal steroids in the control of gonadotropin II (GTH II) (homologous to LH) secretion was investigated in the Atlantic croaker (Micropogonias undulatus) using gonadectomy (Gx) and steroid replacement paradigms. Gonadectomy in males and females during the late gonadal recrudescence phase elicited significant increases in the gonadotropin response to stimulation by an LHRH analog (LHRHa), without altering basal GTH II secretion. Slow-release silicone elastomer implants of testosterone or estradiol significantly inhibited LHRHa-induced GTH II secretion in gonad-intact and Gx males, and in Gx females, whereas 5alpha-dihydrotestosterone, a nonaromatizable androgen, was ineffective. Pretreatment of fish with an aromatase inhibitor, 1,4, 6-androstatrien-3,17-dione, 2 days before the administration of testosterone implants, completely blocked the negative effect of testosterone on LHRHa-induced GTH II secretion in males, but only partially restored it in females. This suggests that the negative feedback of testosterone in males is primarily mediated by its conversion to estradiol at the level of the hypothalamus and/or pituitary gland, while in females the androgen may also exert a direct inhibitory effect on GTH II secretion, probably mediated via an androgen receptor. In addition, estradiol and testosterone exerted positive effects on basal and LHRHa-induced GTH II secretion during the early-recrudescence phase of the gonadal cycle. The steroids switched to a negative effect on LHRHa-induced GTH II secretion once the fish had fully developed gonads, possibly as a mechanism that prevents a precocious surge in GTH II secretion and final gamete maturation until gametogenesis is complete and the environmental conditions are appropriate for spawning.

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Section: Discussionmentioning

confidence: 90%

Gonadal Stage-Dependent Effects of Gonadal Steroids on Gonadotropin II Secretion in the Atlantic Croaker (Micropogonias undulatus)1

Khan

Hawkins

Thomas

1999

Biology of Reproduction

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“…This initial elevation of plasma E 2 was probably an early response to the GtH II surge resulting from the increased T production by the ovary and the existence at this time of a highly active aromatase system (reviewed by Nagahama et al, 1994). This rise may signal the completion of vitellogenesis in the first batch of oocytes to be matured and may also enhance GtH II synthesis (Weil & Marcuzzi, 1990) in preparation for the pre-ovulatory surge of GtH II. With the subsequent inhibition of aromatase activity by GtH II (Fostier, 1995), E 2 decreased and T increased further in the plasma, whereas with the subsequent inhibition/activation of other ovarian enzymes the steroidogenic shift was completed with the eventual production of the MIS (Nagahama et al, 1994).…”

Section: Histological Examination Of White Bass Oocytesmentioning

confidence: 99%

Reproductive biology and endocrine regulation of final oocyte maturation of captive white bass

Mylonas

Magnus

Klebanov

et al. 1997

Journal of Fish Biology

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The ovarian development, and plasma levels of gonadotropin II (GtH II) and sex-steroid hormones at the end of vitellogenesis were examined in captive white bass Morone chrysops. The changes in plasma hormone levels and oocyte morphology associated with gonadotropinreleasing hormone agonist (GnRHa)-induced final oocyte maturation (FOM) were studied. Although plasma 17 -oestradiol (E 2 ) and oocyte diameter increased, there were no changes in GtH II, testosterone (T), 17,20 -dihydroxy-4-pregnen-3-one (17,20 -P) or 17,20 ,21dihydroxy-4-pregnen-3-one (17,20 ,21-P) in non-hormone-treated females, and no FOM was observed. Treatment with a sustained-release GnRHa delivery system (GnRHa implant) induced two FOM cycles separated by about 24 h, with the release of approximately equal numbers of eggs in each spawn. Plasma GtH II levels were elevated significantly throughout FOM, reaching a maximum of 9·07 1·55 ng ml 1 in ovulated fish. Both plasma E 2 and T increased soon after the GnRHa treatment, but E 2 declined in fish undergoing germinal vesicle (GV) migration. Plasma T increased further during FOM (7·55 2·87 ng ml 1 ), but declined precipitously at ovulation. A surge in plasma 17,20 -P and 17,20 ,21-P (4·11 0·97 ng ml 1 and 3·10 0·77 ng ml 1 , respectively) was observed in females undergoing GV breakdown (GVBD). Based on the involvement of different sex-steroid hormones, FOM was separated into two stages. Early FOM included lipid-droplet coalescence and GV migration, and was associated with elevations in plasma GtH II and T. Late FOM included GVBD and yolk-globule coalescence, and was associated with elevations in plasma GtH II, 17,20 -P and 17,20 ,21-P. The results of this study point to the absence of a surge in plasma GtH II as the missing link in the reproductive axis responsible for the failure of captive white bass to undergo FOM at the end of vitellogenesis. Sustained elevation of plasma GtH II via treatment with a GnRHa implant induced two consecutive spawns with an overall egg production two-to eightfold higher than previously obtained from captive broodstocks, and similar to annual egg production values reported for wild fish. 1997 The Fisheries Society of the British Isles

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“…Pituitary collection. At each defined stages of spermatogenesis, 10 to 30 animals were anesthetized with phenoxy-ethanol before pituitary removal, as described for females (Weil and Marcuzzi, 1990).…”

Section: Pituitary Response To Salmon Gnrh (Sgnrh) In Control and Stementioning

confidence: 99%

“…Cell cultures. Cultures were performed as described for such a study in females (Weil and Marcuzzi, 1990), using the technique previously set up for this species (Weil et al, 1986).…”

Section: Pituitary Response To Salmon Gnrh (Sgnrh) In Control and Stementioning

confidence: 99%

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Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout spermatogenesis and influence of steroid hormones

Weil

Marcuzzi

1990

General and Comparative Endocrinology

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Using primary cultures of whole dispersed pituitary cells collected from rainbow trout at different stages of spermatogenesis, basal and GnRH-induced GtH release and cell GtH content were studied in control and steroid-pretreated cultures. Steroid pretreatments were performed for 3 days with 11-ketotestosterone (11KT) and 17 alpha-hydroxy,20 beta-dihydroprogesterone (17 alpha 20 beta p) at levels corresponding to those circulating at the time of spermiation (50 and 20 ng/ml, respectively). In control cultures, basal GtH release and cell GtH content increased with the stage of spermatogenesis in a characteristic pattern as predicted from in vivo results concerning plasma and pituitary GtH contents. The pituitary response to salmon GnRH (sGnRH) also varied as indicated by the decrease in the minimal effective dose of GnRH able to induce a significant GtH release with the advancement of spermatogenesis: 10(-7) M at the spermatocyte stage, 10(-9) M at prespermiation and spermiation. Steroid pretreatments were shown to have a direct effect on pituitary gonadotrophs and particularly on pituitary response to sGnRH, depending on the stage at which they are applied. At the beginning of spermatogenesis both of them induced an increase in GtH release and at prespermiation they have a slight negative effect, significant only with 17 alpha 20 beta P. At spermiation they have no effect except for 17 alpha 20 beta P which increased the response to 10(-8) M of sGnRH. Results are discussed in relation to hormonel changes (gonadotropin and steroid) observed by different authors during the sexual cycle.

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Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout oogenesis and influence of steroid hormones

Cited by 30 publications

References 31 publications

Gonadal Stage-Dependent Effects of Gonadal Steroids on Gonadotropin II Secretion in the Atlantic Croaker (Micropogonias undulatus)1

Gonadal Stage-Dependent Effects of Gonadal Steroids on Gonadotropin II Secretion in the Atlantic Croaker (Micropogonias undulatus)1

Reproductive biology and endocrine regulation of final oocyte maturation of captive white bass

Cultured pituitary cell GtH response to GnRH at different stages of rainbow trout spermatogenesis and influence of steroid hormones

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