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Activin (AA, AB and BB) is a dimeric protein that belongs to the transforming growth factor- (TGF-) superfamily of growth factors and is involved in the regulation of many physiological and developmental processes. Recently, we have demonstrated that porcine activin stimulated goldfish gonadotropin-II (GTH-II) and growth hormone (GH) secretion from dispersed pituitary cells in static culture and pituitary fragments in perifusion. The action of activin in the goldfish is unique in that it has an acute stimulatory effect on the secretion of GTH-II and GH, whereas in mammals activin usually exhibits long-term stimulatory actions on FSH secretion. The action mechanism of activin is different from that of gonadotropin-releasing hormone (GnRH). Using domain-specific antibodies against mammalian activin subunits, we subsequently demonstrated the existence of immunoreactive activin subunits (A and B) in the goldfish ovary, testis, pituitary and brain, suggesting endocrine, paracrine and autocrine roles for activin in the regulation of goldfish reproduction. Both activin A and B subunits have been cloned from goldfish genome by polymerase chain reaction (PCR). Using the PCR fragments as probes, we have cloned a full length cDNA coding for activin B subunit from the goldfish ovary. Both activin A and B subunits show high homology to those of other vertebrates with the B subunit much more conserved (93 and 98% identity with human and zebrafish B subunit, respectively). The identity of the cloned B subunit was further confirmed by expression in the Chinese hamster ovary (CHO) cells and detection of the specific activity of activin in the culture medium. The messenger RNA of activin B subunit is expressed in a variety of goldfish tissues including ovary, testis, brain, pituitary, kidney and liver, suggesting a wide range of physiological roles for activin in the goldfish. We have also cloned a full length cDNA coding for the activin Type IIB receptor from the goldfish ovary, suggesting that activin may have paracrine or autocrine actions on the ovarian functions. The identity of the cloned receptor was confirmed by specific binding of125 I-activin on COS-1 cells transfected with the cloned Type IIB receptor. 相似文献
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Patrick Prunet Jean-François Gonnard Gilles Paboeuf 《Fish physiology and biochemistry》1993,11(1-6):131-137
The involvement of γ-aminobutyric acid (GABA) in the control of prolactin (PRL) release was investigated in rainbow trout
using both perifused pituitary fragments and pituitary cells in primary culture. In our perifusion system, infusion of GABA
(10−6 to 10−4 M) caused an inhibition of PRL release (between 20 and 40%). Administration on perifused pituitary fragments of 3APS, a GABAa
agonist, mimicked this inhibitory effect. Moreover, bicuculline, a specific antagonist of GABAa receptors, totally abolished
GABA effect. When tested on cultured pituitary cells during 40h exposure, GABA (10−5 M) caused a significant decrease in PRL release (24.5%). Baclofen, a specific agonist for GABAb receptor tested at 10−6 and 10−5 M, also inhibited PRL released from cultured pituitary cells. These results demonstrate that GABA inhibits PRL release by
acting directly on pituitary cells and that probably both types of GABA receptor (a and b) are involved in this regulation.
Résumé Nous avons étudié l'implication de l'acide γ-aminobutirique (GABA) dans le controle de la sécrétion de prolactine (PRL) chez la truite arc-en-ciel en utilisant à la fois des fragments d'hypophyse perifusés et des cellules hypophysaires en culture. Dans notre système de périfusion, le GABA (10−6 à 10−4 M) inhibe la libération de PRL (entre 20 et 40%). L'administration sur les fragments d'hypophyse périfusés de 3APS, un agoniste des récepteurs GABAa, reproduit ces effets inhibiteurs. De plus, la bicuculline, un antagoniste spécifique des récepteurs de type GABAa, abolie complètement les effets du GABA. Lorsqu'il est testé pendant 40h sur des cellules en culture, le GABA (10−5 M) réduit de manière significative la libération de PRL (24.5%). Le Baclofen, un agoniste spécifique des récepteurs GABAb testé à 10−6 et 10−5 M, inhibe aussi la libération de PRL par les cellules en culture. Ces résultats démontrent que le GABA inhibe la libération de PRL en agissant directement sur les cellules hypophysaires et que les 2 types de récepteurs GABA (a et b) sont impliqués dans cette régulation.相似文献
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Francis Gonnet Alain Barret Dominique Grouselle Patrick Prunet 《Fish physiology and biochemistry》1989,7(1-6):301-308
Hypothalamic control of prolactin (PRL) release in immature rainbow troutSalmo gairdneri was investigated using anin vitro perifusion system of the rostral pars distalis. Hypothalamic extract of trout induced a dose-dependent stimulation of PRL
release. A similar effect was observed when infusing the medium from a 24h static incubation of the hypothalamus. Extracts
from different control tissues (muscle, liver, gut) did not changein vitro release, thus confirming the specificity of this stimulatory effect. Hypothalamic extract from adult male rat, known to contain
PRL release inhibiting factors, stimulatedin vitro PRL secretion in rainbow trout. This suggests that PRL cells are predominantly influenced by PRL releasing factors. Measurement
of TRH and serotonin content in trout hypothalamus indicated consistent physiological levels of these two factors. HPLC studies
of hypothalamic extract showed that immunoreactive — TRH eluted at the same place as labelled TRH standard. Moreover, pizotifen,
a serotonin antagonist, partially inhibited the stimulation observed with trout hypothalamic extract. These results suggest
that, in immature rainbow trout, PRL release is under stimulatory hypothalamic control and that serotonin and probably TRH
play a major role in this control. 相似文献
4.
It has been established that secretion of gonadotropin (GtH) and growth hormone (GH) release in goldfish are both stimulated
by GtH-releasing hormone (GnRH); in addition GtH secretion is inhibited by dopamine D2 mechanisms. In the present study, depletion of protein kinase C (PKC) in goldfish pituitary cells reduced the GtH and GH
responses to GnRH and an activator of PKC in static culture. In perifusion studies, GtH released in response to sGnRH analog
was greatly attenuated in PKC-depleted cells, however, hormone responses to forskolin were enhanced. Stimulation of dopamine
D2 receptors reduced the GtH, but not the GH, responses elicited by PKC activators. These results indicate that PKC participates
in the GtH and GH responses to natural neuroendocrine regulators in the goldfish.
Résumé Il a été établi que chez le poisson rouge, les sécrétions de gonadotropine (GtH) et d'hormone de croissance (GH) sont toutes les deux stimulées par la gonadolibérine (GnRH); de plus, la sécrétion de GtH est inhibée par des mécanismes dopaminergiques de type D2. Dans le présent travail, la déplétion de la teneur en protéine kinase C (PKC) dans des cellules hypophysaires de poisson rouge réduit les résponses en GtH et GH au GnRH et à un activateur de la PKC de cellules maintenues en incubation statique. Dans des cellules maintenues en périfusion et soumises à une déplétion en PKC, la GtH libérée en réponse à un analogue du sGnRH est fortement diminuée, cependent les réponses hormonales à la forskoline sont augmentées. La stimulation des récepteurs dopaminergiques D2 réduit, dans le cas d'action d'activateur de la PKC, la réponse en GtH mais pas en GH. Ces résultats indiquent que la PKC est impliquée dans les mécanismes de régulation de GtH et GH par des facteurs neuroendocriniens naturels.相似文献
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采用脑垂体离体灌流孵育系统,研究细胞外 Ca~(2+)和 K~+对鲤鱼脑垂体基础的和鲑鱼促性腺激素释放激素(sGnRH)刺激的生长激素(GH)分泌的影响。离体灌流孵育的鲤鱼脑垂体基础 GH分泌和 sGnRH 刺激的 GH 分泌都是细胞外 Ca~(2+)依赖的,缺细胞外 Ca~(2+)存在时,基础 GR分泌显著下降,2分钟脉冲式 sGnRH 刺激的 GH 分泌反应接近消失。Ca~(2+)通道阻滞剂异搏定以剂量依存形式显著抑制基础的和2分钟脉冲式sGnRH 刺激的 GH 分泌,表明细胞外 Ca~(2+)的作用至少部分通过细胞膜电位敏感性 Ca~(2+)通道。50mM K~+显著刺激基础GH 分泌,并显著加强高剂量sGnRH 刺激的GH 分泌,且K~+的作用是细胞外 Ca~(2+)依赖的。 相似文献
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