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See detailModulation of testosterone-dependent male sexual behavior and the associated neuroplasticity.
Charlier, Thierry; Seredynski, Aurore ULg; Niessen, Neville-Andrew ULg et al

in General and Comparative Endocrinology (2013)

Steroids modulate the transcription of a multitude of genes and ultimately influence numerous aspects of reproductive behaviors. Our research investigates how one single steroid, testosterone, is able to ... [more ▼]

Steroids modulate the transcription of a multitude of genes and ultimately influence numerous aspects of reproductive behaviors. Our research investigates how one single steroid, testosterone, is able to trigger this vast number of physiological and behavioral responses. Testosterone potency can be changed locally via aromatization into 17b-estradiol which then activates estrogen receptors of the alpha and beta subtypes. We demonstrated that the independent activation of either receptor activates different aspects of male sexual behavior in Japanese quail. In addition, several studies suggest that the specificity of testosterone action on target genes transcription is related to the recruitment of specific steroid receptor coactivators. We demonstrated that the specific down-regulation of the coactivators SRC-1 or SRC-2 in the medial preoptic nucleus by antisense techniques significantly inhibits steroid-dependent male-typical copulatory behavior and the underlying neuroplasticity. In conclusion, our results demonstrate that the interaction between several steroid metabolizing enzymes, steroid receptors and their coactivators plays a key role in the control of steroid-dependent male sexual behavior and the associated neuroplasticity in quail. [less ▲]

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See detailThe endocrine control of energy homeostasis in chickens
Decuypere, Eddy; Everaert, Nadia ULg; Song, Zhigang et al

in General and Comparative Endocrinology (2013)

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See detailThe endocrine control of energy homeostasis in chickens.
Song, Zhigang; Everaert, Nadia ULg; Wang, Yufeng et al

in General and comparative endocrinology (2013), 190

Energy homeostasis (balance) depends on the relationship between the amount of consumed feed energy and energy expenditure. Coordination of energy expenditure and feed intake (appetite) is necessary for ... [more ▼]

Energy homeostasis (balance) depends on the relationship between the amount of consumed feed energy and energy expenditure. Coordination of energy expenditure and feed intake (appetite) is necessary for the regulation of body composition. The hypothalamus integrates peripheral and central signals to generate satiety or hunger. Birds and mammals utilize common signaling molecules but some molecules possess different/opposite functions. If relevant, particular differences with the mammalian regulatory system are highlighted in this review. For example, obestatin had no significant effect on feed intake of chicks, but it was claimed to decrease food intake in mammalian species. Ghrelin displayed appetite-stimulating effects in mammals but appetite-decreasing effects in birds. Recently, the function of the hypothalamic AMPK signaling pathway on feed intake regulation has received considerable attention in poultry. Alpha-lipoic acid might exert its appetite-decreasing effect by the AMPK signaling pathway. This review discusses the central regulation of energy homeostasis, role of (an)orexigenic peptides, effect of feed deprivation on hypothalamic neuropeptide gene expression and provides a model for involvement of AMPK in the regulation of avian energy balance. [less ▲]

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See detailFasting alters protein expression of AMP-activated protein kinase in the hypothalamus of broiler chicks (Gallus gallus domesticus).
Song, Zhigang; Liu, Lei; Yue, Yunshuang et al

in General and comparative endocrinology (2012), 178(3), 546-55

An experiment was conducted to investigate the effects of fasting and re-feeding on hypothalamic 5'-AMP-activated protein kinase (AMPK) levels and (an)orexigenic neuropeptides. Male Arbor Acres chicks (7 ... [more ▼]

An experiment was conducted to investigate the effects of fasting and re-feeding on hypothalamic 5'-AMP-activated protein kinase (AMPK) levels and (an)orexigenic neuropeptides. Male Arbor Acres chicks (7-day-old, n=160) were allocated to four equal treatment groups: control chicks (fed ad libitum for 48 h, C48), chicks that were fasted for 48 h (F48), chicks that were first fasted for 48 h and then re-fed for 24h (F48C24), and chicks that were fed ad libitum for 72h (C72). Fasting for 48 h significantly (P<0.05) increased the ratio of phosphorylated AMPKalpha to total AMPKalpha and phosphorylated LKB1 to total LKB1, whereas re-feeding for 24h reduced these ratios to that of the ad libitum fed C72 chicks. The gene expressions of agouti-related peptide (AgRP), neuropeptide Y (NPY), melanocortin receptor 4, melanin-concentrating hormone, prepro-orexins and carnitine palmitoyltransferase-1 were significantly (P<0.05) increased in the fasted chicks relative to the ad libitum fed C48 group. The gene expression of pro-opiomelanocortin (POMC), as well as cocaine- and amphetamine-regulated transcript (CART) was not affected by the nutritional status. Fasting significantly (P<0.05) decreased the mRNA levels of fatty acid synthase (FAS) and sterol regulatory element binding protein-1 (SREBP-1). The results suggest that the LKB1/AMPK signal pathway is involved in the energy homeostasis of fasted chicks, and its possible role in feed intake regulation might be mediated by the AgRP/NPY rather than the POMC/CART pathway. [less ▲]

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See detailEffects of sex steroids on aromatase mRNA expression in the male and female quail brain.
Voigt, Cornelia; Ball, Gregory F; Balthazart, Jacques ULg

in General and Comparative Endocrinology (2011), 170(1), 180-8

Castrated male quail display intense male-typical copulatory behavior in response to exogenous testosterone but ovariectomized females do not. The behavior of males is largely mediated by the central ... [more ▼]

Castrated male quail display intense male-typical copulatory behavior in response to exogenous testosterone but ovariectomized females do not. The behavior of males is largely mediated by the central aromatization of testosterone into estradiol. The lack of behavioral response in females could result from a lower rate of aromatization. This is probably not the case because although the enzymatic sex difference is clearly present in gonadally intact sexually mature birds, it is not reliably found in gonadectomized birds treated with testosterone, in which the behavioral sex difference is always observed. We previously discovered that the higher aromatase activity in sexually mature males as compared to females is not associated with major differences in aromatase mRNA density. A reverse sex difference (females>males) was even detected in the bed nucleus of the stria terminalis. We analyzed here by in situ hybridization histochemistry the density of aromatase mRNA in gonadectomized male and female quail that were or were not exposed to a steroid profile typical of their sex. Testosterone and ovarian steroids (presumably estradiol) increased aromatase mRNA concentration in males and females respectively but mRNA density was similar in both sexes. A reverse sex difference in aromatase mRNA density (females>males) was detected in the bed nucleus of subjects exposed to sex steroids. Together these data suggest that although the induction of aromatase activity by testosterone corresponds to an increased transcription of the enzyme, the sex difference in enzymatic activity results largely from post-transcriptional controls that remain to be identified. [less ▲]

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See detailRapid increase in aggressive behavior precedes the decrease in brain aromatase activity during socially mediated sex change in Lythrypnus dalli.
Black, Michael P; Balthazart, Jacques ULg; Baillien, Michelle et al

in General and Comparative Endocrinology (2011), 170(1), 119-24

In the bluebanded goby, Lythrypnus dalli, removal of the male from a social group results in a rapid behavioral response where one female becomes dominant and changes sex to male. In a previous study ... [more ▼]

In the bluebanded goby, Lythrypnus dalli, removal of the male from a social group results in a rapid behavioral response where one female becomes dominant and changes sex to male. In a previous study, within hours of male removal, aromatase activity in the brain (bAA) of dominant females was almost 50% lower than that of control females from a group in which the male had not been removed. For those females that displayed increased aggressive behavior after the male was removed, the larger the increase in aggressive behavior, the greater the reduction in bAA. To investigate whether decreased bAA leads to increased aggression, the present study used a more rapid time course of behavioral profiling and bAA assay, looking within minutes of male removal from the group. There were no significant differences in bAA between control females (large females from groups with the male still present), females that doubled their aggressive behavior by 10 or 20 min after male removal, or females that did not double their aggressive behavior within 30 min after male removal. Further, individual variation in bAA and aggressive behavior were not correlated in these fish. Whole brain decreases in aromatase activity thus appear to follow, rather than precede, rapid increases in aggressive behavior, which provides one potential mechanism underlying the rapid increase in androgens that follows aggressive interactions in many vertebrate species. For fish species that change sex from female to male, this increase in androgens could subsequently facilitate sex change. [less ▲]

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See detail17β-estradiol levels in male zebra finch brain: combining Palkovits punch and an ultrasensitive radioimmunoassay
Charlier, Thierry ULg; Po, Kevin WL; Newman, Amy EM et al

in General and Comparative Endocrinology (2010), 167

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See detailAt least two expressed genes for transcription factors Pitx2 and Rpx are present in common carp and are upregulated during winter acclimatization.
Kausel, G.; Vera, T.; Valenzuela, G. et al

in General and Comparative Endocrinology (2010), 169(3), 250-257

The mechanisms of seasonal acclimatization in eurythermal fish such as common carp are not fully understood. Here, we concentrate on the regulation of pituitary factors, as this organ was shown to be ... [more ▼]

The mechanisms of seasonal acclimatization in eurythermal fish such as common carp are not fully understood. Here, we concentrate on the regulation of pituitary factors, as this organ was shown to be highly affected by seasonal changes. We cloned and sequenced two different cDNAs for each of the transcription factors Pitx2 and Rpx, known to play a role in pituitary development. We show that these genes are conserved throughout evolution, to different degrees depending on the specific domain considered. Finally, we show that the cDNAs for both factors are clearly up-regulated during the winter season, in sharp contrast to other regulators such as Pit1 or pituitary hormone genes such as prolactin (prl) and growth hormone (gh). Our results suggest that increased expression of Pitx2 and Rpx contributes to seasonal adaptation of common carp to winter conditions. [less ▲]

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See detailOvarian steroidogenesis inhibition by constant photothermal conditions is caused by a lack of gonadotropin stimulation in Eurasian perch
Milla, S.; Mandiki, S. N. M.; Hubermont, P. et al

in General and Comparative Endocrinology (2009), 163(3), 242-250

In fish, the reasons for the inhibition of reproduction by constant photothermal conditions of rearing are far from clear. In an in vivo experiment, two groups of females reared under natural (4-28 ... [more ▼]

In fish, the reasons for the inhibition of reproduction by constant photothermal conditions of rearing are far from clear. In an in vivo experiment, two groups of females reared under natural (4-28 degrees C) or constant photothermal conditions (20-22 degrees C, photoperiod 12/12) were investigated for gonad development, sex-steroids (testosterone-T, 17-beta-estradiol-E2 and 11 Keto-Testosterone-11KT) dynamics and brain aromatase activity in January, February and March. Two days before each sampling date, a group of females reared under constant conditions was injected with HCG (Human Chorionic Gonadotropin: 100 Ul/kg) and evaluated for the same parameters. In addition, in vitro ovarian steroidogenesis capacity for each female was determined with or without stimulation by HCG and/or IGF-1 (insulin-like Growth Factor-1). The results indicate that vitellogenesis stage is the limit ovarian stage never reached in females submitted to constant photothermal conditions. This was associated with gonadogenesis delay and low levels of circulating sex-steroids (T, E2 and 11KT). Nevertheless, HCG injections partly counteracted the plasma steroid deprivation, indicating that ovaries from fish reared under constant photothermal conditions suffer from a lack of gonadotropin stimulation, maybe caused by plasma LH suppression. Such finding was confirmed by the in vitro ovary incubation test. HCG and IGF-1 treatments induced broad testosterone and 17-beta-estradiol elevations and the exposure to constant photothermal conditions, in some cases, decreased that response to HCG. In conclusion, we show that the inhibition of reproductive cycle in Eurasian perch females by constant photothermal conditions of rearing may be related to lower sex-steroid levels and to an inhibition of ovarian regulation by gonadotropins (at least LH), probably stopping gonadogenesis before vitellogenesis stage. (C) 2009 Elsevier Inc. All rights reserved. [less ▲]

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See detailAre rapid changes in gonadal testosterone release involved in the fast modulation of brain estrogen effects?
Cornil, Charlotte ULg; Stevenson, Tyler J; Ball, Gregory F

in General and Comparative Endocrinology (2009)

Estradiol facilitates the expression of male sexual behavior in Japanese quail within a few minutes. These rapid behavioral effects of estradiol could result from rapid changes in its local production in ... [more ▼]

Estradiol facilitates the expression of male sexual behavior in Japanese quail within a few minutes. These rapid behavioral effects of estradiol could result from rapid changes in its local production in the preoptic area by aromatase, the enzyme converting testosterone into estradiol. Alternatively, aromatase activity may remain constant but fluctuations of local estradiol production could arise from rapid changes in the concentration of the enzymatic substrate, namely testosterone. Rapid increases of circulating testosterone levels have been observed in males of various species following social encounters. Surprisingly, in quail, the interaction with a female seems to result in a decrease in circulating testosterone levels. However, in that study conducted in quail, the samples were collected at intervals longer than the recently observed rapid effects of estradiol on sexual behavior. In the present study we investigated whether plasma testosterone concentrations fluctuate on a shorter time-frame. Eleven male were tested 5 min before and 5, 15 or 30 min after being allowed to have visual access to a female or to copulate with a female for 5 min. Both types of interactions resulted in a significant decline in circulating testosterone levels at latencies as short as 5 min. These data demonstrate that the decrease in testosterone levels is initiated shortly after sexual encounters. Because visual interactions with a female did not result in a rapid increase in testosterone concentrations, these findings rule out the possibility that a rapid rise in circulating testosterone levels participates in the rapid increase in brain estrogen synthesis and its facilitatory effects on copulatory behavior. [less ▲]

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See detailRelationship between plasma leptin-like protein levels, begging and provisioning in nestling thin-billed prions Pachyptila belcheri.
Quillfeldt, Petra; Everaert, Nadia ULg; Buyse, Johan et al

in General and comparative endocrinology (2009), 161(2), 171-8

While there have been many studies in various species examining the physiological role of leptin, there are so far no data in free-living seabirds. In the present study, we assess whether leptin is ... [more ▼]

While there have been many studies in various species examining the physiological role of leptin, there are so far no data in free-living seabirds. In the present study, we assess whether leptin is expressed in thin-billed prions (Pachyptila belcheri) and we investigate its relationship with feeding-related parameters including body condition, begging intensities and provisioning rates. We showed by Western Blot analysis using leptin-specific antibody that leptin-like protein (14-16kDa) is expressed in adipose tissue and liver of nestling thin-billed prions. Plasma leptin-like protein levels, determined by RIA, were in the same range (1-3ng/ml) as in other avian species and increased with age. In two breeding seasons, the plasma leptin-like protein levels were negatively correlated with provisioning rates (R=-0.67 and -0.35 in 2003 and 2004, respectively, P<0.05) indicating that endogenous leptin may be an anorexigenic hormone in wild birds. Plasma leptin-like protein levels were positively correlated with begging intensities (R=0.43 and 0.37 in 2003 and 2004, respectively, P<0.05), and this may be because hungry nestling seabird chicks with low body conditions increased their begging intensities. Plasma leptin-like protein levels did not correlate either with plasma triglyceride or glucose levels in thin-billed prions. Overall, these findings show the presence of leptin-like protein in free-living seabirds and provide new insights into its function and its possible role in feeding-associated behaviours. [less ▲]

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See detailIsolation of pregnancy-associated glycoproteins of the American bison (Bison bison) at first half of pregnancy
Kiewisz, J.; Melo de Sousa, Noelita ULg; Beckers, Jean-François ULg et al

in General and Comparative Endocrinology (2008), 155(1), 164-175

This paper describes the successful purification and characterisation of pregnancy-associated glycoproteins (PAG) extracted from placenta (3-4 months) of American bisons (Amb). Chorionic AmbPAG proteins ... [more ▼]

This paper describes the successful purification and characterisation of pregnancy-associated glycoproteins (PAG) extracted from placenta (3-4 months) of American bisons (Amb). Chorionic AmbPAG proteins were purified from foetal cotyledonary tissues (CT) and liquid cotyledonary-carrying proteins (LCP) leaking from damaged cells. Our protocols successfully indicated the usefulness of AmbPAG protein identification, especially from LCP fraction. The AmbPAGs were extracted, precipitated and eluted during DEAE cellulose chromatography. The richest protein fractions were further chromatographed on VVA (Vicia villosa agglutinin affinity column), then characterised by mono- and bi-dimensional electrophoresis, Western blot and N-terminal amino acid (aa) sequence. After being transferred to PVDF membranes, three selected VVA-purified AmbPAG isoforms differing in molecular masses and isoelectric points (Ip 4-4.6) were selected for sequencing. One identified N-terminal 25 aa sequence of AmbPAG72 kDa CT form was identified as completely new (RGSNI_TSLPLQNVIDLFYVGNITIG). Two other AmbPAG proteins purified from different sources (74 kDa CT and 76 kDa LCP forms; RGSNLTIHPLRNIRDIFYVGNITIG) were identical or corresponded to N-terminus of various bovine PAGs (boPAG). The two AmbPAGs (74 kDa CT and 76 kDa LCP) revealed identical micro-sequence to boPAG7; and were similar mainly to bovine PAG4, -6, -15 and -17 precursors that were identified by full-length sequencing derived from cDNA cloning. The novel sequence of the AmbPAG (72 kDa CT) was related to some boPAG and various other ruminant PAG precursors (caprine and ovine). All three identified AmbPAG sequences were also relatively similar to mature forms of purified native boPAG56-75kDa proteins. This is the first report indicating aa sequences of native AmbPAG proteins purified from placenta (CT and LCP) of bison species. The N-terminal sequences of the AmbPAGs have been deposited in the EMBL-EBI database (UniProtKB; Accession Nos.: P84916, P84917 and P84918). (C) 2007 Elsevier Inc. All rights reserved. [less ▲]

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See detailNeurosteroids, immunosteroids, and the Balkanization of endocrinology.
Schmidt, Kim L; Pradhan, Devaleena S; Shah, Amit H et al

in General and Comparative Endocrinology (2008), 157(3), 266-74

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic ... [more ▼]

Traditionally, the production and regulation of steroid hormones has been viewed as a multi-organ process involving the hypothalamic-pituitary-gonadal (HPG) axis for sex steroids and the hypothalamic-pituitary-adrenal (HPA) axis for glucocorticoids. However, active steroids can also be synthesized locally in target tissues, either from circulating inactive precursors or de novo from cholesterol. Here, we review recent work demonstrating local steroid synthesis, with an emphasis on steroids synthesized in the brain (neurosteroids) and steroids synthesized in the immune system (immunosteroids). Furthermore, recent evidence suggests that other components of the HPG axis (luteinizing hormone and gonadotropin-releasing hormone) and HPA axis (adrenocorticotropic hormone and corticotropin-releasing hormone) are expressed locally in target tissues, potentially providing a mechanism for local regulation of neurosteroid and immunosteroid synthesis. The balance between systemic and local steroid signals depends critically on life history stage, species adaptations, and the costs of systemic signals. During particular life history stages, there can be a shift from systemic to local steroid signals. We propose that the shift to local synthesis and regulation of steroids within target tissues represents a "Balkanization" of the endocrine system, whereby individual tissues and organs may become capable of autonomously synthesizing and modulating local steroid signals, perhaps independently of the HPG and HPA axes. [less ▲]

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See detailEndocrine correlates of the breeding asynchrony between two corsican populations of blue tits (Parus caeruleus)
Caro, S. P.; Balthazart, Jacques ULg; Thomas, D. W. et al

in General and Comparative Endocrinology (2005), 140(1), 52-60

Analyses of the development of the reproductive system in seasonally breeding birds in the framework of long-term ecological studies are rare. Here, we present the first results of such a study in two ... [more ▼]

Analyses of the development of the reproductive system in seasonally breeding birds in the framework of long-term ecological studies are rare. Here, we present the first results of such a study in two Corsican populations of a European passerine bird, the blue tit (Parus caeruleus). The two study populations occupy different oak habitats and are separated by only 25 km. Despite their close proximity, they show a one-month difference in onset of egg laying, even after controlling for altitude. This micro-geographic difference in breeding date appears adaptive because both study populations raise chicks when food is most plentiful. In our study, males reached their maximum song activity during the egg-laying stage while maximal testosterone levels and testes sizes were reached 2-3 weeks before egg laying. The rate of development of the reproductive system in males was much faster in the earlier population, in spite of a similar onset of gonad development and song activity for the two study populations. No change in the volume of the song-control nuclei (HVC and RA) could be detected during the study period. Development of brain nuclei was completed 2-3 months before the beginning of intense sexual activity. (C) 2004 Elsevier Inc. All rights reserved. [less ▲]

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See detailTransfer of Tilapia (Oreochromis niloticus) to a hyperosmotic environment is associated with sustained expression of prolactin receptor in intestine, gill and kidney
Sandra, O.; Le Rouzic, P.; Rentier-Delrue, Françoise ULg et al

in General and Comparative Endocrinology (2001)

Expression of tilapia prolactin receptor (tiPRL-R) has been characterised in the intestine, gill and kidney of tilapia species Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL ... [more ▼]

Expression of tilapia prolactin receptor (tiPRL-R) has been characterised in the intestine, gill and kidney of tilapia species Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL binding sites have been analysed in these organs during adaptation tilapia to a hyperosmotic environment. [less ▲]

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See detailRecombinant prolactin Receptor Extracellular Domain of Rainbouw trout (Oncorhynchus mykiss): subcloning, preparation and characterization
Sandowski, Y.; Cohen, Y.; Le Rouzic, P. et al

in General and Comparative Endocrinology (2000), 118

The cDNA of the extracellular domain of rainbow trout (Oncorhynchus mykiss) prolactin receptor (trPRLR-ECD) was cloned in the prokaryotic expression vector pMON to enable its expression in Escherichia ... [more ▼]

The cDNA of the extracellular domain of rainbow trout (Oncorhynchus mykiss) prolactin receptor (trPRLR-ECD) was cloned in the prokaryotic expression vector pMON to enable its expression in Escherichia coli after induction with nalidixic acid. The bacterially expressed trPRLR-ECD protein, contained within the refractile body pellet, was solubilized in 4.5 M urea, refolded, and purified on a Q-Sepharose column, pH 8, by stepwise elution with NaCl. The bioactive monomeric 26-kDa fraction was eluted in 0.2 M NaCl, yielding 20 mg/2.5 L of induced culture. The purified protein was over 98% homogeneous, as shown by SDS-PAGE in the presence or absence of reducing agent and by chromatography on a Superdex column. Binding experiments using [125I]ovine placental lactogen (oPL) as a ligand revealed that human growth hormone (hGH), oPL, and ovine prolactin (oPRL) were the most effective competitors, with respective IC50 values of 1.32, 2.27, and 2.70 nM. Chicken (ch) PRL did not compete at all, and homologous trPRL was much less effective, with a corresponding IC50 value of 1826 nM. Gel-filtration was used to determine the stoichiometry of trPRLR-ECD's interaction with oPL, hGH, and oPRL. Only oPL yielded a 2:1 complex, whereas hGH and oPRL formed only 1:1 complexes, with excess trPRLR-ECD being seen at the initial 2:1 trPRLR-ECD:hGH or trPRLR-ECD:oPRL ratios. No studies were performed with chPRL because of its inability to compete with [125I]oPL or with trPRL because of its low affinity toward trPRLR-ECD. The present results agree with previous findings indicating, as in mammals, that homologous PRL interacts transiently with its receptor and suggest that transient homologous PRL-induced homodimerization of the receptor is sufficient to initiate a biological signal, despite the fact that, in classical binding experiments, only low specific binding can be detected. [less ▲]

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See detailIdentification and modulation of a growth hormone-binding protein in rainbow trout (Oncorhynchus mykiss) plasma during seawater adaptation.
Sohm, F.; Manfroid, Isabelle ULg; Pezet, A. et al

in General and Comparative Endocrinology (1998), 111(2), 216-24

A soluble protein that specifically bound 125I-human growth hormone (hGH) was identified in rainbow trout plasma, using HPLC-gel filtration. The binding affinity of the protein for hGH was 1.2 x 10(9)M-1 ... [more ▼]

A soluble protein that specifically bound 125I-human growth hormone (hGH) was identified in rainbow trout plasma, using HPLC-gel filtration. The binding affinity of the protein for hGH was 1.2 x 10(9)M-1. 125I-rainbow trout GH (tGH) was also able to bind to the protein albeit with a lower affinity (6.6 x 10(7)M-1) than hGH. Crosslinking experiments using 125I-hGH revealed two specific bands of 150 and 130 kDa. The complex 125I-hGH-BP could be precipitated by a monoclonal anti-GH receptor antibody, suggesting a close relationship between the plasma GH-BP and the GH receptor. A fourfold increase in the hGH binding to the GH-BP was shown 48 h after transfer of the fishes from freshwater to seawater. The increase in binding was related to a high binding capacity without significant changes in binding affinity. These results suggest a potential role of this related GH-BP as an index of GH effects during seawater adaptation in salmonids. [less ▲]

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See detailHypothalamic and Thyroidal Regulation of Growth Hormone in Tilapia
Melamed, P. M.; Eliahu, N. A.; Levavi-Sivan, Berta et al

in General and Comparative Endocrinology (1995), 97

A radioimmunoassay (RIA) for recombinant tilapia growth hormone (GH) was established and validated. The ability of various hypothalamic factors to regulate GH secretion in the tilapia hybrid (Oreochromis ... [more ▼]

A radioimmunoassay (RIA) for recombinant tilapia growth hormone (GH) was established and validated. The ability of various hypothalamic factors to regulate GH secretion in the tilapia hybrid (Oreochromis niloticus x Oreochromis aureus) was studied. Somatostatin1-14 (SRIF1-14; 10-100 micrograms/kg) was found to reduce circulating GH levels in a dose-dependent manner. SRIF1-14 (0.1-1000 nM) inhibited GH release from perifused pituitary fragments (ED50 0.83 nM). Human growth hormone-releasing hormone fragment 1-29 (hGHRH1-29; 100 micrograms/kg) doubled circulating GH levels and modestly stimulated GH secretion in vitro. Carp growth hormone-releasing hormone (cGHRH) stimulated GH secretion in vitro to a similar degree at the same dose (1 microM). Injection of salmon gonadotropin-releasing hormone (sGnRH) superactive analog (10-100 micrograms/kg) increased plasma GH levels sixfold. sGnRH also stimulated GH release in vitro (ED50 142.56 nM). Dopamine (0.1-10 microM) and the D1 DA receptor agonist SKF 38393 increased GH secretion from perifused pituitary fragments dose-relatedly. Thyrotropin-releasing hormone (TRH) had no effect on GH secretion from perifused pituitary fragments, but increased plasma GH levels, as did bovine thyroid stimulating hormone (bTSH). The increased plasma GH in the bTSH-treated fish coincided with a dramatic increase in T4; however, TRH increased GH without changing T4 levels. T3 increased the synthesis of GH by isolated pituitaries (incorporation of [3H]leucine). SRIF1-14 seems to be a most potent hypothalamic regulator of GH secretion in tilapia; sGnRH and DA both increased GH secretion, although sGnRH elicited considerably greater responses at lower doses. Two forms of GHRH increased GH levels, although the unavailability of the homologous peptide prevented an accurate evaluation of its importance in regulating GH secretion. The thyroid axis (TRH, TSH, and T3) stimulates both synthesis and release of GH, although TRH did not appear to have a direct effect on the level of the pituitary. [less ▲]

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See detailAbsence of tiGh effect on adaptability to brackish water in Tilapia (Oreochromis niloticus)
Auperin, B.; Leguen, I.; Rentier-Delrue, Françoise ULg et al

in General and Comparative Endocrinology (1995)

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this ... [more ▼]

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this process. Plasma levels of growth hormone do not change upon transfer to brackish water. Treatment of intact tilapia in fresh water with growth hormone prior to transfer did not enable the fish to preadapt to brackish water: the duration of the hydromineral imbalance after transfer was the same in treated animals and controls. The major osmoregulatory role of prolactin in fresh water led us to test the hypothesis that prolactin might antagonize the effect of growth hormone on adaptation to brackish water. Growth-hormone-treated hypophysectomized animals, however, exhibited no increased osmoregulatory capacity as compared to hypophysectomized controls, confirming the absence of a growth-hormone-related osmoregulatory effect. When prolactin and growth hormone were coinjected, growth hormone also proved unable to oppose the Na+ retaining effect of prolactin, in both brackish and fresh water. Surprisingly, hypophysectomized animals adapt better to brackish water than do sham-operated animals. This result is discussed in light of the effects of prolactin and cortisol on osmoregulation in brackish water and we suggest that an important event which allows O. niloticus to adapt to hyperosmotic environment is the reduction of plasma PRL upon transfer to brackish water. [less ▲]

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