Mammalian Gonadotropins Research Articles

Optimizing the gonadoliberin dosage and evaluating the egg quality in the preseason and seasonal artificial reproduction of pond-reared sterlet Acipenser ruthenus

Sterlet Acipenser ruthenus is the smallest in size, early maturing, yet third in production scale among the sturgeon species and as such presents a good model to study reproductive biology. The present study aimed to evaluate the effects of preseason artificial reproduction and reduction of hormonal dosage on the egg quality in pond-reared sterlet. Therefore, a series of three trials were conducted in the period 2021 and 2022 (21 and 22) that evaluated three dosages of mammalian gonadotropin releasing hormone analog des-Gly10-(d-Ala6)-GnRH (40, 20, and 10 µg/kg) in both preseason (January) and seasonal (April) spawning batches (PRE and SEA). The greatest embryo survival was achieved in SEA-21-10 (84.8 ± 5.8 %) and the lowest in PRE-21-40 (31.0 ± 40.7 %). Overall results indicated that a dosage of 10 µg/kg leads to the highest embryo survival. Considering the season, latency time was significantly longer in preseason reproduction being on average about 6 h prolonged (35.1 ± 2.8 h vs. 41.4 ± 2.9 h) and it directly affected the embryo survival (linear correlation r = − 0.769, P = 0.003). Likewise, preseason reproduction yields more variable egg quality, due to impaired performance of later ovulating fish most likely due to lower oocyte maturation competence. The present study found expected latency time at 14 °C to be 37–41 h in the preseason and 31–41 h in season, while the recommended dosage is 10 µg/kg des-Gly10-(d-Ala6)-GnRH. Future studies should develop in vitro tools to evaluate the oocyte maturational competence to improve the egg quality in the preseason.

Drosophila Corazonin Neurons as a Hub for Regulating Growth, Stress Responses, Ethanol-Related Behaviors, Copulation Persistence and Sexually Dimorphic Reward Pathways.

The neuronal mechanisms by which complex behaviors are coordinated and timed often involve neuropeptidergic regulation of stress and reward pathways. Recent studies of the neuropeptide Corazonin (Crz), a homolog of the mammalian Gonadotrophin Releasing Hormone (GnRH), have suggested its crucial role in the regulation of growth, internal states and behavioral decision making. We focus this review on Crz neurons with the goal to (1) highlight the diverse roles of Crz neuron function, including mechanisms that may be independent of the Crz peptide, (2) emphasize current gaps in knowledge about Crz neuron functions, and (3) propose exciting ideas of novel research directions involving the use of Crz neurons. We describe the different developmental fates of distinct subsets of Crz neurons, including recent findings elucidating the molecular regulation of apoptosis. Crz regulates systemic growth, food intake, stress responses and homeostasis by interacting with the short Neuropeptide F (sNPF) and the steroid hormone ecdysone. Additionally, activation of Crz neurons is shown to be pleasurable by interacting with the Neuropeptide F (NPF) and regulates reward processes such as ejaculation and ethanol-related behaviors in a sexually dimorphic manner. Crz neurons are proposed to be a motivational switch regulating copulation duration using a CaMKII-dependent mechanism described as the first neuronal interval timer lasting longer than a few seconds. Lastly, we propose ideas to use Crz neuron-induced ejaculation to study the effects of fictive mating and sex addiction in flies, as well as to elucidate dimorphic molecular mechanisms underlying reward behaviors and feeding disorders.

Obtaining Xenopus laevis Eggs.

Nearly a century ago, studies by Lancelot Hogben and others demonstrated that ovulation in female Xenopus laevis can be induced via injection of mammalian gonadotropins into the dorsal lymph sac, allowing for egg production throughout the year independent of the normal reproductive cycles. Hormonally induced females are capable of producing thousands of eggs in a single spawning, which can then be fertilized to generate embryos or used as a substrate for generation of egg extracts. The protocol for induction of ovulation and subsequent egg collection is straightforward and robust, yet some of its details may vary among laboratories based on prior training, availability of necessary reagents, or the experimental objectives. As the goal of this protocol is not to describe every single variation possible for acquiring eggs but to provide a simple and clear description that can be easily applied by researchers with no prior working experience with X. laevis, we focus on describing the method we use at the National Xenopus Resource-that is, inducing ovulation in X. laevis via dorsal lymph sac injection of gonadotropic hormones and the stimulation of egg laying through application of gentle pressure to the females.

Comparison of artificial spawning effectiveness of hCG, CPH and GnRHa in combination with dopamine inhibitors in a wild strain of ide Leuciscus idus (L.) in hatchery conditions

Optimization of artificial reproduction, by increasing the survival rate of embryos and hatching rate, is of major importance for reducing genetic diversity, especially in fish captured from their natural habitat that subsequently spawn in hatcheries. The artificial reproduction of ide, Leuciscus idus (L.) was conducted in controlled conditions. The spawning agents included: different doses of human chorionic gonadotropin (hCG) that was compared with common carp pituitary homogenate (CPH), Ovopel – a commercial agent for induction of spawning that contains mammalian gonadotropin releasing hormone analogue (mGnRHa) with dopamine antagonists (DA): metoclopramide (MET) and Ovaprim – a commercial agent containing salmon gonadotropin releasing hormone analogue (sGnRHa) and a dopamine antagonists (DA): domperidone (DOM). There were no ovulations in females from control groups. There were no differences between the ovulation rates (90 %) or embryo survival (> 92 %) and hatching rates (> 91 %) when there was administration of hCG doses between 500 and 1000 IU/kg. When there was comparison of different spawning agents, the ovulation rate was 100 % for all treated groups. There were the shortest and longest latency times to the time of ovulation after administration of CPH (26 h) and hCG (79 h), respectively. The greatest embryo survival (> 93 %) and hatching (> 91 %) rates occurred as a result of hCG administration with these values being slightly greater than when there was treatment with Ovaprim. The association between latency time and hatching rate indicated that when there was a slower final oocyte maturation (FOM) there were greater hatching rates.

The role of the 3′ region of mammalian gonadotropin β subunit gene in the luteinizing hormone to chorionic gonadotropin evolution

CGβ subunits comprise a unique carboxyl-terminal peptide (CTP) that has multiple O-linked glycans and extends serum half-life of the protein. It has evolved by incorporating a previously untranslated region of the LHβ gene into the reading frame. Although CTP-like sequences are encrypted in the LHβ genes of several mammals, the CGβ subunit developed only in primates and equids. To study this restriction in evolution, we examined whether the cryptic CTP decoded from the bovine LHβ gene (boCTP) possesses key characteristics of the human (h) CGβ-CTP. The boCTP does not impede several crucial aspects of hormone biosynthesis, but compared to the hCGβ-CTP, the stretch lacks O-glycans and determinants for circulatory survival. O-glycan deficiency and the associated incapacity to extend serum half-life is a major drawback of the boCTP. This may explain why LH did not evolve into CG in ruminants and consequently alternative mechanisms evolved to delay luteolysis early in gestation.

EFFECTS OF MAMMALIAN GONADOTROPHS AND TESTOSTERONE ON THE MALE SEXUAL CYCLE OF THE LIZARD (LACERTA S. SICULA RAF.) DURING THE AUTUMN SPERMATOGENESIS

SUMMARY The effects of mammalian gonadotropins on spermatogenesis in Lacerta s. sicula Raf. was studied during the autumn thermic refractory period. During this period the mammalian gonadotropins induce a stimulation of spermatogenesis and of the epididymis. FSH acts preferentially on the spermatogonial multiplication and on the primary spermocytes; LH acts on all the stages of spermatogenesis, but in particular on spermiohistogenesis and spermiation; moreover it causes a marked development of the epididymis and of the SSC. The effects of gonadotrophins are temperature dependent: below 18°C stimulation concerns only the early stages of spermatogenesis and spermiation does not occur; at 27°C a complete spermatogenesis with maximum spermiation occurs. At 30°C gonadotrophins induce a strong stimulation of the gonad, but this stimulation is accompanied by frequent degenerative phenomena of the secondary spermatocytes and spermatids. LH is more capable than FSH of limiting this degeneration. Testosterone does ...

Thyrotropic activity of recombinant human glycoprotein hormone analogs and pituitary mammalian gonadotropins in goldfish (Carassius auratus): Insights into the evolution of thyrotropin receptor specificity

Thyrotropin (TSH) is a pituitary glycoprotein hormone heterodimer that binds to its G-protein coupled receptor (TSH-R) at the thyroid to promote the synthesis and secretion of thyroid hormone. Very little is known about TSH–TSH-R interactions in teleost fish. Mammalian gonadotropins have been reported to have an intrinsic ability to activate teleost fish TSH-Rs, suggesting the TSH-R in teleost fish is more promiscuous than in other vertebrates. In this study we utilized the goldfish T4-release response and recombinant human TSH analogs as in vivo tools to evaluate the structural constraints on hormone–receptor interactions. We found that four positively charged lysines substituted for neutral or negatively charged amino acids within positions 11–20 of the glycoprotein hormone subunit α (GSUα) significantly increased biological activity of hTSH in fish, as it does in mammals. We further found that bovine follicle stimulating hormone but not luteinizing hormone, whose GSUα subunits also contain four lysine or arginine amino acid residues in the N-terminal portion of GSUα, was thyrotropic in goldfish, suggesting gonadotropin β subunit contributes to the heterothyrotropic activity. Though recombinant human FSH did not produce a dose-dependent increase in T4, thyrotropic activity could be acquired with the addition of positively charged amino acids at the N-terminal portion of its GSUα, confirming the importance of the charge on those amino acids for activation of the goldfish TSH-R. These studies demonstrate that mammalian glycoprotein hormone analogs can be utilized to evaluate the conservation of receptor binding and activation mechanisms between fish and mammals.

Optimisation of an oviposition protocol employing human chorionic and pregnant mare serum gonadotropins in the Barred Frog Mixophyes fasciolatus (Myobatrachidae)

BackgroundProtocols for the hormonal induction of ovulation and oviposition are essential tools for managing threatened amphibians with assisted reproduction, but responses vary greatly between species and even broad taxon groups. Consequently, it is necessary to assess effectiveness of such protocols in representative species when new taxa become targets for induction. The threatened genus Mixophyes (family Myobatrachidae) has amongst the highest proportion of endangered species of all the Australian amphibians. This study developed and optimised the induction of oviposition in a non-threatened member of this taxon, the great barred frog (Mixophyes fasciolatus).MethodsGravid female M. fasciolatus were induced to oviposit on one or more occasions by administration of human chorionic gonadotropin (hCG) with or without priming with pregnant mare serum gonadotropin (PMSG). Treatments involved variations in hormone doses and combinations (administered via injection into the dorsal lymph sacs), and timing of administration. Pituitary homogenates from an unrelated bufonid species (Rhinella marina) were also examined with hCG.ResultsWhen injected alone, hCG (900 to 1400 IU) induced oviposition. However, priming with two time dependent doses of PMSG (50 IU, 25 IU) increased responses, with lower doses of hCG (200 IU). Priming increased response rates in females from around 30% (hCG alone) to more than 50% (p = 0.035), and up to 67%. Increasing the interval between the first PMSG dose and first hCG dose from 3 to 6 days also produced significant improvement (p<0.001). Heterologous pituitary extracts administered with hCG were no more effective than hCG alone (p = 0.628).ConclusionsThis study found that M. fasciolatus is amongst the few amphibian species (including Xenopus (Silurana) and some bufonids) that respond well to the induction of ovulation utilising mammalian gonadotropins (hCG). The optimal protocol for M. fasciolatus involved two priming doses of PMSG (50 IU and 25 IU) administered at 6 and 4 days respectively, prior to two doses of hCG (100 IU), 24 hours apart. This study is also the first to demonstrate in an amphibian species that responds to mammalian gonadotropins that an increase in the ovulation rate occurs after priming with a gonadotropin (PMSG) with FSH activity.

An invertebrate [hydroxyproline]-modified neuropeptide: Further evidence for a close evolutionary relationship between insect adipokinetic hormone and mammalian gonadotropin hormone family

An octapeptide of the adipokinetic hormone (AKH) peptide family is identified in the corpora cardiaca of the stink bug, Nezara viridula, by ESI-MSN (electrospray ionization multistage MS). This is the second AKH in N. viridula and it has a hydroxyproline residue at position 6, whereas the major AKH (known as Panbo-RPCH) has Pro as the sixth amino acid residue. The correct sequence assignment of [Hyp6]-Panbo-RPCH is confirmed by retention time and MS spectra of the synthetic peptide. Various extraction procedures were followed to ascertain whether the hydroxylation is an artefact of extraction, or whether it is due to a true post-translational modification at the prohormone level. The proline hydroxylation is unique for invertebrate neuropeptides, while it has been described in the vertebrate gonadotropin-releasing hormone (GnRH). The current finding is another piece of evidence that AKH and GnRH form a peptide superfamily and are closely related evolutionarily. Biologically, [Hyp6]-Panbo-RPCH is active in vivo as an AKH, causing hyperlipaemia in the stink bug at low doses, indicating again that it is an endogenous, mature and functional hormone in this insect species.

Immunisation of male mice with a plasmid DNA vaccine encoding gonadotrophin releasing hormone (GnRH-I) and T-helper epitopes suppresses fertility in vivo

Immunisation against mammalian gonadotrophin releasing hormone (GnRH-I) linked to large carrier proteins has been shown to disrupt fertility. However, various studies have shown that the carrier protein causes epitope suppression of the hapten response, resulting in short-lived immunoneutralisation, followed by a return of fertility. A range of strategies has been used to resolve this, with limited success. The aim of this study was to construct a plasmid DNA vaccine encoding GnRH-I and T-helper epitopes. A 498 bp long vaccine construct in pcDNA3.1+ was administered to male mice in conjunction with a Hemagglutinating Virus of Japanese Envelop (HVJ-E) vector or in saline solution. The vaccine efficacy was evaluated in terms of GnRH-I specific IgG antibody response, serum testosterone levels, testicular spermatogenesis and the ability to produce offspring. The vaccine appeared to induce higher anti-GnRH-I IgG antibody response and insult the fertility axis, which was characterised by a drop of epididymal sperm counts, reduction of serum testosterone levels, suppressed testicular spermatogenesis and a significant decrease in litter numbers compared to control animals. The end-point vaccine efficacy was much higher in the HVJ-E vector mediated immunisation, than in saline alone.

Isolation and Characterization of the Follicle-Stimulating Hormone β Subunit Gene and 5’ Flanking Region of the Chinook Salmon

In this study we have isolated the follicle-stimulating hormone β subunit gene from the Chinook salmon (csFSHβ). This gene encodes for a protein that is highly similar to those isolated from other salmonids and shares all of the structural constraints seen in mammalian gonadotropins, including twelve conserved cysteines and a putative N-linked glycosylation site. The organization of the gene follows the conserved pattern regarding the numbers and positions of the introns, although the csFSHβ gene contains a particularly large 6.2-kb first intron due to the inclusion of several transposon-like elements. Isolation of 1.2 kb of the 5′ flanking region of the csFSHβ gene and subsequent analysis in silico have revealed a number of putative elements which appear highly conserved in teleost FSHβ gene promoters and are thus likely involved in basal and hormone-induced transcriptional regulation. The functionality of this 1.2-kb fragment in driving expression of a reporter gene and its response to GnRH was shown in gonadotropes, while the overexpression of AP-1 factors, Sf-1, estrogen receptor or Smad1 revealed that the promoter is responsive to these transcription factors. Our current study has opened the way for future analysis to verify the role of these factors in mediating hormonally induced transcription of this gene.

Gonadotropin Hormone and Receptor Sequences from Model Teleost Species

Fish offer some advantages for the study of vertebrate reproductive physiology. Only a few of the genes encoding the components of the hypothalamic-pituitary-gonadal axis have been identified from model teleosts. This study describes a combination of database searching and molecular approaches to identify the FSH and LH gonadotropin beta-subunits (fshb and lhb, respectively), and the LH receptor (lhr) from two model teleost species: zebrafish (Danio rerio) and Fugu (Takifugu rubripes). Sequence and phylogenetic analyses were used to examine the relationships that exist between gonadotropins and their receptors from species representing several piscine orders. The gonadotropin alpha-subunit (Cga) is highly conserved among teleosts and tetrapods. The presence of a genomic pseudogene (cgap) was also noted in zebrafish. Generally, teleostean FSHbeta protein sequences share less identity with each other than do LHbeta protein sequences, supporting the hypothesis that FSHbeta diverged more rapidly during teleost evolution. Interestingly, and uniquely, zebrafish Fshb lacked two highly conserved cysteine residues in the "determinant loop" which is thought to contribute towards receptor binding and specificity. Teleost gonadotropin receptor sequences clearly diverged into two distinct groups, FSHR and LHR. As has been seen with mammalian gonadotropin receptor transcripts, splice variants of zebrafish lhr were also observed.

Receptor-selective determinants in catfish gonadotropin seat-belt loops

Mammalian gonadotropins are highly selective. Charge differences between the Cys 10–11 sequence of FSHβ and LHβ/CGβ seat-belt loops determine the ability of these hormones to interact with the LH-R. Selective FSH-R binding is mainly dependent on the presence of an FSHβ-specific sequence between Cys 11–12 of the seat-belt loop. Intriguingly, African catfish LHβ (cfLHβ) lacks a positively charged Cys 10–11 region and stimulates both catfish LH-R and FSH-R with comparable potencies. Our studies on the promiscuous behaviour of cfLH using chimeric gonadotropins revealed that the Cys 10–11 region of cfLHβ contains cfLH-R-selective determinants, whereas the Cys 11–12 region of cfLHβ confers FSH-R-stimulating activity to cfLH. Hence, the location of receptor-selective determinants appeared to be fairly well conserved throughout evolution, despite the low sequence identity between mammalian and catfish seat-belt loops. Moreover, various structure–function differences between gonadotropins are discussed in the context of the different (female) reproductive strategies between mammalian and non-mammalian species that required the divergence to a more specific LH-R-stimulating activity of one of the gonadotropins in mammals.

Pro7.33(303) of the human GnRH receptor regulates selective binding of mammalian GnRH

Mammalian gonadotropin releasing hormone (GnRH) receptors have a conserved acidic residue (Glu 7.32(301) or Asp 7.32(302) ) in extracellular loop (ECL) three that confers selectivity for mammalian GnRH, which has Arg 8 . Comparison of mammalian and non-mammalian GnRH receptors suggested that the acidic residue is not the only determinant of ligand selectivity in mammalian receptors. The acidic residue is followed by a conserved Pro 7.33 in mammalian GnRH receptors, but not non-mammalian receptors. Unique structural constraints imposed by Pro residues suggested that Pro 7.33 determines selective binding of Arg 8 -containing GnRH, by stabilising the conformation of the third extracellular loop of the receptor. Substituting Pro 7.33(303) or introducing Pro to position 7.31 decreased affinity for GnRH, but not analogs lacking Arg 8 . Substituting Pro 7.33(303) changed the predicted α-helix content of the loop–helix interface. These results show that Pro 7.33(303) of the human GnRH receptor is required for selective high affinity binding of mammalian GnRH and supports the hypothesis that Pro 7.33(303) stabilises a loop conformation that is necessary for selective ligand binding.

Pro 7.33(303) of the human GnRH receptor regulates selective binding of mammalian GnRH

Mammalian gonadotropin releasing hormone (GnRH) receptors have a conserved acidic residue (Glu 7.32(301) or Asp 7.32(302)) in extracellular loop (ECL) three that confers selectivity for mammalian GnRH, which has Arg 8. Comparison of mammalian and non-mammalian GnRH receptors suggested that the acidic residue is not the only determinant of ligand selectivity in mammalian receptors. The acidic residue is followed by a conserved Pro 7.33 in mammalian GnRH receptors, but not non-mammalian receptors. Unique structural constraints imposed by Pro residues suggested that Pro 7.33 determines selective binding of Arg 8-containing GnRH, by stabilising the conformation of the third extracellular loop of the receptor. Substituting Pro 7.33(303) or introducing Pro to position 7.31 decreased affinity for GnRH, but not analogs lacking Arg 8. Substituting Pro 7.33(303) changed the predicted α-helix content of the loop–helix interface. These results show that Pro 7.33(303) of the human GnRH receptor is required for selective high affinity binding of mammalian GnRH and supports the hypothesis that Pro 7.33(303) stabilises a loop conformation that is necessary for selective ligand binding.

Spawning induction and hormonal levels during final oocyte maturation in the silver perch ( Bidyanus bidyanus)

The silver perch ( Bidyanus bidyanus Mitchell) (Teraponidae), is a native Australian freshwater fish that, due to its high potential for aquaculture, was introduced to Israeli fish farming. The objective of this study was to find an optimal method for inducing spawning of silver perch. The agents tested for this purpose were: human chorionic gonadotropin (hCG; 150 or 200 IU/kg BW); salmon gonadotropin releasing hormone analogue (sGnRHa at 10, 20, 30, or 40 μg/kg BW); mammalian GnRH analogue (mGnRHa at 30 μg/kg) and the combination of sGnRHa at 20 μg/kg and domperidone at 5 mg/kg BW. Based on spawning success and relative fecundity, sGnRHa at the dose of 30 μg/kg was found to be more efficient than hCG, mGnRHa or sGnRHa with domperidone. Since domperidone does not improve the GnRHa effect on final oocyte maturation (FOM) and spawning, it is suggested that the dopaminergic inhibition during the stages of FOM in the silver perch is weak. Therefore, the use of GnRHa alone is sufficient to induce spawning in this fish. Immunoreactive gonadotropin (IR-GtH) and estradiol levels increased after a single injection of sGnRHa, and peaked after 24 h. Plasma levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P) also increased significantly 24 h after the injection of mGnRHa, 12 h before spawning, suggesting that 17,20-P is the maturation-inducing steroid in silver perch. In order to reveal whether the heterologous gonadotropin may elicit an immunological reaction, silver perch was subjected to prolonged treatment with hCG. This treatment resulted in no detectable titer of antibodies against the mammalian gonadotropin. In conclusion, although hCG has no deleterious effects in this fish, and is the more commonly used for spawning induction, sGnRHa at 30 μg/kg is the recommended treatment for spawning induction of female silver perch under the conditions prevailing in Israeli aquaculture.

Hand-stripping of semen and semen quality after maturational hormone treatments, in African catfish Clarias gariepinus

In the hatchery-bred African catfish, Clarias gariepinus, spontaneous semen release does not occur and hand-stripping is practically impossible. This reproductive dysfunction may be due to a lack of a pre-spawning gonadotropin (luteinizing hormone—LH) surge. To test this hypothesis, the effects of hormones that increase plasma LH levels were analyzed. Mammalian gonadotropin releasing hormone analogue (mGnRHa), mGnRHa plus pimozide, a dopamine antagonist (mGnRHa-PIM), ovaprim (salmon GnRHa plus domperidone, a dopamine antagonist), carp pituitary suspension (carp-PS), Clarias pituitary suspension and combinations of carp-PS and ovaprim were tested. Stripped fluid, when present, was compared to intratesticular semen, 12 or 24 h after injection (latency time). Plasma LH levels increased ( P<0.05) 2 h after injection in all hormone treatments, compared to control fish. Stripping of a few drops of fluid, containing some viable spermatozoa, was possible in four out of five males treated with two injections of carp-PS, sampled 12 h later, and in 13 out of 24 males treated with combinations of carp-PS and ovaprim. Spermatocrit, sperm concentration and hatching rates obtained with stripped fluid, however, were very low compared to those obtained with intratesticular semen, from the same males. The number of sperm cells collected per kg body weight increased only in fish treated with two consecutive injections of carp-PS and a 12-h latency time. Treatments using single injections of pituitary suspensions and treatments with mGnRHa, mGnRHa-PIM or ovaprim did not facilitate hand-stripping of viable sperm cells, nor did they increase the number of sperm cells collected per kg. Based on these results, it is unlikely that hatchery-bred catfish males are not strippable because of a lack of an LH surge.

Internalization kinetics of the gonadotropin-releasing hormone (GnRH) receptor

This study quantified the agonist-induced endocytotic and recycling events of the mammalian gonadotropin releasing hormone receptor (GnRH-R) and investigated the role of the intracellular carboxyl (C)-terminal tail in regulating agonist-induced receptor internalization kinetics. The rate of internalization for the rat GnRH-R was found to be exceptionally low when compared with G-protein coupled receptors (GPCRs) which possess a cytoplasmic C-terminal tail (thyrotropin-releasing hormone receptor (TRH-R), catfish GnRH-R (cfGnRH-R) and GnRH/TRH-R chimeric receptor). These data provide evidence that the presence of a functional intracellular cytoplasmic C-terminal tail is essential for rapid internalization of the studied GPCRs.

Single Injections of Human Chorionic Gonadotropin or Mammalian Gonadotropin Releasing Hormone Analog at Low Dosages Induce Ovulation in White Bass

Abstract Spawning trials were conducted to determine an efficacious dosage of human chorionic gonadotropin (hCG) and to investigate the potential of mammalian gonadotropin releasing hormone analog (mGnRHa) to induce ovulation in white bass Morone chrysops. White bass broodstock were habituated to indoor tanks and subjected over several months to photoperiod-temperature regimes simulating the seasons to induce gonadal maturation. Various hCG dosages (0, 10, 25, 50, 150, 170, 250, 280, and 830 IU/kg body weight) were tested in single injections. We demonstrated that white bass can be successfully spawned with an hCG dosage as low as 50 IU/kg. However, this dosage did not result in all fish ovulating in a subsequent trial. We found no significant differences between 150 IU hCG/kg and higher dosages in ovulation response (ovulation success and time to ovulation), egg production (number of eggs/kg), or egg quality (fertility and hatch rates). Single injection of mGnRHa at 50 μg/kg did not consistently cause ov...

Internalization kinetics of the gonadotropin-releasing hormone (GnRH) receptor.

This study quantified the agonist-induced endocytotic and recycling events of the mammalian gonadotropin releasing hormone receptor (GnRH-R) and investigated the role of the intracellular carboxyl (C)-terminal tail in regulating agonist-induced receptor internalization kinetics. The rate of internalization for the rat GnRH-R was found to be exceptionally low when compared with G-protein coupled receptors (GPCRs) which possess a cytoplasmic C-terminal tail (thyrotropin-releasing hormone receptor (TRH-R), catfish GnRH-R (cfGnRH-R) and GnRH/TRH-R chimeric receptor). These data provide evidence that the presence of a functional intracellular cytoplasmic C-terminal tail is essential for rapid internalization of the studied GPCRs.