Differential distribution and response to experimental sexual maturation of two forms of brain gonadotropin-releasing hormone (GnRH) in the European eel, Anguilla anguilla

Using specific radioimmunoassays for the two GnRH molecular forms present in the European eel, Anguilla anguilla, (mGnRH and cGnRH II), we compared their distributions in the pituitary and different parts of the brain of female silver eels, as well as the modifications of their levels in experimentally matured female eels (treated with carp pituitary extract). In control eels, mGnRH levels were higher than cGnRH II levels in the pituitary, olfactory lobes and telencephalon, di- and mesencephalon, while the opposite was found in the posterior part of the brain (met- and myelencephalon). Experimental sexual maturation of the gonads significantly increased mGnRH levels in the pituitary and anterior parts of the brain; such a positive effect was not observed on the low cGnRH II levels, which were, in contrast, reduced. These data indicate that the positive feedback of gonadal hormones on GnRH, that we previously demonstrated, would specifically affect the mGnRH form. The differential distribution and control of mGnRH and cGnRH II suggest that these two forms have different physiological roles in the eel. The large increase in mGnRH during sexual maturation suggests the prime implication of this form in the neuroendocrine control of reproduction.

Dopamine functions as a growth hormone-releasing factor in the goldfish, Carassius auratus

In vivo and in vitro approaches have been used to examine the role of dopamine (DA) as a growth hormone (GH)-releasing factor in the goldfish. DA stimulated GH release from perifused pituitary fragments of goldfish in a dose-dependent manner. The GH-releasing effect of DA was seasonal, being the highest in sexually regressed fish, intermediate in recrudescent fish, and the lowest in sexually mature (prespawning) fish. The GH response to DA was blocked by the D1 antagonist (+)SCH23390, confirming the involvement of D1 receptors in DA-stimulated GH release. In studies using static incubation of pituitary cells, somatostatin, a known physiological GH-release inhibitor in the goldfish, abolished the GH response to DA. Intraperitoneal injection of apomorphine, a non-selective DA agonist, also increased the plasma GH levels and enhanced the linear body growth of goldfish. These results strongly suggest that DA, by acting through DA D1 receptors, functions as a GH-releasing factor in the goldfish.

The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro

The effects of thyrotropin-releasing hormone (TRH) on growth hormone (GH) and gonadotropin (GtH) release, and the influences of somatostatin (SRIF), the dopamine agonist apomorphine (APO) and extracellular calcium on basal and TRH-induced GH release were examined using an in vitro perifusion system for pituitary fragments of common carp (Cyprinus carpio). Five minute pulses of different dosages of TRH stimulated a rapid and dose-dependent increase in GH release from the perifused pituitary fragments with an ED50 of 9.7 ± 2.3 nM. TRH was ineffective on GtH release. SRIF significantly inhibited basal and TRH-induced GH release from the perifused pituitary fragments, and the effects of SRIF were dose-dependent. APO induced a dose-dependent increase in basal and TRH-stimulated GH release from the perifused pituitary fragments. Increasing the concentrations of extracellular calcium from 0 mM to 1.25 mM resulted in an increase in basal and TRH-induced GH release. The high dose of calcium (6.25 mM) caused a slight decrease in basal and TRH-induced GH release compared with those at a concentration of 1.25 mM.

Cloning and sequencing of goldfish activin subunit genes: strong structural conservation during vertebrate evolution

Inhibin and activin are structurally related dimeric peptides sharing two distinct but related subunits, beta A and beta B. By using polymerase chain reaction (PCR), we have cloned and sequenced activin beta A and beta B genes encoding the mature region of the peptides from the goldfish genomic DNA. A single form of beta A and two forms of beta B subunits were found. There is high identity with mammalian counterparts; the goldfish beta A subunit has 78% protein sequence identity with human beta A subunit, and the two beta B subunits have more than 94% sequence identity with human beta B subunit. This is the first demonstration of the activin family of peptides in the fishes.

Actions of goldfish neuropeptide Y on the secretion of growth hormone and gonadotropin-II in female goldfish

Neuropeptide Y (NPY) has been recently characterized in the goldfish and the sequence deduced from goldfish brain cDNA clones reveals that goldfish NPY (gNPY) has over 86% identity with human NPY (hNPY) (Blomqvist et al., 1992, Proc. Natl. Acad. Sci. USA 89, 2350-2354). In the present study, we used synthetic gNPY to investigate the role of NPY in the regulation of growth hormone (GH) and gonadotropin-II (GtH-II) in the goldfish. The dose-response relationships of gNPY on GH and GtH-II release were first tested using an in vitro perifusion system for pituitary fragments. It was found that gNPY stimulated both GH and GtH-II release in a dose-dependent manner, with ED50 values of 1.89 +/- 0.9 nM for GH and 4.19 +/- 2.9 nM for GtH-II. In addition, the C-terminal fragment gNPY (18-36) stimulated the release of both GH and GtH-II, but with lower potency than did the intact molecule. These results confirm our previous findings using hNPY. The interactions of gNPY and other GH and GtH-II regulators were also examined in the present studies. Prolonged infusion of sGnRH induced initial peak releases of GH and GtH-II, followed by a second phase of sustained hormone release at a reduced level. Application of a 5-min pulse of gNPY during the second phase of sGnRH action further stimulated GH and GtH-II release, but only to the levels similar to those induced by gNPY alone. Prolonged infusion with gNPY induced a rapid desensitization of GH and GtH-II release; the hormone levels returned to basal within 25 min in the continued presence of gNPY. Administration of 5-min pulse of sGnRH during the desensitization phase of continuous gNPY perfusion induced a similar GH response to that induced by sGnRH alone, whereas the GtH-II responses to sGnRH given during gNPY infusion were smaller than the responses to sGnRH alone, suggesting that the mechanisms of gNPY stimulation on GH and GtH-II release may be somewhat different. The gNPY-induced GH release was blocked by somatostatin, a known GH inhibitor; the gNPY-induced GtH-II release was reduced by dopamine, a known inhibitor for GtH-II. Finally, intraperitoneal injection of gNPY induced time- and dose-dependent increases in serum GH and GtH-II levels. Together, these results suggest that NPY may play a physiological role in the regulation of GH and GtH-II secretion in the goldfish.

In vitro and in vivo evidence that dopamine exerts growth hormone-releasing activity in goldfish

We have previously demonstrated that dopamine (DA) and the DA D1 agonist SKF 38393 stimulate growth hormone (GH) release from perifused pituitary fragments of the goldfish, suggesting an involvement of DA D1 receptors in GH regulation. In the present study, the role of DA on GH release and body growth of the goldfish was further investigated both in vivo and in vitro. DA consistently stimulated GH release in a dose-dependent manner from perifused goldfish pituitary fragments. The GH-releasing action of DA was seasonal, being the highest in sexually regressed fish, intermediate in recrudescent fish, and the lowest in sexually mature (prespawning) fish. Somatostatin, a known GH-release inhibitor in the goldfish, suppressed basal GH release and abolished the GH response to DA in perifused pituitary fragments as well as pituitary cells under static incubation. Intraperitoneal administration of the nonselective DA agonist apomorphine and the D1 agonist SKF 82958 increased the plasma GH levels in the goldfish. These GH responses were blocked by simultaneous treatment with the D1 antagonist Sch 23390 but not the D2 antagonist pimozide. Apomorphine administered orally also induced a similar elevation in plasma GH levels. Long-term feeding with apomorphine was found to be stimulatory to the body growth of goldfish. These results provide evidence that the neurotransmitter DA, by acting through DA D1 receptors in the pituitary, also functions as a GH-releasing factor in the goldfish.

Seasonal variation of neuropeptide Y actions on growth hormone and gonadotropin-II secretion in the goldfish: effects of sex steroids

The effects of neuropeptide Y (NPY) on growth hormone (GH) and gonadotropin-II (GtH-II) release in different reproductive stages were studied using perifused pituitary fragments of female goldfish. The GH and GtH-II release responses to 5-min pulses of NPY were relatively small in sexually regressed fish (July), intermediate in recrudescent fish (December), and maximal in sexually mature (= prespawning) fish (May). To test if sex steroids can modulate NPY action, the effects of in vivo implantation of 17 beta-estradiol (E2) and testosterone (T) (both at 100 micrograms/g dosage) on NPY-induced GH and GtH-II secretion were examined. In sexually regressed goldfish, implantation of T significantly enhanced NPY-induced GH and GtH-II release from perifused pituitary fragments; implantation of E2 potentiated the NPY-induced GtH-II, but not GH release. However, steroid implantation did not affect responses to NPY when this experiment was repeated using pituitaries from sexually mature fish. To test the hypothesis that steroids may act directly at the level of the pituitary to potentiate NPY action, pituitary fragments taken from sexually regressed goldfish were incubated with 100 nM T for 24 h, and the GH and GtH-II responses to 5-min challenges of NPY assessed in the presence of T. Both GH and GtH-II responses to NPY were not affected by treatment with T in vitro, suggesting that T does not act directly at the level of the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

[Fracture of the femoral neck: therapeutic approach]

The therapeutic approach for treatment of femoral neck fractures is reviewed. The choice of implant is dependent primarily on patient age and amount of fracture displacement. Hemiarthroplasty remains the treatment of choice for displaced femoral neck fractures in older or debilitated patients. Internal fixation is always indicated in healthy and active subjects, whether the fracture is displaced or undisplaced. Internal fixation with three cancellous screws provides good mechanical stability without compromising head vitality when compared to other implants.

Testosterone enhances GABA and taurine but not N-methyl-D,L-aspartate stimulation of gonadotropin secretion in the goldfish: possible sex steroid feedback mechanisms

The effects of gonadal steroids on GABA-, taurine (TAU)- and N-methyl-D,L-aspartate (NMA)-induced gonadotropin-II (GTH-II) release were investigated in male and female goldfish in vivo. In sexually regressed goldfish (both sexes mixed), intraperitoneal implantation for 5 to 10 days with solid Silastic pellets containing testosterone (100 micrograms/g), oestradiol (100 micrograms/g) or progesterone (100 micrograms/g) was previously shown to elevate serum sex steroid levels to values comparable to those in sexually mature animals, and to potentiate gonadotropin-releasing hormone-stimulated GTH-II release. In the present study, testosterone but not oestradiol or progesterone enhanced the stimulatory effects of exogenous GABA (100 micrograms/g) on GTH-II release in vivo. TAU (1 mg/g) stimulated GTH-II release in sexually regressed mixed sex and sexually recrudescent male goldfish, and both testosterone and oestradiol implantation enhanced GTH-II release induced by TAU. The glutamate agonist NMA (25 to 50 micrograms/g) was also found to stimulate GTH-II release; however it was relatively less effective in elevating serum GTH-II levels than GABA and TAU, and its effects were not modulated by sex steroid treatments. Pretreatment of goldfish with alpha-methyl-p-tyrosine to deplete brain and pituitary catecholamines did not affect NMA action on GTH-II release. Our results indicate that GABA, TAU and NMA are involved in the neuroendocrine regulation of GTH-II release in goldfish, and support the idea that testosterone participates in the positive feedback regulation of pituitary gonadotropin release in a non-mammalian vertebrate by enhancing GABA- and TAU-stimulated GTH release in vivo.

Neuropeptide-Y stimulates growth hormone and gonadotropin-II secretion in the goldfish pituitary: involvement of both presynaptic and pituitary cell actions

We have previously reported that neuropeptide-Y (NPY) stimulates GH and gonadotropin-II (GtH-II) release from perifused pituitary fragments in the goldfish. Since the teleost pituitary is directly innervated by neurosecretory terminals from the brain, we further investigated the possible sites of action of NPY. Both synthetic human NPY and NPY-(18-36), an agonist selective for the NPY Y2-receptor, stimulated GH and GtH-II release from the pituitary fragments; the magnitude of the response to NPY (18-36) was smaller than that to the whole molecule of NPY. NPY also stimulated the release of GH and GtH-II from perifused dispersed pituitary cells. In contrast, NPY-(18-36) had no effect on either GH or GtH-II release from dispersed pituitary cells. These data suggest that Y2 action is not direct at the level of pituitary cells, but may be indirect through actions on nerve terminals in the pituitary. The hypothesis that the action of NPY on GH and GtH-II release is mediated in part by GnRH was then tested. Both NPY and NPY-(18-36) stimulated the GnRH release from preoptic-anterior hypothalamic slices and pituitary fragments with similar potency. Furthermore, a GnRH antagonist significantly reduced the effects of NPY on both GH and GtH-II release in perifused pituitary fragments. Similar to previous findings, NPY, when given at 55-min intervals, desensitized the hormone responses in pituitary fragments. Similarly, the same treatment with NPY in perifused dispersed pituitary cells induced desensitization of GH and GtH-II responses. Together, these results suggest that 1) more than one type of NPY receptors are present in the goldfish pituitary; and 2) NPY has at least two sites of action in the pituitary. One site of action is the pituitary cells, where NPY directly stimulates GH and GtH-II secretion; the second is the nerve terminals, where NPY presynaptically stimulates GnRH release via Y2-like receptors, and GnRH, in turn, stimulates GH and GtH-II release.

Immunocytochemical evidence for the presence of inhibin and activin-like proteins and their localization in goldfish gonads

In previous studies, we have demonstrated that inhibin and activin are stimulatory to goldfish gonadotropin release. In the present study, the distribution of immunoreactive inhibin and activin subunits (alpha, beta A, and beta B) in goldfish gonads was examined with domain-specific antibodies against mammalian inhibin and activin subunits, using the avidin-biotin-peroxidase complex method. In the ovary, follicle cells surrounding the oocyte were heavily stained with anti-porcine beta A and human beta B subunits. The cytoplasm of previtellogenic oocytes, at all stages of the ovarian cycle, also showed strong reactions with anti-beta A and beta B. As ovarian recrudescence progressed, oocytes that started to accumulate cortical vesicles gradually lost their immunoreactivity, with the reaction intensity inversely proportional to the amount of cortical vesicles in the oocyte; when oocytes became full of cortical vesicles, the oocytoplasm was no longer immunoreactive to anti-beta A and beta B. The staining with antiporcine alpha subunit was similar to that with anti-beta A and beta B but the reaction intensity was weaker than that with anti-beta A and beta B. In the testis, the mature sperm in the tubular lumen exhibited a strong immunoreaction to anti-alpha antibody, while the interstitial tissue was completely negative. However, the immunoreactivities with anti-beta A and beta B in the testis were exclusively restricted to the interstitial tissues. These results provide evidence for the presence of inhibin and activin-like molecules in the goldfish and reveal the distribution of these molecules in the goldfish gonads.

Effects of sex steroid treatments on gonadotropin-releasing hormone-stimulated gonadotropin secretion from the goldfish pituitary

The effects of gonadal steroids on the gonadotropin (GTH) release response to salmon gonadotropin-releasing hormone (sGnRH), chicken gonadotropin-releasing hormone-II (cGnRH-II), and the sGnRH analogue, [D-Arg6, Trp7, Leu epsilon, Pro9]-N-ethylamide-GnRH (sGnRH-A), were investigated using an in vitro perifusion system for goldfish pituitary fragments. Gonad-intact male and female goldfish were implanted intraperitoneally (i.p.) with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g); pituitaries were removed 5 days later for perifusion experiments. In vivo treatment with T or E2 potentiates sGnRH-, cGnRH-II-, and sGnRH-A-induced GTH secretion from pituitary fragments of sexually regressed and sexually recrudescent goldfish in vitro. Testosterone (100 nM; 24 h) treatment in vitro has a direct effect on the pituitary to increase sGnRH responsiveness, and this potentiating effect of T was blocked by the protein synthesis inhibitor cycloheximide (25 microM). In sexually regressed goldfish, in vivo T implantation enhanced the serum GTH response to sGnRH-A (0.01 microgram/g; 6 h) 7-fold. ED50 estimates for in vitro pituitary GTH responsiveness to sGnRH-A were 1.0 +/- 0.1 nM and 0.1 +/- 0.1 nM (p < 0.05) for blank and T-implanted groups, respectively. Radioligand (125I-sGnRH-A) binding studies demonstrated that enhanced pituitary responsiveness was independent of changes in pituitary GnRH receptor affinity or number. These results demonstrate that sex steroids increase pituitary sensitivity to GnRH peptides in the goldfish.

Growth hormone and gonadotropin secretion in the common carp (Cyprinus carpio L.): in vitro interactions of gonadotropin-releasing hormone, somatostatin, and the dopamine agonist apomorphine

The effects of salmon gonadotropin-releasing hormone (sGnRH) and the superactive agonist [D-Arg6, Pro9NEt]-sGnRH (sGnRH-A) on growth hormone (GH) and gonadotropin (GtH) release were examined using a perifusion system for pituitary fragments of the common carp (Cyprinus carpio). Perifusion of 2-min pulses of different concentrations of sGnRH or sGnRH-A stimulated a rapid and dose-dependent increase in GH release: ED50 values for sGnRH and sGnRH-A in stimulating GH release were 2.8 +/- 0.7 and 0.5 +/- 0.1 nM, respectively, indicating that the superactivity of sGnRH-A for stimulation of GtH release also applies in induction of GH release. Exposure of the pituitary fragments to 10 nM sGnRH or sGnRH-A alone resulted in increases in GH and GtH release on a similar temporal course. Apomorphine (10, 100, and 1000 nM) significantly inhibited basal and GnRH-induced GtH release in a dose-dependent manner and significantly stimulated basal GH release; however, APO did not enhance GnRH-induced GH release. Somatostatin (100 nM) significantly blocked basal release and 10 nM sGnRH- and sGnRH-A-induced GH release, but was ineffective on GtH release. Treatment with somatostatin (100 nM) in combination with apomorphine (100 nM) caused an increase in sGnRH-induced GH release compared to treatment with somatostatin alone; whereas, on GtH there was a significant decrease in basal and GnRH-induced levels, compared to treatment with somatostatin alone. These results indicate that GH release in common carp is regulated by somatostatin as GH release inhibitor. sGnRH and sGnRH-A act as GH-releasing factors; the mechanisms by which GnRH stimulates GH and GtH secretion are independent. The dopamine agonist apomorphine stimulates GH release and inhibits GtH release directly at the pituitary level.

Interactions of gonadal steroids with brain dopamine and gonadotropin-releasing hormone in the control of gonadotropin-II secretion in the goldfish

In goldfish it is known that intraperitoneal implantation with testosterone (T) or estradiol (E2) potentiates the serum gonadotropin-II (GtH-II) response to gonadotropin-releasing hormone (GnRH) without affecting basal GtH-II levels. Since the release of GtH-II in goldfish is under a tonic dopaminergic inhibitory tone, the possibility of sex steroids modulating brain and pituitary dopamine was examined in vivo and in vitro. Implantation of females with either T or E2 (100 micrograms/g in solid silastic pellets) also potentiated the increase in serum GtH-II in response to the dopamine antagonist, domperidone (10 micrograms/g). High-performance liquid chromatography measurements showed that steroid implantation had no effect on dopamine content in the telencephalon including preoptic area, hypothalamus, and pituitary. However, the present study demonstrates that T or E2 can increase pituitary dopamine turnover rates following tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine (240 micrograms/g). In vitro perifusion of pars distalis fragments from E2- or T-treated fish also showed a potentiation of salmon GnRH (sGnRH)-induced GtH-II release compared to controls. However, exposure to pituitary fragments from control and steroid-treated fish to increasing doses of the dopamine agonist LY 171555 did not demonstrate a significant difference in the sensitivity of the gonadotrophs to dopamine. Testosterone-induced alterations in DA turnover are dissociable from the positive action of T on pituitary responsiveness, since the potentiating effect of T implantation was not affected by severe depletion of brain and pituitary DA levels by alpha-methyl-p-tyrosine pretreatment. These data demonstrate that in gonad-intact goldfish, sex steroids enhance pituitary responsiveness to GnRH but basal serum GtH-II levels are maintained by a concomitant increase in DA turnover in the pituitary.

Influence of the reamer shape on intraosseus pressure during closed intramedullary nailing of the unbroken femur: a preliminary report

The generation of intramedullary pressure during reaming of the femur was compared for two different reamer systems: the AO/ASIF universal reamer and the Gray flexible reamer system (Howmedica), while reaming in 9 oncologic patients undergoing prophylactic nailing of metastatic femora as indicated by impending fractures (unbroken femora). An intracranial fibre optic catheter pressure-monitoring device inserted through the distal supracondylar cortex was used to perform measurements. Preliminary data are presented. Maximum pressures of up to 450 mmHg were recorded during reaming with the smaller 9.0 and 9.5 mm theta reamers. Rapid penetration of the reamer in both proximal and distal metaphyses caused much higher pressures than reaming the cortex of the diaphysis. Speed of penetration and volume of the reaming shaft were found to be important parameters. No significant differences between maximal pressures generated by the two types of reamers could be observed.

Interactions of estradiol with gonadotropin-releasing hormone and thyrotropin-releasing hormone in the control of growth hormone secretion in the goldfish

The effects of testosterone (T) and estradiol (E2) on serum growth hormone (GH) concentrations were investigated throughout the seasonal reproductive cycle of the female goldfish. Gonad-intact female goldfish were implanted intraperitoneally for 5 days with silastic pellets containing no steroid (blank), T(100 micrograms/g) or E2 (25-100 micrograms/g). In blank-implanted females, seasonal variations in serum GH were evident; maximal serum GH levels were found in spring while minimal GH levels were found in summer and early autumn. Implantation of E2-containing silastic capsules stimulated increases (2-4 times control) in serum GH levels throughout the reproductive cycle. Implantation of T did not affect serum GH at any time of the year. One possible mechanism by which E2 could exert its effects may be through alteration of pituitary sensitivity to GH-releasing factors. The decapeptide salmon gonadotropin-releasing hormone (sGnRH) is found in the brain and pituitary of goldfish and stimulates gonadotropin (GTH) and GH secretion. In contrast, thyrotropin-releasing hormone (TRH) stimulates GH, but not GTH, release from pars distalis fragments obtained from sexually regressed (ED50 = 5.7 +/- 3.8 nM; August) or sexually mature (ED50 = 0.53 +/- 0.28 nM; March) fish; in vivo E2 treatment resulted in a 3-fold increase in the in vitro GH response to TRH. Furthermore, E2 treatment increased sGnRH-stimulated GH release by approximately 4-fold. These results demonstrate that E2 but not T stimulates GH secretion throughout the reproductive cycle of female goldfish. Furthermore, sGnRH and TRH stimulate GH release in a teleost, and these stimulatory responses are enhanced by physiological levels of E2.

Effects of porcine follicular fluid, inhibin-A, and activin-A on goldfish gonadotropin release in vitro

Inhibin and activin are important reproductive regulators in mammalian species and have been demonstrated to be highly conserved in structure. The present study examines the effects of porcine follicular fluid (pFF; a crude inhibin and activin preparation) and purified porcine inhibin-A and activin-A on goldfish gonadotropin-II (GTH-II) release. In studies using primary cultures of dispersed goldfish pituitary cells in static incubation, treatments with pFF, inhibin-A, and activin-A for 10 h caused dose-dependent increase in GTH-II release. In perifusion studies using goldfish pituitary fragments, basal GTH-II release was significantly elevated after 12-h exposure to 500 micrograms/ml pFF. Furthermore, GnRH-induced GTH-II secretion was potentiated by pretreatment with pFF. When pFF was applied in the form of 5-min pulses, a rapid dose-related stimulation of GTH-II was observed. Similarly, challenges with 2-min pulses of 15, 150, and 1500 pM inhibin-A and activin-A stimulated GTH-II release by goldfish pituitary fragments in a rapid and dose-dependent manner. This acute stimulatory action of inhibin on goldfish GTH-II release was completely abolished after pretreatment with specific inhibin antibodies. The acute actions of inhibin and activin on GTH-II release are probably not due to the release of endogenous GnRH from nerve terminals in the pituitary fragments or binding to the GnRH receptors. First, a specific GnRH antagonist did not block the actions of inhibin and activin. Second, dopamine, a potent inhibitor of GnRH-stimulated GTH-II secretion in goldfish, was only partially effective in decreasing inhibin- and activin-induced GTH-II release. Third, the stimulatory effects of inhibin and GnRH on GTH-II release were additive. These lines of evidence also indicate that the mechanisms mediating inhibin and activin stimulation of goldfish GTH-II release may be somewhat different from those of GnRH. These results demonstrate that in contrast with the usual inhibitory effects of inhibin on GTH release in mammals, both inhibin and activin exert long term and acute stimulatory actions on GTH-II release in the goldfish.

Isolation and characterization of hypothalamic growth-hormone releasing factor from common carp, Cyprinus carpio

A growth hormone-releasing factor (GRF)-like peptide was isolated from the hypothalamus of common carp, Cyprinus carpio, by acid extraction, gel filtration chromatography, immunoaffinity chromatography using antiserum directed against rat GRF, and multiple steps of HPLC using octadecyl columns. Based on Edman degradation and peptide mapping, this teleost GRF was established to be a 45-residue peptide with the following primary structure: His-Ala-Asp-Gly-Met-Phe-Asn-Lys-Ala-Tyr-Arg-Lys-Ala-Leu-Gly-Gln-Leu-Ser- Ala-Arg - Lys-Tyr-Leu-His-Thr-Leu-Met-Ala-Lys-Arg-Val-Gly-Gly-Gly-Ser-Met-Ile-Glu- Asp-Asp-Asn-Glu-Pro-Leu-Ser. Carp GRF is closely related structurally to peptides of the glucagon-secretin superfamily, and more particularly to mammalian vasoactive intestinal peptide (VIP) precursors and the N-terminal portion of mammalian GRFs. A synthetic replicate of this peptide is highly potent [50% effective dose (ED50) approximately 0.08 nM] in stimulating GH release from cultured goldfish pituitary glands and in elevating serum GH levels 30 min after injection (0.1 micrograms/g) in goldfish.

Distinct sequence of gonadotropin-releasing hormone (GnRH) in dogfish brain provides insight into GnRH evolution

In vertebrates, gonadotropin-releasing hormone (GnRH) belongs to a family of decapeptides characterized by the conservation of residues 1, 2, 4, 9, and 10. In the jawed vertebrates only positions 5, 7, and 8 in the GnRH molecules vary. We have now purified two forms of GnRH from the brains of spiny dogfish (Squalus acanthias) by using reverse-phase high-performance liquid chromatography. The primary structures were established by automated Edman degradation and mass spectral analysis. The distinct structure of the first form (dogfish GnRH) is pGlu-His-Trp-Ser-His-Gly-Trp-Leu-Pro-Gly-NH2 (pGlu represents pyroglutamyl). The second peptide is identical to a form of GnRH originally isolated from chicken brains (chicken GnRH-II; pGlu-His-Trp-Ser-His-Gly-Trp-Tyr- Pro-Gly-NH2) and is widespread throughout the vertebrates. We are aware of no other species of cartilaginous fish in which the primary structures of two forms of GnRH have been determined. The presence of chicken GnRH-II in dogfish supports the idea that chicken GnRH-II is the oldest GnRH to evolve in jawed vertebrates. With the addition of the dogfish GnRH structure to the family, two main structural branches of GnRH can be delineated. The physiological effects of dogfish GnRH included the release of not only gonadotropin but also growth hormone from goldfish pituitary fragments.

Amino Acid Neurotransmitters and Dopamine in Brain and Pituitary of the Goldfish: Involvement in the Regulation of Gonadotropin Secretion

An isocratic high-performance liquid chromatographic technique was developed to measure levels of gamma-aminobutyric acid (GABA), glutamate, and taurine in the brain and pituitary of goldfish. Accuracy of this procedure for quantification of these compounds was established by evaluating anesthetic and postmortem effects and by selectively manipulating GABA concentrations by intraperitoneal administration of the glutamic acid decarboxylase (GAD) inhibitor 3-mercaptopropionic acid or the GABA transaminase inhibitor gamma-vinyl GABA. The technique provided a simple, rapid, and reliable method for evaluating the concentrations of these amino acids without the use of complex gradient chromatographic systems. To investigate the relationship between neurotransmitter amino acids and the control of pituitary secretion of gonadotropin, the effects of injection of taurine, GABA, or monosodium glutamate on GABA, glutamate, taurine, and, in some instances, monoamine concentrations in the brain and pituitary were evaluated and related to serum gonadotropin levels. Injection of taurine caused an elevation in serum gonadotropin concentrations. In addition, injection of the taurine precursor hypotaurine but not the taurine catabolite isethionic acid elevated serum gonadotropin levels. Intracerebroventricular injection of either GABA or taurine also elevated serum gonadotropin concentrations. Pretreatment of recrudescent fish with alpha-methyl-p-tyrosine reduced pituitary dopamine concentrations and also potentiated the serum gonadotropin response to taurine. Injection of monosodium glutamate caused an increase of glutamate content in the pituitary at 24 h; this was followed by a decrease at 72 h after administration. Pituitary GABA, taurine, and dopamine concentrations underwent a transient depletion after monosodium glutamate administration, and this was associated with an elevation of serum gonadotropin content.(ABSTRACT TRUNCATED AT 250 WORDS)

A reduction in pituitary dopamine turnover is associated with sex pheromone-induced gonadotropin secretion in male goldfish

In goldfish, the gonadal steroid, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P), functions as a potent preovulatory female sex pheromone which stimulates rapid elevations in serum gonadotropin (GtH) levels and subsequent increases in milt production in males. GtH secretion in goldfish is known to be regulated by the stimulatory actions of gonadotropin-releasing hormone (GnRH) and the inhibitory actions of dopamine (DA). This study specifically examined whether the 17,20 beta-P-induced elevation in male GtH is caused by pheromone-mediated changes in DA inhibition at the level of the pituitary. First, we have demonstrated that dihydroxyphenylacetic acid (DOPAC) is the primary metabolite of DA catabolism in the brain and pituitary gland of goldfish. Second, we measured changes in circulating levels of GtH and changes in pituitary content of DA and its metabolite, DOPAC, as well as possible alterations in DA turnover rate (DOPAC/DA ratio) following short-term exposure of male goldfish to water-borne 17,20 beta-P. Water-borne 17,20 beta-P consistently increased serum GtH levels in males within 20 min of exposure and maintained elevated levels for up to 120 min. Although changes in pituitary DA content were not observed during periods of high GtH release, coincident reductions in pituitary levels of DOPAC were measured within 45 min of exposure to the pheromone. More importantly, there was a significant decrease in the rate of DA turnover in the pituitary, as assessed by comparing the ratio of DOPAC to DA present, at 20, 45, and 120 min of exposure. Since the reduction of DA turnover in the pituitary is inversely correlated with periods of increased GtH release, the present results suggest that water-borne 17,20 beta-P causes an abatement of DA release to the pituitary. Based on the latency of the GtH response to water-borne 17,20 beta-P, a rapid reduction of DA turnover in the pituitary appears to be at least part of the neuroendocrine trigger for 17,20 beta-P-induced GtH release in male goldfish.

Influence of GABA on gonadotrophin release in the goldfish

The influence of GABA on pituitary gonadotrophin (GTH) release in the goldfish was studied by means of in vivo and in vitro techniques. It was found that GABA injected intraperitoneally caused an increase of serum GTH levels in regressed or early maturing fish, but not in late maturing animals. Moreover, injection of a GABA transaminase inhibitor caused a significant increase of GABA within the hypothalamus and pituitary, and a dose-dependent increase in serum GTH levels. To determine if this effect could be exerted directly at the level of the pituitary, dispersed pituitary cells in static incubation or in perifusion were exposed to increasing concentrations of GABA or its agonists muscimol and baclofen. None of these drugs was able to modify the spontaneous or GnRH-induced secretion of GTH, indicating that the in vivo effect of GABA was most likely mediated via another hypothalamic factor. Using in vitro incubation of pituitary slices, it was found that GABA caused a dose-related stimulation of GnRH release at the level of the pituitary, providing a possible explanation for the observed in vivo stimulatory effect of GABA on GTH release. Since the seasonal effect of GABA in vivo indicated a possible interaction of GABA with sexual steroids, GABA was given intraperitoneally to female goldfish implanted with either testosterone or estradiol. We found that the stimulatory effect of GABA on GTH release was abolished in estradiol-treated females but was still observed in testosterone-implanted fish. Moreover, estradiol but not testosterone caused a decrease of the GABA concentration within the telencephalon.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine stimulates growth hormone release from the pituitary of goldfish, Carassius auratus, through the dopamine D1 receptors

Previously, we have demonstrated that ip injection of apomorphine, a nonselective dopamine (DA) agonist, increases serum GH levels in the goldfish, suggesting a possible role of DA in GH regulation. In the present study, the effects of DA on GH release in the goldfish were further characterized using an in vitro perifusion system for pituitary fragments. DA increased GH release in a dose-dependent manner with an ED50 of 0.26 +/- 0.06 microM. SKF38393, a DA D1 agonist, mimicked the GH-releasing effect of DA with an ED50 of 0.41 +/- 0.12 microM. Stereoselectivity consistent with mammalian DA D1 systems was demonstrated for the GH response to SKF38393; only the (+)- but not (-)-enantiomer of SKF38393 induced a dose-dependent GH release. Two other D1 agonists, SKF77434 and SKF82958, were also found to have GH-releasing activity. In contrast, high doses (up to 1 microM) of the DA D2 agonists, bromocriptine and LY171555, did not affect basal GH levels. The receptor specificity for DA-stimulated GH release was further investigated by using D1 and D2 antagonists; the D1 antagonists SCH23390 and SKF83566 completely abolished the GH response to DA or the D1 agonist SKF38393, whereas the D2-specific antagonists domperidone and (-)-sulpiride were not effective in this respect. Taken together, the present study demonstrates that DA is stimulatory to GH release from the pituitary of goldfish, and its action is mediated through receptors resembling the mammalian DA D1 receptors. The apparent similarities of the DA D1 receptor pharmacology between the goldfish and the mammals also indicate that D1 receptor is highly conserved during vertebrate evolution.

Activity of vertebrate gonadotropin-releasing hormones and analogs with variant amino acid residues in positions 5, 7 and 8 in the goldfish pituitary

All non-mammalian vertebrates as well as marsupial mammals have two or more forms of gonadotropin-releasing hormone (GnRH) in the brain. Goldfish brain and pituitary contains two molecular forms of GnRH, salmon GnRH ([Trp7, Leu8]m-GnRH; s-GnRH) and chicken GnRH-II ([His5, Trp7, Tyr8]m-GnRH; cII-GnRH). Both sGnRH and cII-GnRH stimulate gonadotropin (GtH) as well as growth hormone (GH) release from the goldfish pituitary. The purpose of the present study was to study the activity of the five known forms of GnRHs as well as analogs of mammalian GnRH (m-GnRH) with variant amino acid residues in positions 5, 7 and 8 in terms of binding to GnRH receptors, and release of GTH and GH from the perifused fragments of goldfish pituitary in vitro. All five vertebrate GnRH peptides stimulated both GtH and GH release in a dose-dependent manner, although their potencies were very different. cII-GnRH was somewhat more active than s-GnRH in releasing GtH, whereas s-GnRH tended to have a greater potency than cII-GnRH in terms of GH release. Both chicken GnRH-I (cI-GnRH) and lamprey GnRH (l-GnRH) were significantly less potent than mGnRH, s-GnRH and cII-GnRH in releasing GtH and GH. cII-GnRH binds with higher affinity for the high affinity binding sites compared to all other native peptides. The activity of [Trp7]-GnRH was similar to both s-GnRH and cII-GnRH in releasing GtH and GH. Substitution of His5 resulted in a significant decrease in GtH releasing potencies compared to mGnRH, sGnRH and cII-GnRH. [His5]-GnRH also had lower GH releasing potency than mGnRH and sGnRH. Tyr8, His8 and Leu8 substitutions caused significant decreases in GtH releasing potencies compared to mGnRH, s-GnRH and cII-GnRH, but did not cause a significant change in GH releasing potency. The combination of [His5, Trp7]-GnRH had GtH and GH releasing activities similar to m-GnRH, s-GnRH and cII-GnRH.(ABSTRACT TRUNCATED AT 400 WORDS)

Properties of common carp gonadotropin I and gonadotropin II

Two gonadotropins, GtH I and GtH II, were extracted with 35% ethanol-10% ammonium acetate, pH 6.1, from female common carp pituitary glands and purified by ion-exchange chromatography on a DE-52 column followed by gel filtration on a Sephadex G-75 column. Molecular weights of GtH I and GtH II as determined by SDS-PAGE were 45,000 and 35,000, respectively. Both GtHs dissociate into two subunits following reduction with beta-mercaptoethanol. These subunits contain different N-terminal amino acids (Tyr and Gly for GtH I; Tyr and Ser for GtH II). GtH I was acid stable and did not dissociate into subunits following treatment with 0.1% trifluoroacetic acid; GtH II readily dissociated into subunits by this treatment. GtH I and GtH II have distinct elution profiles on reverse-phase HPLC. The N-terminal amino acid sequence of the beta-subunit of GtH II was identical to that of common carp maturational GtH described by other workers suggesting that GtH I is a newly identified molecule. This was supported by radioimmunoassay analysis. GtH II and a common carp maturational GtH preparation (F11 cGtH; Peter et al., 1982, J. Interdiscipl. Cycle Res. 13, 229-239) had similar immunological activity in tests with antisera to the beta-subunit of maturational GtH whereas GtH I had low (less than 6%) cross-reactivity. GtH I, GtH II, and F11 cGtH were equipotent in tests with antisera to the alpha-subunit of maturational GtH suggesting these molecules contain a similar alpha-subunit. In vitro bioassays using goldfish revealed that GtH I and GtH II share the same spectrum of biological activities causing stimulation of ovarian and testicular steroidogenesis and induction of oocyte final maturation. The demonstration of two chemically distinct GtHs in common carp is similar to what has been described for chum and coho salmon.