Biomedical subjects

R E Peter

Publications and source records attributed to R E Peter.

At least 55 records · Page 3Linked to original sources

PubMed1996

Expression of salmon gonadotropin-releasing hormone (GnRH) and chicken GnRH-II precursor messenger ribonucleic acids in the brain and ovary of goldfish.

The complementary DNAs (cDNA) encoding the [Trp7Leu8]gonadotropin-releasing hormone (salmon GnRH; sGnRH) precursor and the [His5Trp7Tyr8]GnRH (chicken GnRH-II; cGnRH-II) precursor of the goldfish brain were isolated and sequenced using reverse transcription and rapid amplification of cDNA ends (RACE). The sGnRH precursor cDNA consists of 540 bp, including an open reading frame of 282 bp, and the cGnRH-II precursor cDNA consists of 682 bp, including an open reading frame of 258 bp. The 94 amino acid-long goldfish sGnRH precursor and 86 amino acid-long goldfish cGnRH-II precursor have the same molecular architecture as GnRH precursors identified to date in other vertebrate species. Using two sets of primers designed to be sense and antisense to the goldfish brain sGnRH precursor cDNA sequence, reverse transcription-polymerase chain reaction (RT-PCR) amplification of total RNA from brain and ovary at gonadal recrudescent, mature ( = prespawning), and postovulatory stages resulted in two predicted sizes of PCR products. The intensities of staining signals of ethidium bromide were similar between brain and ovary samples. The same RT-PCRs were carried out with two sets of primers for cGnRH-II precursor cDNA, resulting in two PCR products of predicted size; however, the ethidium bromide staining signals are much weaker for products amplified from ovarian cDNA than that from brain cDNA. Restriction enzyme analysis verified the expected RT-PCR products. Sequence analysis of ovarian sGnRH precursor cDNA generated by RACE of total RNA from recrudescent ovarian tissue revealed the identical sequence to that of the brain sGnRH cDNA. Northern blot analysis detected a single mRNA transcript of approximately 650 bases for the sGnRH precursor in both the brain and ovary, and 750 bases for the cGnRH-II precursor in the brain. These results demonstrate that two forms of GnRH precursor (sGnRH and cGnRH-II) mRNA are expressed in goldfish brain tissue and that the sGnRH transcript and a low level of cGnRH-II transcript are also expressed in the goldfish ovary.

Amino Acid Sequence↗

PubMed1996

Growth hormone-releasing hormone immunoreactivity in the brain, pituitary, and pineal of the goldfish, Carassius auratus.

Using antisera directed against carp growth hormone-releasing hormone (cGHRH), the distribution of immunoreactive (ir) structures in the brain, pituitary, and pineal of the goldfish, Carassius auratus, was investigated. The antisera were produced in rabbits by administration of cGHRH(1-44)-NH(2) followed by cGHRH(1-45)-OH for different periods of time, both coupled to human alpha-globulins via bisdiazotized benzidine as immunogen. Immunoreactive perikarya were visualized in the nucleus preopticus periventricularis (NPP), nucleus lateralis tuberis (NLT), nucleus of the lateral lemniscus (NLL), and the pineal. The preoptic area and area ventralis telencephali seemed to receive innervation from the NPP cells. The fibers of the NLT cell bodies extended caudally along the infundibular floor and innervated the hypophysis. The processes of the NLL perikarya extended rostrally along the lateral lemniscus, curved ventrally along the outer margin of the glomerular nuclear complex, and extended to the dorsal area of the lateral recess, while issuing fascicles that branched off and fanned out to innervate extensively the nucleus diffusus of the hypothalamic inferior lobes and the nucleus lateralis tori; several fiber bundles branched off and extended toward the lateral areas of the paraventricular organ area and even into the rostral region of the hypothalamic inferior lobes. A small percentage of the corticotrophs of the rostral pars distalis, a few cells in the central area of the pars intermedia (PI), and neurohypophysial fibers in the peripheral area of the PI of the pituitary gland had colocalization of GHRH-ir; GHRH-ir fibers in the rostral and proximal pars distalis were sparse. It is suggested that the GHRH-ir perikarya of the diencephalon may stimulate growth hormone release either by modulating the activity of somatotrophs or of other hypothalamic neurosecretory neurons. The innervation of the hypothalamic inferior lobe by GHRH-ir perikarya of the NLL suggests some influence on feeding processes. Presence of GHRH in the pineal implies involvement in some daily cyclic activity.

Animals↗

PubMed1996

Regulation of growth hormone secretion by amino acid neurotransmitters in the goldfish (I): Inhibition by N-methyl-D, L-aspartic acid.

High levels of the amino acid neurotransmitter glutamate were found in the goldfish hypothalamus and pituitary using high performance liquid chromatography with fluorometric detection. A specific polyclonal antibody to glutamate was generated in the rabbit for immunocytochemistry. Localization studies demonstrated that glutamatergic neurons of undetermined origin innervate the particular part of the goldfish adenohypophysis where somatotrophs and gonadotrophs are located. Intraperitoneal and brain third ventricle injection of the glutamate agonist N-methyl-D,L-aspartic acid (NMA) inhibited GH release in vivo. The gonadal steroid estradiol plays an important role in regulating GH secretion by stimulating basal serum GH levels and enhancing the inhibitory effects of NMA on GH secretion. Taken together, these results demonstrate that glutamate is an important regulator of GH secretion in goldfish.

Animals↗

PubMed1996

Sexual dimorphism of galanin-like immunoreactivity in the brain and pituitary of goldfish, Carassius auratus.

A sexually dimorphic distribution of galanin (GAL)-like immunoreactive (ir) neurons and fibers was found in the brain and pituitary of goldfish. The rostralmost GAL-ir perikarya were found in the area ventralis telencephali pars supracommissuralis dorsal to the anterior commissure. In the diencephalon, there was several GAL-ir perikarya in the nucleus preopticus periventricularis (NPP). Males had many GAL-ir perikarya in the nucleus preopticus pars parvocellularis (NPOpp) and isolated GAL-ir perikarya in the NPO pars magnocellularis, and lateral to the NPO; in females GAL-ir perikarya were not found in these sites. A large GAL-ir neuronal aggregation was observed in the nucleus lateralis tuberis pars posterioris (NLTp). Several ir perikarya were present in the nucleus posterioris tuberis; however, unlike in other regions the males revealed fewer neurons than females. Besides the established innervation of the pituitary gland by the NPP, NPO and NLT, the present study revealed GAL-ir perikarya of these nuclei apparently also innervating the telencephalon, thalamus, optic tectum, tegmentum and even some areas of the rhombencephalon. Isolated perikarya were found in the nucleus posterioris periventricularis, the dorsal vicinities of the nucleus recessus lateralis (NRL), nucleus recessus posterioris, and nucleus saccus vasculosus, and in the medulla oblongata ventral to the vagal lobes. In the pituitary gland, GAL-ir fibers ramify and terminate among the pars distalis cells. A small percentage of growth hormone-secreting cells colocalize GAL. In males, most GAL-ir cells of the proximal pars distalis (PPD) showed granular ir product in the entire cell, and some had one or two large granules; in females the ir PPD cells showed clusters of a few fine ir granules of uniform size in each. Sexual dimorphism was also found in the olfactory bulb, telencephalon, infundibulum, mesencephalic tegmentum, optic tectum and medulla oblongata, the males having a more extensive GAL-ir fiber system than the females. Galanin may play a role in both hypophysiotropic and motor functions.

Animals↗

PubMed1996

Characterization of cholecystokinin binding sites in goldfish brain and pituitary.

The characterization and distribution of cholecystokinin (CCK)/gastrin binding sites were determined in the goldfish central nervous system (CNS). Binding of 125I-sulfated CCK octapeptide (125I-CCK-8s) in tissue sections was found to be saturable, reversible, time dependent, and displaceable by CCK/gastrin-like peptides. Analysis of saturable equilibrium binding revealed a high-affinity binding site (dissociation constant of 0.706 +/- 0.188 nM), which also displayed high affinity for gastrin-17s and caerulein. Lower affinities were observed for the nonsulfated forms of CCK-8 and gastrin-17. These findings suggest that a single primitive CCK/gastrin receptor exists in the goldfish CNS. The distribution of CCK/gastrin binding sites in the goldfish brain and pituitary revealed high densities within the telencephalon and preoptic hypothalamus, as well as within hypothalamic nuclei associated with the brain feeding center. High densities of binding sites were also localized within the midbrain tegmentum and optic tectum of the midbrain, the facial lobe and vagal lobe of the hindbrain, and within the pituitary pars distalis. Overall, these findings support previous studies that indicate that CCK/gastrin-like peptides play a role in the central regulation of feeding behavior and pituitary hormone secretion in fish.

Animals↗

PubMed1995

Structural modifications of non-mammalian gonadotropin-releasing hormone (GnRH) isoforms: design of novel GnRH analogues.

Three natural forms of vertebrate gonadotropin-releasing hormone (GnRH) provided the structural basis upon which to design new GnRH agonists: [His5,Trp7,Leu8]-GnRH, dogfish (df) GnRH; [His5,Asn8]-GnRH, catfish (cf) GnRH; and [His5,Trp7,Tyr8]-GnRH, chicken (c) GnRH-II. The synthetic peptides incorporated the position 6 dextro (D)-isomers D-arginine (D-Arg) or D-naphthylalanine (D-Nal) in combination with an ethylamide substitution of position 10. The in vitro potencies for LH and FSH release of these analogues were assessed using static cultures of rat anterior pituitary cells. Efficacious peptides were examined for their gonadotropin-II and growth hormone releasing abilities from perifused goldfish pituitary fragments. Rat LH and FSH release was measured using homologous radioimmunoassays, whereas goldfish growth hormone and gonadotropin-II release were determined using heterologous carp hormone radioimmunoassays. The receptor binding of the most potent analogues was determined in bovine pituitary membrane preparations. Substitution of D-Nal6 into [His5,Asn8]-GnRH increased the potency over 2200-fold compared with the native ligand (cfGnRH) in cultured rat pituitary cells. This was equivalent to a 55-fold greater potency than that of the native mammal (m) GnRH peptide. Substitution of D-Nal6 or D-Arg6 into dfGnRH or cGnRH-II resulted in potencies that were related to the overall hydrophobicity of the analogues. The [D-Nal6,Pro9NEt]-cfGnRH bound to the bovine membrane preparation with an affinity statistically similar to that of [D-Nal6,Pro9NEt]-mGnRH (kd = 0.40 +/- 0.04 and 0.55 +/- 0.10 nM, respectively) in cultured rat pituitary cells. All analogues tested released the same ratio of FSH to LH. In goldfish, the analogues did not possess superagonistic activity but instead desensitized the pituitary fragments at lower analogue doses than that of the sGnRH standard suggesting differences in receptor affinity or signal transduction.

Amino Acid Sequence↗

PubMed1995

Characterization and distribution of bombesin binding sites in the goldfish hypothalamic feeding center and pituitary.

Bombesin (BBS)/gastrin-releasing peptide (GRP) binding sites were characterized and their distribution examined in the goldfish brain and pituitary by radioligand binding and autoradiography. Binding of 125I-[Tyr4]-BBS-14 to tissue sections was found to be saturable, reversible, time-dependent and displaceable by BBS/GRP-like peptides. Analysis of saturable equilibrium binding revealed a one-site model fit with a Kd of 0.665 +/- 0.267 nM. This binding site displayed high affinity for members of the BBS subfamily of peptides, including GRP10 (Ki; 0.292 +/- 0.038 nM) and GRP27 (Ki; 2.034 +/- 1.597 nM), but showed no affinity for the BBS8-14 fragment. While an approximate 100-fold lower binding affinity was displayed by the binding site for neuromedin B (Ki; 6.15 +/- 28.2 nM), litorin was highly effective in displacing radiolabeled BBS binding (Ki; 1.469 +/- 0.427 nM). The localization of saturable and high affinity BBS/GRP binding sites in specific areas of the goldfish brain and pituitary generally revealed a similar anatomical distribution to BBS/GRP-like immunoreactive material reported previously by our laboratory. Quantitative densitometric analysis of radiolabeled BBS binding to brain nuclei and the pituitary revealed a moderate concentration of BBS/GRP binding sites in the hypothalamic feeding area, including the nucleus diffusus libi inferioris, nucleus recessus lateralis, nucleus lateral tuberis, and nucleus anterior tuberis. Other brain nuclei known to influence the brain feeding center which contained a high density of BBS/GRP binding sites included nuclei of the dorsal and ventro-medial telencephalon, the preoptic hypothalamus, and the optic tectum. High densities of BBS/GRP binding sites were also localized in the dorsal cerebellum, and nucleus habenularis. In the pituitary, BBS/GRP binding sites were present in high concentration in the neurointermediate lobe, with a relatively lower density localized in the pars distalis. The present study further supports a role for BBS/GRP-like peptides in the regulation of feeding behavior and anterior pituitary hormone secretion in teleosts.

Amino Acid Sequence↗

PubMed1995

Nature and distribution of gonadotropin-releasing hormone (GnRH) in the brain, and GnRH and GnRH binding activity in serum of the spotted dogfish Scyliorhinus canicula.

The distribution of different molecular forms of gonadotropin-releasing hormone (GnRH) in the brain and serum of the spotted dogfish, Scyliorhinus canicula, was investigated by an indirect immunofluorescence method, using antisera against salmon (s-), chicken-II (cII-) and mammalian (m-) GnRHs, and by reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with radioimmunoassays. Five GnRH molecular forms were demonstrated on the basis of the retention time in the RP-HPLC system. The characteristics of four of these GnRH peptides are consistent with those of m-, cII-, dogfish (df-), and sGnRH. The fifth form appears to be novel. Immunoreactive sGnRH structures were confined to the diencephalon; whereas cIIGnRH and mGnRH were found in the telencephalon and diencephalon. cIIGnRH- and dfGnRH-like molecules were detected in the serum. Moreover, a specific, low-affinity GnRH binding protein (GnRH-BP) was found in the serum of the spotted dogfish. The binding of [125I]sGnRHA to the serum GnRH-BP was dependent on incubation time, equilibrium being reached within 1 hr at 4 degrees; binding was rapid and completely reversible. Scatchard analysis yielded a linear plot with a Kd of 7.9 x 10(-7) M. The presence of a GnRH-BP in spotted dogfish serum suggests a probable action of GnRH via the general circulation.

Animals↗

PubMed1995

Evidence that the inhibitory effects of stress on reproduction in teleost fish are not mediated by the action of cortisol on ovarian steroidogenesis.

Ovarian follicles of goldfish, common carp, and the sparid Pagrus auratus (New Zealand snapper) were incubated in vitro to assess the effects of cortisol (F) on ovarian steroidogenesis. Unstimulated goldfish follicles produced little testosterone (T) or 17 beta-estradiol (E2), whereas both carp and snapper follicles spontaneously produced E2 and to a lesser extent T. Goldfish follicles produced increased amounts of E2 in response to treatment with human chorionic gonadotropin (hCG), whereas carp and snapper follicles did not. However, stimulation of carp follicles with maturational carp gonadotropin (cGTH-II) resulted in dose-dependent increases in production of E2. Treatment of follicles of all three species with T resulted in E2 production to levels as high as or higher than those following treatment with hCG or cGtH-II. Cotreatment of follicles with T and hCG or cGTH-II did not result in higher E2 production than treatment with T alone. Goldfish follicles treated with 25-hydroxycholesterol showed increases in E2 production that were similar to those occurring following treatment with T. Treatment of follicles with F at a range of doses up to 1 microgram.ml-1 had no inhibitory effect on T or E2 production in any treatment combination in any of the species examined. In several cases, follicles incubated with T and/or hCG produced more E2 in the presence of F than they did without F. The results suggest either that the observed inhibitory effects of stress in a range of teleost species are not mediated by F or that they arise higher in the endocrine pathway than at the level of ovarian steroidogenesis.

Animals↗

PubMed1995

Bombesin-like immunoreactivity in the forebrain and pituitary and regulation of anterior pituitary hormone release by bombesin in goldfish.

The presence and distribution of bombesin (BBS)/gastrin-releasing peptide (GRP)-like immunoreactivity (IR) was examined in the goldfish pituitary and forebrain. BBS/GRP-like IR nerve fibres were consistently observed throughout the pituitary neurointermediate lobe (NIL); occasionally, BBS/GRP-like material was localized in cells and few fibres within the pars distalis. Within the goldfish forebrain, sparse, fine-beaded BBS/GRP-like IR fibres and few perikarya were detected in the preoptic hypothalamus. BBS/GRP-like IR material was also present in the ventro-posterior hypothalamus and the hypothalamic inferior lobes, and, in particular, within the nucleus lateral tuberis pars anterioris (NLTa) and nucleus lateral tuberis pars posterioris (NLTp), nucleus anterior tuberis (NAT), nucleus recessus lateralis (NRL), nucleus recessus posterioris (NRP), and the nucleus diffusus lobi inferioris (NDLI). Several BBS/GRP-like IR perikarya were observed in periventricular regions of the NLT, NRL, and NRP. Finally, BBS/GRP-like IR material was detected in the nucleus habenularis, the nucleus rotundus, several thalamic nuclei, and the optic tectum of the dorso-posterior diencephalon. The presence of BBS/GRP-like IR material within the preoptic hypothalamus, hypophysial stalk, and in the pituitary suggests that BBS-like peptides may regulate pituitary hormone release in fish. Perifusion of goldfish pituitary fragments with initial pulses of 0.1, 10, 100 or 1,000 nM BBS stimulated both growth hormone (GH) and gonadotropin (GtH-II) release. Repeated pulses of the same dose of BBS generally stimulated GH and GtH-II release to a similar magnitude. These studies provide initial evidence that BBS/GRP-like peptides are present within the central nervous system of teleost fish. The anatomical distribution of BBS/GRP-like IR in goldfish hypothalamic feeding center supports our previous report indicating a role for BBS in the central regulation of food intake in fish. Additionally, the presence of BBS/GRP-like IR material in the pituitary and brain areas associated with the regulation of anterior pituitary hormone secretion, as well as evidence demonstrating a direct action of BBS at the level of the goldfish pituitary to modify GH and GtH-II secretion, indicates that BBS/GRP-like peptides likely act to regulate pituitary hormone release in teleosts.

Animals↗

PubMed1994

A new gonadotropin-releasing hormone (GnRH) superagonist in goldfish: influence of dialkyl-D-homoarginine at position 6 on gonadotropin-II and growth hormone release.

The two native forms of gonadotropin-releasing hormones (GnRH) present in goldfish, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate gonadotropin-II (GTH-II) and growth hormone (GH) release both in vivo and in vitro. In our previous study using perifused goldfish pituitary fragments, many mammalian GnRH antagonists, especially those with D-Arg6, showed weak to strong stimulation of GTH-II and GH release. In the present study, the dose-related stimulation of GTH-II and GH release by [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-Arg6, Trp7, D-Ala10] mGnRH (analog J) and [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-hArg(Et2)6, D-Ala10] mGnRH (analog K) was demonstrated; the stimulatory potency of both analogs was significantly lower than that of native sGnRH. In the presence of analogs J and K, cGnRH-II stimulated GTH-II release was significantly suppressed. Further, GTH-II and GH stimulation by 2 microM of analog K was significantly suppressed by a 'true' GnRH antagonist, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6] mGnRH (analog E). These results indicate that analogs J and K increase GTH-II and GH release in goldfish by acting on GnRH receptors on gonadotrophs and somatotrophs. Since analog K, having [D-hArg(Et2)6], strongly stimulated GTH-II release, the potency of [D-hArg(Et2)6] or [D-hArg(CH2CF3)2(6)] substituted analogs to stimulate GTH-II and GH release from the perifused goldfish pituitary fragments was tested. Among the peptides tested, [D-hArg(Et2)6, Pro9-NHEt] sGnRH had a higher potency in stimulating GTH-II release than any other analog tested in the present or in previous studies. For stimulation of GH release, [D-hArg(Et2)6, Pro9-NHEt] sGnRH and [D-Arg6, Pro9-NHEt] sGnRH were the most potent analogs tested; analogs of mGnRH were less potent than sGnRH, indicating the importance of Trp7, Leu8 residues in the native peptide. These results suggest the importance of [D-Arg6] or alkylated [D-Arg6] in determining the intrinsic activity and potency of GnRH peptides in goldfish.

Amino Acid Sequence↗

PubMed1994

Seasonal variations in gonadotropin responsiveness, self-priming, and desensitization to GnRH peptides in the common carp pituitary in vitro.

Seasonal variations of the GtH release response to salmon GnRH (sGnRH) and [D-Arg6,Pro9NEt]-sGnRH (sGnRH-A) were investigated in female common carp at different stages of the reproductive cycle using perifused pituitary fragments. The responsiveness to sGnRH and sGnRH-A varied seasonally in common carp pituitaries in vitro, with the greatest GtH release response in pituitaries from sexually mature (preovulatory) fish compared to pituitaries from sexually regressed fish. The magnitude of this seasonal change in the GtH release response was greater for sGnRH-A than for sGnRH, and sGnRH-A has a higher potency than sGnRH, particularly in pituitaries from sexually mature fish. Desensitization of perifused pituitary fragments to sGnRH and sGnRH-A, and a self-priming effect of sGnRH-A on the GtH release response, caused by repeated pulse administrations of the GnRH peptides, varied with the stage of reproductive cycle of the common carp. Using pituitaries from sexually regressed female common carp, desensitization occurred only when a high dose of sGnRH or sGnRH-A was given as repeated pulses at short time intervals, and no self-priming was observed by repeated administrations of sGnRH and sGnRH-A. Using pituitaries from sexually mature female common carp, desensitization occurred when a high dose of sGnRH and both high and low dosages of sGnRH-A were given as repeated pulses at short time intervals. Self-priming, largely due to the increase in basal GtH levels, occurred in response to repeated pulses of low dosages of sGnRH-A given at long intervals.

Animals↗

PubMed1994

Regional distribution and in vitro secretion of salmon and chicken-II gonadotropin-releasing hormones from the brain and pituitary of juvenile and adult goldfish, Carassius auratus.

The content of salmon (sGnRH) and chicken-II (cGnRH-II) gonadotropin-releasing hormones was measured in discrete brain regions and pituitaries of juvenile and postspawning adult goldfish, using specific radioimmunoassays. In juveniles, the content of both peptides was low. sGnRH was the predominant form in telencephalon-preoptic area (T-POA) (sGnRH:cGnRH-II ratio = 2.06 +/- 0.66) and diencephalon (DIEN) (sGnRH:cGnRH-II ratio = 2.72 +/- 0.32), whereas cGnRH-II was predominant in cerebellum-brain stem (STEM) (sGnRH:cGnRH-II ratio = 0.47 +/- 0.05). Equal amounts of the two peptides were present in pituitary (PIT) (sGnRH:cGnRH-II ratio = 1.04 +/- 0.18). In adults, the content of both peptides in all regions was significantly increased. The increase in sGnRH exceeded that of cGnRH-II in T-POA and PIT, resulting in an increased sGnRH:cGnRH-II ratio in these tissues (T-POA, 3.55 +/- 0.26; PIT, 7.85 +/- 2.28). In DIEN and STEM, the increase in cGnRH-II content equaled or exceeded that of sGnRH; the sGnRH:cGnRH-II ratio was unchanged in STEM (0.39 +/- 0.06) and decreased in DIEN (1.23 +/- 0.13). The secretion of sGnRH and cGnRH-II was investigated under static in vitro incubation conditions. Both forms of the peptide were secreted from T-POA slices and PIT fragments from juvenile and adult fish. Secretion was significantly increased under potassium depolarizing conditions. Secretion of the two peptides was proportional to their content in tissues from both juvenile and adult goldfish.

Aging↗

PubMed1994

Functional evidence regarding receptor subtypes mediating the actions of native gonadotropin-releasing hormones (GnRH) in goldfish, Carassius auratus.

In goldfish, two native gonadotropin-releasing hormone (GnRH) peptides, salmon GnRH (sGnRH) and chicken-II GnRH (cGnRH-II), stimulate gonadotropin (GTH-II) and growth hormone (GH) secretion. In the present study we tested whether sGnRH and cGnRH-II act through different or the same population of GnRH receptors on GTH and GH cells, using various approaches. A GnRH antagonist [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH (analog C) equally inhibited GTH-II release by sGnRH and cGnRH-II. Similarly, [Ac-D(2)Nal1,4Cl-D-Phe2,D-(3)Pal3,6]cGnRH-II (analog N) suppressed GTH-II stimulation by the two GnRH peptides equally. Further, in the continued presence of 100 nM sGnRH, a 100 nM pulse of cGnRH-II failed to cause additional GTH-II release and vice versa. Prolonged exposure of pituitary fragments to 100 nM sGnRH or cGnRH-II resulted in desensitization and reduced the GTH-II response to a subsequent pulse of either sGnRH or cGnRH-II equally. All these results indicate that both sGnRH and cGnRH-II act through the same population of GnRH receptors on gonadotrophs. Similarly, the GH responses obtained with (i) analog N treatment, (ii) pulse challenge to cGnRH-II during prolonged sGnRH treatment and vice versa, and (iii) desensitization studies suggest that both sGnRH and cGnRH-II act through the same population of GnRH receptors on somatotrophs. However, the properties of GnRH receptors on GTH-II and GH cells are different. Analog C stimulated GH release but not GTH-II release. In contrast, [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,D-Arg6]mGnRH stimulated GTH-II release but weakly suppressed GH release. These results indicate that sGnRH and cGnRH-II act on the same population of receptors on GTH cells and on a functionally distinct population of receptors on GH cells.

Amino Acid Sequence↗

PubMed1994

Activin-like peptides in somatotrophs and activin stimulation of growth hormone release in goldfish.

Activin and inhibin, dimeric protein hormones originally isolated from mammalian gonads, are involved in the regulation of pituitary gonadotropin secretion. Using domain-specific antibodies against activin and inhibin alpha, beta A, and beta B subunits, the present study demonstrates that immunoreactive activin and inhibin subunits, especially beta A, exist in goldfish pituitary. Immunocytochemical staining with anti-gonadotropin-II and anti-growth hormone showed that the pituitary cells containing immunoreactive activin beta subunits are somatotrophs. This is different from the situation in mammals where it is the gonadotrophs that produce activin molecules within the pituitary. The staining with anti-beta B was overall weak compared to that with anti-beta A, but both appear to localize in the same cells. Strong immunostaining with the anti-inhibin alpha subunit was also observed in the goldfish pituitary; however, the immunoreactivity is dissociated from those of beta A and beta B, and mainly associated with nerve fibers in the neurointermediate lobe. Based on this evidence, it is suggested that the goldfish pituitary predominantly produced activin-like molecules. Both porcine activin and inhibin stimulate growth hormone release from perifused goldfish pituitary fragments. Taken together with our previous findings that porcine activin stimulates gonadotropin-II release in goldfish, and the fact that the somatotrophs and gonadotrophs are in close contact with each other in the goldfish pituitary, it is hypothesized that somatotroph-derived activin may exert paracrine actions on the adjacent gonadotrophs to stimulate gonadotropin release and autocrine actions on somatotrophs to stimulate growth hormone secretion. This also provides a mechanism for communication between these two pituitary cell types.

Activins↗

PubMed1994

Episodic growth hormone secretion in the grass carp, Ctenopharyngodon idellus (C. & V.).

The secretory pattern of growth hormone (GH) was studied in sexually immature grass carp (0.5-1.0 kg body wt). Serial blood samples were taken at 15-min intervals during 4- to 6-hr sampling periods via a dorsal aorta cannula. During each 4- to 6-hr sampling period plasma GH profiles demonstrated episodic secretion. Two patterns were observed, consisting either of one episodic of GH secretion (single or several pulses clustered) or two episodes of GH secretion during each sampling period. The interval between the two episodes of GH secretion was 2.6 hr. This is the first demonstration of episodic GH secretion in a teleost.

Animals↗

PubMed1994

In vivo actions of a gonadotropin-releasing hormone (GnRH) antagonist on gonadotropin-II and growth hormone secretion in goldfish, Carassius auratus.

In our previous in vitro studies, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E) suppressed both gonadotropin-II (GTH-II) and growth hormone (GH) release stimulated by sGnRH and cGnRH-II. In the present study analog E significantly inhibited the increases in plasma GTH-II levels stimulated by sGnRH in sexually mature female and sexually recrudescent goldfish. Treatment of goldfish with alpha-methyl-p-tyrosin methyl ester (alpha-MPT) inhibits dopamine synthesis and abolishes the inhibitory actions of dopamine on GTH-II release, resulting in a potentiation of the GTH-II response to sGnRH. Following alpha-MPT pretreatment, analog E significantly reduced basal plasma GTH-II levels, and suppressed both sGnRH and cGnRH-II actions on GTH-II release. Analog E also inhibited the increase in plasma GTH-II levels in sexually mature male goldfish exposed to the female sexual pheromone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha 20 beta-P), demonstrating that the increase in plasma GTH-II levels is due to release of endogenous GnRH. Analog E significantly inhibited the increases in plasma GH levels stimulated by treatment with sGnRH. Implantation of estradiol pellets increases basal plasma GH levels and increases the GH responsiveness to sGnRH in sexually recrudescent goldfish; analog E also suppressed the increase in plasma GH levels stimulated by injection of sGnRH in estradiol-treated fish. Analog E suppressed basal GTH-II and GH levels in fish that were unhandled prior to injection; however, analog E was not effective in reducing basal plasma GTH-II or GH levels in experiments in which the fish were blood sampled or subjected to some experimental manipulation prior to injection of analog E. Analog E also suppressed basal levels of GTH-II in alpha-MPT-treated fish, suggesting that stress inhibition of GTH-II release may be mediated by the dopaminergic system. In summary, the results demonstrate that (i) analog E can suppress the actions of exogenous sGnRH and cGnRH-II on GTH-II and GH release in vivo, (ii) the GnRH system mediates, at least in part, the plasma GTH-II response in sexually mature male goldfish following exposure to the female sexual pheromone 17 alpha 20 beta-P, and (iii) endogenous GnRH peptides are important in the regulation of basal plasma levels of GTH-II as well as GH, particularly in low stress conditions.

Animals↗

PubMed1994

Bombesin acts to suppress feeding behavior and alter serum growth hormone in goldfish.

The acute effects of a single injection of bombesin (BBS) on feeding behavior and serum growth hormone (GH) levels in goldfish were examined. When injected intraperitoneally (IP), BBS (0.5-100 ng/g) caused a dose-dependent decrease in food intake within 30 and 45 min of administration; maximal suppression was achieved at 50 ng/g BBS and was accompanied by an elevation in serum GH levels. Associated with IP injection of BBS was a pronounced spitting out behavior in which food pellets were taken into the oral cavity but immediately expelled. When injected into goldfish deprived of food for 72 h, 50 ng/g BBS was still potent in suppressing feeding behavior and increasing serum GH. Additionally, IP injection of BBS (10 or 100 ng/g) into groups of fish caused a significant increase in circulating serum GH levels at 1.5 h postinjection. Finally, when injected into the third brain ventricle (ICV), 60 ng/g BBS also caused a suppression in food intake and a concomitant increase in serum GH. Groups of fish injected ICV with 5 or 50 ng/g BBS also exhibited a graded increase in serum GH levels at 45 min postinjection. Overall, these data are the first to demonstrate in any lower vertebrate that a neuropeptide acts to suppress food intake and cause concomitant alterations in circulating serum GH levels, following either peripheral or central administration.

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