bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long-Term Inhibitory Effects of Somatostatin and Insulin-Like Growth Factor 1 on Growth Hormone Release by Serum-Free Primary Culture of Pituitary Cells from European Eel (Anguilla anguilla)
Authors: Rousseau Karine , Huang Yung-Sen , Le Belle Nadine , Vidal Bernadette , Marchelidon Jacques , Epelbaum Jacques , Dufour Sylvie 
Published: April 2003

To investigate the ability of hypothalamic and peripheral factors to directly regulate growth hormone (GH) release in a primitive teleost, the European eel (<i>Anguilla anguilla</i> L.), we used primary cultures of dispersed pituitary cells. When cultured for 12 days in a serum-free medium, pituitary cells continuously released large amounts of GH, which exceeded the initial cellular content. Somatotropin-release inhibiting hormone (SRIH-14) dose-dependently inhibited GH release (EC<sub>50</sub> 0.75 n<i>M</i>) up to a maximal inhibitory effect of 95%. No desensitization of somatotropes to SRIH was observed over the 12 days of culture. Use of receptor subtype-selective SRIH agonists suggests the existence on eel somatotropes of SRIH receptor(s) related to the mammalian sst<sub>2</sub>/sst<sub>3</sub>/sst<sub>5</sub> class rather than to the sst<sub>1</sub>/sst<sub>4</sub> class. Insulin-like growth factor 1 (IGF1) dose-dependently inhibited GH release (EC<sub>50</sub> 0.03 n<i>M</i>) up to a maximal inhibitory effect of 85%, without desensitization. IGF1 and IGF2 were equipotent in inhibiting GH release, whereas insulin was 1,000 times less active, suggesting the implication of a receptor related to the mammalian IGF type 1 receptor. These results indicate that eel somatotropes are active in vitro without any specific additional factors, and suggest the existence of a dominant inhibitory control of GH release in vivo. Two potential candidates for this chronic negative regulation are a neurohormone, SRIH and a circulating factor, IGF1. These data underline the early evolutionary origin of the molecular and functional SRIH-GH-IGF1 neuroendocrine axis in vertebrates.
Dehydration-Induced Renin Secretion: Involvement of Histaminergic Neurons
Authors: Kjær Andreas , Knigge Ulrich , Jørgensen Henrik , Warberg Jørgen 
Published: April 2003

Renin secretion is controlled locally in the kidneys as well as via central neuronal mechanisms. The neuronal mechanisms are not fully understood but may involve the neurotransmitter histamine (HA) since centrally infused HA stimulates renin secretion. This, however, does not prove that HA is of any physiological importance for the regulation of renin secretion. Dehydration is a physiological stimulus of renin secretion and, therefore, we studied the possible role of hypothalamic histaminergic neurons in dehydration-induced renin secretion in conscious male rats. In addition, we expanded on our previous investigations of HA-induced renin secretion. Twenty-four hours of dehydration induced a 3-fold increase in plasma renin activity (PRA). Pretreatment with the HA synthesis inhibitor α-fluoromethylhistidine inhibited the dehydration-induced PRA secretion by 80% whereas pretreatment with the H<sub>1</sub> receptor antagonist mepyramine (MEP) or the H<sub>2</sub> receptor antagonist ranitidine (RAN) inhibited the PRA response to dehydration by approximately 40%. In euhydrated control rats, none of the HA-blocking agents had any significant effect on basal PRA secretion. Central administration of HA stimulated PRA almost 2-fold and the maximum concentration of PRA was reached after 15 min. Pretreatment with the H<sub>1</sub> receptor antagonist MEP or the H<sub>2</sub> receptor antagonist RAN totally inhibited the HA-induced PRA secretion. We conclude that HA activates renin secretion via H<sub>1</sub> and H<sub>2</sub> receptors and that HA seems to be a physiological mediator of dehydration-induced renin secretion via activation of H<sub>1</sub> and H<sub>2</sub> receptors. The effect is probably indirect and may among others involve the catecholaminergic and serotonergic systems.
Selective Inhibition of Magnocellular Vasopressin Neurons by Hypoosmolality: Effect on Histamine- and Stress-Induced Secretion of Adrenocorticotropin and Prolactin
Authors: Kjær Andreas , Knigge Ulrich , Jørgensen Henrik , Warberg Jørgen 
Published: April 2003

We investigated the effect of selective inhibition of magnocellular arginine vasopressin (AVP) and oxytocin neurons on histamine (HA)- and restraint-stress-induced adrenocorticotropin (ACTH) and prolactin (PRL) secretion in conscious male rats. The inhibition of magnocellular neurons was obtained by inducing chronic hypoosmolality via continuous exposure of the rats to the AVP V<sub>2</sub> receptor agonist 1-deamino(8-<i>D</i>-arginine)vasopressin (DDAVP) which was released from osmotic pumps implanted subcutaneously. In DDAVP-treated rats, plasma osmolality and sodium concentration were 273 mosm/l and 130 mmol/l, respectively. In control rats, the corresponding values were 291 mosm/l and 139 mmol/l. HA (270 nmol) administered intracerebroventricularly or 5 min of restraint stress stimulated ACTH and PRL secretion 4- to 11-fold in normoosmolar rats. In hypoosmolar rats, the HA-induced ACTH response was inhibited more than 40% whereas the restraint-stress-induced ACTH response was unaffected. Conversely, the PRL response to HA in hypoosmolar rats was unaffected whereas the PRL response to restraint stress was inhibited by 40%. In summary, chronic hypoosmolality inhibits HA-induced ACTH and restraint-stress-induced PRL secretion indicating involvement of magnocellular AVP in these responses.
Evidence for GnRH Regulation by Leptin: Leptin Administration Prevents Reduced Pulsatile LH Secretion during Fasting
Authors: Nagatani Shoji , Guthikonda Padma , Thompson Robert C. , Tsukamura Hiroko , Maeda Kei-Ichiro , Foster Douglas L. 
Published: April 2003

Administration of leptin during undernutrition improves reproductive function, but whether this occurs at the level of the brain, pituitary, or gonads is not yet clear. The present study tested the hypothesis that one important mechanism is the control of pulsatile gonadotropin-releasing hormone (GnRH) secretion. Our approach was to determine if leptin could prevent the marked suppression of pulsatile luteinizing hormone (LH) secretion which occurs during fasting. Leptin (3 µg/g i.p.; three times/48 h) or vehicle was administered during a 48-hour fast in adult ovariectomized and estrogen-treated ovariectomized rats (n = 5–7/group). LH was measured in blood samples collected every 6 min for 2 h before and after fasting. In vehicle-treated animals, plasma insulin and leptin levels decreased after fasting. As expected, the LH pulse frequency also decreased markedly. When circulating leptin remained artificially elevated during fasting, the suppression of LH pulse frequency did not occur. Leptin treatment maintained a high LH pulse frequency in the presence or absence of estrogen. The finding that leptin modulates LH pulse frequency indicates that this fat-derived hormone conveys information about nutrition to mechanisms which regulate pulsatile gonadotropin-releasing hormone secretion. Because this occurs in the absence of estrogen, the mechanism does not necessarily involve modulation of negative feedback.
Identification and Characterization of a Receptor from Goldfish Specific for a Teleost Growth Hormone-Releasing Hormone-Like Peptide
Authors: Chan Koon-Wing , Yu Kei-Li , Rivier Jean , Chow Billy K.-C. 
Published: April 2003

In mammals, growth hormone-releasing hormone (GHRH), acting via the GHRH receptor, plays an important role in the regulation of growth hormone (GH) synthesis and secretion as well as the proliferation and differentiation of somatotropes in the pituitary. In fishes, information concerning the functional role of the characterized GHRHs is limited. For that reason, a putative goldfish GHRH receptor cDNA was characterized in this study. The receptor cDNA is 2,243 bp in length, encoding a 438-amino-acid-long polypeptide with 7 putative transmembrane-spanning regions, which is a characteristic of G-protein-coupled receptors. The receptor, when expressed in COS-7 cells, showed minimal responses (2-fold cAMP responses) when stimulated with 100 n<i>M</i> of human GHRH, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). However, this receptor was found to be specific for a carp GHRH-like peptide isolated from the brain of common carp <i>(Cyprinus carpio)</i>; there was a significant and dose-dependent increase in intracellular cAMP (a maximum response of 22-fold increase with an EC<sub>50</sub> of 0.1 n<i>M</i>) when the transfected cells were stimulated with this peptide. As a preliminary study to investigate the functional role of this receptor, the tissue distribution of the mRNA was analyzed by reverse-transcription-polymerase chain reaction. The receptor mRNA was found to be present in the brain, pituitary, gut, gill, heart, liver, skeletal muscle, spleen, ovary and testis. Together with a goldfish PACAP type 1 receptor and a VIP1 receptor recently isolated in our laboratory, characterization of this putative GHRH receptor provides the molecular basis for the future understanding of the neuroendocrine control of growth and reproduction by these neuropeptides in goldfish as well as other teleosts.
Nitric Oxide (NO) Stimulates Gonadotropin Secretion in vitro through a Calcium-Dependent, cGMP-Independent Mechanism
Authors: Pinilla Leonor , González Dolores , Tena-Sempere Manuel , Aguilar Enrique 
Published: April 2003

In the last few years, nitric oxide (NO) has emerged as an important intra- and intracellular messenger involved in the control of hypothalamic-pituitary function. The present experiments were undertaken in order to evaluate the pituitary component in the modulatory action of NO on gonadotropin secretion, as well as the second messenger pathway(s) involved. In a first step, we assessed LH and FSH secretion by hemipituitaries incubated in the presence of increasing concentrations of sodium nitroprusside (SNP), a potent NO donor, and cyclic guanosin monophosphate (cGMP), the second messenger for a wide range of NO actions. In addition, given that SNP induces the release of NO and cyanide ions, the response to SNP was tested in the presence of hemoglobin (an NO scavenger) or rhodanese + sodium thiosulfate (inactivators of cyanides) in order to ensure that the effects of SNP on gonadotropin secretion were mediated by the release of NO. SNP (10<sup>–4</sup>–10<sup>–3</sup> <i>M</i>) stimulated gonadotropin secretion in our incubation system, whereas cGMP, at all doses tested, was ineffective. Similar results were obtained using dispersed pituitary cells. The stimulatory action of SNP is attributable to its ability to induce NO release since it was blocked by hemoglobin, but preserved after incubation with rhodanese + sodium thiosulfate. In further experiments, we aimed to identify the mechanism(s) underlying SNP-induced gonadotropin secretion. First, to evaluate the involvement of calcium (Ca<sup>2+</sup>), the effects of SNP were analyzed in a calcium-free medium, after depletion of Ca<sup>2+</sup> stores by caffeine, in the presence of the Ca<sup>2+</sup> chelator ethylene glycol bis (<i>p</i>-aminoethyl ether) N,N-tetra-acetic acid (EGTA), and after incubation with the Ca<sup>2+</sup> channel blockers verapamil and nifedipine. Second, to confirm that cGMP is not involved in the stimulatory action of SNP, the effects of the latter on gonadotropin secretion were tested in the presence of the antagonists of the guanylyl cyclases oxadiazoloquinoxaline and LY 83,583. Our results showed that the stimulatory action of SNP on gonadotropin release is blunted in Ca<sup>2+</sup>-free medium and after incubation with EGTA, verapamil, nifedipine, and caffeine. On the contrary, the effect of SNP remained unaltered after antagonization of guanylyl cyclases. We conclude that NO, acting at the pituitary level, stimulates gonadotropin secretion through a calcium-dependent, cGMP-independent mechanism.
Site-Specific Induction of Fos Immunoreactivity in Preoptic and Hypothalamic NADPH-Positive Neurons during Glucoprivation
Authors: Briski Karen P. , Sylvester Paul W. 
Published: April 2003

Neuronal nitric oxide synthase, e.g. NADPH diaphorase (NADPH-d), catalyzes formation of the free radical, nitric oxide (NO), and occurs within brain structures that have functional significance for energy fuel homeostasis. The following studies examined whether populations of NADPH-d-positive neurons in the hypothalamus and nearby preoptic area express immunoreactivity for the nuclear transcription factor, Fos, in response to glucose substrate imbalance. Eight days after bilateral ovariectomy (OVX) and subcutaneous implantation of silastic capsules containing 30 µg estradiol benzoate/ml, female rats were injected i.p. with the glucose antimetabolite, 2-deoxy-D-glucose (2DG; 400 mg/kg), or the vehicle, saline. The animals were sacrificed by transcardial perfusion 2 h after these treatments. Sections at 150-µm intervals throughout preoptic area and anterior and tuberal regions of the hypothalamus were processed for dual cytoplasmic NADPH-d enzyme activity and nuclear Fos-immunoreactivity (-ir). The glucose antimetabolite elicited expression of nuclear Fos-ir by NADPH-d-positive neurons in several neural structures, including the medial preoptic area, median preoptic nucleus, anterior commissural, periventricular magnocellular supraoptic nucleus, paraventricular nucleus, and medial part of the bed nucleus of the stria terminalis. In contrast, the extensive populations of NADPH-d-positive neurons in the ventromedial hypothalamic nucleus and lateral hypothalamic area showed very little immunolabeling for Fos in response to glucoprivation. This demonstration of nuclear immunoreactivity for Fos suggests that cellular glucopenia elicits the transcriptional activation, via AP-1 regulatory sites, of multiple populations of hypothalamic neurons characterized by the functional capacity to generate NO, and thus that this gaseous neurotransmitter may fulfill a role(s) in central neural mechanisms governing regulation of compensatory motor responses to metabolic imbalance.
Estrogen Transiently Increases Delayed Rectifier, Voltage-Dependent Potassium Currents in Ovine Gonadotropes
Authors: Cowley MichaelA. , Chen Chen , Clarke IainJ. 
Published: April 2003

Treatment of gonadotropes with estrogen (E) changes the electrophysiological response to gonadotropin-releasing hormone (GnRH) such that the cells are hyperpolarised immediately after stimulation with GnRH and then generate action potentials more frequently than non-E-treated cells. We investigated the role of K<sup>+</sup> current in this altered response to GnRH using cultures of ewe pituitary cells enriched for gonadotropes. K<sup>+</sup> current density was measured using nystatin-perforated whole-cell recordings in the voltage clamp mode. Treatment of cells with E for 16–20 h significantly (p < 0.01) increased the unit K<sup>+</sup> current to 180% of that in vehicle-treated cells. Outward current in these cells flows predominantly through voltage-dependent, delayed rectifier K<sup>+</sup> channels (I<sub>K</sub>), and E alters the magnitude of this current. The effect of E to increase the K<sup>+</sup> current was dose- and time-dependent and was maximal after 16–20 h. The unit K<sup>+</sup> current values returned to pre-treatment levels after 36 h of E treatment. Several cells were studied both before and after E treatment and the average effect of E on these cells was to increase the unit K<sup>+</sup> current by 90%. The time-course of the effect of E on K<sup>+</sup> current density is the same as the effect of E to increase LH release in vitro and in vivo. We conclude that the increase in K<sup>+</sup> current may be an important part of the mechanism whereby E acts on gonadotropes to facilitate the LH surge which triggers ovulation.
Regulation of Hypothalamic Proopiomelanocortin by Leptin in Lean and Obese Rats
Authors: Korner Judith , Chua Jr. Streamson C. , Williams Julie A. , Leibel Rudolph L. , Wardlaw Sharon L. 
Published: April 2003

The mechanisms by which leptin influences energy homeostasis are not entirely understood. Several observations indicate that proopiomelanocortin (POMC) is involved in the regulation of food intake and may be a mediator of leptin action. To further study this interaction, a sensitive solution hybridization assay was used to compare the levels of POMC mRNA in the medial basal hypothalamus (MBH) of lean (+/+, +/<i>fa<sup>f</sup></i>) and obese leptin receptor-deficient <i>(fa<sup>f</sup>/fa<sup>f</sup>)</i> rats. POMC peptide products were also measured by RIA in the same animals. Cytoplasmic POMC RNA levels were significantly reduced by 53% in obese rats as compared with lean controls: 0.30 ± 0.04 vs. 0.64 ± 0.07 pg/µg total RNA (p < 0.02). Significant reductions in mean concentrations of hypothalamic POMC-derived peptides from the same dissections were detected in the obese rats vs. lean controls: α-MSH 1.77 ± 0.07 vs. 2.34 ± 0.10; β-EP 4.06 ± 0.24 vs. 5.86 ± 0.36; γ<sub>3</sub>-MSH 5.32 ± 0.20 vs. 6.52 ± 0.12 ng/mg protein (p < 0.001). To determine whether leptin stimulates POMC gene transcription, the acute effect of an intracerebroventricular (i.c.v.) injection of leptin (5 µg) on POMC primary transcript was quantified in the MBH of lean rats after a 16-hour fast. There was a significant 167% increase in mean POMC hnRNA levels 3 h after i.c.v. leptin injection (1.15 ± 0.22 pg/MBH; p < 0.02), but not after 1 h (0.76 ± 0.08 pg/MBH), compared to saline controls (0.69 ± 0.08 pg/MBH). 4 h after the injection of leptin, POMC hnRNA was still increased, but to a lesser extent (140%), as compared with control animals (p = 0.006). These studies demonstrate for the first time in the leptin receptor-deficient rat that there is an associated decrease in POMC gene expression and peptide levels in the MBH. Furthermore, the acute increase in the levels of POMC primary transcript in non-obese rats after a single i.c.v. injection of leptin supports a role for leptin in the regulation of POMC gene transcription. Taken together, these studies provide further evidence that POMC is an important mediator of the effects of leptin on food intake and energy expenditure.
Perimembrane Localization of the Estrogen Receptor α Protein in Neuronal Processes of Cultured Hippocampal Neurons
Authors: Clarke Charlotte H. , Norfleet Andrea M. , Clarke Mark S.F. , Watson Cheryl S. , Cunningham KathrynA. , Thomas Mary L. 
Published: April 2003

There is clear evidence of rapid, nongenomic responses to estrogen in a variety of neuronal model systems. To address the question of whether some of these rapid estrogen signals might be transduced by the classical estrogen receptor (ER) α or a closely related protein in nontransformed neurons, we undertook the present study using isolated fetal rat hippocampal neurons. Several antibodies developed to detect ERα were tested in this system and showed positive membrane staining in nonpermeabilized neurons. MC-20, an affinity purified anti-ERα, rabbit polyclonal IgG antibody which does not recognize ERβ was selected to carry out the majority of the experiments. When permeabilized, the hippocampal neurons exhibited low levels of nuclear staining for ERα, but abundant labeling for ERα throughout the entire cell including the neurites. In addition to traditional immunocytochemistry controls, incubation of neurons for 24 h in the presence of 10 µ<i>M</i> antisense oligonucleotide directed against the translation start site of ERα reduced ERα immunoreactivity throughout the neurons providing further evidence that the immunostaining was specific for ERα. Confocal and conventional microscopy demonstrated that the antigen was predominately extranuclear and localization of ERα in the neurites suggests that the receptor is in close proximity to the plasma membrane. This localization is consistent with a role for ERα as a transducer of rapid, nongenomic estrogen responses in hippocampal neurons.
Identification of Epidermal Growth Factor mRNA-Expressing Cells in the Mouse Anterior Pituitary
Authors: Honda Junichi , Oomizu Souichi , Kiuchi Yuko , Komatsu Noriko , Takeuchi Sakae , Takahashi Sumio 
Published: April 2003

Epidermal growth factor (EGF) produced within the pituitary gland is associated with the growth of pituitary cells in rats. The aim of the present study was to localize EGF- and EGF receptor-expressing cells, and to clarify the involvement of EGF in DNA replication in 2-month-old male mouse pituitary cells. In situ hybridization of the pituitaries of these mice demonstrated that EGF mRNA was expressed in the anterior and intermediate lobes. Within the anterior pituitary, EGF mRNA-expressing cells were medium-sized and round, and made up 40% of the total number of secretory cells. EGF receptor mRNA was only detected in anterior pituitary cells. Forty-seven percent anterior pituitary cells expressed EGF receptor mRNA. An immunocytochemical study showed that most somatotropes and some mammotropes expressed EGF mRNA. When anterior pituitary cells were enzymatically dissociated and cultured in serum-free medium, RT-PCR demonstrated both EGF mRNA and EGF receptor mRNA expression. Treatment with EGF (1 and 10 ng/ml) for 5 days stimulated DNA replication in mammotropes and corticotropes. These results indicate that the DNA replication in mammotropes and corticotropes is regulated by the paracrine and/or autocrine activity of EGF produced at least in part by these cell types themselves.
Stress-Induced Alterations in Corticotropin-Releasing Hormone and Vasopressin Gene Expression in the Paraventricular Nucleus during Ontogeny
Authors: Dent Gersham W. , Okimoto Darren K. , Smith Mark A. , Levine Seymour 
Published: April 2003

From postnatal day (PND) 4 to 14, neonates display a minimal pituitary-adrenal response to mild stress, the so-called ‘stress hyporesponsive period’ (SHRP). During the SHRP, maternal deprivation (MD) alters the pituitary-adrenal system, enabling neonates to become endocrine responsive to specific stimuli. We have previously reported that during the SHRP, mild stress enhances corticotropin-releasing hormone (CRH) messenger RNA (mRNA) expression in the paraventricular nucleus (PVN). Insofar as elevated CRH mRNA was observed both in the presence and absence of adrenocorticotropin (ACTH) release, we hypothesized that other ACTH secretagogues may participate in the pituitary stress response. During the SHRP, does arginine vasopressin (AVP) complement the actions of CRH which might be reflected centrally by the enhanced biosynthesis of both neuropeptides? To test this hypothesis we examined the time course of stress-induced CRH and AVP mRNA in the PVN at PND 6, 12, and 18. As an index of neural activity, <i>c-fos</i> mRNA in the PVN was also examined. Restraint was used as the stressor and MD was employed to enable an endocrine response during the SHRP. Despite the absence of stress-induced ACTH, in nondeprived pups during the SHRP, CRH mRNA was rapidly enhanced. In their maternally deprived (DEP) counterparts, ACTH levels were increased, and a significant induction of CRH mRNA was only observed at day 12. AVP mRNA levels were elevated in DEP 12-day-old pups at 15, 30 and 60 min. In rats beyond the SHRP, plasma ACTH levels, CRH and AVP mRNA were all enhanced following restraint. At PND 18, elevated CRH mRNA was not observed until 4 h after stimulus. Following restraint, <i>c-fos</i> mRNA was increased at all three ages, although the magnitude of <i>c-fos</i> response was less during the SHRP. These results demonstrate that when restraint elicits prototypical ACTH release, the neonatal central response is to enhance the biosynthesis of both AVP and CRH. If nucleic acid changes correlate with release, the increased synthesis of both neuropeptides may indicate the potential for AVP to synergize with CRH during the neonatal stress response.