bluuebunny/crossref_metadata_2025_split huggingface dataset:
Desensitization of Pituitary Cells by Gonadotrophin‐Releasing Hormone or its Analogues in the Superfusion System: Different Pattern for Males and Females
Authors: Horvath Judit E. , Kéri† György , Seprödi Attila , Teplán István , Flerkó Béla 
Published: September 2006

AbstractThe effect of a 6‐h infusion of gonadotrophin‐releasing hormone (GnRH) or its analogues on dispersed anterior pituitary cells from male or female rats was investigated. The cells were stimulated with 3‐min pulses of K+ and GnRH. Thereafter GnRH (1 nM) or GnRH analogues ([D‐Trp6]GnRH‐ethylamide ([D‐Trp6]GnRH, 50 pM), [D‐Phe6, Gln8]GnRH‐ethylamide (Folligen, 100 pM) and [Asu6]GnRH‐ethylamide ([Asu6]GnRH, 33 pM)) were applied for 6 h. In cells from female rats this treatment resulted in a 20‐fold increase in luteinizing hormone (LH) secretion during the first 90‐min period of the 6‐h incubation. Following this a gradual decrease in LH release occurred, and during the fourth 90‐min period the amount of LH secreted was only one‐third or less of the initial value. The pituitary cells of male rats responded to the same treatment with only a 7‐fold rise of LH secretion during the first period. In the second 90‐min of the 6‐h incubation a 20% to 30% increase was observed. Even in the fourth 90‐min period the amount of LH secreted was two‐thirds or more greater than that of the first 90‐min period. When using 10‐fold greater concentrations of the same peptides in males, the increase in hormone secretion in the second 90‐min was not seen and the hormone release decreased to around 50%. We found definite differences in the responses of male and female rat pituitary cells to the 6‐h infusion of GnRH or its analogues: the initial amplitude of the response in females was higher but desensitization was stronger. In males, the initial response was weaker; however, even using doses one magnitude greater, the level of desensitization did not reach the values obtained in females. The results were similar both with GnRH and the analogues. The responses to 3‐min K+ and GnRH stimuli given after the 6‐h incubation were strongly reduced in cells from female rats compared to the initial responses; however, in cells from male rats the reaction was higher or unchanged. The ratio of LH released by the final K+ stimulus relative to the actual LH content of the cells decreased in females but increased in males. Our data show that the differences between the pattern of desensitization in cells from male and female rats may be caused by the differences in the amount and ratio of immediately releasable hormone and the hormone replenishment into these pools.
Galanin Message‐Associated Peptide‐Like Immunoreactivity in the Nervous System of the Blowfly: Distribution and Chromatographic Characterization
Authors: Lundquist C. Tomas , Rökaeus Åke , Nässel Dick R. 
Published: September 2006

AbstractGalanin message‐associated peptide (GMAP) is a flanking peptide in mammalian preprogalanin located C‐terminally of galanin (GAL). GMAP‐like immunoreactive (LI) material in the brain of the blowfly Phormia terraenovae was analysed by radioimmunoassay combined with reversed‐phase high‐performance liquid chromatography and immunocytochemistry and compared to GAL‐LI material. A sensitive radioimmunoassay, developed against a species‐conserved portion of mammalian GMAP (synthetic porcine GMAP(19–41)amide), was applied to serially diluted blowfly head extracts. High‐performance liquid chromatography combined with radioimmunoassay showed that the GMAP‐LI material eluted as several different components with one major component coeluting with the synthetic GMAP fragment. One GMAP‐LI peak co‐eluted with a GAL‐LI component of the extract. By immunocytochemistry it was shown that a distinct set of GMAP‐LI neurons and neurosecretory cells is present in the blowfly brain and thoracico‐abdominal ganglion. About 150 GMAP‐LI cell bodies were found in the brain, distributed in the protocerebrum, tritocerebrum and suboesophageal ganglion. Several hundred GMAP‐LI cell bodies were detected in the medulla of the optic lobe. In the fused thoracico‐abdominal ganglion there are about 70 GMAP‐LI cell bodies distributed in a segmental fashion. Several of the GMAP‐LI neurons also contain GAL‐LI material whereas some do not. In addition, there are GAL‐LI neurons that do not react with the GMAP antiserum. Some of the GMAP‐LI interneurons and neurosecretory cells could be traced in detail enabling a resolution of putative sites of action of the peptide.
Pineal Photoreceptor Cells in Culture: Fine Structure, and Light/ Dark Control of Cyclic Nucleotide Levels and Melatonin Secretion
Authors: Falcoón Jack , Bégay Valérie , Besse Colette , Ravault Jean‐Paul , Collin Jean‐Pierre 
Published: September 2006

AbstractTrout pineal photoreceptor cells were dissociated by trypsin‐DNase digestion and further purified by a Percoll gradient centrifugation. Total cells or purified photoreceptor cells were then embedded in a collagen gel, or layered on culture‐treated polycarbonate membranes, or maintained in suspension, with RPMI 1640 medium or BGjb medium. It has been shown that cells maintain a rhythmic production of melatonin for at least seven 24 h light/dark cycles under these conditions. In this complementary study, the morphofunctional state of the photoreceptor cells was examined 1) by electron (transmission, scanning) microscopy, and 2) by pharmacological tests under different lighting conditions. Using polycarbonate membranes together with RPMI 1640 medium appeared the most suitable. The segmented organization of photoreceptor cells was well preserved when using the culture‐treated membranes. It tended to disappear in cells embedded in the collagen gel and was lost after passage through the Percoll gradient. However, this one allowed obtention of an homogeneous population of photoreceptors, as recognized by their intracellular components. Intracellular organelles were rather well preserved in the embedded photoreceptors. The study also provides novel information on the nature of second messengers involved in the photoperiodic control of melatonin production in photoreceptor cells. From the effects of an adenylyl cyclase activator and a phosphodiesterase inhibitor it appeared that 1) total cells and Percoll‐selected cells behaved similarly, 2) the nocturnal rise in melatonin secretion was associated with an increase in cAMP content, and 3) a fall in cAMP may be a mechanism through which light reduces melatonin secretion by photoreceptor cells. Cyclic GMP, the metabolism of which also appeared to be controlled by light, did not seem involved in the photoperiodic control of melatonin production. The method proposed herein offers interesting perspectives for the study of the photoneuroendocrine properties of isolated photoreceptor cells.
Adenosine Inhibits Alpha‐Melanocyte‐Stimulating Hormone Release from Frog Pituitary Melanotrophs. Evidence for the Involvement of A1 Adenosine Receptors Negatively Coupled to Adenylate Cyclase
Authors: Chartrel Nicolas , Tonon Marie‐Christine , Lamacz Marek , Vaudry Hubert 
Published: September 2006

AbstractAdenosine is recognized as an important modulator of cell activity. In particular, adenosine regulates the secretion of adrenocorticotropin from anterior pituitary cells. However, the possible role of adenosine on the pars intermedia has never been investigated. In the present study, we have examined the effect of adenosine on α‐melanotropin (α‐MSH) secretion from the intermediate lobe of the pituitary of the frog (Rana ridibunda), using the perifusion technique. When whole neurointermediate lobes were exposed to graded doses of adenosine (10−9 to 10−4 M), a dose‐dependent inhibition of a‐MSH release was observed. Repeated pulses of adenosine (5 ± 10−5 M) induced a reproducible inhibition of α‐MSH secretion without any desensitization phenomenon. The effect of adenosine was mimicked by the non‐selective agonist 5′‐N‐ethylcarboxamide‐adenosine and the highly specific adenosine A, receptor agonist N6‐[R‐phenylisopropyl]‐adenosine (R‐PIA). In contrast the selective adenosine A2 receptor agonist, CGS 21680, induced a slight stimulation of α‐MSH release. Adenosine‐induced inhibition of α‐MSH secretion was blocked by the non‐selective adenosine antagonist, 8‐(p‐sulfophenyl)‐theophyline. Adenosine and R‐PIA also inhibited α‐MSH secretion from acutely dispersed pars intermedia cells. Adenosine did not block thyrotropin‐releasing hormone‐induced α‐MSH release from perifused neurointermediate lobes. In contrast, adenosine inhibited both acetylcholine‐evoked and muscarine‐evoked α‐MSH secretion. Finally, R‐PIA induced a significant inhibition of basal and forskolin‐stimulated cyclic AMP levels in whole neurointermediate lobes. The present results demonstrate that adenosine exerts a direct inhibitory effect on α‐MSH release from melanotrope cells through activation of the A1 receptor subtype, negatively coupled to adenylate cyclase. These data suggest that adenosine may play a physiological role in the regulation of hormone release from the intermediate lobe of the pituitary.
Dysregulation of the Hypothalamus‐Pituitary‐Adrenal Axis in Male and Female, Genetically Obese (ob/ob) Mice
Authors: McGinnis Ralph , Walker Joseph , Margules David , Aird Fraser , Redei Eva 
Published: September 2006

AbstractThe autosomal, recessive obesity of ob/ob mice is associated with hypercorticosteronemia and amelioration of most symptoms of obesity following adrenalectomy. Increased adrenocorticotropic hormone (ACTH) secretion has been hypothesized on the basis of several reports of higher pituitary ACTH content in ob/ob mice compared to lean littermates. However, the only measurement of ACTH blood concentration found lower levels in ob/ob mice than in leans suggesting that hypercorticosteronemia might result solely from an enhanced adrenal response to ACTH and also suggesting that the ob/ob's elevated pituitary ACTH content might be due to decreased ACTH secretion rather than increased ACTH synthesis. In our study, basal serum ACTH levels were higher in ob/ob males and females compared to sex‐matched lean littermates. Anterior pituitary ACTH synthesis was also elevated as indicated by increased content of ACTH and proopiomelanocortin mRNA in obese mice of both sexes; however hypothalamic corticotropin‐releasing factor content was not different in lean and obese mice. Basal serum ACTH and corticosterone (CS) levels showed normal circadian rhythm in both phenotypes and sexes, but the circadian increase in CS level was much greater in obese mice than in leans despite equal serum ACTH increases in the two phenotypes. Ether stress at both peak and trough of the circadian rhythm also stimulated much larger serum CS increases in obese mice even though ACTH increases were again equal in the two phenotypes. Taken together, these results strongly indicate that ob/ob mice have increased synthesis and secretion of pituitary ACTH despite the presence of chronically elevated serum CS. This hyperactivity of the hypothalamo‐pituitary‐adrenal axis appears to be most pronounced in ob/ob females since pituitary ACTH content was equal in obese males and females despite much higher circulating CS levels in the females. Furthermore, the results also indicate an enhanced response to ACTH by the adrenal cortex of the obese mouse. Thus, ob/ob mice exhibit abnormal hypothalamo‐pituitary‐adrenal axis function with hyperactivity occurring at the level of pituitary ACTH synthesis/secretion as well as at the level of adrenocortical response to ACTH.
Diencephalic Noradrenaline Depletion Impairs the Corticosterone Response to Footshock but does not Affect Conditioned Fear
Authors: Selden Nathan R. W. , Robbins Trevor W. , Everitt Barry J. 
Published: September 2006

AbstractThis study tested the hypothesis that hypothalamic noradrenaline (NA) depletion induced by 6‐hydroxydopamine alters neuroendocrine, but not behavioural, responses to aversive stimuli. Sham‐operated and NA depleted rats were exposed to pairings of an auditory (clicker) CS and (footshock) US in a distinctive environment. Subjects were tested for preference of a ‘safe’ environment over the one in which they were shocked, as a measure of effective conditioning to the contextual stimuli present in the distinctive environment. Subjects were also tested, in a separate operant chamber, for the suppression of drinking in the presence of the auditory stimulus, as a measure of effective conditioning to the explicit auditory CS. Blood samples were collected immediately following each phase of the behavioural experiment and were later analysed for plasma Corticosterone concentration.Behavioural and Corticosterone responses of individual control animals to the CS were positively correlated, consistent with previous results. This correlation was not present in the NA depleted group. The lesioned rats also showed a severely attenuated Corticosterone response to the footshock US. By contrast, NA depletion had no effect on any behavioural measure of CS or contextual conditioning. Together with previous experiments, these results suggest that diencephalic NA projections are more likely to mediate neuroendocrine, and coeruleo‐cortical NA projections are more likely to mediate behavioural responses to conditioned and unconditioned aversive stimuli.
Changes in Proopiomelanocortin Primary Transcript Levels in the Anterior Pituitary Accompany Increased Adrenocorticotropin Secretion During the Diurnal Surge
Authors: Kwak Seung P. , Young Elizabeth A. , Akil Huda , Watson Stanley J. 
Published: September 2006

AbstractProopiomelanocortin (POMC) gene transcription in the anterior pituitary varies during stress and glucocorticoid feedback. These changes appear to parallel alterations in peptide release. The diurnal rhythm of the hypothalamo‐pituitary‐adrenal axis also involves the periodic excursion of adrenocorticotropin (ACTH) levels in plasma, but it is not clear whether the diurnal release is accompanied by changes at the transcriptional level. In the present study, we have initially characterized the heteronuclear species of POMC (hnPOMC) RNA found in the anterior pituitary by a Northern blot analysis and subsequently used this method to quantitate relative changes in the levels of heteronuclear transcript during diurnal stimulation. Two species of RNA migrating at 6.0 kb and 4.1 kb were found in the nuclear fraction of the anterior pituitary. Successive probing by various POMC cRNAs indicated that the 6.0 kb fragment was the primary transcript and the 4.1 kb fragment corresponded to the intron A‐containing processing intermediate of POMC.The nuclear species were quantitated after acute swim stress and during the diurnal ACTH secretion. Acute swim increased plasma ACTH levels by 243% after 30 min. This was paralleled by a 214% increase in the primary transcript RNA levels. Endogenous circadian stimulation in the evening produced a smaller rise of plasma ACTH (79%), and was accompanied by a 34% increase in POMC hnRNA levels. Nuclear processing intermediate (4.1 kb) and the mRNA levels did not vary during the evening. These results suggest that the diurnal mechanism transiently increases ACTH release as well as POMC gene transcription in the anterior pituitary. Release and transcription appear to be tightly coupled during circadian activation as well as during stress.
Vasoactive Intestinal Polypeptide/Peptide Histidine Isoleucine‐Immunoreactive Neuron Systems in the Basal Hypothalamus of a Rat Strain with Deficient Prolactin Release in Response to Stress
Authors: Ceccatelli S. , Fahrenkrug J. , Eneroth P. , Hökfelt T. 
Published: September 2006

AbstractThere is evidence for involvement of vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) in control of prolactin secretion. In fact VIP‐ and PHI‐like immunoreactivities have been demonstrated in the hypotha/amic paraventricular nucleus and at the median eminence level. Using immunohistochemistry we have compared the distribution of immunoreactive VIP and PHI in the hypothalamus of male Sprague‐Dawley rats and BS rats, a rat strain which has a deficient release of prolactin after stressful stimuli. Quantitative information was obtained by radioimmunoassay for VIP. VIP‐ and PHI‐positive cell bodies were found in the parvocellular part of the paraventricular nucleus in colchicine‐treated rats and in nerve fibres within the median eminence of untreated rats to the same extent in both strains. Furthermore, intravenous injection of VIP caused a significant increase in serum prolactin tevets in both strains. However, at the median eminence level in BS rats, the blood vessels located in the lateral aspects of the median eminence did not show the dense VIP/PHI innervation seen in Sprague‐Dawley rats. Also, a thick VIP/PHI‐positive nerve bundle present on the surface of the median eminence of Sprague‐Dawley rats could not be seen in BS rats. Radioimmunoassay analysis revealed that VIP levels in the median eminence were twice as high in Sprague‐Dawley as compared to BS rats. Taken together, these results suggest that the defect in the prolactin release mechanism present in BS rats is not confined to the paraventricular system or the pituitary, but could be due to a deficit in VIP/PHI in fibres associated with portal vessels at the median eminence level.
Ontogeny of Expression and Glucocorticoid Regulation of the Arginine Vasopressin Gene in the Rat Hypothalamic Paraventricular Nucleus
Authors: Grino Michel , Burgunderf Jean‐Marc 
Published: September 2006

AbstractCorticotropin‐releasing factor and arginine vasopressin (AVP) are the two major hypothalamic factors that regulate anterior pituitary adrenocorticotropin secretion during stress. We have previously reported that the expression of the corticotröpin‐releasing factor gene in the hypothalamus and its regulation by glucocorticoids were not mature during the first week of life in the rat, i.e. during the stress non‐responsive period. In this report, we studied the ontogeny of expression of the AVP gene in the hypothalamic paraventricular nucleus in rats using in situ hybridization. AVP mRNA was detected as early as day 20 of gestation (E20) both in the parvocellular and the magnocellular portion of the paraventricular nucleus. The levels of expression of the AVP gene increased steadily from E20 to the third day after birth (P3) and remained stable from P3 to P14. Bilateral surgical adrenalectomy induced an increase in AVP mRNA levels in the parvocellular portion of the paraventricular nucleus, but not in the magnocellular portion, in both 7‐day‐old and 14‐day‐old rats, suggesting that the glucocorticoid regulation of the AVP synthesizing neurons of the paraventricular nucleus is mature in the developing postnatal rat.
Long‐Term Treatments with Morphine and Naloxone have Sex‐Differentiated Effects on Luteinizing Hormone Secretion in Chronically Catheterized Fetal Pigs
Authors: Behrens‐Herrler Sadie , Parvizi Nahid 
Published: September 2006

AbstractShort‐ (one bolus injection) and long‐term (repeated injections over a period of at least 7 days) effects of drugs on pituitary function in pig fetuses were studied to investigate the influence of morphine and naloxone on luteinizing hormone secretion in the chronically catheterized pig fetus between days 102 and 110 of gestation (term: 113±1 SD day). Both substances were intravenously administered in two doses: 0.1 mg and 1 mg/fetus. Repeated injections at 2‐day intervals enabled us to study short‐ as well as long‐term effects. Morphine acutely inhibited luteinizing hormone secretion both in male and female fetuses. Long‐term treatment with morphine at both doses caused an inhibition of basal luteinizing hormone (levels before treatment on each day) in females (0.1 mg: r=−0.60, P<0.001; 1 mg: r=−0.45, P<0.05) while male fetuses were unaffected. Naloxone did not have any short‐term effects, either in females or in males. In the long‐term study, however, naloxone at 1 mg dose decreased basal luteinizing hormone levels in male fetuses (r=−0.55, P<0.01), whereas in females no effect was evident. Co‐administration of 0.1 mg naloxone +0.1 mg morphine abolished the long‐term inhibitory effect observed in females when 0.1 mg morphine alone was given. These results indicate that the link between opioids and the luteinizing hormone system is functional in the pig from at least 2 weeks before birth. Furthermore, there is a sex difference in the long‐term effects of both morphine and naloxone. The origin of the apparently paradoxical long‐term effect of naloxone in male fetuses remains unclear.
Sex‐Related Differences in Chromogranin A, Chromogranin B and Secretogranin II Gene Expression in Rat Pituitary
Authors: Fischer‐Colbrie R. , Schmid K. W. , Mahata S. K. , Mahata M. , Laslop A. , Bauer J. W. 
Published: September 2006

AbstractChromogranin A, an acidic secretory protein, is widely distributed throughout diverse endocrine cells and the central and peripheral nervous systems. Chromogranin A is co‐stored and co‐secreted from secretory vesicles together with the endogenous hormones or neurotransmitters. Recently, two peptides derived from the Chromogranin A precursor have been shown to inhibit secretion from endocrine cells. In the present study, we investigated the regulation of the biosynthesis of Chromogranin A by estrogen in various tissues. In the pituitary, steady‐state levels of Chromogranin A mRNA were markedly reduced by 64% in estrogen‐treated male rats. At the protein level, a comparable decrease was found. Chromogranin B and secretogranin II, two other secretory proteins co‐stored with Chromogranin A, were slightly increased by estrogen. In pituitaries of female rats Chromogranin A mRNA and protein levels were significantly lower than in males. For Chromogranin B on the other hand, a 2‐fold increase of mRNA levels was found. Our observations demonstrate that physiologic concentrations of estrogen strongly affect Chromogranin A levels in the pituitary resulting in a sex‐related difference in Chromogranin A gene expression. Based on these and previous results demonstrating increased biosynthesis of Chromogranin A by glucocorticoids and calciferol, we suggest that a typical and characteristic feature of the Chromogranin A gene is its regulation by at least three different classes of steroid hormones.