Inhibition of stress-induced adrenocorticotropin and prolactin secretion mediating hypophysiotropic factors by antagonist of AMPA type glutamate receptor.
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Glutamate is the dominant excitatory neurotransmitter in a large number of physiological processes including neuroendocrine regulation. Some pharmacological studies have shown that different subtypes of glutamate receptor, such as the N-methyl-D-aspartic acid (NMDA) and alpha-amino-3-hydroxy-5-methy-4-isoxazolepropionic acid (AMPA) receptors, are involved in stress-induced adrenocorticotropin (ACTH) and prolactin secretion. However, the roles of the respective glutamate receptors and the mechanism of ACTH and prolactin secretion during stress via these receptors have not been investigated in detail. In the present study, we evaluated the role of AMPA-type glutamate receptor in ACTH and prolactin regulation under restraint stress in adult male rats. Male rats pretreated with a selective AMPA receptor antagonist, 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 50 microg), through a lateral ventricle cannula were stressed by immobilization. Administration of NBQX inhibited ACTH and prolactin secretion in response to restraint stress. However, NBQX had no significant effects on the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis, as measured by the accumulation of 3, 4-dihydroxyphenylalanine (DOPA). In addition, administration of NBQX suppressed stress-induced prolactin secretion in the male rats pretreated with alpha-MT, an inhibitor of dopamine synthesis, and infused with dopamine solution (2.5 microg/200 microl/10 min). These results indicated that the effects of NBQX on prolactin secretion might be mediated by non-dopamine mechanisms. The contents of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the median eminence (ME) of the male rats decreased during restraint stress; however, the fluctuations in CRH and AVP were eliminated by NBQX administration. These results suggest that stress-induced ACTH and prolactin release mediated by neurotransmission via AMPA receptors might be partly attributable to hypophysiotropic regulatory factors in the hypothalamus. (+info)
Regulation of the expression and secretion of urocortin 2 in rat pituitary.
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We previously demonstrated that urocortin 2 (Ucn 2) is expressed in the proopiomelanocortin (POMC) cells of rat pituitary. However, the regulatory mechanism of pituitary synthesis and secretion of Ucn 2 remained to be clarified. We hypothesized that hypothalamic hormones and glucocorticoids may control the expression and secretion of pituitary Ucn 2, as Ucn 2 is expressed in POMC-expressing cells in the pituitary. Thus, in the present study, we tested this hypothesis using primary culture of rat pituitary cells. The secretion of Ucn 2 from the anterior and intermediate pituitary cells was significantly increased by 50 mM KCl. In the anterior pituitary cells, corticotropin-releasing factor (CRF) increased mRNA expression levels and secretion of Ucn 2, although arginine vasopressin (AVP) did not induce any significant change in Ucn 2 expression or secretion. Under these conditions, both CRF and AVP increased ACTH secretion, but only CRF increased the level of POMC mRNA expression. Dexamethasone inhibited Ucn 2 and POMC mRNA expression levels, while it inhibited the secretion of only Ucn 2. In the intermediate pituitary, CRF increased both the mRNA expression levels and secretion of Ucn 2. Furthermore, dopamine did not affect either the mRNA expression level or secretion of Ucn 2 although it inhibited beta-endorphin secretion in the intermediate pituitary cells. These results suggest that the mRNA expression and secretion of Ucn 2 in POMC cells of the pituitary are positively regulated by CRF and negatively regulated by glucocorticoids. (+info)
GH deficiency with central precocious puberty: a new rare disorder associated with a developmental defect of the hypothalamic-pituitary area.
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CONTEXT: GH deficiency (GHD) associated with central precocious puberty (CPP) has been widely reported in cases of arachnoid cyst, septo-optic dysplasia, brain tumors, or after cerebral radiation therapy. However, idiopathic GHD associated with CPP has been reported in only one isolated case. OBJECTIVE: To evaluate the occurrence and clinical features of the association of nonacquired GHD and CPP. DESIGN AND SETTING: This was a retrospective multicenter study. PATIENTS AND METHODS: The study population was identified through a French nationwide multicenter network (about 3000 patients). We reviewed the medical records of all subjects diagnosed with nonacquired GHD and CPP, with or without developmental abnormalities of the hypothalamic-pituitary axis on cerebral magnetic resonance imaging (MRI), and without any known associated anomaly. RESULTS: We identified four patients with either isolated GHD (n=1) or multiple anterior pituitary hormone deficiencies (n=3). Clinical signs of CPP occurred at 6.4 +/- 2.3 years in boys and 7.5 +/- 0.5 years in girls, and GnRH analog therapy was started at 4.2 +/- 1.6 years after the initiation of recombinant human GH treatment. Cerebral MRI demonstrated ectopic neurohypophysis associated with anterior pituitary hypoplasia in three out of the four patients. The morphology and position of the anterior pituitary and neurohypophysis were normal in one patient who displayed a persistence of the craniopharyngeal canal. CONCLUSIONS: CPP is very rare in patients with nonacquired GHD and is mostly associated with developmental defects in the hypothalamic-pituitary area. Whether molecular mechanisms governing development and activation of the hypothalamic-pituitary axis share dependent factors remains to be explored. (+info)
Effect of stress on the expression of GnRH and GnRH receptor (GnRH-R) genes in the preoptic area-hypothalamus and GnRH-R gene in the stalk/median eminence and anterior pituitary gland in ewes during follicular phase of the estrous cycle.
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The RT-PCR (reverse transcription polymerase chain reaction) technique was used to analyze GnRH mRNA and GnRH-R mRNA in the preoptic area, anterior and ventromedial hypothalamus, and GnRH-R mRNA in the stalk/median eminence and anterior pituitary gland of follicular ewes subjected to short (3 h during one day) or prolonged (5 h daily during four consecutive days) footshock stimulation. To analyze relationship between expression of GnRH and GnRH-R genes with LH secretion the blood samples were collected at 10 min intervals to determine LH levels in control and stressed animals. The concentration of GnRH mRNA increased significantly in the preoptic area, anterior and ventromedial hypothalamus of ewes subjected to short stress. The prolonged stressful stimuli significantly decreased GnRH mRNA levels in all analyzed structures. In short stressed ewes the significant augmentation of mRNA encoding GnRH-R was detected in the preoptic area, entire hypothalamus, stalk/median eminence and anterior pituitary gland. The GnRH-R mRNA was significantly reduced in all tested structures of animals subjected to prolonged footshocking except for the preoptic area, where GnRH-R mRNA did not differ from control values. The changes in GnRH mRNA and GnRH-R mRNA levels under short or prolonged stress were associated with an increase or decrease of LH concentration in blood plasma, suggesting the existence of a direct relationship between GnRH mRNA and GnRH-R mRNA expression with LH secretion. The results indicate that the expression of both GnRH gene and GnRH-R gene, as well as LH secretion in ewes during the follicular phase of the estrous cycle, are dependent upon the kind of stress. (+info)
Sex difference in link between interleukin-6 and stress.
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Inflammation contributes to disease development, and the neuroimmunoendocrine interface is a potential site of action for inflammatory products like IL-6 to affect health. Although plasma IL-6 can stimulate the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis, the precise role, if any, for IL-6 in the HPA response to nonimmunological stressors is unclear. The purpose of this study was to test the hypothesis that IL-6 in the stalk median eminence (SME) can be directly involved in stimulating ACTH secretion in response to acute stress in female swine. This study was undertaken as a result of finding IL-6 localized to the external zone of the SME next to the hypophyseal portal vessels. Results indicate that content of IL-6 in the SME decreases in response to acute stress along with an increase in nuclear phosphorylated signal transducer and activator of transcription-3 (pSTAT-3) in pituitary corticotrophs and a simultaneous increase in plasma concentrations of IL-6 and ACTH. Furthermore, we show that females concomitantly display greater SME content of IL-6 and greater HPA responsiveness to stress, thereby suggesting that IL-6 release from the SME is an integral factor contributing to enhanced stress responsiveness in females. Our results provide evidence for a direct link between IL-6 and ACTH release and reveal a sex difference in this relationship. (+info)
Oxytocin action at the lactotroph is required for prolactin surges in cervically stimulated ovariectomized rats.
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Cervical stimulation induces two daily rhythmic prolactin surges, nocturnal and diurnal, which persist for several days. We have shown that a bolus injection of oxytocin initiates a similar prolactin rhythm, which persists despite low levels of oxytocin after injection. This suggests that oxytocin may trigger the cervical stimulation-induced rhythmic prolactin surges. To investigate this hypothesis, we infused an oxytocin antagonist that does not cross the blood-brain barrier for 24 h before and after cervical stimulation and measured serum prolactin. We also measured dopaminergic neuronal activity because mathematical modeling predicted that this activity would be low in the presence of the oxytocin antagonist. We thus tested this hypothesis by measuring dopaminergic neuronal activity in the tuberoinfundibular, periventricular hypophyseal, and tuberohypophyseal dopaminergic neurons. Infusion of oxytocin antagonist before cervical stimulation abolished prolactin surges, and infusion of oxytocin antagonist after cervical stimulation abolished the diurnal and significantly decreased the nocturnal surges of prolactin. The rhythmic prolactin surges returned after the clearance of the oxytocin antagonist. Hypothalamic dopaminergic activity was elevated in antiphase with prolactin surges, and the antiphase elevation was abolished by the oxytocin antagonist in the tuberoinfundibular and tuberohypophyseal dopaminergic neurons, consistent with the mathematical model. These findings suggest that oxytocin is a physiologically relevant prolactin-releasing factor. However, the cervical stimulation-induced prolactin surges are maintained even in the absence of oxytocin actions at the lactotroph, which strongly suggests the maintenance of prolactin surges are not dependent upon oxytocin actions at the pituitary gland. (+info)
Microdialysis methods for in vivo neuropeptide measurement in the stalk-median eminence in the Rhesus monkey.
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Direct measurement of neuropeptides in the hypothalamus is essential for neuroendocrine studies. However, the small quantities of peptides released at their neuroterminals and relatively large molecular sizes make these measurements difficult. We have evaluated microdialysis probes with two membrane materials (polycarbonate and polyarylethersulfone, both: molecular cut off 20,000 Da) in vitro, and adapted the method for in vivo hypothalamic sample collection in non-human primates. The results of in vitro experiments showed that the polyarylethersulfone membrane yielded a several fold higher recovery rate than the polycarbonate membrane. In in vivo experiments, a guide cannula with stylet was inserted into the medial basal hypothalamus through the permanently implanted cranial pedestal under light sedation. The stylet was replaced by a microdialysis probe and artificial CSF was infused. The results indicated that the neuropeptide luteinizing hormone-releasing hormone was readily measurable in dialysates collected at 10 min-intervals, and responded to neuroactive substances applied through the probe. The animals were fully conscious except for the initial hour of sampling. After the experiment the animal was returned to the home cage, and later similarly examined during several additional experiments. Therefore, the microdialysis method described here is a highly useful tool for neuroendocrine studies in non-human primates. (+info)
Endothelin-1 and endothelin-3 stimulate prostaglandin E2 secretion from the rat median eminence.
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The in vitro effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on the release of prostaglandin (PG)E2 from the rat median eminence were investigated. The addition of ET-1 from 10(-9) M to 10(-6) M stimulated PGE2 release in a dose-dependent manner (from 10.5 +/- 2.1 to 54.4 +/- 5.6 pg/ME fragment/30 min; mean +/- SEM, p less than 0.001). ET-3 also stimulated the release of PGE2 from 10(-7) M to 10(-5) M dose dependently (from 18.1 +/- 0.7 to 60.9 +/- 17.4 pg/ME fragment/30 min p less than 0.05). The time course effect of ET-3 (10(-6) M) showed that PGE2 release was stimulated within five minutes (control, 1.5 +/- 0.5; ET-3, 15.8 +/- 3.0 pg/ME fragment/5 min, p less than 0.01). These results suggest that ET-1 and ET-3 have some physiological effects on the rat median eminence. (+info)