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Objectives: Ghrelin, an endogenous growth hormone secretagogue, is a known accelerator of feeding behavior and suppresses pulsatile secretion of luteinizing hormone (LH) in ovariectomized rats. However, the mechanisms underlying this action remain unclear. We examined the effects of naloxone (NAL), a specific opioid antagonist, on the suppression of pulsatile LH secretion by ghrelin to determine whether β-endorphin (β-END) is involved in this suppressive effect. Methods: Ghrelin was administered intracerebroventricularly, and NAL was injected intravenously in ovariectomized rats; then, serum LH concentrations were measured by radioimmunoassay in blood samples drawn every 6 min for 2 h to analyze pulsatile secretion. Results: Administration of ghrelin significantly reduced mean LH concentration and pulse frequency. Coadministration of NAL with ghrelin significantly restored mean LH concentration and pulse frequency. Conclusion: Suppressive effect of intracerebroventricular injection of ghrelin on pulsatile LH secretion was mediated by β-END, suggesting that hypothalamic ghrelin suppressed pulsatile gonadotropin-releasing hormone secretion via β-END in female rats. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Aims: The present study aims at evaluating the effect of a 2-week treatment with testosterone (T), dihydrotestosterone (DHT) and estradiol valerate (E2V) on brain and plasma β-endorphin (β-END) concentrations in gonadectomized rats of both sexes. Methods: Eight groups of female and 8 groups of male Wistar rats were included. For each sex, 1 group of gonad-intact and 1 group of gonadectomized rats were employed as controls (placebo). The other groups received subcutaneous T at the doses of 10 and 100 μg/kg/day (female rats) or 1 and 5 mg/kg/day (male rats). Subcutaneous DHT was administered at the doses of 1, 10, 100 μg/kg/day (female rats) or 0.1, 1 and 5 mg/kg/day (male rats). E2V was administered subcutaneously at 0.05 mg/kg/day. β-END levels were measured in different brain areas and plasma. Results: Ovariectomy (OVX) induced a significant decrease in β-END in all brain areas analyzed as well as in plasma. Orchidectomy (OCX) reduced opioid concentration in the hypothalamus, anterior pituitary and neurointermediate lobe. In OVX rats, T replacement as well as E2V significantly increased β-END concentration in all brain areas and in plasma. In the OCX group, T and E2V did not influence β-END concentrations in different hypothalamic areas. However, they produced a significant rise in β-END levels in the hypothalamus, neurointermediate lobe, anterior pituitary and plasma. Conversely, DHT replacement did not affect β-END levels at any dose administered, either in males or females. Conclusions: The sensitivity of the endogenous opiatergic system to T administration seems to be sex-related. This effect is particularly evident in the brains of female animals where this endogenous endorphin elicits a much greater response than it does in males that have undergone gonadal steroid depletion and subsequent T replacement. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The increased use of hormonal therapies has led to the study of the properties of different progestin molecules and their effects on the central nervous system. The central and peripheral levels of neurosteroid allopregnanolone and the opioid peptide β-endorphin (β-END) are regulated by estrogens. The aim of the present study was to investigate the effects of a 2-week oral treatment with micronized progesterone or medroxyprogesterone acetate (MPA) alone or in addition to estradiol valerate (E2V) on central and peripheral allopregnanolone and β-END levels in ovariectomized (OVX) female rats. Thirteen groups of Wistar OVX rats received one of the following treatments: oral progesterone (2, 4 or 8 mg/kg/day); oral MPA (0.05, 0.1 or 0.2 mg/kg/day); E2V (0.05 mg/kg/day); E2V + progesterone (0.05 mg/kg/day + 2, 4 or 8 mg/kg/day), or E2V + MPA (0.05 mg/kg/day + 0.05, 0.1 or 0.2 mg/kg/day) for 14 days. One group of fertile and one group of OVX rats were used as controls. The concentration of allopregnanolone was assessed in the frontal and parietal lobes, hypothalamus, hippocampus, anterior pituitary, adrenals and serum, while the β-END content was assessed in the frontal and parietal lobes, hypothalamus, hippocampus, anterior and neurointermediate pituitary, and plasma. E2V administration reverted the ovariectomy-induced reduction in allopregnanolone and β-END. Progesterone and MPA increased allopregnanolone levels in all tissues except in the adrenal gland. The combined administration of progesterone or MPA and E2V determined a further increase in allopregnanolone levels with respect to E2V alone except in the adrenal gland and hippocampus only after MPA treatment. Progesterone did not affect β-END levels in the frontal and parietal lobes, hippocampus and anterior pituitary, while it caused an increase plasma, hypothalamic and neurointermediate pituitary β-END levels. MPA only affected β-END levels in the hippocampus and in the neurointermediate lobe. The combined administration of progesterone or MPA and E2V did not alter the effect of estradiol or it determined a further dose-dependent increase in β-END levels. In conclusion, this study demonstrates that progesterone and MPA have a similar but not identical effect on central and peripheral allopregnanolone and β-END levels. Their association with an estrogenic compound does not interfere with the positive effects produced by estrogen on allopregnanolone and β-END brain content. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Objectives: To observe the multiple immunoregulating effects of β-endorphin (β-END) on synovium cells of collagen-induced arthritis (CIA) in rats and to determine whether the regulation involves the transcriptional factor-κB (NF-κB) signal pathway. Methods: CIA was induced in female Wistar rats by immunization with native bovine type-II collagen emulsified with complete Freund’s adjuvant. Synovial cells in the knees of the CIA rats were cultivated, and the effects of β-END, β-END receptor inhibitor (naloxone, Nal) in proliferation and apoptosis of the synovial cells were assayed by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, flow cytometry, and DNA integrity, respectively. The effects of β-END and Nal on mRNA expression of several cytokines in the synovial cells, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, regulated upon activation normal T-cell expressed and secreted (RANTES), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2) and MMP-9 were estimated by quantitative reverse transcription-polymerase chain reaction. Effects of β-END and Nal on NF-κB activity were analyzed using luciferase gene reporter assays. The effects of β-END and Nal on p65NF-κB expression of the synovial cells were examined using Western blot. Results: 75% of the rats were demonstrated to have established the CIA model successfully. β-END was shown to exert multiple effects on synovial cells of CIA rats including decreased proliferation, induced apoptosis, and downregulation of TNF-α, IL-1β, IL-6, RANTES, iNOS, MMP-2 and MMP-9 mRNA expression. β-END seemed to play an immunoregulating role by downregulating the activity and expression of NF-κB. It was found that the β-END receptor blockage could counteract all the effects. Conclusions: β-END ameliorates synovial cell functions of CIA rats through binding with receptors and downregulating the NF-κB signal pathway. This suggests that β-END, by blocking the activity and expression of NF-κB, is a potential anti-inflammatory and anti-rheumatic agent against CIA. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

A number of reports suggest that β-endorphin (β-END) may play an important role in the regulation of cell proliferation and neuronal differentiation. Proopiomelanocortin (POMC), the common precursor ofadrenocorticotropic hormone and β-END, is detected very early in embryonic life in hypothalamic neurons of the developing rat. However, very little is known about the degree to which POMC is processed to β-END during fetal and early postnatal life. Thus, it was the objective of the present study to estimate the hypothalamic content of POMC mRNA, as well as the biosynthesis and posttranslational processing of POMC by hypothalamic neurons on fetal day 20 and on days 1, 8 and 22 of postnatal life. Hypothalamic POMC mRNA, as determined by Northern blot analysis, was higher on fetal day 20 than on postnatal days 1, 8 and 22. A higher rate of incorporation of [[sup 3] H]phenylalanine into β-END immunoreactive peptides was observed on fetal day 20 than on postnatal day 1. However, the rate of incorporation was significantly increased by day 8 of postnatal life and was similar to that on day 22. POMC was processed to β-lipotropin (β-LPH) and β-END at all ages examined, but the relative proportions of POMC:β-LPH:β-END changed during development. Thus, β-END accounted only for 34.89 ± 6.14% of the total [[sup 3] H]phenylalanine-labeled β-END immunoreactive peptides on fetal day 20, while it accounted for 57.37 ± 5.20, 62.81 ± 1.38 and 79.25 ± 6.57% on days 1, 8 and 22 of postnatal life, respectively. Thus, POMC is processed to a considerable extent into β-END-sized peptides by the fetal hypothalamus and may influence brain development. Furthermore, the rate of processing of hypothalamic POMC into β-END increases with development, probably due to the increased activity of the enzymes specific for POMC processing.Copyright © 2000 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Mating in female rats induces an acute prolactin (PRL) release within 60 min and twice-daily surges of PRL throughout the first 10 days of pregnancy to maintain luteal function. Little is known about the brain mechanism whereby the vaginocervical stimulation is processed to induce PRL release. Our recent results revealed an increase in Fos expression in the arcuate nucleus (ARC) following mating in the intact estrous rat, suggesting that a neuronal network in the brain area may participate in conveying and integrating the genitosensory stimulation. To further investigate the phenotype of activated neurons in the ARC, the present study examined whether β-endorphin (β-END) and/or dopamine (DA) neurons are activated by mating, and if so, whether activation is involved in the mating-induced acute release of PRL and the establishment of the twice-daily surges of PRL. In experiment 1, proestrous rats receiving intromissions (mated group) from males or mounts without intromission (mounted group) were sacrificed along with rats taken directly from their home cage (control group) 60 min after the beginning of mating or mounting. Expression of Fos in β-END neurons and expression of fos-related antigen (FRA) in DA neurons, which were labeled by tyrosine hydroxylase (TH) antibody in the ARC were examined by double-label immunocytochemistry. In experiment 2, proestrous females with indwelling atrial catheters were mated with males. Naloxone (10 μl/min, 2 mg/10 min), an opiate antagonist, or saline was infused before, during and after mating. Blood samples were collected during the mating session and also at several times 3 days after mating. The results showed that mating induced a significant increase in the percentage of β-END/Fos colabeled neurons and a significant decrease in the number of β-END cells in all subdivisions of the ARC. In contrast, neither the percentage of FRA/TH colabeled cells nor the number of TH cells was influenced by mating. Mating induced an acute increase in PRL release in saline-treated control animals within 30 min and a subsequent diurnal surge (18.00 h) and a nocturnal surge of PRL (2.00 h) 3 days after mating. Naloxone infusion during mating blocked the mating-induced acute PRL response and the diurnal surge of PRL 3 days after mating, but affected neither the nocturnal surge of PRL nor the incidence of pregnancy. These results demonstrate that (1) β-END neurons but not DA neurons in the ARC are activated in response to mating in proestrous rats, and (2) the mating-induced activation of β-END neurons may participate in the acute response of PRL release to mating and the memory mechanism for the establishment of the diurnal PRL surge, but not the nocturnal PRL surge in early pregnancy. These results lead to a conclusion that endogenous opioid peptides may be involved in the neuronal transmission of genitosensory stimulation to induce PRL secretion.Copyright © 2000 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Monensin has been shown to cause nonexocytotic release of catecholamines from adrenal medullary and PC12 cells. We examined the effect of monensin on peptide secretion with cultured melanotropes from the rat pituitary as a model. 1 μM monensin caused an immediate, transient increase in β-endorphin secretion. The effect was still seen in a calcium-free medium, but was totally abolished in a sodium-free medium. Intracellular calcium concentration was measured with Fura 2: no increase was observed during monensin stimulation. Hypo-osmolar medium mimicked the effect of monensin, causing a 12-fold transient increase in β-endorphin secretion. This effect was not abolished in either calcium-free or sodium-free medium. No increase in the number of exocytotic figures captured by tannic acid incubation was observed during 5 min of incubation with 1 μM monensin or hypo-somolar medium. We thus show that monensin causes β-endorphin secretion from the melanotrope and that this effect is due to sodium influx and resultant cell swelling. The calcium independency and lack of increase of exocytotic figures suggest that swelling-induced secretion is nonexocytotic, possibly via transient exocytotic pore opening.Copyright © 2000 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The effect of stress- or lipopolysaccharide (LPS) endotoxin-induced release of ACTH, β-endorphin (β-END) and prolactin (PRL) was investigated in two groups of conscious male rats: (1) Rats pretreated with different H[sub 3] receptor agonists, which inhibit neuronal histamine (HA) synthesis and release, and (2) rats with bilateral posterior hypothalamic lesion, which destroys the histaminergic perikarya exclusively localized in the mammillary nuclei. The H[sub 3] receptor agonists R(α)methyl-HA, BP 2-94 or imetit injected intraperitoneally (ip) had no effect on basal secretion of ACTH or PRL but inhibited the ACTH and PRL responses to restraint stress and the ACTH response to LPS endotoxin. LPS had no effect on PRL secretion. The inhibitory effect of the agonists was prevented by prior ip administration of the H[sub 3] receptor antagonist thioperamide. Bilateral lesion of the posterior hypothalamus inhibited the ACTH, β-END and PRL responses to restraint stress, ether stress and LPS endotoxin, whereas sham operation had no effect compared to nonoperated control rats. In addition, posterior hypothalamic lesion inhibited the PRL response but not the ACTH and β-END responses to activation of serotonergic neurons induced by ip administration of the 5-HT precusor 5-hydroxytryptophan in combination with the 5-HT re-uptake inhibitor fluoxetine. Thus, serotonergic pathways were not damaged by the lesions.The present results support our previous findings that inhibition of neuronal HA synthesis by α-fluoromethylhistidine as well as blockade of H[sub 1] or H[sub 2] receptors inhibit the ACTH, β-END and PRL responses to stress and LPS endotoxin and further substantiate an important role of histaminergic neurons in the mediation of the stress-induced release of pituitary stress hormones. Furthermore, in accordance with our previous findings, the lesion experiments indicated the existence of an interaction between the histaminergic and serotonergic system in regulation of the stress- and LPS-induced PRL release. [ABSTRACT FROM AUTHOR]

The gas nitric oxide (NO) is an important messenger in brain signaling. Along with many other functions, NO is thought to influence the expression and/or release of various hypothalamic hormones (corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH) and vasopressin). To learn more about the role of NO in neuroendocrine mechanisms, we studied in mutant mice lacking neuronal isoform of NO synthase (nNOS) the cellular expression of CRH, neurophysin (the carrier protein of vasopressin/oxytocin) and pro-opiomelanocortin (POMC), as well as of the POMC-derived peptides β-endorphin (β-END), α-melanocyte-stimulating hormone (α-MSH) and corticotropin (ACTH) by use of immunohistochemistry and in situ hybridization. Additionally, the remaining NO-generating capacities of the nNOS minus mice were investigated by NADPH-diaphorase histochemistry and citrulline immunohistochemistry as well as by immunohistochemical localization and Western blot analysis of endothelial NOS (eNOS) and nNOS isoforms. Amongst all hypothalamic peptides under investigation, only β-END was found to be altered in mutant mice. A morphometric analysis of β-END producing neurons of the arcuate nucleus revealed that significantly less cells were immunoreactive in mutant mice, whereas the expression of the precursor POMC as well as of other POMC-derived peptides was found to be unchanged. In addition to that, fewer β-END-immunoreactive fibers were found in the paraventricular nucleus of nNOS minus mice in comparison to wild-type animals. Hence, the reduction of hypothalamic β-END is probably a posttranslational event that might reflect a disturbed endorphinergic innervation of those hypothalamic neurons which normally express nNOS. [ABSTRACT FROM AUTHOR]

In this study we examined the possible interplay of amylin (AMY) and salmon calcitonin (sCT) in the central control of growth hormone (GH) and prolactin (PRL) secretion in male rats. For this purpose we first compared effects of central intracerebroventricular (i.c.v.) admininstration of various doses of AMY (2.5–2,500 ng/rat) and sCT (2.2–220 ng/rat) on β-endorphin (β-END, 0.5 µg/rat)-induced GH and PRL secretion. AMY and sCT dose-dependently inhibited β-END-induced GH secretion, whereas only sCT was able to inhibit β-END-induced PRL secretion. To examine whether the GH inhibitory effect of AMY was due to the possible cross-reactivity of AMY and sCT on the same receptors in the CNS, we pretreated some rats with the AMY antagonist (AMY[sub 8–37] , 2.5 µg/rat, i.c.v.). AMY[sub 8–37] significantly enhanced the GH-stimulatory action of β-END. AMY[sub 8–37] , administered prior to AMY and sCT, significantly removed the inhibitory effect of both AMY and sCT on β-END-induced GH release, suggesting that both peptides mediate their response on GH through a common receptor. In vitro competition binding studies on rat hypothalamic membranes have shown that both AMY and sCT compete with [[sup 125] I]rAMY binding with half inhibition (IC[sub 50] ) values of 3.6 × 10[sup –11] and 1.6 × 10[sup –10] M, respectively. Binding of [[sup 125] I]sCT was inhibited by sCT with an IC[sub 50] of 1.09 × 10[sup –10] M and to a lesser extent by AMY with an IC[sub 50] of 1.3 × 10[sup –6] M. Thus it is possible that the two peptides recognize a common hypothalamic receptor but with different affinities (sCT > AMY). Overall these data indicate that AMY behaves as a mimic of sCT in the central control of GH secretion. The failure of AMY, at variance with sCT, to modify the PRL-releasing activity of β-END indicates that different receptor subtypes for sCT are involved in the endocrine effects of sCT and only those mediating the modulatory action of GH respond to AMY. [ABSTRACT FROM AUTHOR]

Orphanin FQ (OFQ) is a novel heptadecapeptide whose structure resembles that of dynorphin A[sub 1–17] . Its receptor shares appreciable homology with µ-, δ- and κ-opioid receptors, and is highly expressed in the hypothalamus. The present study examined the effects of OFQ on neurons within the arcuate nucleus (ARC) of the mediobasal hypothalamus, using intracellular recordings from coronal slices. In current clamp, OFQ produced a hyperpolarization of ARC neurons, including those immunopositive for β-endorphin, tyrosine hydroxylase and gonadotropin-releasing hormone. This hyperpolarization was dose-dependent, insensitive to antagonism by naloxone and was associated with a decrease in input resistance. In voltage clamp, OFQ produced an outward current associated with an increase in conductance. Varying the extracellular K[sup +] concentration shifted the reversal potential for the OFQ response to the degree predicted by the Nernst equation. Furthermore, barium chloride markedly attenuated both the OFQ-induced hyperpolarization and decrease in input resistance. Administration of maximally effective concentrations of OFQ, followed by coadministration of maximal concentrations of either OFQ and the µ-opioid receptor agonist DAMGO or OFQ and the GABA[sub B] receptor agonist baclofen produced additive hyperpolarizations and outward currents. If DAMGO was applied first, followed by the coadministration of DAMGO and OFQ, then the responses were occluded. Taken together, these results indicate that OFQ inhibits β-endorphin neurons, as well as A[sub 12] dopamine and GnRH neurosecretory cells, within the ARC by activating a subset of inwardly-rectifying K[sup +] channels. This suggests that OFQ is not only an antiopioid peptide, but that it also modulates the hypothalamo-pituitary axis and, ultimately, reproductive behavior. [ABSTRACT FROM AUTHOR]

Although glucocorticoids clearly inhibit proopiomelanocortin (POMC) gene transcription and peptide synthesis in the anterior pituitary, the effects of glucocorticoids on POMC in the hypothalamus are still unclear, even though most POMC neurons in the arcuate nucleus are known to have glucocorticoid receptors. In this study, we have therefore examined the effect of adrenalectomy (ADX) and glucocorticoid replacement on POMC mRNA and peptide (β-EP and α-MSH) levels in the medial basal hypothalamus (MBH) of the rat. POMC mRNA was measured by a sensitive solution hybridization S1 nuclease protection assay, and β-EP and α-MSH were measured by radioimmunoassay. In a first experiment, animals were studied 7 days after ADX or sham surgery. The mean POMC mRNA concentration was 1.01 ± 0.14 pg/µg RNA (means ± SE) in the intact animals and decreased to 0.55 ± 0.07 pg/µg RNA in the MBH of the ADX animals (p < 0.005). β-EP levels decreased in parallel from 4.30 ± 0.18 to 3.36 ± 0.11 ng/mg protein (p < 0.001); α-MSH levels decreased from 3.25 ± 0.21 to 2.41 ± 0.16 ng/mg protein (p < 0.005). In a second experiment, animals were studied 2 weeks after ADX. POMC mRNA levels again fell significantly from 1.15 ± 0.19 pg/µg RNA in the intact animals to 0.51 ± 0.06 pg/µg in the ADX animals (p < 0.01). β-EP levels fell also, but this was not significant. In a third experiment, all animals underwent ADX, and half of them received daily subcutaneous injections of dexamethasone (20 µg). Nine days after ADX, the mean POMC mRNA level was 0.66 ± 0.04 pg/µg RNA in the saline-treated animals and increased to 0.98 ± 0.08 pg/µg RNA in the dexamethasone-treated animals (p < 0.005). A parallel increase in β-EP levels from 5.03 ± 0.41 to 6.01 ± 0.53 ng/mg protein was also noted, but this was not statistically significant. We conclude that POMC gene expression is significantly inhibited in the MBH at 1 and 2 weeks after ADX. This effect was reversed by glucocorticoid replacement with doses close to the physiological range. The parallel changes in POMC mRNA and peptide levels strongly suggest that, in contrast to the anterior pituitary, low doses of glucocorticoids stimulate the biosynthesis of POMC in the MBH of ADX rats. [ABSTRACT FROM AUTHOR]