摘要:

The precise sites and mechanisms by which gonadal steroids influence the activity of neuroendocrine cells controlling pituitary hormone secretion are poorly understood. The present study has determined the distribution of estrogen receptor (ER)-immunoreactive cells in the monkey hypothalamus and examined whether ERs are expressed by luteinising hormone-releasing hormone (LHRH)-and&slash;or dopamine-containing neurones. The distribution of ER-immunoreactive cells was determined in ovariectomised (n = 2) and estrogen plus progesterone-treated (n = 2) cynomolgus macaques and in a single ovariectomised African green monkey. Large numbers of cells immunoreactive for the ER were detected in the preoptic area, bed nucleus of the stria terminalis, periventricular area and ventromedial and arcuate nuclei of all monkeys irrespective of the steroid status. Smaller numbers of ER-immunoreactive cells were found in the paraventricular, but not supraoptic nucleus. Double-labeling experiments in sections from all 5 monkeys revealed that none of the 432 LHRH neurons examined possessed detectable ER immunoreactivity. Neurones stained for tyrosine hydroxylase (TH) were identified in the A11, A12, and A14 cell groups and, although Al 1 and A12 neurones were intermingled amongst and found adjacent to ER-immunoreactive cells, none of the 1,652 TH-immunoreactive cells examined contained ER immunoreactivity. These results show that ER-immunoreactive cells in the monkey hypothalamus are distributed in a manner similar to that observed in other mammalian species although not all brain regions reported to contain progesterone receptors (PRs) in these species of monkey were found to express ERs. The double-labelling experiments provide further evidence that LHRH neurones do not possess ERs and indicate that, as in other species, estrogen influences on primate LHRH neurones are indirect and/or non-genomic in nature. Unlike the rat and sheep, no evidence was found for ER immunoreactivity in hypothalamic dopaminergic neurones of the monkey. The discrepancy in ER and reported PR receptor localisation within specific hypothalamic nuclei as well as in dopaminergic neurones raises the possibility that not all PR-containing cells may express ERs in the primate hypothalamus.

ISSN:0028-3835    

DOI:10.1159/000126810

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Previous works have suggested an interactive stimulatory effect of progesterone (P) and serotonin (5-HT) on luteinizing hormone release. The purpose of the present study was to determine whether 5-HT via 5-HT1A receptors interacts with P in the process of luteinizing hormone-releasing hormone (LHRH) release. Using fetal hypothalamic neurons in primary cell cultures the first goal of this study was to determine the effects of 5-HT1A receptor agonists on LHRH secretion. 8-Hydroxy-2 (di-n-propylamino) tetralin (8-OH-DPAT) or ipsapirone (10–5M) significantly stimulated LHRH release. Pharmacological studies have allowed to rule out the possible involvement of α2-or β-adrenore-ceptors, or 5-HT uptake sites, in the stimulatory effect of 8-OH-DPAT on LHRH release, thus demonstrating the specific involvement of 5-HT1A receptors in the stimulation of LHRH release. The second goal was to test the ability of P to stimulate LHRH release from fetal hypothalamic neurons. P (10–6M) applied for 30 or 120 min significantly stimulated LHRH secretion. The maintenance of the stimulation of LHRH release by P after a cycloheximide treatment or by an impermeable analog of P, P-3-BSA, has suggested a nonge-nomic effect of P on LHRH release. The effects of a pretreatment of cells by P on 8-OH-DPAT-induced LHRH release were tested. While 10–7M P alone did not stimulate LHRH release, this concentration of steroid potentiated the LHRH response to 10–5M 8-OH-DPAT. These findings led to the conclusion that P acting at the level of the plasma membrane potentiates the stimulatory effect of 5-HT1A receptor agonists on LHR

ISSN:0028-3835    

DOI:10.1159/000126828

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Since high concentrations of prolactin (PRL) enhance the hypothalamic release of corticotropin-releasing factor (CRF), and CRF decreases the hypothalamic secretion of luteinizing hormone (LH)-releasing hormone (LHRH), it could be that CRF is involved in the suppressed secretion of LH during hyperprolactinemia. The aim of this study was to explore this possibility in hyperprolactinemic male rats. Hyperprolactinemia, induced by insertion of 3 pituitary glands under the kidney capsule, decreased plasma LH levels by 68% and caused a 2-fold increase in plasma corticosterone. Intracisternal administration of the CRF antagonist α-helical CRF(9–41) induced both in pituitary-grafted rats and in normoprolactinemic controls a 2 to 3-fold increase of LH in the plasma sample taken 1 h after injection of α-helical CRF(9-41). Plasma levels of LH in pituitary-grafted rats were 2-3 times higher during intracere-broventricular infusion for 7 days with CRF antiserum than during saline infusion. Furthermore, after infusion of CRF antiserum for 7 days into the lateral brain ventricle plasma LH levels had increased by 270% in normoprolactinemic male rats. These results indicate that hypothalamic CRF is involved in the control of LH release in male rats. To further investigate whether CRF is involved in the effect of PRL on LH secretion, we infused PRL, alone or together with CRF antiserum, for 7 days into the lateral brain ventricle of normoprolactinemic male rats. After 7 days of PRL infusion, LH levels had decreased by 45%, whereas plasma corticosterone was 150% higher. This action of PRL on LH and corticosterone was prevented when besides PRL also CRF antiserum was infused. On the basis of these results it is suggested that the reduced secretion of LH and the increased secretion of corticosterone during hyperprolactinemia is at least partly due to a direct effect of PRL on the hypothalamus. Furthermore, hypothalamic CRF seems involved in the control of LH secretion, and hyperprolactinemia may enhance the hypothalamic activity of CRF-producing neur

ISSN:0028-3835    

DOI:10.1159/000126811

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Melatonin inhibits gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) release from neonatal rat anterior pituitary. Melatonin has been shown to decrease the concentration of several second messengers in neonatal pituitary, but it is not known which of them transduces the melatonin effect on LH release. In order to determine the mechanism of melatonin action, we tested the effect of melatonin on GnRH-induced LH release in the presence of specific drugs affecting second messengers. The calcium channel antagonist nifedipine inhibited LH release from cultured pituitary to a similar degree as melatonin and prevented the inhibitory effect of melatonin on LH release. The calcium channel agonist Bay K potentiated the GnRH-stimulated LH release and reduced the inhibitory effect of melatonin on LH release. These data strongly suggest that melatonin inhibits LH release via inhibition of calcium influx through voltage-sensitive channels. The cyclic AMP (cAMP) derivative 8-bromo-cAMP potentiated GnRH stimulation of LH release but did not prevent the melatonin-induced inhibition of LH release. However, when used in combination with Bay K, which reduced only partially the melatonin effect by itself, 8-bromo-cAMP completely blocked the melatonin effect. This observation suggests that decreased cAMP accumulation may also be involved in transduction of the melatonin effect on LH release.

ISSN:0028-3835    

DOI:10.1159/000126823

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

It is well known that chronic supraphysiological doses of glucocorticoids (GC) inhibit GH secretion in vivo, and stimulate GH secretion from the somatotropes in vitro. It has been suggested that GC exert an inhibitory role in the hypothalamus surpassing the GC-positive effect at the somatotrope level. To test the hypothesis that GC can affect growth hormone-releasing factor (GRF) and somatostatin (SS) at the hypothalamic level, we studied the effect of corticosterone on the immunoreactive content of GRF (IR-GRF) and SS (IR-SS) in cells and media of fetal hypothalamic cells in culture. After 20 days in culture, cells were incubated with serum-free medium containing corticosterone (from 0.3 to 300 nM) for 48 h. Corticosterone had a dual effect on IR-GRF. Concentrations in the range of the glucocorticoid receptor Kd (3 nM) increased peptide content, whereas higher concentrations (30 and 300 nM) decreased IR-GRF content in cells and media. Conversely, corticosterone increased SS cell content, only at a concentration of 3 nM, inducing a 2- to 3-fold increment in media content with the highest doses (30 and 300 nM). These results demonstrated that both GRF and SS are modulated by corticosterone in primary fetal rat hypothalamic cultures. Whereas GRF exhibited a dual response, stimulatory and inhibitory, at low and high corticosterone doses, respectively, SS showed a parallel increase with the corticosterone concentrations.

ISSN:0028-3835    

DOI:10.1159/000126824

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Evidence for a central site of action of growth-hormone-releasing peptide (GHRP-6) was sought by (1) counting the number of Fos-positive nuclei within the brain following intracerebroventricular or intravenous injection of peptide and non-peptide GH secretagogues and (2) characterizing the electrophysiological responses of neuroendocrine arcuate neurones (recorded in vivo) following intravenous injection of GHRP-6. Conscious male rats were chronically implanted with intracerebroventricular or intravenous catheters. Dense nuclear Fos staining was induced throughout the ventral arcuate nucleus of rats injected intracerebroventricularly with low doses of GHRP-6 but not in rats injected with the endogenous GH-releasing hormone GHRH or in vehicle-treated controls. The non-peptidyl GH secretagogues L-692,585 and L-692,429 also induced Fos expression in the arcuate nucleus, and the pattern of distribution was similar to that described for GHRP-6. No increase in Fos expression was observed in rats given a systemic injection of a high dose of GHRH. In pentobarbitone-anaesthetized male rats, the effects of intravenous injection of GHRP-6 on the electrical activity of arcuate neurones was predominantly excitatory for putative neuroendocrine cells and inhibitory for the remaining unidentified cells. These results suggest that (1) GHRP-6 and non-peptidyl GH secretagogues have a central site of action involving the activation of a subpopulation of arcuate neurones and (2) this action is not mimicked by the central or peripheral effects of GHRH.

ISSN:0028-3835    

DOI:10.1159/000126825

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

We have recently reported oral and parenteral bioactivity for a new GH-releasing peptide, hexarelin. In the present study, we have examined the neuroendocrine mechanism by which hexarelin and GHRP-6, two GH-releasing peptides, mediate their actions. Although previous studies have looked at the role of growth hormone-releasing hormone (GHRH) and somatostatin in regulating the action of GHRP-6 in culture and in stressed animals, our study looked at the role of both somatostatin and GHRH in regulating the action of hexarelin as well as GHRP-6 in conscious and freely-moving, nonstressed rats. Adult male rats, prepared with indwelling jugular catheters, were pretreated i.v. with either control antiserum (CTLas), growth hormone-releasing hormone antiserum (GHRHas), somatostatin antiserum (SSas), or both GHRHas and SSas. Animals were then treated i.v. with 25 µg/kg of either hexarelin or GHRP-6 4 h after i.v. antisera pretreatment. Blood samples were collected every 20 min for the 3 h prior to peptide treatment and at 5, 10, 15, 20, 40 and 60 min following hexarelin or GHRP-6 injection. The peak plasma GH responses in rats pretreated with CTLas were 552 ± 125 ng/ml following hexarelin administration and 386 ± 132ng/ml following GHRP-6 administration. Rats pretreated with SSas exhibited peak GH responses following hexarelin or GHRP-6 of 702 ± 115 and 312 ± 42 ng/ml, respectively. These plasma GH responses were similar to those observed in the CTLas-pretreated animals. Hexarelin injection resulted in a peak GH response of 372 ± 106 ng/ml in GHRHas-pretreated rats, while GHRP-6 injection resulted in a peak response of 135 ± 40 ng/ml. Rats pretreated with both GHRHas and SSas responded to hexarelin administration with a GH peak of 322 ± 66 ng/ml and to GHRP-6 with a response of 134 ± 39 ng/ml. GH responses noted in these animals were similar to the responses noted in GHRHas-pretreated rats. The GH responses elicited following either GHRHas or both GHRHas and SSas pretreatment were significantly lower than those responses observed in rats pretreated with either CTLas or SSas alone. Repeated measures analysis of the variance of peak plasma GH responses as well as of the area under the GH response curves allowed us to reach the following conclusions: (1) hexarelin was more effective in eliciting GH release than was GHRP-6 at the dose tested; (2) GHRHas inhibited the GH response to both hexarelin and GHRP-6, and (3) SSas pretreatment did not affect the GH response to the GH-releasing peptides. Therefore, we conclude that these two GH-releasing peptides elicit GH release via a GHRH-dependent pathway. In addition, because both hexarelin and GHRP-6 are bioactive regardless of circulating somatostatin tone, these GH-releasing peptides must also act to suppress somatostatin release from the hypothalamus or somatostatin effectiveness at the p

ISSN:0028-3835    

DOI:10.1159/000126826

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Hexarelin (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) is a new synthetic growth hormone (GH)-releasing hexapeptide. The mechanism of action of hexarelin in man is not fully elucidated. As for other GH-releasing peptides, an action on both the pituitary gland and the hypothalamus has been hypothesized. In the present study, we evaluated the modulation of GH-releasing activity of hexarelin in man. In a first experiment conducted on 6 healthy male volunteers, we studied the interaction of the maximally effective intravenous dose of hexarelin (2 µg/kg i.v.) with GH-releasing hormone (GHRH, 2 µg/kg i.v.) and somatostatin (2 µg/kg/h i.v.). In a second experiment involving another 6 male subjects, we evaluated the interaction of hexarelin with neuroactive substances, such as pirenzepine (0.6 mg/kg i.v.), pyridostigmine (120 mg p.o.) and arginine (0.5 g/kg i.v.), thought to modulate endogenous somatostatin secretion. Hexarelin induced a higher increase in GH levels as compared to GHRH (integrated output calculated as area under the curve AUC0-120 4,693 ± 691 vs. 1,494 ± 102 µg·min/l p < 0.01). Coadministration of hexarelin and GHRH produced a higher GH response than hexarelin alone (AUCo-120 7,395 ± 450 µg·min/1, p < 0.05). Somatostatin abolished the GH response to GHRH (AUC0–120 363 ± 89 µg·min/1, p < 0.01), while it only blunted that to hexarelin (AUCo-120 1,314 ± 297µg·min/l, p < 0.05). Pirenzepine blunted the GH response to hexarelin (AUC0–120 1,931 ± 446 vs. 4,586 ± 674 µg·min/1, p < 0.05) while pyridostigmine and arginine did not modify the GH response to the hexapeptide (AUC0–120 5,179 ± 771 and 4,743 ± 774 µg·min/1). Thus, the GH-releasing activity of hexarelin is greater than that of GHRH and is even enhanced by the neurohormone. Hexarelin differs from GHRH in that its effect is only blunted by exogenous somatostatin or pirenzepine and is not potentiated by pyridostigmine or arginine. These results indicate that, in man, hexarelin and GHRH may have different mechanisms of action and that the potent GH-releasing activity of hexarelin is partially refractory

ISSN:0028-3835    

DOI:10.1159/000126827

出版商:S. Karger AG    

年代:1995

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126812

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

In a double-blind, placebo-controlled trial, the effects of recombinant human growth hormone were studied on cerebrospinal fluid concentrations of growth hormone, insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), monoamine metabolites, neuropeptides and endogenous opioid peptides. Twenty patients, 10 patients in each of 2 groups, with adult-onset, growth hormone deficiency were treated for 1 month with recombinant human growth hormone (0.25 U/kg/week) or placebo. All the patients received the appropriate thyroid, adrenal and gonadal hormone replacement. In cerebrospinal fluid, the mean concentration of growth hormone increased from 13.3 ± 4.4 to 149.3 ± 22.2 µU/1 (p = 0.002), during recombinant human growth hormone treatment. The cerebrospinal fluid IGF-1 concentration increased from 0.67 ± 0.04 to 0.99 ± 0.10 µg/1 (p = 0.005) and the IGFBP-3 concentration rose from 13.4 ± 1.25 to 17.5 ± 1.83 µg/l(p = 0.002). The dopamine metabolite homovanillic acid decreased from 282.1 ± 36.0 to 234.3 ± 26.5 nmol/l (p = 0.02) and the vasoactive intestinal peptide decreased from 4.1 ± 0.6 to 3.7 ± 0.4 pmol/l (p = 0.03). Cerebrospinal fluid immunoreactive β-endorphin increased from 24.4 ± 1.8 to 29.9 ± 2.1 pmol/l (p = 0.002). There were no significant changes compared to baseline in the cerebrospinal fluid concentrations of enkephalins, dynorphin A, the norepinephrine metabolite 3-methoxy-4-hydroxyphenyl-ethyleneglycol, the serotonin metabolite 5-hydroxyindoleacetic acid, γ-aminobutyric acid, somatostatin or corticotropin-releasing factor. We conclude that treatment with recombinat human growth hormone causes a tenfold increase in growth hormone in the cerebrospinal fluid, thereby indicating that recombinant human growth hormone passes the blood-cerebrospinal fluid barrier. The cerebrospinal fluid concentrations of IGF-1 and IGFBP-3 increased significantly. Simultaneously, the cerebrospinal fluid concentrations of homovanillic acid and vasoactive intestinal peptide decreased and the concentration of β-endorphin immunoreactivities increased significantly. These changes might explain the improved quality-of-life in patients with growth hormone deficiency following replacement therapy wi

ISSN:0028-3835    

DOI:10.1159/000126813

出版商:S. Karger AG    

年代:1995

数据来源: Karger