摘要:

The endothelins consist of a family of vasoconstrictor peptides originally isolated from endothelial tissue which are now known to be involved in neuroendocrine regulation. However, while there are data indicating the involvement of endothelins in the modulation of the hypothalamo-pituitary-adrenal (HPA) axis, the precise mechanisms involved have been unclear. We have therefore used a previously validated rat hypothalamic explant system in order to investigate the possible modulation of the neurohypophyseal hormones vasopressin and oxytocin, and corticotropin-releasing hormone (CRH), by endothelin-1 (ET-1) and endothelin-3 (ET-3). Following a period of stabilisation, the release of vasopressin, oxytocin and CRH remained approximately constant in successive 20-min incubations. Addition of ET-1 stimulated the release of vasopressin at a dose of 0.1 nmol/l (p < 0.05), and both vasopressin and oxytocin at 10 nmol/l (p < 0.01 and 0.05, respectively). The release of vasopressin and oxytocin induced by 10 nmol/l ET-1 were both totally blocked by co-incubation with either 1 or 10 µmol/l of the specific ETA receptor subtype antagonist cyclo (D-Trp-D-Asp-Pro-D-Val-Leu) (BQ-123). ET-1 had no effect on CRH release in the dose range of 0.1-1,000 nmol/l. In case any possible stimulation of CRH might be masked by simultaneous generation of nitric oxide (NO), an inhibitor of CRH secretion, addition of ET-1 was also carried out in the presence of the NO synthase inhibitor, L-NO-Arg: ET-1 was again without effect in this dose range. ET-3 had no effect on any hormone at any concentration. It is concluded that ET-1 may be involved in the control of both vasopressin and oxytocin secretion, most probably at receptors relatively unresponsive to ET-3, the ETA recpetor. Any direct effect of the endothelins on the HPA axis is likely to be exerted via hypothalamic vasopressin rather than CRH

ISSN:0028-3835    

DOI:10.1159/000126796

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The secretion of oxytocin (OXT) from the neurohypophysis is modulated by the actions of opioids acting via ĸ-receptors. The vasopressin (AVP)-contain-ing nerve terminals in the neurohypophysis contain the ĸ-opioid agonist dynorphin, but endogenous opioid restraint of OXT secretion is observed even when AVP release is not activated, suggesting that another source of opioids is responsible for modulating OXT secretion. We now report that acute stimulation of the rat neural lobe in vivo results in depletion of the neural lobe content of OXT, AVP, dynorphin A1–17, dynorphin A1–8 and met-enkephalin (Met-Enk). The dynorphin content is depleted to a similar extent as that of OXT and AVP; a correlation analysis suggests that while most dynorphin is co-secreted with AVP, a significant portion is co-secreted with OXT, consistent with a co-localisation of dynorphin with OXT. Met-Enk was depleted to a lesser extent than either hormone, consistent with a partial localisation in non-releasable pools. However, depletion of Met-Enk was also observed following naloxone-precipitated opioid withdrawal accompanying selective hypersecretion of OXT, suggesting co-secretion of OXT and Met-Enk. Met-Enk is a µ-opioid receptor agonist, but extended forms of Met-Enk, as we now report, are active at neurohypophysial K-rec

ISSN:0028-3835    

DOI:10.1159/000126797

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Substance P (SP) which is synthesized and secreted by anterior pituitary cells has been suggested to alter pituitary functions as a local modulator. We determined which cell type(s) of rat anterior pituitary gland secretes SP. A new technique, named the sandwich cell immunoblot assay (CIBA), was developed to identify two protein substances that are secreted simultaneously from the same cells. Monodispersed anterior pituitary cells were sandwiched with pairs of transfer membranes and incubated to absorb secretory substances on the membranes. Small reference points for identifying the location of cell blots were simultaneously put on the pairs of transfer membranes after the incubation. The validity of the sandwich CIBA was revealed by the following: (1) cell blots were detected at the same locations on the pairs of transfer membranes that were immunostained with the same antisera against the anterior pituitary hormones, and (2) the areas of these cell blots detected at the same locations on different membranes correlated well. When one of the pair of transfer membranes was immunostained for SP and the remaining immunostained for one of the anterior pituitary hormones, it was found that 78 and 27% of SP-immunoreactive cell blots showed also GH and TSH immunoreactivity, respectively. None of the SP-immunoreactive cell blots showed immunoreactivity for PRL, ACTH, LH or FSH. These results suggest that the sandwich CIBA is useful to identify two substances cosecreted from a cell and that a subpopulation of rat somatotropes or thyrotropes cosecretes SP.

ISSN:0028-3835    

DOI:10.1159/000126798

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

To elucidate the mechanisms of the impaired pituitary response to growth hormone-releasing hormone (GHRH) in aged animals on a cellular basis, a reverse hemolytic plaque assay was performed on dispersed pituitary cells from young (8-month-old) and old (26-month-old) male F344 rats. The proportion of growth hormone (GH)-plaque forming somatotropes, i.e., actually functioning somatotropes, was reduced in old rats to 50-60% of that in young rats under both unstimulated and GHRH-stimulated conditions. The response of dispersed cells to GHRH, however, seemed to remain unchanged with age when expressed as a percent increase of plaque-forming cells from the basal value. The mean diameter of plaques, which reflects the average amount of GH secreted from a single cell, was not smaller in old rats under either the unstimulated or stimulated conditions. There was also no difference between the two age groups in the frequency distribution of the plaque size of functioning somatotropes. The stimulation by forskolin, a compound that directly activates membrane-bound adenylate cyclase and consequently provokes the cyclic adenosine-3,5’-monophosphate (cAMP) pathway for GH secretion in somatotropes, produced almost the same results as those by GHRH stimulation. It was concluded, therefore, that the impaired response of the pituitary gland to GHRH could be due mostly to a reduction in the density of functioning somatotropes rather than to impairments in steps of the GHRH-cAMP signal pathway in somatotrope

ISSN:0028-3835    

DOI:10.1159/000126799

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

This study was designed to examine whether cyclosporine (CyA) acts on the endocrine system by modifying the pulsatile secretion pattern of prolactin and LH. Both pituitary-grafted and sham-operated rats were submitted to a subcutaneous vehicle or CyA (5 mg/kg) treatment daily for 10 days beginning on the day of surgery. Pituitary grafting and/or CyA administration changed the pulsatile pattern of prolactin observed in sham-operated animals. The mean values of serum prolactin were significantly increased by pituitary grafting and the treatment with CyA further increased them. The mean half-life of prolactin was significantly increased in pituitary-grafted rats and was not changed by CyA administration, although it was decreased in sham-operated rats. The frequency of prolactin pulses was significantly decreased in pituitary-grafted as compared to sham-operated controls and was not further modified by CyA administration. However, in sham-operated rats a significant decrease of this parameter was observed. Duration of the prolactin peaks was significantly increased by pituitary grafting, and was not modified by CyA administration in any of the groups studied. The absolute amplitude of the prolactin peaks was significantly increased in pituitary-grafted as compared to sham-operated animals, and the treatment with CyA further increased this parameter in both groups. Mean values of LH were significantly increased in pituitary-grafted as compared to control rats. CyA administration significantly increased LH levels in sham-operated rats and decreased them in pituitary-grafted animals. The mean half-life, the pulse frequency and the duration of LH peaks were not modified by either pituitary grafting or CyA administration. The absolute amplitude of LH peaks was significantly increased in pituitary-grafted animals as compared to the sham-operated group. Cy administration increased the absolute amplitude of LH peaks in sham-operated and reduced it in pituitary-grafted animals. The data suggest that CyA might act by modifying the pulsatile secretory patterns of prolactin and LH.

ISSN:0028-3835    

DOI:10.1159/000126800

出版商:S. Karger AG    

年代:1994

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126801

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Participation of central 5HT receptors in the inhibition of LH pulsatility during refractoriness to short days (SD) in ewes has been suggested by previous in vivo studies using various 5HT-antagonist such as ketanserin. In the present study, binding of [3H]ketanserin in ewe brain sections was similar to that described in the brain of other species and could correspond with an interaction at 5HT2 receptors sites. Rosenthal analysis from the caudate nucleus was linear (Kd = 3 nM). The displacement studies from the cortex slices showed that the 5HT antagonists such as methysergide, ketanserin, cyproheptadine and spiperone competed with the labelled ligand at nanomolar concentrations whereas serotonin was less active. However, the first 3 drugs recognized different populations of binding sites. Prazosin, an α1-adrenergic antagonist was inactive, but a slight inhibition of [3H]ketanserin binding was induced by pyrilamine, an H1 histaminic antagonist, within a nanomolar range. Methysergide (10–6M), which does not bind to H1 receptors, was therefore used to determine the nonspecific binding. Quantitative analysis of the binding of 3 nM [3H]ketanserin on sections of the ewe brain at the preopticohypothalamic level was then carried out by autoradiography. The highest binding densities were observed in the caudate nuclei (64.0 fmol/mg tissue Eq) and the mammillary bodies (52.7 fmol/mg tissue Eq) whereas intermediate or low densities were found in the other structures. The anatomical distribution of the labelling was similar to that described in other species for 5HT2 receptors. Ketanserin binding in these areas was compared between two groups of ovariectomized estradiol-treated Ile-de-France ewes, submitted to artificial short days (SD: 8L: 16D), one group with a high LH pulsatility (responsive to SD) and the other one with a low LH pulsatility (photorefractory to SD). Binding densities were similar for each one of the studied regions between the two groups, except in the ventrolateral part of the mediobasal hypothalamus, where ewes exhibiting high LH pulsatility had a more than 2-fold higher binding density than those with a low LH pulsatility (mean ± SEM, 14.6 ± 1.4 vs. 5.7 ± 1.0 fmol/mg tissue Eq, respectively; p < 0.0016). These results suggest that [3H]ketanserin binding sites in the ventromedial part of the mediobasal hypothalamus could be associated to the regulation of the photoperiodic inhibition of LH at the time of establishment of refractoriness to short days in the Ile-de-Franc

ISSN:0028-3835    

DOI:10.1159/000126802

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The present studies utilized a phaimacologic approach to evaluate the role of corticosterone-preferring mineralocorticoid receptors (type I or MR) versus classic glucocorticoid receptors (type II or GR) in the regulation of basal pituitary luteinizing hormone (LH) secretion in vivo in male rats. Animals bearing indwelling intracardiac venous catheters received a subcutaneous (s.c.) injection of either vehicle, the MR antagonist, RU 752 (0.5 or 5.0 mg/kg body weight), or the GR antagonist, RU 486 (0.5 or 5.0 mg/kg body weight). Additional groups of rats were implanted with indwelling intracerebroventricular (i.c.v.) cannulas and intravenous catheters for drug administration and blood withdrawal, respectively, and injected i.c.v. with vehicle or graded doses (0.1, 1.0 or 10.0 µg/rat) of RU 752 or RU 486. The MR RU 752 failed to alter plasma LH concentrations regardless of dose or route of administration. In contrast, the GR antagonist, RU 486, elicited significant, dose-dependent increases in circulating LH when given either s.c. or i.c.v. Animals injected s.c. with either 0.5 or 5.0 mg RU 486/kg body weight showed elevated plasma LH levels; while the magnitude of this secretory response was not different between the two drug-treated groups, hormone levels remained elevated over baseline for a longer period of time in rats given the higher dose. Central administration of RU 486 at a dose of either 1.0 or 10.0 µg also resulted in elevated LH release; both the magnitude and duration of this increase in plasma LH were dose-dependent. In additional experiments, groups of rats were pretreated with vehicle or the synthetic GR agonist, RU 362, before administration of RU 486. These studies showed that the stimulatory effect of RU 486 on peripheral LH was abolished by prior interaction of GR with the exogenous ligand. In summary, the ability of the GR antagonist, RU 486, to promote an increase in plasma LH concentrations in intact male rats suggests that endogenous glucocorticoids exert a tonic inhibitory tonus on in vivo LH release in these animals, and that GR mediate these suppressive effects. Observations that drug-induced elevations in circulating LH were abolished by pretreatment with the GR agonist, RU 362, suggest that the stimulatory effects of RU 486 on hormone release were achieved by an antiglucocorticoid action. The current findings that plasma LH was increased following intracranial administration of RU 486 implicate central GR in neuroendocrine mechanisms governing pituitary L

ISSN:0028-3835    

DOI:10.1159/000126803

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Susceptibility to inflammatory disease in infantile Lewis (LEW/N) female rats seems to be related to their impaired hypothalamo-pituitary-adrenal (HPA) axis response to different inflammatory stimuli, while the relative resistance to this type of disease in Fischer (F344/N) female rats is apparently due to their potent HPA axis response to the same stimuli. In the present study, we attempted to elucidate whether there is an impairment in the HPA axis response in the juvenile female LEW/N rat to inflammatory and noninflammatory stimuli, and also to determine whether the endogenous sex-steroid environment influences the HPA axis function in both strains of rats. For these purposes, juvenile F344/N and LEW/N rats of both sexes were submitted to different treatments: (a) inhalation of normal atmosphere or ether vapors for 1 min (Ether); (b) i.p. injection of vehicle alone or containing CRH (0.5 µg/rat), arginine vasopressin (AVP; 5 µg/rat), angiotensin II (AII; 5 µg/ rat), insulin (INS; 0.3 IU/rat), bacterial lipopolysaccharide (LPS; 100 µg/rat) or snake venom (SV; 100 µg/rat). Rats were then killed at different time intervals (in min) after treatments: 20 for Ether, AVP and CRH, 30 for AII, 45 for INS, 60 for SV and 120 for LPS. Our results indicate: (1) the existence of a clear sexual dimorphism in the rat HPA axis function under both basal and stress conditions, with a general hyperresponse in females compared with males to a variety of neuroendocrine stressors; in F344/N female rats, a hyperresponse to different inflammatory stimuli was also found; (2) a decreased ACTH secretion in plasma to CRH and inflammatory stimuli (LPS and SV) in LEW/N vs. F344/N female rats, and (3) an intact hypothalamo-corticotrope response to Ether, AII, INS and AVP treatments in female LEW/N rats. Our findings demonstrate the existence of a sexual dimorphic pattern in the rat HPA axis function, under basal and stimulated conditions, and further support the hypothesis that decreased corticotrope response to CRH-mediated events might be responsible for the high susceptibility of the LEW/N female rat to autoimmune dis

ISSN:0028-3835    

DOI:10.1159/000126804

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Over the past decades, strong evidence has accumulated that growth hormone (GH) has immunostimulatory properties. Therefore, an investigation was conducted on 10 acromegalic patients and 9 age- and sex-matched healthy controls to determine whether plasma GH concentrations correlate with changes in several immune parameters, including serum concentrations of immunoglobulins, lymphocyte subsets, lymphocyte transformation with phytohemagglutinin (PHA), natural killer (NK) cell activity as well as phagocytic and metabolic burst activity. While NK cell activity, serum concentrations of immunoglobulins (IgG, IgM, IgA) and metabolic burst activity were within the normal range in both groups, a significantly enhanced phagocytic activity was observed in the acromegalic patients. Surface markers on T lymphocytes (CD3, CD4, CD8), B lymphocytes (CD 19) and NK cells (CD 16/56) were normal in both groups; however, in the acromegalic subjects, CD4+ and CD8+ cells showed a significant higher expression of transferrin receptors (CD71), indicating enhanced T-cell activity. The lymphocyte transformation response to PHA at the highest concentration tested showed a tendency to be elevated in acromegalics; however, the difference failed to be significant. Long-lasting and pronounced elevation of GH in acromegaly induces significantly enhanced phagocytic activity, but only negligible changes in most patients in lymphocyte phenotype and in the lymphocyte response to PHA.

ISSN:0028-3835    

DOI:10.1159/000126805

出版商:S. Karger AG    

年代:1994

数据来源: Karger