摘要:

Studies both in vivo and in vitro have provided evidence that LH secretion can be altered by angiotensin II (AII) or atrial natriuretic peptide (ANP); however, the physiological significance of these endogenous neuropeptides in the control of gonadotropin release is still unclear. We studied the effects of central immunoneutralization of these neuropeptides on LH and FSH release in ovariectomized rats. Antisera directed against AII or ANP were microinjected into the third cerebral ventricle (3V) of conscious, unrestrained rats with indwelling external jugular catheters and blood samples were withdrawn immediately prior to the injections and at various intervals thereafter. Plasma LH was not altered initially but by 2 h was significantly lower in the animals injected with antiserum directed against AII (AB-AII) than in controls injected with normal rabbit serum (NRS). Values remained low for 6 h. By 24 h they had returned to levels similar to those of NRS-injected controls. On the other hand, in animals injected with antiserum against ANP (AB-ANP) plasma LH levels were significantly higher than those of controls (NRS) after a delay of 4 h. Values were still significantly elevated at 24 h. There was no difference in plasma FSH concentrations between control groups (NRS) and groups injected with either AB-AII or AB-ANP. These results indicate that endogenous AII and ANP play no role in the control of FSH release, at least in ovariectomized rats but that these neuropeptides play a role in LH release which is stimulated by AII and inhibited by ANP since the immunoneutralization decreased and increased, respectively, the plasma levels of this hormone. Thus, our results indicate that endogenous AII and ANP have physiological significance in the control of LH release.

ISSN:0028-3835    

DOI:10.1159/000125410

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

In order to evaluate the actions of calcitonin gene-related peptide (CGRP), a neuropeptide which is found within the hypothalamus, male and ovariectomized (OVX) female rats were injected intraventricularly (third ventricle, 3 V) with varying doses of CGRP or antiserum directed against the peptide and the effect on plasma growth hormone (GH) and prolactin (Prl) concentrations studied. Intraventricular injection of the peptide (0.5 or 5.0 µg; 0.125 or 1.25 nmol) induced a suppression of GH release in conscious, OVX female and intact male rats. Conversely, intraventricular injection of diluted (1:10) highly specific antiserum against the peptide produced the reverse effect and a transient elevation in plasma GH occurring 2 h after the injection in males. A longer-lasting elevation occurred in OVX females which persisted for the 24-hour duration of the experiment. The elevation was delayed as has been the case with other antisera suggesting that the site of action was at some distance from the site of injection into the 3V. Since the peptide had an action to inhibit GH release from dispersed, overnight cultured anterior pituitary cells in vitro at doses of 10–11M, it is not certain from these results whether or not the effects of the peptide are exerted directly on the hypothalamus or the pituitary, but the results indicate a physiologically significant action of this peptide to suppress GH release. Similarly, intraventricular injection of the peptide produced a dose-related suppression of Prl release in OVX animals; however, antiserum directed against the peptide failed to alter Prl release. In males, only the lower 0.5-µg dose effectively inhibited Prl release. There was an action of the peptide to increase Prl release by dispersed cells in vitro. Therefore, the suppressive effect of the peptide on Prl release following its intraventricular injection must be exerted on the hypothalamus to either augment the release of Prl-inhibiting factors or suppress the release of Prl-releasing factors. This action does not appear to be physiologically significant in the types of animals tested since the antiserum had no eff

ISSN:0028-3835    

DOI:10.1159/000125411

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Transient removal of dopamine (DA) potentiates the prolactin (PRL) releasing action of thyrotropin releasing hormone (TRH) in cultured lactotrophs. We have determined if this potentiating action on PRL release is related to the intracellular processing of PRL by studying this phenomenon in cells in which PRL was pulse-labeled at varying times. Anterior pituitaries from ovariectomized estradiol-treated rats were dispersed and cultured on plastic coverslips. Cells were incubated for 24 h in media containing 500 nM DA. Cells were exposed to three consecutive 20-min incubation periods. During the first period all cells were maintained in 500 nM DA, during the second period half of the cells were removed from DA inhibition and during the third period DA inhibition was restored and the cells challenged with 100 nM TRH. In experiments involving labeling of PRL, cells were incubated in leucine-free media containing 100 µCi/ml [3H] leucine for 1 h prior to treatment, for 1 h starting 5 h prior to treatment or for 16 h starting 24 h prior to treatment. Total PRL (by radioimmunoassay) and radiolabeled PRL (by liquid scintillation after electrophoretic isolation) were determined both in media and cells. The withdrawal of DA alone resulted in a 2-fold stimulation of total PRL release. The efficacy of TRH to release total PRL was also increased 2- to 4-fold after transient DA withdrawal. Whereas release of 1-hour-old labeled PRL was not affected by DA withdrawal, 5-hour-old and 8- to 24-hour-old [3H] PRLs were stimulated 2.6- and 2-fold, respectively. TRH stimulation of 5-hour-old [3H] PRL release was potentiated 6-fold (from 150 to 900% over the basal) by transient removal of DA. On the other hand, TRH stimulation of 8- to 24-hour-old [3H] PRL release (180% over the basal) was not affected by the prior escape from the action of DA. TRH did not affect the release of 1-hour-old [3H] PRL either under constant or after the transient removal of DA. These results suggest that the regulated release of PRL is highly dependent on the age of the hormone. The potentiation of TRH-induced PRL release evoked by DA removal was only observed with hormone synthesized from 4 to 5 h earlier. PRL synthesized up to 1 h before was constitutively released and neither DA withdrawal nor addition of TRH affected its secretion in spite of the observation that its relative rate of basal release was not different from that of 4- to 5-hour-old PRL. PRL synthesized more than 8 h earlier was regulated independently by TRH and DA, however, transient removal of DA had no effect on potentiation of the TRH response. Therefore PRL stored for prolonged periods of time cannot be coupled to the biochemical events mediating the potentiating effect of transient DA removal on the action of TRH

ISSN:0028-3835    

DOI:10.1159/000125412

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

This research was intended to study the effects of perinatal haloperidol administration on the postnatal secretion of prolactin (PRL) with the aim of investigating the existence of a ‘critical period’ during which the lack of dopamine influence could cause long-term alterations in the secretion of this hormone. A first group of animals, composed of pregnant rats, was injected daily with haloperidol (1 mg/kg) from day 16 of gestation to delivery. A second group of newborn rats received the same dose from days 2 to 6 after birth. Pituitary and serum PRL were measured weekly by radioimmunoassay during the 1st postnatal month in pups from the injected mothers, in postnatally injected rats, and in controls. The results showed a significant increase in the pituitary amounts of PRL that was more intense after the prenatal treatment, especially in the females. In serum, the prenatal treatment induced PRL levels higher than in the controls, whereas the postnatally injected group exhibited a V-shaped response which has been described as characteristic of neuroleptic withdrawal. These data confirm the existence of a ‘critical period’ during which perinatal administration of haloperidol alters the postnatal PRL production and secretion patterns. The persistence of high PRL contents in pituitary may reflect an alteration in the hormone synthesis and/or an increase in the rate of somatomammotrophes that differentiate into lactotrophes after suppression of dopamine influence. The high PRL levels in serum indicate a failure in the control of PRL release, perhaps after damaging the tuberoinfundibular neurons as a consequence of the high prolactinemia induced by the tr

ISSN:0028-3835    

DOI:10.1159/000125413

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The delayed and sustained suppression of LH secretion induced by the administration of LHRH into the third cerebral ventricle of the ovariectomized ewe suggests the activation of a neuroendocrine mechanism involving components separate from the LHRH system. Endogenous opioid peptides are involved in regulating LHRH secretion but our recent work shows they do not mediate this inhibition. There is, however, clear evidence for a role for each of the components of the hypothalamopituitary-adrenal axis in the suppression of LHRH/LH secretion. Thus, the relationship between the central administration of LHRH, changes in plasma cortisol and LH secretion was investigated. Injection of LHRH (21 pmol) into the third cerebral ventricle of ovariectomized ewes caused a significant and rapid rise in plasma cortisol to a maximum of 4–5 times pre-injection values, followed by a delayed but sustained reduction in LH secretion. There was a high correlation (r = -0.902) between the increase in cortisol and the reduction in LH. Both the stimulatory effect of central LHRH on plasma cortisol and the inhibitory effect on plasma LH were blocked by prior central treatment with an LHRH antagonist. Intravenous infusion of cortisol, to reach levels observed after central LHRH administration, reduced LH secretion (although not to the levels which followed central LHRH) due in part to a reduction in pituitary responsiveness to LHRH. These experiments provide evidence that cortisol, either alone or in combination with another component(s) of the hypothalamopituitary-adrenal axis, may play a role in the LHRH-induced inhibition of LHRH/LH secretion in the shee

ISSN:0028-3835    

DOI:10.1159/000125414

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

We have characterized putative androgen receptor binding sites in five separate biopsy samples of human temporal cortex from epilepsy patients using an in vitro exchange assay with soluble fractions and pH]5α-dihydrotestosterone as radioligand. The results revealed highly specific, saturable binding with an apparent affinity constant (K < j) of ∼2 nM with a moderate capacity (Bmax) of ∼50 fmol/mg protein. In competition studies, we found that only testosterone and 5α-dihydrotestosterone competed effectively (i.e. at low nanomolar concentrations) for [3H]5α-dihydrotestosterone binding sites. These data indicate the presence of androgen receptors in human cortex that are pharmacologically very similar to that previously described in rodent and infrahuman primate CNS, and suggest the existence of a possible mechanism whereby circulating androgens might influence neuronal events in human

ISSN:0028-3835    

DOI:10.1159/000125415

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

It has been previously shown that in normal women during the periovulatory period, prolactin (PRL) levels increase after the administration of nonspecific stimuli, such as growth hormone-releasing hormone or gonadotropin-releasing hormone (GnRH). In order to gain insight into the mechanism of this response, we have tested the effect of a naloxone infusion (1.6 mg/h) on the PRL response to GnRH in 5 normal females, aged 20–27 years, tested during the periovulatory period. Naloxone was administered starting 60 min before GnRH administration (100 µg as an i.v. bolus). Naloxone clearly blunted the PRL response (basal 10.7 ± 1.7 ng/ml, peak 11.8 ± 0.2 ng/ml at 30 min, versus: basal 9.0 ± 0.5 ng/ml, peak 20.6 ± 3.9 ng/ml at 45 min after GnRH alone; significance of difference between peaks: p < 0.05). A secondary late increase of PRL levels was observed, reaching about 60% of basal levels at 120 min (16.8 ± 2.6 ng/ml). These data indicate that periovulatory PRL dynamics are altered by naloxone administration and suggest a possible involvement of opioid peptides in the ‘paradoxical’ PRL response to GnRH in norm

ISSN:0028-3835    

DOI:10.1159/000125416

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The concentration of atrial natriuretic peptides (ANF) was measured radioimmunologically in 18 selected microdissected brain areas of rats with inherited diabetes insipidus (Brattleboro rats) and their control rats (Long-Evans rats). In 7 brain areas known to be involved in the regulation of fluid homeostasis or blood pressure (subfornical organ, organum vasculosum lamina terminalis, periventricular preoptic nucleus, perifornical nucleus, nucleus of the solitary tract, tegmentum pontis, arcuate nucleus) ANF concentration was significantly changed. After restoration of antidiuresis with the V2 receptor agonist 1-desamino-8-D-arginine vasopressin (DDAVP) ANF levels of Brattleboro rats adapted at least partly to those of the control rats in all brain areas except the subfornical organ. Furthermore, ANF was then significantly changed in the supraoptic and paraventricular nuclei of DDAVP-treated diabetes insipidus rats. These data show that the central ANF system is sensitive for changes in electrolyte and fluid homeostasis.

ISSN:0028-3835    

DOI:10.1159/000125417

出版商:S. Karger AG    

年代:1990

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000125418

出版商:S. Karger AG    

年代:1990

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000125419

出版商:S. Karger AG    

年代:1990

数据来源: Karger