摘要:

Heterozygous Brattleboro (HZ) rats exhibit a partial genetic deficiency in hypothalamic vasopressin (VP) production. The effects of this abnormality of HZ rats on the capacities of VP-neurons and oxytocin (OT)-neurons to respond to an acute salt-load were examined. Acute salt-loading was induced by intravenous infusion of 18% saline in conscious, chronically catheterized animals and the activities of VP-neurons and OT-neurons were interpreted from plasma concentrations of VP-associated neurophysin, [VP-RNP] and OT-associated neurophysin, [OT-RNP] at different time periods throughout the infusion. Plasma sodium concentration ([Na+]), plasma osmolality (Posm) and mean arterial pressure (MAP) were also monitored. Salt-loading produced significant rises in [VP-RNP] and [OT-RNP]. These rises were accompanied by increases in plasma [Na+], Posm and MAP. Releases of OT-RNP were approximately four times greater than those of VP-RNP. The responsiveness of VP-neurons to increases in Posm in the HZ rat was approximately one-half of that observed for the Long-Evans (LE) rat. Furthermore, the responsiveness of OT-neurons in these animals was approximately one-half of that for LE rats and one-third of that for homozygous Brattleboro (DI) rats. The changes in MAP during salt-loading do not appear to be different for HZ and LE rats. Hence, while VP may be involved in the rise in blood pressure during infusion of hypertonic saline, there is not a direct correlation between plasma levels of VP-RNP (and presumably VP) and rises in blood pressure.

ISSN:0028-3835    

DOI:10.1159/000124709

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Temporal changes in plasma prolactin (PRL) levels caused by the administration of a number of different catechol estrogens to freely-moving conscious male rats were determined. The steroids with a wide range of affinity for the estrogen receptor were given in a single bolus (100 µg/kg) into the right atrium via an indwelling cannula. Plasma PRL concentration was monitored by taking blood samples every 2 min. The effect on PRL secretion was found to be more pronounced when the catechol estrogens were administered to rats bearing implants of estradiol and could not be correlated with their Kd values for the estrogen receptor. The synthetic estrogen, diethylstilbestrol, behaved anomalously by producing an elevation in plasma PRL only in estradiol-primed animals or after prolonged infusion. Diethylstilbestrol-treated rats showed no PRL response to 2-hydroxyestrone unlike those bearing Silastic capsules of estradiol. The experiments support the hypothesis that catechol estrogens generally act as short-term dopamine agonists, lowering PRL, but that those which possess estrogenic activity also show a more prolonged PRL-elevating effect. Thus, the overall action of this group of steroids will be determined by factors which influence these two parameters

ISSN:0028-3835    

DOI:10.1159/000124710

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Ultrastructural localization of immunoreactive corticotropin-releasing factor (CRF) was visualized for the first time in the human hypothalamus and pituitary gland with specific antibodies against human/rat CRF. In the hypothalamus most of the positive immunoreactivity to CRF was present in granules with a wide range of diameters, 50–250 nm, in the perikarya of parvocellular neurons in the paraventricular nucleus. Among these, neurosecretory type granules, 100–150 nm in diameter, were dominant, and small vesicles, 50–80 nm in diameter, were sparse. Some of surfaces of rough endoplasmic reticulum and polyribosomes were also positive in some of these cells. CRF-positive reactions were also observed in the nerve fibers of the pituitary stalk and the posterior pituitary gland revealing two types of granules: small vesicles, 50–80 nm in diameter, and neurosecretory granules, 100–150 nm in diameter. These results support the theory that the human CRF, which is identical to rat CRF, is synthesized in parvocellular neurons of paraventricular nucleus, transported in nerve fibers, and controls ACTH secretion in the human anterior lobe of pituitary gland via the port

ISSN:0028-3835    

DOI:10.1159/000124711

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

With the recent development of highly specific ligands for the µ, δ and Kopioid receptors it was of interest to define the effects of activation of each of these receptor types on LH and prolactin (PRL) secretion. The compounds were infused (10 µl/h) at various concentrations into the third cerebroventricle of unanesthetized, ovariectomized rats. The µ agonist, DAGO, at both 1 and 10 µg/h caused a significant suppression of LH secretion and a significant stimulation of PRL release. DPDPE, the δ agonist, had no effect on either hormone at 1 µg/h but inhibited LH secretion at 10 µg/h. There was still no effect of this high dose of DPDPE on PRL release. The Kagonist, U50,488H, had no effect on either hormone at 10 µg/h, but at 100 µg/h produced a significant suppression of LH release and a highly variable increase in PRL. Coinfusion of 100 µg/h of naloxone with the high dose of each of the agonists completely blocked the responses of both hormones to each of the agonists with one exception: the highly variable stimulation of PRL by U50,488H was not affected, thus indicating a nonspecific effect of U50,488H on PRL secretion. These results demonstrate that: (1) activation of the µ receptors produces an inhibition of LH secretion and a stimulation of PRL release; (2) activation of the δ receptors produces an inhibition of LH secretion but has no effect on PRL release, and (3) activation of the Kreceptors produces an inhibition of LH release and a variable stimulation of P

ISSN:0028-3835    

DOI:10.1159/000124712

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Continuous infusions of growth hormone-releasing hormone (GHRH) attenuate the subsequent growth hormone (GH) response to GHRH. To test whether this phenomenon can occur in the absence of GH pool depletion, we examined the effects of continuous infusions of 10 nM GHRH and of 10 nM somatostatin (SRIH), separately or in combination, on dispersed, perifused rat anterior pituitary cells. Columns of these cells were given either GHRH alone for 5 h, GHRH and SRIH together for 3 h followed by GHRH alone, or SRIH alone for 3 h followed by GHRH or medium. SRIH blunted both basal GH release and the GH response to GHRH, without affecting the subsequent GH responses to GHRH. The GHRH infusions attenuated the subsequent GH response to GHRH, even when GH release was initially prevented by the concurrent infusion of SRIH. Furthermore, the degree of attenuation was similar in the presence or absence of SRIH, suggesting that pool depletion plays little role in the desensitization process under these experimental conditions. The results are consistent with the hypothesis that a short-term infusion of GHRH leads to attenuation of the GH response in rat anterior pituitary cells primarily through receptor effects rather than through GH pool depletion.

ISSN:0028-3835    

DOI:10.1159/000124713

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study was undertaken in order to better characterize the functional state of anterior pituitary gland in young and old rats by using prolactin secretion and incorporation of radioactive phosphate into phosphatidylinositol (PI) as markers. The in vitro incorporation of radiolabeled phosphate into anterior pituitary PI was significantly (p< 0.01) greater in young (3–5 months) than in aged (24–25 months) male Sprague-Dawley rats. No significant difference was found in the incorporation by pituitary tissue of 32P into phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Also, the extent of prolactin secretion from isolated pituitary was significantly greater in young than in aged rats, while the prolactin pituitary content was significantly higher in aged animals. In vitro dopamine (DA) decreased the incorporation of 32P into PI, both in young and old pituitary glands, and inhibited prolactin secretion into the incubation medium. Brain cortex-phosphatidylserine (BC-PS), a pharmacologically active purified phospholipid, capable of stimulating the dopaminergic system in the hypothalamus and of decreasing prolactin secretion both in humans and rats in vitro and in vivo, inhibited the incorporation of labeled phosphate into PI of pituitary glands from either young or old rats, but did not alter the prolactin secretion from the glands incubated in vitro. Baseline prolactin plasma levels did not differ significantly between young and old rats either when blood was collected from the trunk after decapitation or underwent sampling from chronically cannulated rats. Chronic administration of BC-PS (15 mg/kg i.p. for 30 days) had a similar effect on prolactin plasma levels both in aged and young rats, while the phosphate incorporation into PI was significantly decreased only in young rats’ pituitaries. All together these data support the view that unchanged prolactin levels observed in old rats is the results of some adaptive compensatory mechanisms involved in the control of prolactin secr

ISSN:0028-3835    

DOI:10.1159/000124714

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The distribution of serotonin (5-HT) and tyrosine hydroxylase (TH) was examined in the hypothalamus of juvenile baboons, 24 h after infundibular stalk section. Simultaneous immunostaining for 5-HT with peroxidase-antiperoxidase (PAP) and TH with 15 nm colloidal gold (IGS) was performed on Vibratome sections from 3 operated and 1 control female. Light microscopy revealed fine 5-HTimmunopositive (5-HT+) fibers, presumably axons, in the suprachiasmatic nuclei and ventromedial hypothalamus (VMH) after stalk section. In addition, focal accumulations of swollen and heavily stained 5-HT+ fibers occurred on the side of the surgical approach. Enlarged fibers were densest in the medial preoptic area, lateral and VMH areas, and the median eminence. TH immunoreactivity (TH+) in VMH cell bodies and axons was only slightly increased over that in controls. Electron microscopy of areas of 5-HT+ and TH+ overlap (medial VMH and adjacent periventricular zone) showed that 5-HT+ profiles were mostly unmyelinated axons and irregular varicosities. A few myelinated 5-HT+ axons were also observed. TH+ perikarya, dendrites, axons and terminals showed gold labeling characteristic for this enzyme. However, colocalization of 5-HT (PAP) and TH (IGS) was present in a number of fiber varicosities in experimental animals only. Both single- and double-labeled profiles occurred in individual thin sections, thus arguing against antibody cross-reactivity. These results indicate that: (1) hypothalamic 5-HT+ fibers project to the median eminence in primates; (2) 5-HT fibers become more obvious after stalk section due to accumulation of transmitter; (3) focal 5-HT+ immunoreactivity in the hypothalamus can increase dramatically after distant and mild surgical trauma, and (4) coexistence of 5-HT and TH in single neurons can appear after acute stalk section and/or trauma in experimental animals. These findings might represent uptake of exogenous 5-HT or amplified expression of endogenous neurotransmitter, suggesting that plasticity of transmitter phenotype might follow acute surgical and/or endocrine intervention in mature primate brain. Neuroendocrine studies employing the stalk-sectioned primate might thus be radically affected.

ISSN:0028-3835    

DOI:10.1159/000124715

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study attempts to determine whether part of the corticotropin-releasing factor (CRF)-like materials present in the ‘posterior pituitary’ is composed of authentic CRF and examines whether the concentration of that peptide may be modulated by circulating glucocorticoids. Analysis of crude extracts of neurointermediate lobes () of rat pituitaries by reverse-phase HPLC, coupled with a specific radioimmunoassay (RIA), revealed the presence of a major component eluting with the same retention time as rat CRF (rCRF) and, importantly, which was indistinguishable by RIA from the synthetic peptide. Also, two minor forms eluted earlier than rCRF upon HPLC; one of these forms matched the elution position of r[Met(O)21,38]CRF. All three species did show biological activity and stimulated ACTH release from pituitary cells. Essentially the same elution profile was generated by median eminence (ME) extracts. Immunoreactive CRF (CRFi) content of the was about 3% of that ot the ME and was found to undergo a significant increase as a result of long-term adrenalectomy while, in contrast, CRFi content of the ME was decreased. This effect of adrenalectomy was completely antagonized by dexamethasone treatment. This study thus provides strong evidence for the presence of authentic CRF within the of the rat pituitary and also shows that tissue concentration of that peptide was modulated by glucocortico

ISSN:0028-3835    

DOI:10.1159/000124716

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Although sexual behavior during the rat estrous cycle is dependent on estradiol and progesterone, under some conditions, it can be induced by treatment with estradiol alone. Either chronic exposure to estradiol (estrogen-induced sexual behavior) or an acute large injection of estradiol in estradiol-primed rats (estrogen-facilitated sexual behavior) is capable of inducing sexual receptivity. It has been suggested that this progesterone-independent sexual behavior is referable to estradiol interaction with neural progestin receptors. A series of experiments was performed to investigate the possible dependence of estrogen-induced and estrogen-facilitated sexual behavior on neural progestin receptors. In the first series of experiments, the progesterone antagonist, RU 486, which inhibits progesterone-facilitated sexual behavior by interaction with progestin receptors, was injected into rats that were sexually receptive as a result of continuous exposure to estradiol. In the second series of experiments, RU 486 was injected prior to or following an acute large dose of estradiol (1 mg) in an attempt to block estradiol-facilitated lordosis. Although RU 486 was effective in inhibiting progesterone-facilitated sexual behavior in an identical procedure, in no case was RU 486 effective in inhibiting sexual behavior induced by estradiol alone. These findings, together with the fact that rats in which sexual behavior is facilitated by estradiol show much lower levels of soliciting behaviors than progesterone-facilitated rats, suggest that estradiol does not facilitate sexual behavior through the same mechanism as progesterone.

ISSN:0028-3835    

DOI:10.1159/000124717

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

To investigate the simultaneous effects of dexamethasone on peripheral and central adrenocorticotropic hormone (ACTH) systems, rats were treated with dexamethasone or saline for 4 days. Pituitary, plasma, hypothalamus and cerebrospinal fluid (CSF) were then collected and analyzed for ACTH immunoreactivity. Additionally, hypothalamic tissue extracts were analyzed for corticotropin-releasing hormone (CRH) immunoreactivity. Dexamethasone significantly lowered peripheral levels of ACTH as measured in pituitary and plasma. Hypothalamic ACTH content significantly increased while CSF ACTH significantly decreased with dexamethasone treatment. Hypothalamic CRH concentrations showed a small but statistically insignificant decrease. These results (1) suggest that prolonged exposure to dexamethasone affects central as well as peripheral ACTH activity, (2) corroborate our previous findings in rhesus monkeys of decreased CSF ACTH in response to prolonged dexamethasone treatment, (3) suggest that dexamethasone may inhibit the release of ACTH from hypothalamic neurons into the CSF, and (4) provide evidence that the effect of dexamethasone on pituitary ACTH content is of greater magnitude than its effect on hypothalamic CRH.

ISSN:0028-3835    

DOI:10.1159/000124718

出版商:S. Karger AG    

年代:1987

数据来源: Karger