ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05161.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Patients with prolactinoma are commonly treated with the D2 dopamine agonist bromocriptine, which in most cases, normalizes prolactin (PRL) levels. However, resistance to bromocriptine has been observed in 5 to 18% of tested prolactinomas and is associated to a decrease in both D2 receptor density and mRNA levels. In this study, we used quantitative RT‐PCR to investigate whether expression of Gαproteins could be also modified in bromocriptine resistant prolactinomas. No difference in Gαo mRNA levels or in the relative expression of Gαs between bromocriptine sensitive and bromocriptine resistant prolactinomas was observed. In contrast, the relative expression of Gαi2was found to be decreased in bromocriptine resistant prolactinomas when compared to that of bromocriptine sensitive prolactinomas. Interestingly, the relative Gαi2expression was correlated to both bromocriptine inhibition of in vitro PRL secretion and D2 receptor mRNA levels. Bromocriptine resistance could thus result from a decrease in D2 dopamine receptors associated with a decrease in Gαi2exp

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04902.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Osmotically stimulated vasopressin and oxytocin release were measured in pinealectomized and sham operated male rats infused with hypertonic sodium chloride. Neuronal activation in the hypothalamic regions associated with oxytocin and vasopressin release was investigated by quantitative assessment of Fos protein production. The osmotically stimulated release of both vasopressin and oxytocin was significantly lower in pinealectomized animals as compared to sham operated controls. The slope of regression lines between plasma osmolality and hormone concentrations in the sham animals showed a 1.0±0.1 pmol per mosm/kg rise in vasopressin and 2.0±0.4 pmol per mosm/kg rise in oxytocin whilst in the pinealectomized animals these values were significantly lower at 0.4±0.1 pmol vasopressin per mosm/kg and 0.8±0.2pmol oxytocin per mosm/kg. The osmotic thresholds for hormone release were unaffected by pinealectomy. Fos production was also significantly lower in the supraoptic nucleus and organ vasculosum of the lamina terminalis in the pinealectomized rat at 62±20 and 59±9 Fos immunoreactive cells/section as compared to corresponding values of 202±31 and 123±20 Fos immunoreactive cells/section in the shams. These observations suggest that reduced hormone release in the pinealectomized animal is due to lowered responsiveness of central osmoregulatory mechanisms and that melatonin may therefore influence the activation of the magnoce

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.04953.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

We studied osmoregulation of plasma vasopressin in 5 patients with newly diagnosed diabetes mellitus. All patients showed typical symptoms of uncontrolled diabetes mellitus such as marked hyperglycemia, polyuria, and polydipsia, but did not have advanced diabetic complications. Vasopressin release was studied using 5% hypertonic saline infusion test twice: before treatment when the patient was hyperglycemic, and after treatment 1 to 2 months later when the patient was euglycemic. Plasma vasopressin was measured by a sensitive and specific radioimmunoassay. The mean basal plasma vasopressin value in the patients was significantly higher in the hyperglycemic compared with the euglycemic state (3.75±0.70vs1.18±0.46 pmol/l, respectively; P<0.05). The relationship of plasma vasopressin with serum sodium, but not plasma osmolality, during hyperglycemia showed an apparent hypersecretion of vasopressin. In both cases, the sensitivity of the vasopressin response to osmotic stimuli was significantly decreased. During euglycemia, the sensitivity of vasopressin secretion to either sodium or osmolality was almost normal, although a slight rise in the osmostat was observed compared with normal subjects. Together, we found that the positive correlation of vasopressin with sodium or osmolality is maintained but significantly altered in patients with untreated diabetes mellitus. Especially noteworthy is the lowered threshold and decreased sensitivity of osmotically‐induced vasopressin secretion during hyperglycemia, which may be caused by multiple factors such as diabetes‐associated hypovolemia, osmogenic effects of glucose and other osmoles, depletion of the pool of vasopressin available for release, and the metabolic derangement of osmoreceptor/magnocellular

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05124.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Noradrenergic neurons of the locus coeruleus (LC) negatively regulate the endogenous rhythmicity of growth hormone (GH) secretion. These neurons express high concentrations of receptors for somatostatin (SRIH) and galanin (GAL), two neuropeptides which can affect electrical activity of LC neurons and also centrally modulate plasma GH levels. We thus investigated whether somatostatin and galanin receptors located in the LC are involved in GH regulation. Pulsatile patterns of endogenous GH secretion were monitored after unilateral infusion of the peptides into the lateral ventricle (ICV) or into the LC, after lesion of contralateral LC neurons by 6 hydroxydopamine. Neither unilateral LC lesions nor administration of saline affected GH release. When administered ICV, both SRIH (5 μg/μl/15 min) and GAL (1 μg/μl/15 min) resulted in a marked increase in GH secretion. Infusion of SRIH into the LC induced a significant but weaker stimulation of plasma GH as compared to ICV injections. In contrast, infusion of GAL into the LC was ineffective. These results indicate that somatostatin can exhibit direct effects on noradrenergic neurons of the LC involved in GH regulation, whereas central effects of galanin on the hormone are mediated by distinct str

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05115.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The effect of intracerebroventricular (i.c.v.) injection or infusion of various doses of corticotropin‐releasing hormone (CRH) on the LH and FSH surge was studied in pro‐oestrous rats supplied with a jugular vein and an i.c.v. cannula. Additionally, we investigated if arginine vasopressin (AVP) was involved in the CRH‐induced alterations to the surge of gonadotropins. I.c.v. injection of 10 μg CRH given 5 min before the presumed onset of the LH surge caused a strong inhibition of the LH surge and a slight inhibition of the FSH surge. Three to four h after CRH injection, its inhibitory effect diminished. A 6 h i.c.v. infusion of CRH started 1 h before the presumed onset of the LH surge, caused a dose‐related inhibition of the LH and FSH surge. Infusion of 1 μg/h CRH did not suppress the surge of both hormones while infusion of 5 or 10 μg/h CRH inhibited the LH surge. Infusion of 10 μg/h CRH caused a strong suppression of plasma LH during the first 3 h of the LH surge. Despite continuation of CRH infusion, the inhibitory effect disappeared and plasma LH increased to similar levels as in controls at corresponding points of time of the LH surge. The FSH surge was also suppressed by infusion of 10 μg/h CRH. The surge of LH and FSH was not affected by a 9‐h infusion of 10 μg/h CRH started 4 h before the presumed onset of the LH surge. This observation also indicates that the inhibitory effect of CRH may last for only 3–4 h. The surge of LH and FSH was not affected by i.c.v. injections of AVP‐antiserum. However, pretreatment with AVP‐antiserum prolonged the inhibitory effect of CRH on the LH surge. In conclusion, CRH can inhibit the pro‐oestrous LH and to a lesser extent the FSH rise for only 3–4 h after the beginning of CRH administration. AVP may play a role in

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05136.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Previous studies have shown that mu (μ) and kappa (κ) opioid antagonists inhibit suckling‐induced prolactin release. Prolactin responses elicited by pup suckling or opioid administration are mediated, at least in part, by suppression of dopamine (DA) release from tuberoinfundibular dopaminergic (TIDA) neurons in the hypothalamus. We examined the effects of the μ opiate receptor antagonist,β‐funaltrexamine (β‐FNA), and theκopiate receptor antagonist, nor‐binaltorphimine (nor‐BNI) on the activity of TIDA neurons in lactating rats. TIDA neuronal activity was determined by measuring DOPA accumulation in the caudate putamen (CP) and median eminence (ME). The effects of opioid antagonist treatment were determined in pup‐deprived (low circulating prolactin levels) or pup‐suckled rats (high circulating prolactin levels). The accumulation of 5‐hydroxytryptophan (5‐HTP) in the medial preoptic area (MPOA), the anterior hypothalamus (AH) and the median eminence (ME) was quantified as an index of serotonergic activity in the same animals f

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05207.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The distribution of oxytocin binding sites in the brain is highly variable among mammals. Using two species of microtine rodents (voles) with strikingly different patterns of oxytocin binding sites in the brain, we demonstrate that these differences are due to differences in region specific gene expression and not post‐translational processing. The distribution of oxytocin receptor mRNA closely resembles the distribution of oxytocin receptor binding sites in both species. Analysis of the 5′ flanking region of the oxytocin receptor gene from both species reveals few differences in potential regulatory elements which could explain the differences in gene expression. These data suggest that species differences in oxytocin receptor binding are due to species differences in: i) distant DNA sequences further upstream or downstream which may influence expression; ii) the distribution of regulatory proteins such as transcription factors in the brain or iii) epigenetic factors, such as prenatal and perinatal environment which may affect gene expression in the ad

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05188.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Two neurohemal organs of the cockroachLeucophaea maderae, the corpora cardiaca and the lateral heart nerve are known to contain leucokinin immunoreactive material. We examined the corpora cardiaca and the lateral heart nerve to establish whether these neurohemal organs store all 8 known leucokinin isoforms or if the leucokinins have a differential distribution. Extracts of corpora cardiaca and abdominal hearts with attached lateral heart nerve were separated on reversed phase high performance liquid chromatography (rpHPLC), then tested for leucokinin immunoreactivity by a radioimmunoassay (RIA) able to detect all 8 leucokinin isoforms. Extracts from brain and optic lobes were also separated and assayed in the RIA. Synthetic leucokinin 1–8 were subjected to rpHPLC and their different retention times established by RIA for reference. Leucokinin immunoreactive material originating from the corpora cardiaca and lateral heart nerves eluted in fractions corresponding to those of the synthetic leucokinin 1–8. In this study we have thus demonstrated that probably all 8 leucokinin isoforms are stored in the corpora cardiaca and the lateral heart nerve. These observations suggest that all 8 leucokinins are likely to be released as neurohormones into the circulat

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.05219.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The hypothalamic peptides arginine vasopressin (AVP) and oxytocin (OT) have been implicated as mediators of socio‐sexual behaviors in addition to their roles in osmolar homeostasis (AVP), milk ejection and uterine contractility (OT). Within 24 h of parturition, OT and AVP messenger ribonucleic acid (mRNA) levels increase in the hypothalamic paraventricular, and to a lesser degree, the supraoptic nucleus (PVN and SON) of the rat. We previously reported that the prepartum increase in OT mRNA is related to the spontaneous decline in progesterone levels prior to parturition. We also reported that increases in PVN and SON OT mRNA can be induced by exposing the ovariectomized rat to a steroid regimen that mimics the steroid milieu of pregnancy, namely sequential estrogen and progesterone and subsequent progesterone withdrawal. Levels of PVN and SON AVP mRNAs were not affected by progesterone withdrawal in late pregnant rats or the steroid regimen that increased OT mRNA in ovariectomized rats. These observations suggest that other factors, perhaps hormonal, may influence AVP mRNA levels. A decline in testosterone coincident with waning progesterone levels also occurs prepartum. Since peak levels of AVP mRNA prepartum coincide with the prepartum decline in testosterone, we questioned whether declining testosterone levels are important for the increase in AVP mRNA lev

ISSN:0953-8194    

DOI:10.1046/j.1365-2826.1996.52210.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY