摘要:

The present study was carried out to investigate the effects of acute administration of the soluble glucocorticoid receptor agonist, decadron phosphate (DEC, dexamethasone sodium phosphate), on pituitary luteinizing hormone (LH) release in intact adult male rats. DEC was administered intravenously to individual groups of animals at a dose of either 0.05 or 0.5 mg DEC/kg, and the magnitude and time course of drug-induced alterations in plasma LH concentrations were evaluated. DEC was observed to elicit a dose-proportionate decrease in plasma LH within hours after systemic injection. Both doses of DEC significantly reduced the magnitude of exogenous LH-releasing hormone (RH; 10 ng/100 g b.w.)-induced increases in plasma LH at time points coincident with drug-induced decreases in basal LH release. During in vitro perifusion of isolated anterior pituitary tissue fragments, the administration of DEC, via the perifusate, at a concentration of 1.0 µg/ml had no impact upon basal LH release, but did effectively diminish LHRH-stimulated hormone release from perifused tissues. Intracerebroventricular injection of DEC also resulted in a decline in circulating LH. While intracerebroventricular (ICV) administration of 10 ng of DEC had no impact upon circulating LH, higher doses of 100 ng and 1.0 µg significantly depressed circulating LH levels in a dose-related manner. Both of these ICV doses were also found to diminish pituitary responsiveness to LHRH. Lastly, DEC was intravenously administered at a dose of 0.5 mg/kg to groups of orchidectomized and orchidectomized, testosterone (T)-treated male rats. The glucocorticoid receptor agonist had no effect upon circulating LH levels in orchidectomized rats treated with vehicle, but did diminish hormone release in animals injected with T (2 mg/kg b.w.) 24 h before DEC administration. These results demonstrate the acute inhibitory impact of the soluble glucocorticoid receptor agonist DEC on pituitary LH release in intact male rats. The present findings not only support previous reports that glucocorticoid receptor ligands may act directly at the level of the anterior pituitary to suppress LH release, but also provide new evidence that glucocorticoid receptors present within the central nervous system may mediate an inhibitory influence on the neuroendocrine regulation of the LH release. The current results also indicate that the sensitivity of the hypothalamic-pituitary LH neuroendocrine axis to the inhibitory action of glucocorticoids may be diminished in the absence of

ISSN:0028-3835    

DOI:10.1159/000125908

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The effects of noradrenergic and opioid peptidergic receptor blockade, either alone or in combination, on the electrical activity of luteinizing hormone-releasing hormone (LHRH) pulse generator were studied in ovariectomized rats fitted with chronically implanted electrode arrays in the medial basal hypothalamus. Both α- and β-adrenergic receptor antagonists, i.e. phenoxybenzamine (5 mg/kg i.v.) and propranolol (5 mg/kg i.v.), respectively, significantly increased the intervals between characteristic increases (volleys) in hypothalamic multiunit activity (MUA), which were associated with the initiation of LH pulses. In contrast to this, an opioid receptor antagonist naloxone (2 mg/kg i.v.) significantly decreased the intervals between the MUA volleys. Naloxone given after the injection of propranolol induced MUA volleys with a latency of a few minutes. However, when given after the injection of phenoxybenzamine, naloxone failed to induce such immediate MUA volleys. These changes in the intervals between the MUA volleys were faithfully reflected by the pulsatile LH secretion. These results suggest that norepinephrine facilitates LHRH pulse generator activity through both α- and β-adrenergic -eceptors, and that the action of opioid peptides on it requires an α-adrenergic receptor-mediated mecha

ISSN:0028-3835    

DOI:10.1159/000125909

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

A variety of neuroendocrine cells survive and express specific neuropeptide genes for long periods of time in slice explant cultures in the presence of serum. However, before use of these slice explant cultures as experimental models for physiological and pharmacological studies on the regulation of neuropeptide gene expression, it is first necessary to evaluate their characteristics in defined (e.g. serum free) media and to control for the spontaneous electrical and synaptic activity of neurons in these cultures. In this study, brain slices from postnatal day 4 rats were cultured in serum-containing media (SCM) for 12 days to allow thinning, and then maintained in a serum-free, defined media (SFM) for 6 days. Culture slices transferred to SFM appeared healthy and numerous neuroendocrine neurons containing messenger RNA (mRNA) encoding for LHRH and magnocellular neurons containing mRNA encoding for oxytocin (OT) were detected using in situ hybridization histochemistry (ISHH). Each of these neuronal subtypes robustly produced their appropriate gene products as determined by immunocytochemical analysis. Abundant magnocellular OT neurons were found in cultures grown in either SCM or SFM. In contrast, magnocellular vasopressin (VP) neurons were rarely detected under these conditions. Inhibition of spontaneous electrical and synaptic activity in these slice explant cultures was effectively achieved by incubation for the last 2.5 days of culture in the presence of tetrodotoxin (TTX; 10–6M).Densitometric single cell analyses after ISHH was performed on both LHRH and OT cells. Comparisons of the density values (corresponding to mRNA levels), from these slice explants, found that: (1) cellular LHRH mRNA levels decreased in the absence of serum, whereas cellular OT mRNA levels did not significantly change under these conditions; (2) the presence of TTX in the media resulted in an overall decrease in cellular LHRH mRNA values in both SCM and SFM, and (3) the OT neurons in these slice cultures appear to be composed of a heterogeneous population, with one cell subtype responding to TTX with an increase in cellular OT mRNA levels. These data show that factors in serum and spontaneous electrical activity can differentially influence mRNA levels of LHRH cells and magnocellular OT neurons in cultur

ISSN:0028-3835    

DOI:10.1159/000125910

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The effects of hypothyroidism duration on several factors implicated in GH secretion control were studied in the male rat at different maturity stages, ranging from the peripuberal period to adulthood. Thyroid ablation was performed on 22-day-old Wistar male rats maintained on a low iodine diet (T group). Age-paired controls (C group) were fed with the same diet, supplemented with potassium iodide. Subgroups of T and C animals (aged 32, 42, 52, 82 and 112 days) were studied 10, 20, 30, 60 and 90 days after surgery. After pentobarbital anesthesia, jugular blood was withdrawn before and 5 min after an intravenous TRH stimulus, for GH assay. Hypothalamic and pituitary tissues were obtained in order to measure GH, immunoreactive somatostatin (IR-SRIF) and growth hormone-releasing factor (IR-GRF). Growth rate and serum testosterone confirmed that C rats reached sexual maturity by day 30 of the study. Mean ± SE serum GH (ng/ml) increased (p < 0.05) in C animals from day 10 (38.5 ± 5) to day 30 (67.4 ± 7.3), with no significant variations thereafter. The same time sequence pattern was observed in pituitary GH concentrations. In T rats, both serum and pituitary GH decreased progressively from day 10 to 90, being significantly lower than in C at all times of the study. No GH response to TRH could be found in C groups. In contrast, GH increased significantly (p < 0.05) in T animals after TRH at days 20 and 30. Hypothalamic IR-SRIF concentrations (ng/mg protein) increased (p < 0.05) to adult levels in C rats between days 10 (15.7 ± 3) and 30 (26.3 ± 2.8), remaining unchanged thereafter. T animals showed the same pattern up to day 60. On day 90, IR-SRIF decreased abruptly in T (9.7 ± 2.9) as compared to both normal peers (30.8 ± 7.2; p < 0.01) and 60-day T rats (24.3 ± 5.1; p < 0.05). Hypothalamic IR-GRF (ng/mg protein) also increased (p < 0.05) between day 10 (2.9 ± 0.3) and 30 (4.3 ± 0.7) in C animals. This puberal rise did not occur in 30-day Trats, whose IR-GRF was lower (2.6 ± 0.3; p < 0.01) than in C. It can thus be concluded that a decrease in pituitary GH availability is not the only factor implicated in the abnormal GH secretion found in hypothyroidism. An enhanced GH response to TRH was found to coexist with a 94% reduction in pituitary GH content on days 20 and 30 of hypothyroidism. In the normal rat, hypothalamic IR-SRIF and IR-GRF content increased to adult values in the puberal period. The influence of hypothyroidism on the hypothalamic IR-SRIF content is closely related to its duration, occurring only in long-term thyroid deprivation. Hypothyroidism also prevents the puberal rise of IR-GRF, but does not affect the concomitant increase of IR-SRIF. The blunting of the puberal rise in IR-GRF occurs despite the normal testosterone increase in hypothyroid rats, suggesting that the diminished concentration of thyroid hormone impairs the testosterone-mediated I

ISSN:0028-3835    

DOI:10.1159/000125911

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

After bilateral superior cervical ganglionectomy (SCGx) in adult male rats, norepinephrine content of the pituitary neurointermediate lobe () decreased at 12–24 h after surgery to attain concentrations 40–60% of controls between 24 and 60 h after surgery. To assess arginine vasopressin (AVP) secretion during this time, plasma and -AVP levels were measured by radioimmunoassay. In sham SCGx controls, plasma AVP increased about 2-fold within 6 h after surgery and decreased thereafter, to attain presurgical values by 60 h after surgery. In SCGx rats, a significant increase in plasma AVP concentration was observed at the 6th h after surgery, as compared to presurgical concentrations, with a decrease to values significantly lower than those of presurgical controls at 16–18 h after SCGx. As compared to sham-operated rats, significantly higher plasma AVP levels 6 h after surgery and significantly lower plasma AVP levels 16–24 h after surgery were found. -AVP concentration in SCGx and sham-operated ras were significantly lower than presurgical levels at 6 h after surgery. SCGx rats had significantly higher amounts of AVP in at 16–24 h after surgery. The changes in plasma and -AVP levels found 6 or 16 h after SCGx or sham SCGx were unaffected by a prior pinealectomy. Two injections of the α1-adrenoceptor blocker prazosin 45 and 90 min before sacrifice, alone or together with the β-blocker propranolol, prevented the increase in plasma AVP found in SCGx rats 6 h after surgery, and the decrease in plasma AVP and the increase of -AVP found 16 h after SCGx. Propranolol treatment did not modify AVP levels. Neither drug was effective to modify AVP levels in sham-operated controls. The results argue in favor of physiologically relevant projections from superior cervical ganglion neurons to the neurohypophysis which participate in control of

ISSN:0028-3835    

DOI:10.1159/000125912

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Defective regulation of hypothalamic gonadotropin-releasing hormone (GnRH) secretion is the primary defect leading to the inhibition of pituitary gonadotropin secretion and its consequences such as androgen deficiency and infertility in experimental uremia. Previous studies using indirect methods to study presumptive GnRH release and the function of GnRH-secreting neurons have suggested functional disturbances of GnRH neurosecretion; however, the precise biochemical mechanisms involved were not defined. Therefore, in order to clarify the mechanisms of aberrant regulation of hypothalamic GnRH secretion in experimental uremia, we examined basal secretion of GnRH from mediobasal hypothalamus (MBH) in vitro and the GnRH-secretory responses to naloxone, an opiate receptor antagonist in experimental uremia. Using a static incubation system, adult male rats, either intact or castrate, with subtotal nephrectomy demonstrated a significant reduction of GnRH secretion by 25% in intact and by 40% in castrate uremic male rats compared with their nonuremic controls. In contrast, hypothalamic GnRH content of uremic animals was increased significantly (6% in intact and 14% in castrate uremic rats). Despite the fall in basal GnRH release from MBH, the MBH GnRH release response to in vitro stimulation by an opioid blocker (naloxone) and a membrane-depolarizing agent (veratrine) were not diminished in uremic male rats. These findings suggest that the inhibition of pituitary gonadotropin secretion in experimental uremia is likely to be due to a functional defect in suprahypothalamic regulation of GnRH secretion rather than an intrinsic defect in the GnRH-secreting neurons. Further studies are required to clarify the nature of the neuromodulator interactions involved.

ISSN:0028-3835    

DOI:10.1159/000125913

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Possible antagonism between somatostatin (SS) and Carp growth hormone-releasing factor (GRF) on growth hormone (GH) secretion was examined by radioimmunoassay in a dispersed rainbow trout pituitary cell culture system. SS (3 nM) significantly antagonized Carp GRF(l-29; 1 nM, 10 nM)-induced GH secretion. The slope of the dose-response curve for Carp GRF(1–29) with SS was statistically different from that of carp GRF(1–29) alone (p < 0.05) suggesting a noncompetitive antagonism of SS to carp GRF. The Carp GRF(1–29) was also indicated to be a noncompetitive antagonist to SS (p = 0.056). Carp GRF(1–29; 100 nM) was unable to restore the inhibitory effect of SS on GH release after pre-exposure of SS (30 nM) to the pituitary cells. We conclude that SS antagonizes Carp GRF on GH release at the pituitary level in rainbow trout and this antagonism is noncompetitive. SS has a postantagonism to Carp GRF which may implicate some important physiological adaptations in t

ISSN:0028-3835    

DOI:10.1159/000125914

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Using the single-section Golgi impregnation technique, sex differences in hypothalamic ventromedial (VMN) neurons of gonadectomized juvenile and peripubertal rats were assessed. The effect of estrogen treatment on VMN neurons was also investigated. Juvenile rats were gonadectomized at 16 days of age and peripubertal rats at 36 days. At 5 days after surgery, the rats were injected with estradiol benzoate (20 µg/kg) or sesame oil for 2 days after which they were perfused and the brains processed for Golgi impregnation. Estradiol benzoate treatment significantly increased dendritic and soma spine density in juvenile and peripubertal male and female rats. A sex difference was observed in oil- and in estradiol-treated rats, with females exhibiting higher dendritic spine density and a greater response to estrogen priming. Moreover, dendritic and soma spine density was significantly higher in juvenile versus peripubertal rats. It is possible that the sex difference observed in dendritic and soma spine density and in the response to estradiol benzoate treatment is due to an organizational effect of sex steroids

ISSN:0028-3835    

DOI:10.1159/000125915

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The recent development of GnRH-secreting neuronal cell lines (GT1-1, GT1-3 and GT1-7 clones) has provided a model system for the study of the neural regulation of GnRH expression and secretion. We report here that activin-A stimulates GnRH secretion by GT1-7 cells in a dose-dependent manner, with an EC50 of ∼2.5 ng/ml. The maximal response (50% stimulation) was achieved after 2 days of incubation with 20 ng/ml activin-A. Activin-A treatment increased total GnRH (secreted + cellular) in GT1-7 cells, possibly reflecting a stimulation of GnRH biosynthetic rates. The secretory effect of activin-A was also accompanied by a change in the cellular morphology to a more neuronal phenotype. The addition of TGF-β (10 ng/ml), which is structurally related to activins, did not significantly increase secretion of GnRH by GT1-7 cells illustrating the specificity of the activin effect on this cell line. Although inhibin (20 ng/ml) alone did not directly affect the spontaneous secretion of GnRH, it was able to partially block the stimulatory effect of activin. The present study with the GT1-7 clonal cell line suggests that activin, and perhaps inhibin, might act at hypothalamic sites to regulate reproduction through the control of GnRH production and/or secreti

ISSN:0028-3835    

DOI:10.1159/000125916

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The push-pull perfusion technique, in conjunction with specific radioimmunoassays, was used to monitor the release of both arginine vasopressin (AVP) and oxytocin (OXT) within distinct limbic brain areas of conscious female rats. In pregnant rats near term, the release of AVP was greater than that of virgin rats in both the ventral (p < 0.001) and mediolateral (p < 0.001) septal areas; similarly, release of OXT increased in the ventral septal area (p < 0.01) at this time. In contrast, no changes in the levels of either peptide occurred in the dorsal hippocampus. In parturient rats, AVP release tended to decrease in the septal areas but increased fivefold in the dorsal hippocampus (p < 0.001) compared to pregnant animals. In contrast, OXT levels assayed in the same perfusates did not differ from those observed in pregnant animals. Plasma levels of AVP in pregnant rats (p < 0.05) and of OXT in parturient animals (p < 0.01) were found to be increased over levels in virgin rats. The regionally different and peptide-specific changes in release pattern of AVP and OXT in virgin, pregnant and parturient rats may be of physiological significance in antipyresis and behaviors accompanying parturition.

ISSN:0028-3835    

DOI:10.1159/000125917

出版商:S. Karger AG    

年代:1991

数据来源: Karger