摘要:

Glass microknife lesions and immunocytochemistry were used to evaluate luteinizing hormone-releasing hormone (LH-RH)- and somatostatin (SS)-immunoreactive pathways from the preoptic region to the rat median eminence.Cuts were so placed that axons of more caudally located neurons in the periventricular hypothalamic areas were spared. Light and EM observations of LH-RH-immunostained preparations indicated that following the midline periventricular cuts the density of LH-RH labelled axons and axon terminals in the ME appeared similar to that of nonlesioned animals. Following bilateral lateral hypothalamic cuts placed between the preoptic area and the ME, LH-RH immunostaining in the ME was markedly reduced. This provides evidence that the preponderance of LH-RH axons originating from the preoptic area reach the ME by a lateral hypothalamic route. In contrast to the LH-RH findings, midline lesions made using the same coordinates caused a noticeable reduction in SS immunostaining in the arcuate nucleus and ME. There was either no change or only minimal change after the lateral cut. Somatostatin axons arising from the preoptic periventricular nucleus take a periventricular route and contribute to median eminence innervation, but much less extensively than the more caudally located somatostatin neurons in the hypothalamic periventricular nucleus [19].

ISSN:0028-3835    

DOI:10.1159/000123886

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

We investigated whether astroglial cells are a site of action for the effect of melatonin on brain cyclic AMP content. Rat astroglial cell subcultures, identified according to morphological and immunochemical criteria, were used. Addition of melatonin to the cultures did not result in changes of cyclic AMP content. However, melatonin at 0.1–1 µM concentrations was able to impair the cyclic AMP increase elicited by 1 µM norepinephrine or isoproterenol in astroglial cultures. This melatonin effect was also shared by its biologically active analogues 5-methoxytryptophol and 6-chloromelatonin. Serotonin was only effective at a 100-fold greater concentration, while the biologically inactive melatonin metabolite 6-hydroxymelatonin was devoid of activity at any concentration used. These results suggest that methoxyindoles modulate negatively β-adrenoceptor-induced cyclic AMP accumulation in cultured rat astroglial c

ISSN:0028-3835    

DOI:10.1159/000123887

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Cysteamine (CSH) has an inhibitory effect on the secretion of PRL, GH and TSH. The purpose of the present study was twofold: (1) to examine the short-term effects of CSH on PRL secretion, and (2) to elucidate the mechanism of action of CSH. CSH (100 mg/kg) was injected as an intra-atrial bolus to both normal and estradiol-primed male Sprague-Dawley rats. Blood samples were drawn every 2 min for 1 h and assayed for PRL. To determine if the actions of CSH involved PIF release or PIF receptors, a dopamine receptor blocking agent, pimozide (100 µg/kg) was given intra-atrially 1 h after the CSH injection and PRL concentration was monitored. Within 6 min after the CSH injection PRL levels in estradiol-primed rats began to fall, and by 30 min postinjection the levels were well below baseline values. Blocking the dopamine receptors with pimozide did not result in increased PRL levels, indicating that CSH was acting through some mechanism not directly involving dopaminergic PIF receptors. In a separate study, 6 min after the injection of CSH the rats were decapitated and their anterior pituitaries were removed and processed for electron microscopy. Only mammotrophs from estradiol-primed rats treated with CSH showed an extensive rearrangement of rough endoplasmic reticulum (RER) in concentric whorls around the periphery of the cells. These studies show that the inhibition of PRL secretion by CSH begins within 6 min, and is appreciable only when basal PRL levels are increased by estrogen priming. The inhibition by CSH is not mediated through stimulation of PIF release, or PIF receptors or cellular degeneration, but appears to involve rearrangement of RER into a physical obstacle

ISSN:0028-3835    

DOI:10.1159/000123888

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Mediobasal hypothalamic (MBH) slices of male adult rats were superfused at 37 °C with oxygenated Hepes-buffer Locke medium. Bacitracin (2 × 10–5MJ was added to prevent enzymatic degradation of LHRH and SRIF. 6 min pulse of K+ (56 mM), veratridine (15 µM) or the ionophore A 23187 (10–5M), markedly stimulated the release of both neuropeptides. Trifluoperazine, a calmodulin inhibitor, decreased the K+-evoked LHRH and SRIF release in a dose-dependent manner; it was also effective in inhibiting the veratridine-induced neuropeptides release. Phenytoin, a calmodulin-dependent kinase inhibitor, also decreased in a dose-dependent manner the K+-induced LHRH and SRIF release; the basal release of both neuropeptides remained unaffected by either treatment. The ionophore-stimulated release of both neuropeptides was significantly inhibited as well. These data demonstrate that a Ca++-calmodulin kinase system may be involved in the mechanism of depolarization-induced LHRH and SRIF release from hypothalamic nerve ter

ISSN:0028-3835    

DOI:10.1159/000123889

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The purpose of this study was to examine the 24-hour variation in endogenous tyrosine hydroxylase (TH) activity and thus catecholamine (CA) synthesis in the hamster and rat pineal gland. To determine CA synthesis a time course of the accumulation of dihydroxyphenylalanine (DOPA) after DOPA decarboxylase inhibition with m-hydroxybenzylhydrazine (NSD-1015) was measured at 0, 15 and 30 min by liquid chromatography with electrochemical detection. Animals were under long photoperiods (LD 14:10; lights on at 06.00 h). In the hamster pineal gland, CA synthesis was greater in the dark (24.00 h) (0.017 ng/pineal/min) than in the light (12.00 h) (0.008 ng/pineal/min). Similarly, CA synthesis in the rat pineal was 0.037 ng/pineal/min (dark) and 0.005 ng/pineal/min (light). In a 24-hour study, animals were injected with NSD-1015,30 min prior to killing to determine if 24-hour changes were present in CA synthesis. In the hamster, DOPA in the dark (p < 0.001) was significantly greater than in the light (1.33 ± 0.42 ng/pineal at 06.00 h; 0.33 ± 0.07 at 13.00 h) in this study. No significant difference was measured in norepinephrine (NE) concentration during this 24-hour period. In the rat, DOPA accumulation was significantly different (p < 0.001) in the dark as compared to the light (0.86 ± 0.09 ng/pineal at 03.00 h; 0.21 ± 0.08 at 12.30 h). Within this 24-hour period, NE concentration fluctuated significantly between 2.28 ± 0.33 ng/pineal (15.30 h) to 4.65 ± 0.59 (05.30 h). These results indicate for the first time a definite 24-hour rhythm in endogenous TH activity and NE synthesis in the hamster pineal gland even though NE content does not change. In addition, a 24-hour change in CA synthesis and content is present in the rat pineal

ISSN:0028-3835    

DOI:10.1159/000123890

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The differential role of porcine follicular fluid (pFF) in regulating follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release in vivo in situations of different gonadotropin releasing hormone (GnRH) backgrounds was studied. In experiment 1, 2-week ovariectomized rats injected intravenously with 4, 16 or 64 mg of protein from pFF, showed a dose-dependent suppression of FSH over time, with a maximal suppression to 40% of control values by 10 h. LH levels were slightly, but significantly, elevated by the two lower doses, but not by the highest dose of pFF. In experiment 2,64 mg pFF was superimposed (i.v. injection) in ovariectomized rats injected subcutaneously with a high dose of GnRH antagonist (500 µg) 24 h earlier. The pFF suppressed FSH 35% below the level achieved in the absence of GnRH stimulation, with no effect on LH. In experiment 3, the rise in FSH secretion in acutely ovariectomized rats was shown to be inhibited by 8 or 32 mg pFF administered intravenously 3.5 h after surgery. Injection of GnRH (250 or 1,000 ng) 4.5 h after pFF could not overcome the inhibitory action of pFF on FSH, although non-pFF-treated controls responded in a dose-dependent fashion to GnRH stimulation. The expected LH response to GnRH was not affected by pFF, except in the group receiving 1,000 ng GnRH and 8 mg pFF. In these rats, LH was enhanced in one trial, but suppressed in a replicate trial, illustrating the inconsistent effects of pFF on LH under conditions of high GnRH stimulation. These results demonstrate the existence of a component of FSH secretion which is independent of GnRH, but sensitive to the inhibitory effect of pFF, suggesting a site of action of the putative peptide hormone, folliculostatin, distal to the GnRH receptor. Also, pFF always suppresses FSH (due to the action of folliculostatin); its effect on LH depends on the dose and the state of GnRH stimulation, and is probably not a function of folliculostatin per se

ISSN:0028-3835    

DOI:10.1159/000123891

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

To clarify the role and site of action of γ-aminobutyric acid (GABA) in ovine pineal glands, we have investigated the effects of aminooxyacetic acid (AOAA), an inhibitor of GABA transaminase, on endogenous GABA content and β-adrenoceptor mediated pineal function in Merino sheep. A significant elevation of endogenous GABA levels was noted in the glands, but no effect was observed on radioligand binding in vitro to pineal β-adrenoceptors following in vivo administration of AOAA. Incubation of washed pineal membranes with GABA or AOAA had no effect on ligand binding to β-adrenoceptors. Incubation of Merino pineal slices with GABA inhibited isoprenaline-stimulated but not basal serotonin N-acetyltransferase (NAT) activity. Incubation of whole pineal homogenates with GABA was without effect on either isoprenaline-stimulated or basal adenyl cyclase activity. Thus, Merino pineal glands resemble bovine pineals in that β-adrenoceptor mediated melatonin biosynthesis in both species may be regulated in part by GABA. Our results indicate that GABA may exert its effect on Merino pineal NAT activity at a locus distal to the site of action of adenyl cyclase; however, the detailed mechanism and physiological role of this regulation remain to be elucid

ISSN:0028-3835    

DOI:10.1159/000123892

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Tissue specimens of human hypothalami, pituitaries and gastrointestinal tract were studied with an indirect immunoperoxidase technique using 6 different rabbit ovine corticotrophin-releasing factor (oCRF-41) antisera. All these antisera detected oCRF-41-like immunoreactivity in parvocellular neurones of the paraventricular nucleus of the hypothalamus and their nerve terminals adjacent to portal capillaries in the infundibular stem and posterior pituitary. 1 antiserum recognised oCRF-41-like immunoreactivity in the growth hormone cells of the anterior pituitary. 3 other antisera recognised oCRF-41-like immunoreactivity in mucosal cells of the gastric antrum. Pre-treatment of the antisera with sauvagine did not affect the immunostaining of the hypothalamic and gastric cells, but quenched the immunostaining of growth hormone cells in the anterior pituitary. It is concluded that (1) in human hypothalami a CRF is synthesized that is structurally very similar to oCRF-41; (2) in growth hormone cells of the anterior pituitary oCRF-41-like immunoreactive material can be detected which shares antigenic determinants with sauvagine; (3) in mucosal cells of the gastric antrum oCRF-41-like immunoreactivity is present that is comparable but probably not identical to hypothalamic CRF and is not sauvagine-like.

ISSN:0028-3835    

DOI:10.1159/000123893

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The influence of gonadoliberin (GnRH) on the differentiation of rat gonadotrophs in early fetal life was studied both in vivo and in vitro by immunocytology with anti-porcine luteinizing hormone β (pLHβ) serum. Adenohypophysial primordia explanted from 11 to 13 days of gestation were maintained in organ culture in synthetic Parker’s 199 medium enriched with insulin (0.5 µg/ml) and transferrin (5 µg/ml). Cultures lasted to approximate the usual gestation period (21 days). Synthetic GnRH (10–9 or 10–12M) was added to the culture medium during the first day of culture only. In contrast to a previous report, immunoreactive cells were detected in the primordia explanted either at 11 or 12 days of gestation only when cultured in the presence of GnRH. The appearance of positive localization was seen by 17 days. No differences due to GnRH dosage were observed in the mean cytoplasmic area of the cells in the different experimental groups as seen at the equivalent of 21 days. GnRH was not effective in a medium deprived of insulin. GnRH, added 6 h before the end of the culture, could also release the secretory product of gonadotrophs which recently developed the presence of immunoreactive pLHβ material. In these conditions, GnRH was shown to enter the cells as observed by immunocytochemistry on sections obtained after cryoultramicrotomy. Endogenous GnRH was also detected by the same technique in fetal pituitary glands removed from 14 to 21 days of gestation. It was always localized in agranular cells and from 18 days in some granular cells considered as gonadotrophs. In the early fetal life transfer of GnRH from the maternal to the fetal side is very unlikely since very small amounts of radioactivity were detected in 11-day-old fetuses after injection of [125I]-GnRH into pregnant rats. These results suggest that GnRH can stimulate the differentiation of gonadotrophs in early fetal life in synergy with insulin. This is supported by the intracellular presence of GnRH which is most likely of fetal origin, the possibility of the existence of a placental GnRH-like substance being not completel

ISSN:0028-3835    

DOI:10.1159/000123894

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In the Djungarian hamster Phodopus sungorus, the daily temporal pattern of synthesis and release of pineal hormone melatonin, mainly the length of the period of elevated melatonin levels, may be involved in transferring the information on day length to the neuroendocrine-gonadal axis. The present study investigated the time course of adjustment of the rhythm in melatonin production and concentration to the change from long to short photoperiods. Adult female Djungarian hamsters, maintained on a regime of 16 h of light and 8 h of darkness per day (LD 16:8) were transferred to the LD regime 8:16 and the daily rhythms in the pineal melatonin concentration and in the pineal N-acetyltransferase activity, as an indicator of melatonin formation, were studied at various intervals following the transfer. Under LD 16:8, the nocturnal melatonin concentration was elevated for 4.8 h. After 3 days on LD 8:16, no extension of the period of high melatonin levels occurred. 2, 4 and 6 weeks after the transfer to LD 8:16, the period of elevated melatonin levels lasted for 8.1, 9.3 and 11.5 h, respectively. Extension of the melatonin pattern proceeded first predominantly into the morning hours. Only after this extension was completed, a considerable extension into the evening hours began. Extension of the N-acetyltransferase rhythm on short photoperiods proceeded in the same way as that of the melatonin rhythm. The data show that while a change in the photoperiod might be seen by hamsters within 2 weeks after the transfer to LD 8:16, the full shortening of the photoperiod might be recognized only within 6 weeks or later. It is suggested that the gradual extension of the melatonin rhythm might play a role in the time course of adjustment of the reproductive system of Djungarian hamsters to short photoperiods.

ISSN:0028-3835    

DOI:10.1159/000123895

出版商:S. Karger AG    

年代:1984

数据来源: Karger