摘要:

We have developed a model for combined morphological and functional in vitro studies of the isolated mediobasal hypothalamus (MBH) by considering two prerequisites: (1) the tissue must be well preserved, free of morphological artefacts and functionally unimpaired until the end of the in vitro incubation, and (2) the tissue must be processed for morphology in optimal conditions. To test our model we have studied some aspects of the luteinizing hormone-releasing hormone (LHRH) system in 4-month-old male Sprague-Dawley rats. After decapitation the MBH was isolated and put in a flask containing 0.5 ml Hepes-buffered Locke’s medium gassed by 5 ml/min of O2/CO2 (95%/5%) and shaken in a water bath at 37 °C. After a 10-min washing, the medium was changed twice at an interval of 20 min. After the in vitro incubation the tissue was satisfactorily preserved as judged by light- and electron-microscopic analysis. LHRH, somatostatin and thyrotropin-releasing hormone could be demonstrated by alkaline phosphatase or peroxidase-antiperoxidase im-munohistochemistry on semithin sections and by immunogold technique on thin sections. The LHRH secretion was close to basal values after 30 min of incubation (22.1 ± 4.8 pg/MBH) and then remained constant for another period of 20 min (17.6 ± 2.6 pg/MBH). During the second 20 min of incubation LHRH secretion increased in presence of 61.6 mM K+ (110.7 ± 8.7 pg/MBH). Thus the isolated hypothalamus was excitable until the end of the in vitro incubation. We conclude that this model can be successfully used for combined morphological and functional st

ISSN:0028-3835    

DOI:10.1159/000124745

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The potential involvement of the sympathoadrenal system in stress-induced secretion of peptides from the intermediate lobe of the pituitary gland and the activation of the pituitary-adrenal axis was studied. Male Wistar rats were subjected to control procedures, to sympathectomy by chronic administration (8 weeks) of guanethidine and/or to medullectomy by adrenal enucleation 9 weeks prior to exposure to forced immobilization stress for various periods of time. In intact or sham-operated rats, immobilization caused a prompt increase of circulating norepinephrine, epinephrine (EPI), corticosterone and of immunoreactive adrenocorticotropic hormone (ACTHi), α-melanocyte-stimulating hormone (α-MSHi) and β-endorphin (β-ENDi). Peak levels of pituitary hormones were found after 10 min of stress exposure, but fell to less than 30% of these levels after 2.5 h of immobilization. Adrenal medullectomy, which abolished the stress-induced release of EPI, reduced the acute increase of plasma α-MSHi and β-ENDi, but dit not influence the acute increase of plasma ACTHi during immobilization stress. Also in medullectomized plus sympathectomized rats, the initial stress response of circulating ACTHi was not different from that of controls. Adrenal medullectomy with or without additional sympathectomy caused a marked increase in plasma ACTHi concentrations after prolonged stress exposure. We conclude that: (1) catecholamines originating from the adrenalmedulla facilitate the stress-induced secretion of intermediate lobe peptides (α-MSHi, β-ENDi); (2) catecholamines from the sympathoadrenomedullary system do not contribute to the acute release of ACTH during immobilization stress; (3) the sympathoadrenomedullary system is involved in the secondary reduction of circulating ACTHi levels seen during prolonged

ISSN:0028-3835    

DOI:10.1159/000124746

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This study examines the effect of intracerebroventricular infusion of the ‘superactive’ somatostatin (SRIF) analogue cyclo-(N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe) on the plasma adrenocorticotrophic hormone (ACTH) response to hemorrhage in conscious sheep. Hemorrhage (15 ml/kg over 15 min) increased plasma ACTH from 55 + 20 to 815 ± 148 pg/ml at 30 min (p < 0.001). Infusion of the SRIF analogue intracerebroventricularly at 0.08 µg/min for 10 min prior to and for 60 min after commencement of hemorrhage resulted in a partial inhibition of the plasma ACTH response. Infusion of the analogue at 0.8 µg/min blocked the increase in plasma ACTH at 30 min. Plasma ACTH was 21 ± 3 pg/ml as control and 66 ± 47 pg/ml at 30 min. The SRIF analogue had no effect on plasma ACTH in the same animals in control experiments with no hemorrhage. These studies suggest that SRIF may act as a central inhibitor of ACTH release. The mechanism by which the SRIF analogue inhibits ACTH secretion is unknown but could involve inhibition of corticotropin-releasing factor release and/or an inhibition of ACTH release from the pituitary gland. The route of administration of the SRIF analogue and the finding that the SRIF analogue did not prevent systemic corticotropin-releasing factor stimulation of ACTH suggest an effect of the SRIF analogue in the hypo

ISSN:0028-3835    

DOI:10.1159/000124747

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In the present article we report that in vivo LHRH output as measured at the anterior pituitary following castration significantly increased, due to larger and more frequent LHRH signals arriving to this gland. This contrasts with the decreased amplitude and overall mean LHRH release of castrate males bearing a push-pull cannula within the hypothalamus. These divergent results have generated a new thesis regarding the role of gonadal steroids upon the LHRH pulse generator. This thesis submits that following castration there is an increased frequency and decreased amplitude of the LHRH signal from discrete loci within the medial basal hypothalamus, but an increased synchrony of LHRH release throughout the entire hypothalamus, resulting in an increased frequency and amplitude of LHRH arriving at the anterior pituitary.

ISSN:0028-3835    

DOI:10.1159/000124748

出版商:S. Karger AG    

年代:1987

数据来源: Karger