摘要:

These studies investigated the effects of neuropeptide Y (NPY) on in vitro release of luteinizing hormone-releasing hormone (LHRH) from the medial basal hypothalmus (MBH) and tested whether ovarian steroids modulate the LHRH response to NPY. Ovariectomized rats were implanted with 20-mm-long Silastic capsules containing a low concentration of estradiol (E2) (150 µg/ml oil), a high concentration of E2 (250 µg/ml oil), or sesame oil vehicle. Additional animals received high-dose E2 capsules plus an injection of progesterone (15 mg) concomitantly. Two days later, individual MBH fragments were incubated in medium alone for a 30-min period to obtain the basal rate of LHRH release, followed by a second 30-min period in medium containing NPY or saline. Exposure to NPY (10–6M) increased the release of LHRH from MBH of ovarian hormone-treated, but not from hormonally untreated rats. The LHRH response was most pronounced from the MBH of rats treated with either high-dose E2 or E2 plus progesterone. The increase in LHRHrelease was also elicited by 10–7M, but not by 10–8M NPY concentrations, using MBH from E2 plus progesterone-treated rats. In addition, NPY markedly potentiated the KCl-evoked release of LHRH from MBH of ovariectomized, hormonally untreated or low-dose E2-treated rats, under conditions when there was little or no effect of NPY on the basal LHRH release. Further, the release of LHRH stimulated by NPY was not accompanied by increase in the release of norepinephrine or of dopamine. These results strongly suggest that the NPY stimulation of LH secretion after intracerebral administration in steroid-primed rats occurs, in part, as a result of increased release of LHRH. NPY may act at the level of the LHRH neurosecretory terminals in the median eminence as well as at additional sites containing LHRH pe

ISSN:0028-3835    

DOI:10.1159/000124804

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study was undertaken to determine the role of the hypothalamic periventricular (PV) region in the regulation of the secretory pattern of growth hormone (GH) in adult male rats. The PV regions were destroyed stereotaxi-cally by means of a modified Halasz’s knife which was lowered through the midline and rotated several times at the level of the region. In sham-operated controls, the knife was lowered to the same region but no rotation was performed. Serial blood samplings were performed at 10-min intervals for 10 h (10.00–20.00 h), via an intracardiac cannula, at 2, 4 and 6 weeks postoperatively. In 7 sham-operated controls, GH was secreted with a surge period of about 3.5 h, with peak levels of 120–170 ng/ml whole blood and basal levels of about 10 ng/ml whole blood. In 11 PV-lesioned animals, the basal levels of GH were unaltered but the surge period decreased to about 3.0 h and peak levels increased to about twice as high as in sham-operated controls. Somatostatin concentrations in the median eminence of PV-lesioned rats were significantly decreased to about 32% of that of sham-operated rats. The results suggest that, via somatostatin neurons, the PV region plays an inhibitory role in the regulation of periodicity and peak levels of GH secretory b

ISSN:0028-3835    

DOI:10.1159/000124805

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study was concerned with the effects of a transplantable prolactin-secreting pituitary tumor (7315b) on the hypothalamic release of dopamine, luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) in gonadectomized, adrenalectomized male rats bearing subcutaneously a testosterone capsule and a corticosterone pellet. Similar male rats not inoculated with tumor served as controls. The rats were studied 3–4 weeks after tumor inoculation, while they were anesthetized with urethane. Compared to the controls, prolactin levels in the tumor-bearing rats had increased 70-fold, whereas the levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) decreased to 20 and 27%, respectively. In tumor-bearing rats, the secretion of dopamine into hypophysial stalk plasma increased from 2.3 to 4.9 ng/h (p < 0.025), whereas that of LHRH decreased from 127 to 52 ph/h (p < 0.005). Since the use of urethane anesthesia may change quantitatively and qualitatively the effects of hyperprolactinemia, it was decided to study these effects on the in vivo release of LHRH, dopamine and TRH in conscious rats by a push-pull perfusion of the median eminence-arcuate nucleus area. Using this technique, it was found that in tumor-bearing rats the secretion of LHRH decreased from 20.0 to 9.8 pg/15 min·(p < 0.005), whereas that of dopamine increased from 118 to 246 pg/15 min (p < 0.025). The secretion of TRH was not altered by hyperprolactinemia (4.1 vs. 4.4pg/15 min). Thus, push-pull perfusion experiments in conscious, freely moving rats confirm what was found in hypophysial stalk blood obtained from rats under anesthesia, namely, that hyperprolactinemia stimulates dopamine release and inhibits LHRH release. This study also indicates the value of using conscious rats to determine simultaneously the in vivo output of several substances from the hypothalam

ISSN:0028-3835    

DOI:10.1159/000124806

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This study examined the effect of electrical stimulation of the ventral mesencephalic tegmentum versus the dorsal tegmentum region on blood LH levels in freely moving, ovariectomized (OVX) rats, as well as in OVX, estrogen-primed rats. In OVX rats, electrical stimulation (with parameters of 30 Hz, 0.4-msec biphasic pulses, 50–100 µA and 10 s on/off for 1 h) of the ventral tegmentum region with the aim of activating the ventral noradrenergic tract (VNT) failed to affect the pulsatile pattern of blood LH levels characteristic of OVX animals. In sharp contrast, electrical stimulation of the dorsal tegmentum region inside the ascending dorsal noradrenergic tract (DNT) markedly inhibited pulsatile LH release in OVX rats; the mean blood LH levels during the 1-hour stimulation period were significantly decreased when compared with prestimulation control values. Electrical stimulation in the same region near but outside the DNT was ineffective. In OVX rats primed with estradiol benzoate, electrical stimulation in the ventral or dorsal tegmentum region failed to alter the low, nonpulsatile blood levels of LH. The results in OVX rats suggest that selective activation of the ascending noradrenergic fibres of the DNT but not the VNT can inhibit pulsatile LH release in the awake, freely moving animal. These data further support the possible existence of an inhibitory noradrenergic system in the modulation of LH relea

ISSN:0028-3835    

DOI:10.1159/000124807

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Since reports on the influence of melatonin (aMT) on the human endocrine system are scant and inconsistent, the effect of an acute, pharmacological dose of aMT on various hormone levels in healthy males was examined in 3 different experiments. Experiment I: 80 or 240 mg of crystalline aMT were administered per os to 8 volunteers. Before, during and after this treatment, serum levels of aMT, PRL, LH, FSH and testosterone were examined. Although aMT increased at least 1,500-fold over basal levels, only PRL was significantly and consistently elevated after aMT treatment, whereas serum levels of the other hormones were not altered. Experiment II: in 2 subjects, the pulsatile secretion pattern of LH was monitored for 6 h before and 6 h after aMT administration (240 mg p.o.). Neither the amplitude nor the frequency of LH pulses was influenced by the pineal hormone. Experiment III: in 14 volunteers, serum PRL, GH, TSH and cortisol concentrations were examined, once after oral administration of 240 mg aMT and once after placebo. Serum PRL levels were significantly higher after aMT than after placebo; GH showed a slight but not significant trend towards elevation after aMT, whereas other hormones were not altered. An acute pharmacological dose of aMT causes isolated elevation of serum PRL levels and may slightly increase GH. Hormones of the pituitary gonadal axis as well as TSH and cortisol are not altered by aMT.

ISSN:0028-3835    

DOI:10.1159/000124808

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The concentration of calcitonin gene-related peptide (CGRP) in rat tissue extracts was determined by a specific and sensitive radio-immunoassay, and the distribution of its specific binding sites was assessed by radioligand binding studies. A high concentration of immunoreactive CGRP was found at all levels of the spinal cord, in the trigeminal nucleus, in trigeminal and dorsal root ganglia, in the thyroid gland, in blood vessels and in nerves. The highest density of specific binding sites was detected in the cerebellum, where the CGRP content was minimal. The dorsal portion of the spinal cord contained a high concentration of CGRP and its specific binding sites. Specific binding of 125I-CGRP was also demonstrated in a number of other areas of the brain and in certain peripheral tissues. Among the other tissues examined, the spleen, adrenal gland, penis, lungs, bladder, heart and blood vessels all contained a large number of CGRP binding sites, whereas only a negligible number of sites were found in ganglia, nerves, muscle, kidney and liver. The distribution of CGRP and its specific binding sites demonstrated here suggests that CGRP is a neuropeptide with multiple physiological roles.

ISSN:0028-3835    

DOI:10.1159/000124809

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Pulsatile growth hormone (GH) secretion was compared in young (5 months), middle-aged (11 months) and old (25–29 months) female Sprague-Dawley rats under nonanesthetized, free-moving conditions. Mean plasma GH levels were 99.1 ± 9.3 ng/ml in young rats, 56.3 ± 5.8 ng/ml in middle-aged rats and 49.7 ± 4.9 ng/ml in old rats (p < 0.01 for young vs. middle-aged and old rats). In young females, 10 out of 17 rats had GH pulses with peak levels greater than 200 ng/ml, in 6 middle-aged females all GH peaks were below 200 ng/ml, and in old females 13 out of 17 rats showed GH peaks of less than 100 ng/ml. The average peak (amplitude) of GH pulses in the old rats (69.3 ± 8.3 ng/ml) was lower than in the young rats (130.4 ± 17.5 ng/ml, p < 0.01) and somewhat lower than in the middle-aged rats (87.0 ± 8.9 ng/ml). There was no change in intervals between GH pulses. Pituitary GH content in middle-aged and old females (1,189 ± 60 and 1,100 ± 89 µg, respectively) was significantly lower (p < 0.05 and p < 0.01, respectively) than in young female rats (1,464 ± 76 µg). Somatostatin content in the median eminence of old rats (22.4 ± 1.9 ng) was significantly lower than in young rats (28.5 ± 1.6 ng, p < 0.05). It is concluded that GH secretion is reduced in aging female rats, but unlike in aging male rats the decrease is seen at an earlier age. This may account for the relatively early body growth stasis observed in female but not in male rats. Among the possible causes for the decline in GH secretion with aging in these rats are an increase in somatostatin release and a decrease in GHRH release, associated with a reduction in hypothalamic catechol

ISSN:0028-3835    

DOI:10.1159/000124810

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In order to study the involvement of the hypothalamic corticotropin-releasing factor (CRF) in catecholamine-induced adrenocorticotropin (ACTH) secretion, we have measured CRF levels in rat hypophysial portal blood (HPB) after the pharmacological destruction of the ventral noradrenergic bundle (VNAB), using 6-hydroxydopamine (6-OHDA) stereotaxically injected into the VNAB. CRF levels in HPB were measured by radioimmunoassay, and the effects of 6-OHDA injection were controlled by the determination of catecholamine concentrations in the total hypothalamus. VNAB lesions induced a dramatic decrease in norepinephrine and epinephrine hypothalamic concentration. The CRF levels in HPB were also significantly reduced. These results suggest that central catecholamines exert a direct stimulatory control on the CRF release and play a major role in stress-induced ACTH secretion.

ISSN:0028-3835    

DOI:10.1159/000124811

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The concomitant release of corticotropin-releasing factor (CRF), vasopressin (AVP) and somatostatin (SRIF) has been followed from primary cultures of rat hypothalamic neurons. 18-day-old fetal rat hypothalami were dissociated enzymatically and mechanically, then plated and maintained in a serum-containing medium at a density of 2.5 × 106 cells per dish (equivalent to 3 hypothalami). Cultured neurons remained viable for up to 6 weeks, and peptide release was followed by immuno-assay between days 14 and 39 in culture. The incubation media were concentrated on C4 and C8 silica columns to facilitate detection of CRF and AVP. Peptide release was measured at various times up to 4 h, at which point it was still increasing. To optimise measurements, taking into account peptide degradation, a 1-hour incubation period was chosen for further studies. Release of CRF, AVP and SRIF by 56 mM K+ or 10 µM veratridine was statistically significantly greater than basal (p < 0.01) and was Ca2+-dependent. For CRF and AVP, stimulated release increased considerably with the age of culture, whereas SRIF release was steadier. Basal release for all 3 peptides did not fluctuate greatly over this period. Basal and stimulated release of the peptides continued over at least 5 successive 1-hour periods. At day 35 of culture, the peptide content was still increasing in a pattern which paralleled the increasing content in hypothalami freshly removed from age-matched rats. In conclusion, we have demonstrated a development of CRF, AVP and SRIF production by neurons over extended periods in culture as assessed by their peptide content and increasing responses to depolarizing stimuli. Such a system should prove useful in the study of the effects of environmental factors such as steroids, peptides and neurotransmitters on the maturation of peptidergic neurons and the synthesis and release of CRF, AVP and SRI

ISSN:0028-3835    

DOI:10.1159/000124812

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Immunocytochemical studies have identified immunoreactive prolactin (IR-PRL) in the hypothalamus and other areas of the rat brain. However, neither the release of IR-PRL from the hypothalamus nor its subcellular localization have been demonstrated. In this study, the release of IR-PRL from hypothalami obtained from female rats was examined using hypothalamic units incubated in vitro in Krebs-Ringer bicarbonate-glucose buffer. Hypothalamic tissue spontaneously released IR-PRL, and this release was increased by depolarizing concentrations of potassium by a calcium-dependent mechanism. Hypothalamic IR-PRL was also released from hypothalamic tissue obtained from hypophysectomized rats (14 days). The subcellular localization of IR-PRL was investigated using equilibrium-density centrifugation. Tissue homogenates from intact or hypophysectomized rats were centrifuged at 150 g at 4 °C for 10 min, and the supernatants were layered onto continuous sucrose gradients (1.00–1.27 g/ml) and centrifuged at 100,000 g (max.) for 16 h. IR-PRL in pituitary supernatants showed a high equilibrium-density peak with a modal density of 1.23 g/ml. Fractionation of the supernatant from ventral or dorsal hypothalamic tissue resulted in two high-equilibrium density peaks, a primary peak with a modal density of 1.23 g/ml and a smaller peak with a modal density of 1.10 g/ml. Both high-density peaks were maintained in tissue obtained from hypophysectomized rats and were disrupted by homogenization in hypo-osmotic medium. Together, these data suggest that hypothalamic IR-PRL is stored in membrane-bound particles which have densities similar to those of secretory granules and is released by a calcium-dependent mechanism when the tissue is depolariz

ISSN:0028-3835    

DOI:10.1159/000124813

出版商:S. Karger AG    

年代:1987

数据来源: Karger