摘要:

The objective of this study was to determine if endogenous opioid peptides (EOPs) influence the pattern of pulsatile luteinizing hormone (LH) secretion on days 6–8, 14–16 and 22 of gestation in the rat. Unanesthetized animals with two jugular cannulae were initially infused with 0.9% saline during which the control pattern of pulsatile LH release was determined. Possible EOP involvement was then determined by infusion of the EOP receptor antagonist naloxone. Plasma estradiol (E2) and progesterone (P) values increased between days 6–8 and 14–16. While plasma E2 values remained elevated through day 22, plasma P values declined by 90%. As previously reported, mean blood LH levels during the control period on day 22 were higher than on days 6–8 and 14–16 due to an increase in LH pulse frequency. At each stage of gestation naloxone infusion increased mean blood LH levels. This stimulatory action of naloxone was reduced in a dose-dependent fashion by simultaneous infusion with morphine, demonstrating that this effect is mediated via EOP receptors. There was no difference in the in vivo pituitary responsiveness to LH-releasing hormone (LHRH) between rats infused with saline or naloxone at any stage of pregnancy, demonstrating that the stimulatory effect of naloxone was not exerted at the pituitary level. Naloxone increased both the amplitude and frequency of pulsatile LH secretion on days 6–8, and stimulated frequency on days 14–16. The effect on amplitude could not be assessed on days 14–16 because too few rats exhibited pulsatile LH secretion prior to naloxone infusion. The increase in pulse frequency was similar on days 6–8 and 14–16. Although naloxone increased LH pulse amplitude and frequency on day 22, these increases were significantly less than those seen on days 6–8 and 14–16, respectively. Pituitary responsiveness to LHRH was less at all stages of pregnancy in comparison to responsiveness in ovariectomized rats, and progressively declined from days 6–8 through day 22. The lowest responsiveness to LHRH was seen on day 22 and contributed, at least in part, to the diminished increase in LH pulse amplitude in response to naloxone infusion on day 22 compared to days 6–8. The reduced naloxone-induced increment in LH pulse frequency on day 22, occurring coincident with a precipitous decline in plasma P levels, suggests a decreased EOP suppression of pulse frequency at this time. Since recent studies in our laboratory demonstrated that the increase in LH pulse frequency on day 22 is due to loss of the negative feedback action of P on pulsatile LH secretion, we postulate that during pregnancy P suppresses LH pulse frequency through an EOP-mediated mechanism, and as plasma P levels decline on day 22, EOP suppression of pulse frequency is diminished. The result is an increase in LH pulse frequency, and a diminished effect of naloxone on this parame

ISSN:0028-3835    

DOI:10.1159/000124847

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Melatonin administration has been shown to delay sexual maturation in male rats, through an action which involves decreased binding of gonadotropin-releasing hormone (GnRH) in the pituitary and lower pituitary gonadotropin contents. It has been suggested that melatonin must act at a level higher than the pituitary to provoke these effects, but a direct action of melatonin on the pituitary has not been excluded. Using a cell culture system, the gonadotroph responsiveness to GnRH was studied. Pituitaries were obtained either from rats chronically treated with melatonin and showing delayed sexual maturation, or from control rats. In vitro luteinizing hormone and follicle-stimulating hormone response to GnRH was significantly lower when pituitaries were obtained from melatonin-treated rats. However, this diminished response was directly proportional to the amount of gonadotropin contents in cells, so that relative responsiveness, calculated as the amount of gonadotropins released in relation to the gonadotropin content was similar in cells from control and melatonin-treated rats. It is concluded that the effect of melatonin on the pituitary of male rats results from a decrease of gonadotroph growth or gonadotropin synthesis, as a consequence of a change located at the hypothalamic rather than at the pituitary level. This conclusion is further supported by results showing that melatonin added directly in culture medium prior to GnRH does not modify the pituitary responsiveness to GnRH.

ISSN:0028-3835    

DOI:10.1159/000124848

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

An increasing number of messengers have recently been found to coexist with growth hormone (GH)-releasing factor (GRF) in hypothalamic neurons. In view of a possible cosecretion of these substances with GRF into the portal circulation, the effect of synthetic rat hypothalamic GRF(1–43) alone, or together with dopamine (DA), L-dopa, γ-aminobutyric acid (GABA), neurotensin (NT) or galanin (GAL) on GH release was investigated by using dispersed rat anterior pituitary cells in monolayer culture. GRF in concentrations of 10-16–10-7M stimulated GH release from somatotrophs in a dose-related manner. DA (10-5 M), L-dopa (10-8 and 10-5-M) and GABA (10-9 and 10-5M) did not affect basal GH release, whereas DA, but not L-dopa or GABA, significantly suppressed GRF-induced GH secretion. However, the inhibitory effect of DA on GRF-stimulated GH secretion was not observed in the presence of somatostatin (10-6M).NT (10-6M) and GAL (10-6M) did not change basal GH release. GAL, but not NT, inhibited GRF-stimulated GH release, but the addition of NT abolished the inhibitory actions of both GAL and DA. These results indicate that substances, probably coreleased with GRF from the same nerve endings, interact in the regulation of GH secretion at the pituitary l

ISSN:0028-3835    

DOI:10.1159/000124849

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

To evaluate the oα-noradrenergic regulation of arginine vasopressin (AVP) and oxytocin (OT) in normal humans, we measured the effect of the α2-agonist clonidine on concentrations of these neuropeptides in both plasma and cerebrospinal fluid (CSF). Subjects underwent two lumbar puncture studies, one of which was performed 100 min after oral administration of 5 µg/kg clonidine. Plasma AVP and OT were measured at a single time point 10 min before lumbar puncture. Both plasma and CSF AVP were significantly lower in the clonidine condition than in the control (no drug) condition. Neither plasma nor CSF OT differed significantly between conditions. Our data confirm previous reports of α2-noradrenergic inhibition of neurohypophyseal release of AVP into blood, and extend these findings to healthy human subjects. Our data also suggest that AVP appearance in CSF, presumably from extraneurohypophyseal vasopressinergic neurons, is regulated by an inhibitory oα-noradrenergic mecha

ISSN:0028-3835    

DOI:10.1159/000124851

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Angiotensin II (AII; 1.0 µl of 10–10M) injected bilaterally into the anterior hypothalamus-preoptic area of the brain produced a 100% increase in mean whole blood LH concentrations in ovariectomized rats treated with estradiol and progesterone. Injections of equal volumes and concentrations of the peptide into the third cerebral ventricle or into the posterior hypothalamus did not affect blood LH values. The effects of AII administration into the rostral hypothalamus were dose-related and specific. Equimolar injections of angiotensin I or angiotensin III into this region did not significantly affect blood LH levels. Taken together, these data demonstrate that the anterior hypothalamus-preoptic area, compared to the third ventricle or more caudal brain sites, is particularly sensitive to the specific stimulatory actions of AII on LH relea

ISSN:0028-3835    

DOI:10.1159/000124852

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

To pursue the possibility that subdivisions within the medial and lateral septal nuclei are differentially involved in adrenocortical function, plasma samples obtained prior to and following electrical stimulation of the septal nuclei of urethane (1.30 g/kg)-anesthetized female rats were assessed for corticosterone concentration. Hippocampal EEG, ECG, heart rate (HR), mean arterial pressure (MAP) and respiration were routinely monitored, and timed blood samples (0.15 ml) were obtained from a catheterized tail artery. Blood samples were taken 0.5 min prior to and at 5, 10, 15 and 30 min after initiation of stimulation. Whereas no change in Cpd B levels were observed following sham stimulation or stimulation of the corpus callosum, fornix or anterior commissure, stimulation of the septal nuclei produced differential responses. Decreased plasma Cpd B responses followed stimulation of the medial septal nucleus (MS); increases in plasma Cpd B followed stimulation of the dorsal (LSD) and ventral (LSV) division of the lateral septal nucleus. The overall increase in plasma Cpd B levels following LSD and LSV stimulation was 16 and 32%, respectively. The overall decrease in corticosterone concentration subsequent to MS stimulation was 18%. The largest increases in Cpd B levels occurred at 5 min (36%) and 10 min (24%) for LSV and LSD groups, respectively; the largest decrease was noted at 15 min (25%). Plasma Cpd B responses to stimulation of the intermediate area of the lateral septal nucleus produced varying and inconsistent responses. Collectively, these data support the hypothesis that subdivisions within the septal nuclei are differentially involved in adrenocortical function.

ISSN:0028-3835    

DOI:10.1159/000124853

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The effect of lipoxygenase inhibition, leukotriene agonists and antagonists, and 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) was examined in the rat pineal gland in organ culture. To study melatonin secretion pineal explants were incubated for 6 h in tissue culture medium 199 with the different drugs. Melatonin concentration in the pineal gland and the medium was measured by RIA. Exposure of explants to norepinephrine (NE) brought about a 2- to 5-fold increase in both parameters, an effect that was reduced but not abolished, by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA; 10–5M). Lilly 171883 (10–5M) or FPL 55712 (10–5M; both antagonists of leukotrienes) reduced NE-induced melatonin production. Neither NDGA nor Lilly 171883 affected melatonin production in the absence of NE. Leukotrienes C4 and D4 increased melatonin release to the media at all concentrations tested (1–1,000 nM) with a maximum effect at 1 nM (leukotriene C4) and 10 nM (leukotriene D4). Significantly higher tissue melatonin concentrations as compared to controls were observed after exposure of pineal explants to 1 and 100 nM of leukotriene C4, or 100 nM of leukotriene D4. Another 5-lipoxygenase metabolite, 5-HETE, increased pineal melatonin content at concentrations of 1, 10 and 100 nMwhereas only 1,000 nMstimulated melatonin release. These results suggest that the 5-lipoxygenase pathway plays a significant role in NE-stimulated melatonin production by the rat pinea

ISSN:0028-3835    

DOI:10.1159/000124854

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In the rat median eminence immunoreactive galanin nerve fibers and terminals are present in high numbers in the external layer, and fibers in moderate numbers are seen in the internal layer. The possible sources of these galanin-containing fibers were studied by means of radioimmunoassay and immunohistochemistry in rats with different types of hypothalamic lesions. Galanin-like neurons were found both (1) in the magnocellular hypothalamo-neurohypophyseal system and (2) in the parvocellular hypothalamo-median eminence-anterior pituitary system. Cell bodies containing galanin-like immunoreactivity were localized in the supraoptic, magnocellular paraventricular and accessory magnocellular neurons with axons traversing the internal layer and terminating in the posterior pituitary. Surgical isolation of these neurons from the median eminence resulted in a marked depletion of immunoreactive galanin from the internal layer of the median eminence and the posterior pituitary. Due to the retrograde accumulation of axonally transported substances in cells proximal to the lesions, immunoreactive galanin-like cells became visible in the supraoptic and paraventricular nuclei ipsilateral to the knife cuts, and levels of galanin-like immunoreactivity increased in these nuclei 7 days after bilateral transections of the hypothalamo-hypophyseal tract. Immunoreactive galanin fibers in the external layer of the median eminence around the portal capillaries were found to be of paraventricular and arcuate nucleus origin. Bilateral paraventricular lesions caused marked (70%) reduction in levels of galanin-like immunoreactivity in the median eminence. The remaining 30% of the galanin immunoreactivity in the external layer may arise from the arcuate nucleus, which contains a great number of galanin-containing cell bodies. Thus, galanin-like immunoreactivity accumulated retrogradely in parvocellular paraventricular and arcuate nucleus neurons after transections of their fibers in the lateral retrochiasmatic area or in the median eminence, respectively.

ISSN:0028-3835    

DOI:10.1159/000124855

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Modulation of CA1 electrophysiological properties (amplitude, latency, paired-pulse facilitation) by different concentrations of corticosterone (CT) was studied in hippocampal slice preparations from normal (sham) and adrenalectomized (ADX) BALB/c mice. In the sham group, CT effects on the population spike (PS) amplitude were biphasic: at a low dose (200 pM) CT induced a delayed increase; at a moderate dose (2,000 pM), a rapid and partially reversible decrease was observed, and at higher doses (5,000 and 10,000 pM) this decrease was more pronounced after 30 min of washout. Diminution of latency and paired-pulse facilitation were obtained for the CT concentration inducing an increase of the PS amplitude. In the ADX group, similar CT effects were observed for lower doses: a decrease of the PS amplitude was observed for 40 and 100 pM and an increase for 5 pM, but variations of the PS amplitude were weaker than in the sham group. The role of the different CT receptor systems in this neuromodulatory effect is discussed.

ISSN:0028-3835    

DOI:10.1159/000124856

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Eight cycling female rats were implanted with push-pull cannulae over the region of the suprachiasmatic nuclei (SCN) and allowed 7–10 days for recovery. Perfusion of the SCN continued in these freely behaving rats for 5–6 h of the light period and the subjective scotophase. The release of 5-hydroxyindoleacetic acid (5-HIAA) ranged from 10 to 350 pg 5-HIAA/min. Significantly, the amplitude and characteristics of the output of 5-HIAA were highly location dependent in that rostral cannulae placements revealed high amplitude changes with initial mean values of 40 pg 5-HIAA/min, which increased toward the dark phase to mean peak values of 195 pg 5-HIAA/min. Caudal cannulae placements revealed a low amplitude, high frequency, basal type of 5-HIAA release which did not increase toward the dark period (approximately 5 pg/min). 5-Hydroxytryptophan infusion resulted in a significant marked increase in the basal release of 5-HIAA confirming the biochemical viability of the area undergoing perfusion. These results suggest that the in vivo measurement of 5-HIAA from 5-hydroxytryptamine (5-HT) terminals in the region of the SCN could reflect discrete functional activity of serotonergic terminals within specific regions of the SCN in a freely behaving rat. Furthermore, the biochemical viability of these 5-HT terminals and the ability of the rat’s SCN to exhibit marked differential changes in 5-HT activity emphasizes the physiological relevance of this model system to study neuroendocrine events in freely behaving an

ISSN:0028-3835    

DOI:10.1159/000124857

出版商:S. Karger AG    

年代:1987

数据来源: Karger