摘要:

Seven experiments were performed to investigate the sensitivity of the hamster pineal gland to exogenously administered norepinephrine (NE). In these studies NE (1 mg/kg) administration was preceded (10 min earlier) by the injection of the catecholamine uptake inhibitor desmethylimipramine (DM I; 5 mg/kg). When DMIand NE were given at night, the hamsters were exposed to light to depress pineal N-acetyltransferase activity and melatonin values to low levels; the drugs were then given 20 (DMI) and 30 (NE) min later, and the subsequent changes in pineal N-acetyltransferase and melatonin were monitored. The combination of DMI and NE administration anytime during the normal light period or during the first 4 h of the normal dark period failed to stimulate either pineal N-acetyltransferase activity or melatonin levels. Conversely, DMI followed by NE (injected either intraperitoneally or subcutaneously) in the second half of the dark phase typically stimulated pineal melatonin production. Likewise, the NE agonist isoproterenol promoted pineal melatonin production only in the latter half of the dark phase. If hamsters were exposed to continual light at night or if they were superior cervical ganglionectomized, a procedure which sympathetically denervates the pineal gland, the stimulatory effect of NE on melatonin production was significantly suppressed. Thus, the hamster pineal gland is sensitive to NE only during the latter half of the normal dark period and both darkness and an intact sympathetic innervation to the pineal gland are required for the gland to develop maximal sensitivity to the catecholamine. Also, the hamster pineal seems not to exhibit a supersensitivity response to NE following a period of reduced exposure to the catecholamine. The normal nocturnal rise in melatonin production in the hamster pineal gland seems to be determined by two parameters: an increased production and secretion of NE by sympathetic nerve endings in the pineal at night and (2) an increased sensitivity of the β-receptors on the pinealocyte membranes to NE during the late dark phase

ISSN:0028-3835    

DOI:10.1159/000124736

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Although there is a good correlation between the levels of gonadal steroids and sex differences in reproductive behavior and food intake, the neurochemical mechanisms by which a gonadal steroid may regulate these behaviors remain unknown. An important central nervous site for steroid modulation of food intake and reproduction is the ventromedial nucleus of the hypothalamus (VMH). Recently it has been suggested that some of the activities of the VMH are dependent on the neuroactive peptide cholecystokinin octapeptide (CCK). High levels of CCK in the VMH have been measured by radioimmunoassay, and immunohistochemical analysis has revealed a dense plexus of CCK fibers and terminals which appose and make synaptic contact with VMH neurons. There is, however, a paucity of information concerning the presence of CCK-binding sites in the VMH. This study demonstrates high levels of 125I-CCK8 binding in the VMH of male and female rats. Tissue sampled on the morning of estrus revealed depressed levels of CCK binding, and, while ovariectomy itself did not affect binding, ovariectomy followed by estrogen replacement depressed CCK binding. These results provide evidence for an estrogenic effect on CCK-binding sites that may help elucidate a role of CCK in the VMH.

ISSN:0028-3835    

DOI:10.1159/000124737

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The microvascular pressures that perfuse the anterior pituitary gland with blood were not known. We now report the direct measurement of these pressures in the urethane-anesthetized rat. The infundibular stalk and ventral surface of the anterior pituitary gland were surgically exposed via a parapharyngeal approach and a micropressure transducer inserted into the lumen of hypophysial portal vessels under direct microscopic observation. A Weiderhielm-type servo-controlled pressure system was used to record the pressures. Continuous pressure recordings up to 30 min in duration were made in long hypophysial portal vessels ranging in diameter from 10 to 50 µm in adult, female Sprague-Dawley rats. The mean pressure recorded from these vessels was 4.0 cm H2O (2.7 mm Hg.) A small increase in systemic pressure produced by a rapid saline infusion into a cannulated femoral vein resulted in a mirrored but much greater magnitude increase in pressure to the hypophysial portal vessels. This finding suggests that pressure within the portal vessels is in some instances closely coupled to systemic blood pressure. The low pressures recorded in hypophysial portal vessels correlate well with pressures measured in the hepatic portal vasculature. The porosity of fenestrated capillaries surrounding anterior pituitary cells is hemodynamically essential, since the low hydrostatic pressures alone would be inappropriate for rapid and thorough exchange

ISSN:0028-3835    

DOI:10.1159/000124738

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In this study we investigated the effect of insulin on striatal 5-hydroxytryptamine and tryptamine in streptozotocin-diabetic and in normal rats. Streptozotocin-diabetic rats show a reduction in rat striatal tryptophan, 5-hydroxytryptamine, and 5-hydroxyindole acetic acid, an effect observed at 7 or 14 days after the treatment began. In addition, the accumulation of striatal tryptamine in pargyline-treated rats was reduced at 14 days. Insulin administration produced an increase in rat striatal tryptophan concentration that was observed within 2 h following its administration. By 6 h, however, the striatal tryptophan concentrations were significantly reduced. No changes in rat striatal 5-hydroxytryptamine were observed following the insulin administration, but the treatment induced significant increases in 5-hydroxyindole acetic acid that were observed at 2, 3, 4, and 6 h after insulin administration. The administration of insulin to diabetic rats had a tendency to reverse the decreases in 5-hydroxytryptamine metabolism observed in these animals. Treatment with tryptophan (12–25 mg kg–1) markedly increased rat striatal tryptophan, but did not affect 5-hydroxytryptamine metabolism, an effect that was only observed after the administration of higher doses (50–100 mg kg–1). This is in contrast to the effect of insulin that produces a lesser increase in striatal tryptophan accompanied by an increase in 5-hydroxytryptamine metabolism, indicating that in addition to the inrease in tryptophan availability that it produces, it also possesses some other facilitatory effect on 5-hydroxytryptamine met

ISSN:0028-3835    

DOI:10.1159/000124739

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

5-hydroxytryptophan (5-HTP), a serotonin precursor, has been shown to induce LH release in female but not in male rats at 16, 18 and 20 days of age. The purpose of this study was to investigate the role of neonatal gonadal hormones on 5-HTP-induced LH release in male and female rats of 16 and 20 days of age. The following groups of rats were studied (a) control females, (b) androgenized females, (c) control males, and (d) castrated males. Androgenization and castration were performed within 48 h of birth. 5-HTP administration increased LH concentration in normal females and castrated males at 16 and 20 days of age. The LH release response to 5-HTP was significantly lower at 20 than at 16 days of age in both groups. Neonatal androgenization abolished the LH release response in prepubertal female rats. These results indicate that neonatal exposure to androgen is responsible for the sex difference in the LH response to 5-HTP, which may be associated with a regulatory action of serotonin on the cyclic hypothalamic control of gonadotrophin secretion.

ISSN:0028-3835    

DOI:10.1159/000124740

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The role of thyroid hormones on the development of intracellular glucocorticoid receptor concentrations was examined in the hippocampus, hypothalamus, and pituitary of the rat. Adult animals, administered triiodothyronine (T3; 1.0 µg/g body weight) on days 1, 2, and 4 of life or thyroxine (T4; 2.5 µg/g body weight) on days 1 and 2 of life, had significantly elevated glucocorticoid receptor concentrations in the hippocampus, but not in hypothalamus or pituitary. Adult animals treated with propylthiouracil (PTU; 0.2% in the mother’s food), a thyroid hormone synthesis inhibitor, for the first 2 weeks of life showed decreased glucocorticoid receptor concentrations in hippocampus, but not in hypothalamus or pituitary. We then examined whether thyroid hormones might mediate the effects of early stimulation on the development of hippocampal glucocorticoid receptor concentrations. Animals that were handled for 15 min daily (Ha) for the first 2 weeks of life showed increased hippocampal glucocorticoid receptor concentrations as adults compared to nonhandled (NHa) controls. PTU administration blocked the effects of handling, such that Ha/PTU animals showed hippocampal glucocorticoid receptor concentrations that were indistinguishable from those of NHa animals. In contrast, corticosterone administration over the first 2 weeks of life had no effect on adult hippocampal glucocorticoid receptor concentrations. These data suggest that thyroid hormones mediate, in part at least, the development of glucocorticoid receptor concentrations in the hippocampus and that this effect occurs independently of their effects on corticosterone tit

ISSN:0028-3835    

DOI:10.1159/000124741

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This study examines the role of dynorphin-A(1-13) and dynorphin-A(1-10)-amide in the neuroendocrine regulation of anterior pituitary hormones in nonrestrained, adult male rhesus monkeys. The effects of these opioids on plasma concentrations of prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH) and growth hormone (GH) were assessed. Intravenous administration of dynorphin-A(1–13), 1–120 µg/kg, significantly increased plasma PRL levels. Average maximal increases of 90–230% occurred within 5 min and levels remained significantly elevated for up to 120 min. PRL response reached a plateau following the 30 µg/kg dose. Dynorphin-A(1–13) had no observable effects on plasma concentrations of LH, FSH, TSH or GH at any dose level studied. Administration of dynorphin-A(1–10)-amide produced significant dose-dependent increases in plasma PRL concentrations. Dose levels of 1–120 µg/kg produced mean peak increases from 100 to 230%, 5–10 min postadministration. Dynorphin-A(1–10)-amide had no significant effect on plasma concentrations of LH, FSH, TSH or GH. The increases in plasma PRL concentrations induced by dynorphin-A were naloxone-reversible. These results indicate a selective effect of dynorphin-A on the regulatory mechanisms of PRL secretion over that of other anterior

ISSN:0028-3835    

DOI:10.1159/000124742

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Neuropeptide Y (NPY) is present in large quantities in the hypophysiotropic areas of the brain and has a similar distribution pattern as gonadotropin-releasing hormone (GnRH). The aim of this study was to measure GnRH release during perfusion of NPY through the mediobasal hypothalamus of intact and ovariectomized (OVEX) does. Does were fitted with push-pull (PP) cannulae directed into the median eminence and were subjected to subsequent PP perfusion at a flow rate of 20 µl/min for a total of 6 or 8 h. Six intact does and seven OVEX does received intrahypothalamic perfusion of NPY (14 µg/ml) for either 2 or 3.5 h during the 6 or 8 h, respectively, of PP perfusion. The PP samples and femoral vein blood samples were collected at 10-min intervals on ice. Perfusate GnRH and plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) levels were measured by specific radioimmunoassays. The pulsatile parameters of all hormones were analyzed by the ‘PULSAR’ program. Perfusion of NPY significantly decreased mean levels, pulse amplitudes, and pulse frequencies of GnRH in OVEX does. Also, mean levels of LH were decreased, whereas levels of FSH and PRL were unaffected by NPY. In contrast to these inhibitory effects on GnRH in OVEX does, the same NPY perfusion stimulated mean levels and pulse amplitudes of GnRH in intact does. Plasma levels of neither gonadotropin nor PRL were affected significantly by the NPY treatment in intact rabbits. These results indicate that NPY may have central effects on neuronal release of GnRH, and that ovarian factors are critical in the directional mode of these NPY ac

ISSN:0028-3835    

DOI:10.1159/000124743

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Immunoreactive delta sleep-inducing peptide (DSIP) is known to occur in the central nervous system and in body fluids including cerebrospinal fluid, blood and urine. However, the exact nature of the immunoreactive material demonstrated has been a matter of discussion. In the present study, DSIP-like immunoreactivity was demonstrated in the porcine pituitary and adrenal medulla using radioimmunoassay and immunocytochemistry. In the pituitary, the DSIP-like material was present in a subpopulation of the cells storing adrenocorticotropin and α-melanotropin. The DSIP immunoreactive cells in the adrenal medulla were identical with a major population of the noradrenaline-storing cells. High-performance liquid chromatography of tissue extracts revealed one major peak of DSIP-like immunoreactivity which did not coelute with synthetic DSIP. The immunoreactive material may represent N-terminally truncated fragments of DSIP. The present results suggest that the anterior and intermediate lobes of the pituitary and the adrenal medulla are potential sources of DSIP-like peptides

ISSN:0028-3835    

DOI:10.1159/000124744

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The present study was designed to investigate the effect of distinct serotonin (5-HT1A and 5-HT2) agonists and antagonists on renin and corticosterone secretion. Low doses of the selective 5-HT1A agonists 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) (5.0–500.0 µg/kg, i.p.) and ipsapirone (TVX Q 7821; 0.5–2.5 mg/kg, i.p.), and of the 5-hy-droxytryptamine (5-HT) agonist MK-212 (2.0 mg/kg, i.p.), did not elevate plasma renin activity (PRA) and concentration (PRC) 30 min postinjection. Administration of a higher dose of MK-212 (10.0 mg/kg, i.p.) and of higher doses of ipsapirone (5.0–10.0 mg/kg, i.p.), as well as the 5-HT releaser, fenfluramine (5.0 mg/kg, i.p.), resulted in large increases in PRA and PRC. The effects of MK-212 and fenfluramine on PRA and PRC were blocked by pretreatment with the selective 5-HT2 antagonist, LY53857, in a dose-dependent (0.3–1.0 mg/kg, i.p.) manner. LY53857 (1.0 mg/kg, i.p.) by itself did not affect PRA or PRC. LY53857, furthermore, unmasked a renin-suppressive effect of MK-212, since injection of MK-212 (10.0 mg/kg, i.p.) following LY53857 administration led to a reduction in PRA and PRC. MK-212 (2.0 and 10.0 mg/kg), the high doses of 8-OH-DPAT (500.0 µg/kg), ipsapirone (1.0–10.0 mg/kg), and fenfluramine (5.0 mg/kg) all produced an increase in plasma corticosterone levels. The effects of MK-212 and fenfluramine on corticosterone were not inhibited by pretreatment with LY53857. These data suggest that 5-HTIA receptors do not play a role in the regulation of renin secretion, whereas stimulation of 5-HT2 receptors enhances renin release. The data also suggest that MK-212- and fenfluramine-induced corticosterone secretion is not mediated by 5-HT

ISSN:0028-3835    

DOI:10.1159/000124754

出版商:S. Karger AG    

年代:1987

数据来源: Karger