摘要:

The objective of this study was to determine whether the diurnal rhythm of corticosterone (B) alters the response of the pituitary to gonadotropin-releasing hormone (GnRH). Mature female rats housed in constant illumination were ovariectomized (Ovx) and adrenalectomized (Adx), and maintained on either corticosterone (B, 160 μg/ml in drinking water) or 0.9% saline. 3 weeks later a silastic implant of estradiol (E2) was implanted subcutaneously into each animal. For the next 5 days B-maintained rats received a daily injection of either B (250 μg/100 g BW) or vehicle at 05.00 or 17.00 h. Groups of rats were sacrificed at 0, 1, 3, 6, 12 and 18 h after the fifth injection, and plasma B and E2 were measured. Other animals were challenged with GnRH (1.0 ng/100 g BW) at 0, 6, 12 and 18 h after the last B injection. The fifth B injection initiated changes in plasma B which closely mimicked the normal B rhythm in intact rats. E2 levels (approximately 100 pg/ml) remained fairly constant over the same period. In rats receiving B injection at 17.00 h, the response to GnRH was altered by B administration. The LH response was greatest 6 h after B was injected, and animals showed a lower response at other times. The same relationship between circulating B and the response to GnRH could not be demonstrated in rats injected with B at 05.00 h. Animals maintained on saline exhibited higher basal LH levels, a longer mean half-life of LH, and the plasma LH response to GnRH was lower than in animals receiving B therapy. These results indicated that: (1) physiological dosages of B can alter the response to GnRH in constant light rats; (2) B has a potentiating effect on this response, and (3) B may also influence the clearance rate for L

ISSN:0028-3835    

DOI:10.1159/000123120

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The central serotonergic system was manipulated using a serotonin receptor antagonist (cyproheptadine), electrolytic lesioning of the raphe nuclei and neurochemical destruction of the serotonergic terminals in the hypothalamus. The effects of these interventions on ether-induced ACTH secretion were studied in adrenalectomized rats. Serotonin, norepinephrine and dopamine concentrations were measured in the medial basal hypothalamus (MBH) or in individual nuclei of the hypothalamus and of certain midbrain regions. Cyproheptadine pretreatment inhibited ether-induced ACTH hypersecretion in adrenalectomized animals. Neither the electrolytic lesions of the midbrain raphe nuclei, nor the neurotoxic destruction of the hypothalamic serotonergic terminals (by intraventricular administration of 5,6-dihydroxytryptamine) caused any alteration of stimulated ACTH secretion after ether inhalation and/or long-term corticoid deficiency. These results suggest a lack of correlation between the activity of the central serotonergic system and the ACTH releasing effect of ether stress in adrenalectomized rats.

ISSN:0028-3835    

DOI:10.1159/000123121

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Luteinizing hormone-releasing hormone (LHRH) will evoke large increases of circulating LH in all species tested except for the rhesus monkey. Indeed, in the present study we found that an intravenous injection of a relatively large dose of LHRH (20 μg) evoked only a small (2.2-fold) increase in plasma LH levels, as measured by the dispersed interstitial cell bioassay in 4 intact follicular phase monkeys. In contrast, 4 stalk-transected animals exhibited a significantly greater (19.9-fold) increase in plasma LH levels when treated with 20 μg of LHRH within 1 week after surgery. Qualitatively similar differences in responsiveness also existed between the two treatment groups with respect to FSH secretion. 2 stalk-transected monkeys treated with LHRH at weekly intervals for the first 4 weeks after surgery showed progressive declines in the LH secretory response approaching, eventually, that observed in intact animals. In 3 additional monkeys, initiation of estrogen maintenance therapy within 3 h of stalk transection, to achieve mid-follicular phase plasma levels of estradiol, totally abolished hyperresponsiveness to LHRH. Thus, the results of this study demonstrate that a transient increase in pituitary responsiveness to LHRH occurs after hypophyseal stalk transection in rhesus monkeys. Although the results indicate that this phenomenon can be accounted for, in large part, by the absence of estrogen feedback, they do not preclude the possibility that factors other than LHRH and gonadal steroids regulate gonadotropin secretion in monkey

ISSN:0028-3835    

DOI:10.1159/000123122

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Diurnal variations in concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), corticosterone, estradiol-17β and estrone in serum were investigated in 27- to 35-day-old female rats maintained on a 14-hour light and 10-hour dark schedule. Groups of 6–8 rats were decapitated at 3-hour intervals during a 24-hour period. Hormones were measured by radioimmunoassay. LH levels were highly variable over a 24-hour period in rats younger than 32–33 days of age, while in 34- to 35-day-old animals the levels were less variable and a moderate LH peak was seen at 24.00 h. A distinct FSH diurnal rhythm with the peak at 15.00 h was demonstrated in rats older than 32 days of age. The 27- to 28-day-old rat had a diurnal TSH rhythm with the peak at 12.00 h, but older rats had a rhythm with two peaks at 24.00 and 9.00 h. The diurnal corticosterone rhythm analogous to the adult’s was established at 32 days of age, although a significant variation having a peak during the dark period appeared earlier. Similarly, a distinct estradiol rhythm appeared at 29 days of age with the peak at 12.00 h, followed by a change in the peak phase afterwards. Serum estrone levels showed a manifest variation in the 27- to 28-day-old rat, but no variation was observed in the older rats. These results not only confirm the previous reports on the existence of pulsatile LH secretion, and corticosterone and estradiol diurnal rhythms, but also demonstrate the existence of diurnal rhythms in FSH, TSH and estrone levels in the immature female rat. Furthermore, it is possible that the rhythm once developed may change in phase, or even disappear as puberty appr

ISSN:0028-3835    

DOI:10.1159/000123123

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

An attempt was made to correlate the changes in blood concentrations of prolactin and luteinizing hormone (LH) which occur during the estrous cycle of rats with changes in biochemical estimates of the activities of dopamine (DA)- and norepinephrine (NE)-containing neurons in the median eminence. The serum concentrations of prolactin and LH markedly increased on the afternoon and evening (16.00–24.00 h) of proestrus. The steady state concentrations of NE and DA in the median eminence did not change at any time during the estrous cycle, but the α-methyltyrosine-induced decline of NE was increased during the morning of proestrus (8.00–12.00 h) while the decline of DA was decreased (12.00 h). The rate of total catecholamine synthesis (dopa accumulation after a decarboxylase inhibitor) in the median eminence was not markedly altered at any time during the estrous cycle; the lack of change of dopa accumulation on proestrus may be due, in part, to opposing changes in the rates of amine synthesis in NE and DA neu

ISSN:0028-3835    

DOI:10.1159/000123124

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

These studies utilized a prolactin-secreting clonal strain (2B8) of rat anterior pituitary cells. These cells secrete increasing amounts of prolactin in response to thyrotrophin releasing hormone (TRH) and do not produce any other pituitary hormone. In response to TRH and in the presence of calcium in the culture medium the cells demonstrated evoked responses without spike discharge following electrical stimulation. No spontaneous evoked response with spike discharge was observed in 2B8 cells. The evoked responses were not suppressed by tetrodotoxin (TTX) but were markedly suppressed by D-600, or lanthanum chloride. The results suggest that calcium ion flux across the cell membrane may be a necessary component of the intracellular events which lead to the release of prolactin.

ISSN:0028-3835    

DOI:10.1159/000123125

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The characteristics of atropine-sensitive binding of l-[3H]-quinuclidinyl benzilate ([3H]-QNB) to membrane re-suspensions of sheep posterior pituitary indicate that the binding sites represent muscarinic cholinergic receptors. Scat-chard plots of 6 saturation experiments showed a single class of binding sites, with an equilibrium dissociation constant of 16 ± 2 pM and a density equivalent to 1.8 ± 0.2 pmol/g wet weight of tissue. Kinetic analysis of 2 association and 3 dissociation curves yielded mean association and dissociation rate constants of 3.9 × 108M–1 min–1 and 4.3 × 10–3 min–1, respectively. The binding had a detailed pharmacology for 12 drugs consistent with muscarinic receptor identification. In rat neurointermediate lobes, superior cervical ganglionectomy had no demonstrable effect on [3H]-QNB binding. The location(s) and functional role(s) of neurohypophyseal muscarinic receptors remain to be

ISSN:0028-3835    

DOI:10.1159/000123126

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The inhibitory effects of corticosterone, dexamethasone and prednisolone on activity of the hypothalamus-pituitary-adrenal axis were investigated in adrenalectomized rats infused with glucocorticoids for 6h. Infusion of 202 μg corticosterone did not inhibit the plasma ACTH concentration, but 504 μg corticosterone significantly suppressed plasma ACTH levels. Infusion of 20 μg dexamethasone suppressed markedly the plasma ACTH concentration. These data suggest that the degree of inhibition of dexamethasone on ACTH release is about 25 times greater than that of corticosterone. The CRF content of the hypothalamus was not decreased by the administration of 202 μg corticosterone over a 6-hour period, but it was significantly diminished by 504 μg corticosterone. Infusion of 504 μg dexamethasone did not decrease the hypothalamic CRF content; however, infusion of 5 mg dexamethasone effectively suppressed the hypothalamic CRF content. Infusion of 2.5 mg prednisolone did not either decrease the CRF content. These data suggest that the degree of inhibition of natural steroid at the hypothalamus level is stronger than that of synthetic steroids. In rats pretreated with a single injection of dexamethasone (25 μg/200 g boby weight) 22 h prior to the experiments, continuous infusion of 318 μg of dexamethasone significantly suppressed the hypothalamic CRF content, whereas infusion of 504 μg of dexamethasone failed to decrease the hypothalamic CRF content in the rats not pretreated with dexamethasone. This finding suggests that a latent period after the injection of dexamethasone is needed for the appearance of the inhibitory action of synthetic steriods at the level of hypo

ISSN:0028-3835    

DOI:10.1159/000123127

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Luteinizing hormone (LH) and prolactin (PRL) levels were compared in the serum of ovariectomized rhesus macaques (Macaca mulatta) with pituitary-intact (PI) and surgically transected pituitary stalks (SS). After stalk sectioning, LH levels declined and PRL levels rose dramatically. Chronic infusion of intermittent pulses of gonadotropin-releasing hormone (GnRH; 1 μg/min for 6 of every 60 min) into SS females reinitiated LH secretion within a few days despite increased PRL secretion. Continuous infusion of dopamine (10 μg/min/kg of body weight) for 9 days suppressed PRL levels in GnRH-infused SS females to near normal without alteration in basal serum LH levels or pulsatile LH release. A comparable dopamine regimen also failed to modify serum LH patterns in PI monkeys. Immediately after cessation of dopamine, serum PRL levels rose sharply in both PI and SS animals. Injection of estradiol benzoate (42 μg/kg of body weight) into SS monkeys receiving GnRH infusions resulted initially in LH suppression and then in LH release. However, the magnitude of LH release was less and the latency to its onset was longer in SS animals given estrogen than in PI controls with similar serum estrogen concentrations. It is unclear whether the atypical pattern of the estrogen-induced LH release in SS monkeys was due to hyperprolactinemia or other deficiencies in this GnRH-infused model. However, these data indicate that the response of gonadotropes to GnRH stimulation was not altered by a direct action of either PRL or dopamine on the pituitary gland. Conversely, dopamine directly suppressed the lactotrope, which became hypersecretory immediately upon dopamine withdrawal. We have concluded that estrogen-induced inhibition and subsequent augmentation of LH release represents a direct action at a pituitary locus, although effects at additional, nonpituitary loci are not preclud

ISSN:0028-3835    

DOI:10.1159/000123128

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Intracranial administration of progesterone or a serotonergic receptor blocker into either the dorsal hippocampus or corticomedial amygdala, but not the septum, activated lordotic behavior in estrogen-primed female rats. The same intra-amygdaloid sites mediated the effects of both treatments, whereas in the hippocampus the regio superior was responsive to serotonergic receptor blockade and the dentate gyrus was responsive to progesterone. This is the first demonstration that the amygdala and hippocampus participate both in the facilitation of lordosis by progesterone and in a serotonergic system which inhibits female sexual behavior.

ISSN:0028-3835    

DOI:10.1159/000123129

出版商:S. Karger AG    

年代:1981

数据来源: Karger