摘要:

Plasma concentrations of LH, FSH, 17β-estradiol, estrone and progesterone were determined chronologically by radioimmunoassays in two groups of adult female rats exposed to continuous illumination (LL). Group 1 rats showing vaginal estrous cycles were sacrificed at 3- to 6-hour intervals during late proestrus through early estrus of the first 5 cycles after exposure to LL. Group 2 animals which displayed persistent vaginal estrus in an early period of exposure to LL were killed on the 2nd, 3rd, 4th, 5th and 7th days of vaginal estrus. In Group 1 rats, surges of the hormones, except estrone, took place in all the 5 cycles. The occurrence of peak hormone levels in each cycle was invariably delayed after transfer of animals to LL. According to regression analyses, the lengths of secretion cycles of LH, FSH, 17β-estradiol and progesterone in rats under LL were 100.89, 100.46, 101.14 and 101.06 h, respectively. Elevation of 17β-estradiol levels was observed prior to the LH surge, and peaks of progesterone and FSH occurred following it. However, the secretion patterns of these hormones appear to be disrupted with length of exposure to LL. In group 2 rats, the mean concentration of LH during persistent estrus was approximately similar to that on the morning of the days of proestrus of the 4-day cycles of rats placed under an alternating 12-hour light-dark regimen (LD), whereas the mean FSH concentration was continuously low. While the concentrations of 17β-estradiol and estrone in persistent-estrous rats were elevated, progesterone levels remained low. These findings appear to show that the estrous cycles in LL rats are composed of circaquadridian secretion rhythms, longer than 96 h, of gonadotropins and sex steroids so that the estrous cycles are lengthened and the ovulation is delayed. Prolongation of estrus in LL rats may be accounted for by suppression of the ovulatory surge of LH and consequent decrease in secretion of progesterone caused by continued elevation of blood concentrations of 17β-estra

ISSN:0028-3835    

DOI:10.1159/000123964

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The effect of norepinephrine (NOR) has been investigated in 8-day-old newborn rats of both sexes subjected to stress by 2 min ether inhalation or sham stress. The animals were sacrificed either before or 2 and 32 min after the stress or the sham stress prodecure was started. Investigations were also performed on newborns bearing neurotoxic lesions of the arcuate nucleus by neonatal treatment with monosodium-L-glutamate. The effect of NOR was also investigated in vitro on incubated pars distalis. ACTH concentrations in the pituitary, plasma, and the incubation medium were determined by radioimmunoassay. NOR at the dose of 0.2 µg/g was unable to affect plasma ACTH levels during a period of 60 min in unstressed newborns, in contrast to higher doses (0.5, 1, and 5.0 µg/g) which elicited a sharp rise in plasma ACTH levels. Then, NOR was injected (0.2 µg/g) to male and female pups 15 min before the stress or sham stress procedure. 32 min after the beginning of ether inhalation, the pituitary response was greater in NOR-injected than in saline-injected males; in NOR-treated females the rise in plasma ACTH levels was higher at 2 and 32 min than in saline-injected animals. At this latter time, plasma ACTH levels were similar in NOR-treated males and females, while in saline-treated newborns, the response to ether stress was greater and more longlasting in females than in males. No significant rise in plasma ACTH levels was observed in sham-stressed pups. The response to ether inhalation of saline- or NOR-treated males and females was significantly reduced by the α-blocking drug phenoxybenzamine (2 µg/g), but not by the β-blocking agent propranolol (5 µg/g) given to the animals 30 min before the beginning of the stress procedure. The ACTH contents of the pars distalis and pars neurointermedia were unchanged by sham stress or ether stress performed on saline- or NOR-treated animals. Neurotoxic lesions of the arcuate nucleus by neonatal treatment with monosodium glutamate did not significantly affect the basal level of plasma ACTH or its evolution in both sexes in response to ether inhalation. In vitro NOR did not affect the basal or the CRF-induced stimulation of ACTH release. The present data are consistent with an α-stimulatory effect of NOR on the neuroendocrine pathways involved in the pituitary response of the newborn rat to ether stress and suggested mediation through central nervous system rather than direct pituitary actions. The arcuate nucleus was not involved in that type of r

ISSN:0028-3835    

DOI:10.1159/000123965

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Electrolytic lesions of the lateral hypothalamus (LH), but not of the lateral thalamus, prevented the elevation of serum gastrin induced by intracisternal injection of bombesin in rats. Knife cuts through the lateral or the posterior LH border largely abolished the rise in circulating gastrin induced by intracisternal bombesin. Cuts through the medial LH border partly inhibited the response, whereas cuts through the anterior LH border did not modify peptide action. None of the transections altered basal gastrin levels nor the rise in gastric pH and inhibition of gastric acid output induced by intracisternal bombesin. LH lesions did not modify the rise in serum gastrin induced by intravenous bombesin. These results demonstrate that the gastrin-releasing effect of intracisternal bombesin requires the integrity of fibers crossing the posterior, lateral, and medial borders of the LH and is independent of changes in gastric pH. The LH area is not itself necessary for the expression of the inhibitory action of bombesin on gastric acid secretion.

ISSN:0028-3835    

DOI:10.1159/000123966

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The present study examined three aspects of the inhibitory effects of continuous intraventricular infusion of norepinephrine (NE) on pulsatile luteinizing hormone (LH) release in ovariectomized, nonsteroid-primed rats: (1) whether the inhibitory effects of NE infusion were exerted on LH pulse frequency and/or amplitude; (2) whether central nervous system desensitization occurred in response to the inhibitory effects of continuous NE infusion on pulsatile LH secretion, and (3) whether dopamine of serotonin were involved as possible interneuronal transmitter mediators of NE-induced suppression of pulsatile LH release. Unanesthetized rats with external jugular cannulae were bled continuously at a rate of 50 µl whole blood/7 min for 2 h prior to infusion and for 2–3 h during continuous intraventricular infusion of artificial cerebrospinal fluid or NE. Infusion of cerebrospinal fluid had no effect on pulsatile LH release, while continuous infusion of 0.3 or 1.8 µg NE/h for 2–3 h produced suppression of pulsatile LH secretion. Although desensitization to the stimulatory effects of NE on LH release in ovariectomized, steroid-primed rats had been observed to occur rapidly within 90 min after the onset of infusion, desensitization to the inhibitory effect of NE on pulsatile LH release did not occur even after continuous infusion of NE for periods up to 20 h. Mean blood LH levels were as low in rats bled 17–20 h after the onset of NE infusion as in those bled at 0–3 h. The suppressive effect of NE on pulsatile LH release was not prevented by prior blockade of dopamine or serotonin receptors with pimozide or metergoline, respectively. Lastly, in all groups infused with NE, the decrease in mean blood LH levels was due solely to a suppression in LH pulse frequency, as no decrease occurred in pulse amplitude. These experiments demonstrate that (1) the inhibitory effect of NE is exerted solely on LH pulse frequency and suggest that NE suppresses only the firing rate of the presumed luteinizing hormone releasing hormone pulse generator in regulating pulsatile LH secretion; (2) whereas desensitization is rapidly established in the neuronal receptors excitatory to LH release, this phenomenon is not observed when pulsatile LH release is suppressed by NE for much longer periods of time, and (3) dopamine and serotonin are not involved as possible interneuronal transmitter mediators of the inhibitory effects of NE upon pulsatile LH and presumably pulsatile luteinizing hormone releasing hormone

ISSN:0028-3835    

DOI:10.1159/000123967

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Chronic estrogen treatment can lead to development of prolactin (PRL) secreting pituitary tumors. We have tested the ability of diethylstilbestrol (DES) to produce persistent hyperprolactinemia (hyperPRL) in adult male rats and examined the effects of this treatment on hypothalamic-pituitary-testicular function, adenohypophyseal structure, copulatory behavior and fertility. Silastic capsules containing approximately 5 mg DES were subcutaneously implanted into adult male CDP (F-344)/CrlBR rats and removed 15 or 20 weeks later. Extreme hyperPRL, as well as suppression of plasma LH and FSH levels, persisted after DES capsules were removed. In contrast, plasma testosterone levels increased rapidly after removal of DES capsules and reached normal levels within 4–6 weeks. Copulatory behavior was assessed on two occasions between 7 and 14 weeks after removal of the DES capsules and was found to be suppressed in DES-treated rats, as evidenced by significant increases in latencies to mount, to intromit and to ejaculate. Moreover, when the animals were placed with normal females, the interval until conception was significantly greater in DES-treated than in control males. In spite of these differences in copulatory behavior, 10 of 11 DES-treated males were fertile. At autopsy, 44 weeks after capsule implantation (i.e. 24 or 29 weeks after capsule removal), DES-treated rats had marked enlargement of the anterior pituitary, increased weights of the lateral prostate and the adrenals, increased levels of testicular hCG-binding sites, reduced concentration of dopamine and norepinephrine in the median eminence and increased concentration of LHRHin the preoptic area. DES-treated and control rats did not differ with respect to relative weights of the testes, ventral prostate and seminal vesicles and testicular testosterone production in vitro in the presence and in the absence of hCG. Immunocytochemical studies oí the adenohypophysis in a separate group of similarly treated animals revealed marked increases in the total number of parenchymal cells and in the relative proportion of mammotrophs. We conclude that chronic exposure of adult male CDF (F-344) rats to DES resulted in persistent massive mammotroph hyperplasia and that the resulting 20- to 100-fold elevation of peripheral PRL levels in these animals had little, if any, suppressive effect on testicular function, in spite of the drastic reduction in peripheral LH leve

ISSN:0028-3835    

DOI:10.1159/000123968

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Numerous studies have suggested that serotonin (5-HT) is involved in the regulation of anterior pituitary hormone release. In the present study, the 5-HT concentrations of the median eminence and anterior pituitary lobe were measured during the estrous cycle and lactation in order to correlate changes in 5-HT levels with changes in serum luteinizing hormone, follicle-stimulating hormone, and prolactin. On the day of proestrus, median eminence 5-HT concentrations declined significantly between 14.00 and 16.30 h at the beginning of the gonadotropin and prolactin surges. No changes in 5-HT concentrations were found between the morning and afternoon on other days of the cycle. In the anterior pituitary, the levels of 5-HT did not change during the estrous cycle. 5-HT turnover rates were also estimated in the median eminence on proestrus and diestrus 1. The median eminence 5-HT synthesis rate increased in the afternoon of proestrus at 16.30 h. 5-HT was also measured in the anterior pituitary and the median eminence of lactating rats in four experimental situations: mothers with their litter until decapitation, mothers separated from their pups 4 h earlier, and mothers separated from their pups 4 h earlier, after which the pups were allowed to suckle for 5 or 30 min. In spite of the acute changes in circulating prolactin, 5-HT levels in the median eminence were not affected in any situation studied. These results suggest that 5-HT in the median eminence is involved in the control of gonadotropin release. The data further suggest that 5-HT does not act directly on the anterior pituitary to modulate gonadotropin or prolactin release.

ISSN:0028-3835    

DOI:10.1159/000123969

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The ability of somatostatin to inhibit the muscular twitches elicited by field stimulation of rat vas deferens and guinea pig ileum was studied. Evidence should be summarized which would suggest that the presynaptic inhibitory effect of somatostatin on chemical neurotransmission is indirect. Its effect on vas deferens is partly mediated via α2-adrenoceptors and due to the released noradrenaline, in guinea pig ileum, however, it seems likely that it releases an unidentified inhibitory substance which, in fact, inhibits the release of acetylcholine, and thereby twitches of the ileum. The fast tachyphylaxis seen following repeated administration of the peptide is likely due to its indirect action

ISSN:0028-3835    

DOI:10.1159/000123970

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In the present experiment we examined the temporal effects of progesterone (P) upon in vitro dopamine (DA) release from superfused corpus striatum (CS) and medial basal hypothalami (MBH) tissue fragments. In ovariectomized-estrogen-primed adult female rats, P was systemically administered at 0.5, 2, 4, 12 or 24 h prior to sacrifice for CS and at 4 or 24 h for MBH superfusions. Control groups receiving either steroid alone and/or the oil vehicle were included. Progesterone at the 2- to 12-hour periods stimulated spontaneous and amphetamine-evoked DA release and increased post-superfusion tissue concentrations of DA from the CS when compared to controls. At 24 h P apparently produced an active inhibition, with all parameters of DA activity (spontaneous and AMPH-induced DA release), significantly decreased compared to controls. In contrast, P failed to alter the spontaneous or marginal amphetamine response of the MBH but did significantly reduce post-superfusion DA concentration at 24 h. We hypothesize that the dual effect of P upon brain dopaminergic systems (facilitation followed by inhibition), in the CS but not in the MBH represents changes in DA synthesis and release which are coupled in the CS but not in the MBH.

ISSN:0028-3835    

DOI:10.1159/000123971

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In order to investigate the relative contribution of the serotoninergic and catecholaminergic innervation of different brain structures to the control of gonadotropin secretion in the male, adult rats were given bilateral injections of the selective neurotoxins, 5,7-dihydroxytryptamine and 6-hydroxydopamine, into the mediobasal hypothalamus, the medial preoptic area, the amygdala, and the medial forebrain bundle. Serum levels of luteinizing hormone (LH), follicle-stimulating hormone, testosterone, pituitary follicle-stimulating hormone, and LH content were measured 15 days later. The medial preoptic area 5,7-dihydroxytryptamine injections were followed by 2- to 3-fold increases of serum LH and testosterone levels and pituitary LH concentration. The 6-hydroxydopamine injections in the medial forebrain bundle resulted in a 60% decrease of pituitary LH content, associated with serum levels of LH and testosterone which were lowered, although not significantly. None of the treatments seemed to influence either serum or pituitary concentrations of follicle-stimulating hormone. These results suggest a hitherto undocumented major function of the serotoninergic innervation of the medial preoptic area in the control of LH secretion in the male and confirm previous reports indicating that some of the catecholaminergic fibers carried by the medial forebrain bundle can be modulatory for LH secretion.

ISSN:0028-3835    

DOI:10.1159/000123972

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In this study we have characterized binding sites for ovine corticotropin-releasing factor (oCRF) in the rat anterior pituitary gland, and have investigated whether the site of interaction of vasopressin and oCRF is at the plasma membrane level. The binding 125I-oCRF to anterior pituitary membranes was shown to be dependent on temperature, pH and cation concentration. Magnesium was essential for the binding reaction to take place. Two binding sites of Kcι 7.63 × 10-10 and 3.39 × 10–8M were found. Activity of adenylate cyclase in the membrane preparation increased in the presence of oCRF. The activity of the enzyme as well as the binding of 125I-oCRF was found to be influenced by guanosine-5’-triphosphate. Several hypothalamic neurohormones, including vasopressin, failed to alter the binding of 125I-oCRF to anterior pituitary membranes. Moreover, vasopressin failed to influence the stimulation of adenylate cyclase activity induced by oCRF. Preincubation of anterior pituitary segments with oCRF desensitized the corticotropin (ACTH) response to oCRF and decreased the amount of 125I-oCRF bound to membranes prepared from similarly treated pituitaries. The ACTH response to vasopressin remained unchanged. Following a preincubation of anterior pituitary segments with vasopressin, oCRF stimulated ACTH secretion, as well as the binding of 125I-oCRF to pituitary membranes was normal, while the ACTH response to vasopressin was markedly reduced. These results show that separate receptors mediate the action of vasopressin and oCRF. Moreover, the ACTH response to vasopressin and oCRF may be modulated sepa

ISSN:0028-3835    

DOI:10.1159/000123973

出版商:S. Karger AG    

年代:1984

数据来源: Karger