摘要:

Gonadotropin-releasing hormone (GnRH) stimulates luteinizing hormone (LH) release and cyclic guanosine 3’,5-cyclic monophosphate (cGMP) production in rat anterior pituitary cells through a calcium-dependent activation mechanism that involves increased phospholipid turnover and liberation of arachidonic acid. In enriched pituitary gonadotrophs, LH release was stimulated by arachidonic acid and its oxygenated metabolite, 5-hydroxy-6,8, l 1,14-eicosatetraenoic acid (5-HETE), in a dose-dependent manner. The prominent LH responses of purified gonadotrophs to arachidonic acid suggest that the secretory actions of arachidonate are exerted primarily on the gonadotroph and do not involve the participation of other pituitary cell types. Preincubation of pituitary cells with stimulatory concentrations of arachidonic acid for up to 120 min did not alter the subsequent LH responses elicited by GnRH, indicating that the secretory mechanism was unimpaired by arachidonate treatment and that no cross-desensitization occurs during sequential exposure of gonadotrophs to the two stimuli of LH release. Cyclic adenosine 3’,5-monophosphate (cAMP) production was stimulated by 10 µM arachidonic acid to the same degree (about 2-fold) as by GnRH, but did not parallel the progressive LH response to higher arachidonate concentrations. cGMP production was initially stimulated by addition of arachidonic acid but returned to the control value after 5 min, whereas GnRH typically elicited a prolonged cGMP response. In contrast to the calcium-independent action of arachidonic acid, the stimulatory effect of 5-HETE on LH release required the presence of extracellular Ca2+ , as previously observed for GnRH. These findings demonstrate that arachidonic acid and its metabolite, 5-HETE, partially reproduce the actions of GnRH upon LH release and cyclic nucleotide production. The several similarities between the effects of GnRH and those of arachidonic acid and 5-HETE suggest that arachidonic acid and/or its lipoxygenase metabolites participate in the mechanism of LH secre

ISSN:0028-3835    

DOI:10.1159/000124789

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

These studies examine whether αi-noradrenergic receptor stimulation alone is sufficient to facilitate lordosis behavior in ovariectomized, estrogen-primed female guinea pigs and to what extent α2-noradrenergic receptors are involved in this steroid-dependent behavior. Neither of the α1-agonists, phenylephrine or methoxamine, significantly facilitated lordosis in ovariectomized females primed with 10 µg of estradiol benzoate for 1 or 3 days. Animals exhibiting estrogen plus clonidine-facilitated lordosis showed a decrease in the behavior when given one of two α2-antagonists (yohimbine or idazoxan). Idazoxan also attenuated lordosis in animals given estrogen plus progesterone. These findings, in combination with previous findings (that specific α1-antagonists block lordosis), suggest that α2-receptors, in addition to α1-receptors play a role in modulation of lordosis b

ISSN:0028-3835    

DOI:10.1159/000124790

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Recent evidence suggests that the endogenous opioid peptides (EOPs) inhibit luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by suppression of hypothalamic gonadotropin-releasing hormone (GnRH) release, and that the feedback inhibition by EOPs is influenced by ovarian steroids. In the present studies, intact (INT) and ovariectomized (OVX) adult female rabbits were fitted with femoral vein catheters and mediobasal hypothalamic (MBH) push-pull perfusion (PPP) cannulae. One week after brain cannulation, does were subjected to 6 h of PPP and sequential blood sampling. In experiment I, INT (n = 6) and OVX (n = 5) does were infused intravenously with saline for 4 h followed by 2 h of infusion of the opiate antagonist naloxone (NAL; 10 µg/min/kg) while the MBH was simultaneously perfused with media. In experiment II, INT (n = 5) and OVX (n = 5) does were perfused with media for 4 h followed by 2 h of intrahypothalamic (IHP) NAL perfusion (0.2 µg/min). The GnRH in push-pull perfusates and LH and FSH in plasma samples collected at 10-min intervals were measured by specific radioimmunoassays. In INT does, neither intravenous infusion nor IHP perfusion of NAL altered pulsatile parameters of GnRH or LH release. In contrast, both intravenous and IHP NAL administration stimulated GnRH and LH release within 30–50 min in OVX does by marked increases in both GnRH and LH pulse amplitudes. Neither route of NAL administration affected FSH secretion in any of the treatment groups. We conclude that (1) EOPs are involved in the inhibition of hypothalamic GnRH secretion in OVX does; (2) the feedback inhibition by ovarian steroids on the hypothalamic-pituitary axis in the rabbit is sufficient to compromise the effects of EOPs, and (3) under these experimental conditions, the hypothalamic mechanisms which regulate the secretion of pituitary LH and FSH may be independ

ISSN:0028-3835    

DOI:10.1159/000124791

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

In vivo single-unit extracellular recording was used to assess neuronal membrane sensitivity at the level of the midbrain central gray (MCG) to the iontophoresis of luteinizing hormone releasing hormone (LHRH) and β-endorphin (β-END). The percentage of change in firing rate was evaluated to determine the effect of exogenously administered estradiol benzoate (EB) and EB plus progesterone (EB + P) on the membrane sensitivity of these MCG neurons to LHRH and β-END. Ovariectomized adult female rats were primed with EB or EB + P, or nonprimed, 24–48 h prior to recording. EB priming significantly altered the membrane sensitivity of neurons in the MCG to LHRH by increasing the number of cells excited compared to the EB + P group and the nonprimed controls (p < 0.005). The addition of P appeared to negate this effect. Hormonal priming did not alter the response profile for β-END iontophoresis. The results suggest an estrogen-dependent sensitivity to LHRH at the MCG which translates into an increased electrical output, ultimately facilitating lordosis behavior. P treatment dampens this excitation. β-END’s effect on neuronal membrane excitability at the MCG was not distinctly characterized under the hormonal conditions our study evaluated and may reflect a regulatory role under physiological

ISSN:0028-3835    

DOI:10.1159/000124792

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Receptor autoradiography was used to determine the distribution of binding sites for monoaminergic and cholinergic neurotransmitters in the cat median eminence. Results showed that binding sites were differentially distributed in that [3H]-p-aminoclonidine (an alpha-2-adrenergic ligand) and [3H]pyrilamine (an H1-histaminergic ligand) binding were concentrated in the medial region of the external layer of the median eminence while [3H]lysergic acid diethylamide (a serotonergic ligand) and [3H] quinuclidinyl benzilate (a muscarinic cholinergic ligand) binding were concentrated within the lateral region of the external layer. These patterns are coincident with the differential distribution of hypophysiotropic hormones in the median eminence, suggesting that monoamines and acetylcholine may regulate the release of these hormones at the level of the median eminence.

ISSN:0028-3835    

DOI:10.1159/000124793

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This study examines immunoreactive levels of oxytocin (OT) and arginine-vasopressin (AVP) from acid extracts of the paraventricular nucleus (PVN), supraoptic nucleus (SON), anterior commissural nucleus (ACN) and the suprachiasmatic nucleus (SCN) as well as selected extrahypothalamic sites in pregnant or postpartum (PP) rats. Animals are sacrificed between 08.30 and 10.30 h 16 or 22 days after sperm is detected in their vaginal smears or on the morning after parturition. Peptide levels of pregnant or PP animals are compared to levels of ovariectomized (OVXed) rats sacrificed and assayed simultaneously. OT immunoreactive levels in the PVN and SON are significantly elevated in late pregnancy and PP. OT content of the ACN is elevated on day 16, but drops to control levels by day 22 of pregnancy and day 1 PP. Concomitant with the falling OT content in the ACN at the end of pregnancy, samples from the ventral septum have significantly increased OT content on day 1 PP. In extracts including the nucleus of the tractus solitarius (NTS) and dorsal motor nucleus of the vagus (dMX) OT is also elevated on the day after parturition. AVP levels peak on the day before parturition in all hypothalamic nuclei examined. These increases are significantly greater than in OVXed controls in the PVN and SON. AVP levels in the lateral habenula are elevated both on day 16 of pregnancy and on the first day PP. From these data we conclude that nonapeptide levels are altered across late pregnancy and early postpartum in some hypothalamic synthesis sites and in certain limbic and brainstem sites. We also postulate that OT is transported out of the ACN to extrahypothalamic sites around the time of parturition.

ISSN:0028-3835    

DOI:10.1159/000124794

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Quantitative assessment of immunocytochemical staining for gonadotropin-releasing hormone (GnRH) was undertaken to determine the effects of an intracranial implant of melatonin on the GnRH neuronal system in the male white-footed mouse (Peromyscus leucopus). Melatonin-containing pellets stereotaxically placed in the anterior hypothalamic area (AH) caused a 60% reduction in testes weight relative to control mice with melatonin-free pellets in the AH (p< 0.01). Subcutaneous melatonin-containing implants had little effect on reproductive state (p < 0.8). Melatonin pellets in the AH increased significantly both the optical density (OD) for immunostaining of cell bodies in the medial preoptic area and AH (p < 0.04), and the percentage of area covered by GnRH fibers and beads in the median eminence (p < 0.01). The melatonin-induced increase in OD of the GnRH cell bodies was independent of the distance of the cells from the melatonin implant, and there was little apparent effect of melatonin on the size and morphology of the GnRH cell bodies, or the trajectories of their fiber pathways. These results support the hypothesis that the antigonadal action of melatonin in the brain involves suppression of the release, rather than the synthesis of GnRH. Also, this effect may not be mediated via a direct action of melatonin on GnRH neurons. The finding that the brain site and time course for melatonin’s antigonadal action in male. P. leucopus is similar to that found previously in the female is evidence that melatonin may induce gonadal regression, in part, by helping to suppress the tonic secretion of gonadotropin

ISSN:0028-3835    

DOI:10.1159/000124795

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The maternal behaviour of 7 ovariectomized, oestrogen-treated ewes was recorded after intracerebroventricular (ICV) infusions of oxytocin (OT). At weekly intervals 10-min behaviour tests were given starting 1 min after control (saline) or OT infusions. In the ewes’ home pens, 5-, 10- and 20-µg doses of OT significantly increased the frequency of some or all of the maternal behaviours scored (low-pitch bleats, sniffing, licking and approaching/following the lamb), and 3 ewes allowed suckling attempts. Aggressive (head butts) and negative (withdrawal from the lamb) behaviours significantly decreased in frequency. Vaginocervical stimulation (10 min duration) produced similar effects on these behaviours. When the lambs were removed from the ewes’ pens, the ewes exhibited significantly more high-pitch bleats (protest) following OT treatment. When 20 µg OT was given ICV in the absence of oestrogen priming, or when it was given intravenously with oestrogen priming, no significant effects on maternal behaviour were seen. Maternal behaviour was also significantly stimulated in oestrogen-treated ewes in a larger, novel testing environment (an enclosed area of field) following 5- and 20-µg doses of OT. In an additional experiment in the field enclosure it was found that ewes spent significantly more time near a lamb in a cage following both 5- and 20-µg doses of OT. In both experimental settings the high OT doses (10 and 20 µg) significantly increased the frequency of feeding although the effect was not dependent on oestrogen priming. These results demonstrate that central OT may play an important role in stimulating maternal behaviour in t

ISSN:0028-3835    

DOI:10.1159/000124796

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

An influence of thyroid status on the secretory activity of hypothalamic dopaminergic neurons was observed in adult rats and its involvement in the regulation of prolactin (PRL) secretion was examined. The secretory activity of the tuberoinfundibular dopaminergic (TIDA) neurons was evaluated by measurement of dopamine (DA) biosynthesis in the neurons and DA release into hypophysial portal blood. The accumulation of DA and PRL in the adenohypophysis as well as PRL concentration in plasma were also estimated, and the various parameters were studied in thyroidectomized (TX), sham TX, TX rats treated for 7 days with thyroxine (T4; 20 µg/kg body weight daily) as well as in intact rats treated similarly with T4. An enhanced secretory activity of the TIDA neurons was observed in TX compared to sham TX rats, as attested by an increased synthesis of DA in the neurons, a greater concentration of DA in hypophysial portal plasma as well as an augmented accumulation of DA in the adenohypophysis. In the same animals, PRL was reduced in the adenohypophysis and in plasma, reflecting a blunted secretion of PRL in severe hypothyroidism. Treatment of TX rats with T4 for 7 days abolished all effects observed in TX rats, DA synthesis in TIDA neurons of TX rats treated with T4 being even less than in neurons of sham TX animals. A similar treatment with T4 administered to intact rats did not affect the secretory activity of the TIDA neurons nor the secretion of PRL. The present results are supportive of a modulatory influence of thyroid status on the secretion of DA by the TIDA neurons and consequently on PRL secretion by the adenohypophysis in the adult rat, and they are suggestive of direct effects of thyroid hormones on the TIDA neurons

ISSN:0028-3835    

DOI:10.1159/000124797

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The effect of histamine on progesterone synthesis and cyclic adenosine 3’,5’-monophosphate (cAMP) accumulation was studied in superfused and incubated follicles dissected free from immature rats treated with pregnant mare serum gonadotrophin (PMSG). Histamine, like LH, increased the progesterone synthesis, but to a smaller extent. The H2-antagonist, cimetidine, inhibited completely the histamine-induced progesterone increase while the H1-antagonist, pyrilamine, as well as propranolol and atropine did not affect the initial response but modified its duration. The specific H2-agonist, 4-methyΓhistamine, but not the H1-agonist, 2-methylhistamine, mimicked the effect of histamine on progesterone synthesis. In the presence of the phosphodiesterase inhibitor, IBMX, histamine increased tissue levels of cAMP. These results suggest that histamine stimulates progesterone synthesis via the H2-receptor with cAMP acting as secondary intracellular messe

ISSN:0028-3835    

DOI:10.1159/000124798

出版商:S. Karger AG    

年代:1987

数据来源: Karger