摘要:

Recent data indicate that leptin may well play an important regulatory role in the hypothalamo-pituitary-gonadal axis. In order to further unravel the mechanisms by which leptin acts, we have studied the effect of treatment (8 days) of leptin antiserum (5 µl daily; i.c.v.) on LH pulsatility and estrous cycle in adult female rats. The administration of leptin antiserum led to a marked decrease in LH pulsatility as assessed by the area under the curve (13.5 ± 4.7 ng/ml) in comparison to rats treated with normal rabbit serum (114 ± 53 ng/ml; p < 0.01). Furthermore, rats treated with leptin antiserum showed an impairment of reproductive function as shown by the fact that all rats remained in anestrus. In conclusion, these data show that leptin markedly influences LH secretion and the estrous cycle in the female r

ISSN:0028-3835    

DOI:10.1159/000127262

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Oxytocin neurone terminals display a powerful opioid-mediated auto-inhibitory mechanism which restrains secretory activity. In pregnancy, upregulation of this mechanism may underlie the accumulation of large stores of oxytocin in the pituitary. In the present study, conscious pregnant rats were cannulated to allow blood samples to be taken for measurement of oxytocin secretion in response to intravenous administration of cholecystokinin (CCK). In each rat, we measured the secretory response to CCK before and after administration of norbinaltorphine (norBNI), a selective ĸ-opioid antagonist, or of naloxone, a relatively µ-selective anagonist. Throughout pregnancy, the stimulatory effect of CCK was enhanced by prior administration of norBNI. In pregnant rats norBNI also consistently increased basal oxytocin secretion, while naloxone had no effect, suggesting that in pregnancy there is active restraint of oxytocin secretion by endogenous opioids acting at ĸ-receptors. However, in late pregnancy, between days 17 and 20, there was a significant reduction in the efficacy of norBNI in potentiating the oxytocin release in response to CCK, compared to its efficacy either in non-pregnant rats or in rats between days 8 and 13 of pregnancy. This suggests that in late pregnancy, endogenous ĸ-opioid restraint is downregulated. In addition, the present results demonstrate an attenuation in the potency with which CCK evoked oxytocin release in late pregnancy. The attenuation was unrelated to opioid restraint at the level of the pituitary since it coincided with apparent desensitization of this auto-inhibitory mechan

ISSN:0028-3835    

DOI:10.1159/000127263

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000127264

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In a previous study we have shown that a positive correlation exists between 5-hydroxytryptamine (5-HT) activity and female sexual receptivity in the pre-optic area (POA) and median eminence (ME) and that there is a negative correlation in the ventromedial nucleus (VMN), zona incerta (ZI) and arcuate nucleus (ARC). In this report, the possibility that 5-HT receptor density and affinity alter with sexual receptivity has been investigated. Micropunches of the POA, VMN, ARC, ME and the anterior hypothalamus were dissected from ovariectomised rats primed with a submaximal steroid regime (2 µg oestradiol benzoate, OB, followed at 48 h by 0.05 mg progesterone) which induced receptivity (lordosis quotient, LQ, 80–100%) in approximately half the animals, the remaining half usually exhibiting an LQ < 20%. Binding studies were carried out using 3H-ketanserin (5-HT2A ligand) and 3H-8-hydroxy-2-(di-n-propylamine)tetraline (8-OHDPAT; 5-HT1A ligand) and pooled (n = 5) micropunch samples. The Bmax of 5-HT2A receptors in the sexually receptive groups was significantly (p < 0.05) greater in the POA and ME and significantly lower in the VMN, ARC and ZI when compared with values in the non-receptive animals. The KD values of the 5-HT2A receptors did not differ in the two groups (except the ZI, where the KD was lower in receptive rats). Neither the Bmax nor KD of the 5-HT1A receptors differed in the two groups in any area investigated. Administration of the 5-HT2 agonists dimethoxyiodophenylaminopropane and m-chlorophenyl piperazine into the POA resulted in enhanced sexual activity in animals exhibiting a low level of receptivity, after 5 µg OB given alone while ketanserin (5-HT2A antagonist) in the POA inhibited sexual activity in receptive animals primed with the submaximal steroid regime given above. In the same models, neither the 5-HT2 agonists nor the 5-HT2A antagonist affected behaviour when applied to the VMN. The 5-HT1A agonist 8-OHDPAT exerted an inhibitory effect in the VMN. These findings, together with earlier results, show that in receptive animals there is an increase in both 5-HT turnover and 5-HT2A receptors in the POA and ME. Additionally 5-HT2 agonists and an antagonist applied to the POA enhance and reduce sexual activity, respectively. This suggests that the 5-HT2 system in the POA has a stimulatory role in the control of female sexual behaviour. Both 5-HT activity and 5-HT2 receptors are decreased in the VMN, ARC and ZI of receptive animals. 5-HT2 agonists and a 5-HT2A antagonist have no effect in the VMN indicating that there is no 5-HT2-stimulatory or -inhibitory effect in this area, at least in the animal models used in these experiments. However, the VMN is a site of an inhibitory action mediated by the 5-HT1A recept

ISSN:0028-3835    

DOI:10.1159/000127277

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The arcuate nucleus of the hypothalamus houses a number of neurochemically different cell populations. Among these, a dense cluster of small neuropeptide-Y (NPY)-expressing neurons is located in its ventromedial subdivision and a pro-opiomelanocortin (POMC)-expressing neuron population in its ventrolateral part. Furthermore, both neuropeptide Y Y1 and Y2 receptors (Y1-Rs and Y2-Rs) are expressed in the arcuate nucleus. Here we analyse the co-expression of NPY and POMC/adrenocorticotropic hormone with the Y1-R and Y2-R in arcuate neurons using immunohistochemistry and in situ hybridization. Many, but not all, POMC neurons expressed Y1-R mRNA and protein. Conversely, several Y1-R-positive, POMC-negative neurons were found. NPY-positive nerve terminals were found in close apposition to Y1-R-like immunoreactivity localized close to the dendritic and somatic cell membranes. Y2-R mRNA was found in almost all NPY mRNA-expressing neurons, but also in a group of NPY mRNA-negative cells. These results show that the POMC neurons are targets for NPY, which is presumably present in, and released from, fibres originating in the ventromedial arcuate nucleus and which may play a role in NPY-induced feeding. Release of NPY, and possible coexisting messengers, may be controlled by presynaptic Y2-R expressed in NPY neurons. Taken together, the findings support the division of Y1-Rs and Y2-Rs into post- and presynaptic receptors, respectively.

ISSN:0028-3835    

DOI:10.1159/000127265

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

We have utilised standard dissociation techniques to obtain a preparation of subfornical organ (SFO) cells that have been maintained in tissue culture for up to 1 week. Stable (>15 min) whole cell recordings were obtained from 80 cells displaying rapid (<2 ms) voltage-dependent sodium currents (blocked by tetrodotoxin in 10 of 10 cells tested), and current evoked action potentials, which were thus classified as SFO neurons. These neurons had a resting membrane potential of-6 3.8 ± 1.3 mV (mean ± SEM), spike amplitude of 86.8 ± 2.5 mV, and input resistance of 1.2 ± 0.1 GΩ, characteristics which did not change significantly in recordings obtained for up to 6 days after dissociation. Current clamp recording showed that of 65 cells tested with bath application of angiotensin (ANG; 1,000–10 nM), 41 responded to this peptide with decreases in input resistance (control 1.4 ± 0.16 GΩ, after ANG 0.78 ± 0.1 GΩ, p < 0.0001), and depolarisations (mean 18.3 ± 2.0 mV, p < 0.0001). Similar recordings were obtained from viable cells up to 6 days after initial cell dissociation. These studies provide the first description of the basic membrane properties of dissociated SFO neurons. The responsiveness of these cells to ANG supports the conclusion that their properties are similar to those in vivo. These data suggest that use of this technique will permit systematic analysis of the membrane events underlying the actions of multiple ligands on this uniquely specialised group of

ISSN:0028-3835    

DOI:10.1159/000127266

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Differential evaluation of angiotensin II (Ang II) receptors (AT 1A, AT 1B and AT2) expression was performed in dispersed adenohypophyseal cells fractionated by unit gravity sedimentation. Binding of [125I-Sar1-Ile8]-Ang II and its displacement by specific nonpeptidic AT1 (DUP753) and AT2 (PD123319) antagonists was monitored throughout the gradient. Quantification of mRNA levels corresponding to both ATi receptor subtypes (AT 1A and AT1B) was achieved by reverse transcriptase polymerase chain reaction (RT-PCR) amplification in the presence of an AT1 receptor mutant cRNA as internal standard. Fractions were characterised by radioimmunoassay for the five major anterior pituitary hormones and by counting immunocytochemically labelled cells. Quantification of AT1 receptor subtype mRNA levels was also performed in four hypophyseal cell lines secreting prolactin, growth hormone, corticotropin and a gonadotropin subunit. As already described for the whole pituitary, AT1B receptor mRNA is predominantly expressed (80% of total ,AT 1A + ,AT 1B receptor mRNA content), whereas ,AT 1A is expressed at lower level (20%) in dispersed pituitary cells. Most AT1 receptor mRNA and binding co-elute with fractions enriched in lactotropes and corticotropes. In contrast to ,AT 1B, ATtA receptor mRNA is not present in heavier populations of lactotropes or in somatomammotropes. Low ,AT 1B mRNA levels are detected in GH4C1 and in GC cells, two clones which secrete respectively prolactin and growth hormone. In contrast, no AT1 receptor mRNA expression was found in two other cell lines, AtT20 and (XT3.1, which produce pro-opiomelanocortin and gonadotropin. It is concluded that expression of AT1 receptor subtypes is heterogeneous in different populations of lactotropes and corticotropes.

ISSN:0028-3835    

DOI:10.1159/000127267

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Nitric oxide (NO) has recently been shown to modulate pituitary secretion both in vivo and in vitro. The aim of this study was to investigate the effects of this chemical transmitter on spontaneous and growth-hormone-releasing hormone (GHRH)-induced growth hormone (GH) secretion in acromegalic patients, as well as from GH-secreting tumors maintained in vitro. The study was carried out in 7 acromegalic patients (46.2 ± 2 years) and in 5 normal subjects (40.1 ± 1.5 years). GH and prolactin (PRL) secretion were assayed during the administration of isosorbide dinitrate (ID, 5 mg, orally), an NO donor, GHRH, and ID plus GHRH. During ID, a significant (p < 0.05) increase (37%) over basal GH levels was only observed in acromegalics. There was no change in GH levels in response to GHRH or ID plus GHRH in either group. No significant change in PRL levels was observed in either group during ID, while GHRH, with or without ID, induced a slight increase in PRL levels in acromegalics only. Tumor specimens were obtained by selective transsphenoidal adenomectomy, and the cells were plated and incubated for 1 2 and 24 h in the presence of sodium nitroprusside, a releaser of NO (SNP, 0.3 or 0.6 mM), of GHRH (10–8 M) or of both. SNP significantly (p < 0.001) increased GH levels in a dose-dependent manner (R = 0.99, p = 0.02), but was unable to modify the GH response to GHRH. In acromegalics, a significant correlation (R = 0.822, p < 0.045) and a correlation near the limit of significance (R = 0.73, NS) were observed respectively between the in vivo GH response to ID and the in vitro response to SNP at 24 h. No significant effect was observed on PRL secretion during SNP incubations, while GHRH produced a significant increase in PRL after 2 and 24 h incubation in acromegalics. These observations indicate that NO plays a stimulatory role in vivo and in vitro on GH secretion in acromegalic patie

ISSN:0028-3835    

DOI:10.1159/000127268

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Hexarelin (HEX) is a synthetic growth-hormone-releasing peptide (GHRP) which acts via specific receptors at both the pituitary and the hypothalamic level to stimulate GH release both in animals and in man. Like other GHRPs, HEX possesses also significant prolactin-and adrenocorticotropin (ACTH) cortisol-releasing activity, but the mechanisms underlying these effects are even less clear. To clarify the mechanisms by which HEX stimulates the pituitary-adrenal axis in man, in 7 healthy young volunteers we studied the effects of HEX (2.0 µg/kg i.v.) and/or human corticotropin-releasing hormone (hCRH; 2.0 µg/kg i.v.) and /or arginine vasopressin (AVP; 0.17 U/kg i.m.) on ACTH and cortisol secretion. The GH responses to HEX alone and combined with hCRH and/or AVP were also studied. HEX increased ACTH and cortisol secretion (peak, mean ± SEM:26.3 ± 5.1 vs. 15.8 ± 3.1 pg/ml and 145.0 ± 11.4 vs. 131.7 ± 11.7 µg/1, p < 0.01, respectively) to levels overlapping with those induced by AVP (27.9 ± 6.1 vs. 13.1 ± 3.5 pg/ml and 167.6 ± 16.2 vs. 113.3 ± 9.4 µg/lp < 0.01, respectively) and similar to those elicited by hCRH (28.1 ± 4.6 vs. 17.4 ± 3.1 pg/ml and 182.7 ± 22.8 vs. 114.8 ± 12.3 µg/lp < 0.02, respectively). The ACTH but not the cortisol response to hCRH was higher (p < 0.02) than those to HEX when evaluated as area under the curve. The co-administration of HEX and AVP had no significant interaction on ACTH and cortisol peak levels (40.7 ± 5.3 pg/ml and 168.8 ± 13.5 µg/1, respectively). On the other hand, the co-administration of HEX and hCRH had a less than additive effect on ACTH and cortisol secretion (53.3 ± 11.2 pg/ml and 204.0 ± 13.7 µg/1, respectively). CRH and AVP had a true synergistic effect on ACTH (104.9 ± 14.2 pg/ml, p < 0.01) and an additive effect on cortisol secretion (281.3 ± 10.8 µg/1, p < 0.02). HEX did not modify the effect of CRH + AVP on both ACTH (135.5 ± 22.0 pg/ml) and cortisol secretion (261.1 ± 13.2 µg/1). The GH response to HEX (55.7 ± 19.8 vs. 2.7 ± 1.9 µg/1, p < 0.005) was unaffected by the administration of CRH alone (53.5 ± 21.0 µg/1) and/or AVP co-administration (60.2 ± 21.2 and 45.9 ± 10.6 µg/1, respectively). In conclusion, the results of this study demonstrate that GHRPs, beside their well-known GH-releasing activity, possess a remarkable ACTH-releasing activity, overlapping with that of AVP and similar to that of hCRH, two neurohormones which are known to play the major role in the control of the pituitary-adrenal axis. It is noteworthy that HEX shows no synergistic effect with either AVP or hCRH which, on the other hand, truly synergize. This evidence suggests the hypothesis that the ACTH-releasing activity of GHRPs could be, at least partially, independent of both CR

ISSN:0028-3835    

DOI:10.1159/000127269

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000127270

出版商:S. Karger AG    

年代:1997

数据来源: Karger