摘要:

The biological potency of the new, highly potent antagonist [AC-D-Nal (2)1, E-Phe(4Cl)2, D-Pal(3)3 -Cit6, D-Ala10] LH-RH (SB-75) on the pituitary-gonadal system of female castrated and intact ovulating rats was tested. Administration of a single dose (50-100 µg/kg BW) of the antagonist SB-75 inhibited effectively the elevated gonadotrophin levels for 48 h. Pituitary LH and FSH content was not affected by SB-75 treatment. When administered in the early afternoon of the proestrus to intact cycling rats, SB-75 blocked the preovulatory LH surge as well as the primary and secondary FSH surges. However, the secondary FSH surge was not affected by SB-75 treatment when administered on the evening of proestrus suggesting its independence from the LH-RH mechanism. A group of ovariectomized rats was chronically treated with D-Trp6-LH-RH after having been pretreated by administration of a single dose of the antagonist. The initial stimulatory release of LH and FSH initiated by injection of the LH-RH agonist was significantly reduced by pretreatment with the LH-RH antagonist. We conclude that the LH-RH antagonist SB-75 may be used effectively in the field of reproductive dysfunction and endocrinological oncology and may become an invaluable physiological probe in studying the hormonal dynamics of the reproductive endocrine axis

ISSN:0028-3835    

DOI:10.1159/000126527

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The biological activity and immunoreactivity of serum prolactin (PRL) has been shown to fluctuate throughout the estrous cycle of the rat. Since the 24-kDa nonphosphorylated and phosphorylated isoforms from several species have also been shown to differ in their biological and immunoreactivities, we have investigated the possibility that the 24-kDa monomer isoform profile varied throughout the estrous cycle of the rat. The PRL isoform profile was assessed in homogenates of pituitaries and in short-term incubation media. Comparisons between homogenates, which always contained isoforms 1, 2, 3, and 3’ (numbered according to increasing acidity), and media showed nonproportional release of the isoforms at all stages. Of great interest were the release of isoform 1 (a nonphosphorylated form) only at estrus and the lack of release of isoform 3’ (a phosphorylated form) only in the afternoon of proestrus. This lack of release of 3’ was accompanied by a marked increase in the release of isoform 2 (the unmodified polypeptide). These results suggest a unique function for isoform 1 during estrus and a role for increased isoform 2 and absent isoform 3’ during the proestrus surge of PRL. Moreover, they suggest that fluctuations in the biological activity and immunoreactivity of serum PRL during the estrous cycle could be due, at least in part, to fluctuations in the isoform

ISSN:0028-3835    

DOI:10.1159/000126528

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Gonadotropin-releasing hormone (GnRH) immunoreactive cells and fibers were revealed in olfactory regions, the ventral forebrain, and in the midbrain of the musk shrew (Suncus murinus). Immunoreactive neurons in olfactory and telencephalic areas were specific for the mammalian form of GnRH. Cell bodies in the midbrain, however, cross-reacted with an antibody specific for chicken-II GnRH. High-performance liquid chromatography and radioimmunoassay analyses confirmed these results; high levels of chicken II GnRH were present in the midbrain, and mammalian GnRH was detected in both fore-brain and midbrain. In addition, a third, late-eluting form of GnRH was revealed using high-performance liquid chromatography in both forebrain and midbrain of the musk shrew. Midbrain neurons containing GnRH have not been reported previously in a mammal, although mesencephalic GnRH immunoreactivity within cell bodies is common among nonmammalian vertebrates. Likewise, while multiple forms of GnRH have been reported in non-mammalian vertebrates and several metatherian species of mammals, this is the first report on multiple forms of GnRH in the brain of a placental mammal. Taken together, the findings suggest that this primitive eutherian mammal has retained the ability to produce GnRH protein in the midbrain. This feature of the GnRH system has been conserved among nonmammalian vertebrates, but appears to have been lost in modern placental mammal species. The functional significance of this group of neurons has yet to be determined.

ISSN:0028-3835    

DOI:10.1159/000126529

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The regional brain distribution of 125I-somatostatin (SRIH) binding sites was determined by quantitative radioautography in neonatally monosodium glutamate (MSG) treated adult male rats, a procedure which selectively destroys most neurons of the arcuate nucleus. Neonatal MSG treatment did not modify the extrahypothalamic distribution of 125I-SRIH-binding sites. In contrast, the number of 125I-SRIH-labeled cells in the ventrolateral part of the arcuate nucleus was strongly reduced in MSG-treated animals. The effect was selective for the anterior part of the arcuate nucleus and was not found in its posterior part or in the cells located more dorsally, beneath the ependymal zone of the periventricular nucleus. Intracerebroventricular SRIH injections, which increased growth hormone levels in control rats, were totally ineffective in MSG-treated animals. In contrast, the prolactin levels were equally stimulated by intracerebroventricular injections in control and MSG-treated animals. These results demonstrate that extrahypothalamic SRIH-binding sites are not located on neurons originating in the anterior arcuate nucleus neurons. In addition, 125I-SRIH-labeled cells in the ventrolateral part of the arcuate nucleus are necessary for the paradoxical stimulation of growth hormone secretion induced by intracerebroventricular SRIH injection, but do not seem to be essential for the increased prolactin secretion observed under these conditions.

ISSN:0028-3835    

DOI:10.1159/000126530

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Interleukin-2 (IL-2), which plays a major role in the bidirectional intercellular communication between the neuroendocrine and immune systems, suppressed the release of GH from anterior pituitary halves at femtomolar concentrations. It is well established that the release of GH from the anterior pituitary is regulated by growth hormone releasing hormone (GRH) and growth hormone release-inhibiting hormone (somatostatin). Consequently, we studied the possible effect of IL-2 on the release of somatostatin and GRH from the mediobasal hypothalamus (MBH) in vitro. Single MBHs were incubated with fresh Krebs-Ringer bicarbonate (KRB) buffer alone or KRB containing different concentrations of IL-2 (10–15–10–10M) for 30 min. After collection of the media, the MBHs were incubated with KRB containing high potassium (high K+ = 56 mM) without IL·2 for a period of 30 min to study the effect of pretreatment with IL-2 on depolarization-induced somatostatin and GRH release. Experiments were also undertaken to study the effect of IL-2 in the presence of high K+ or IL·2 in the presence of DA (60 µM), a potent stimulator of somatostatin and GRH release. The minimal effective dose of IL-2 which significantly stimulated the release of somatostatin was 10–14M. Depolarization-induced release of somatostatin was reduced significantly by prior treatment with all the concentrations of IL-2 tested (10–13–10–10M). Basal release of GRH was unaltered by the different concentrations of IL-2 but the depolarization-induced release of GRH was significantly lowered by IL-2 (10–13–10–10M). Simultaneous incubation with IL-2 plus high K+ resulted in a significant decrease in GRH release without modifying the release of somatostatin. DA stimulated the release of both somatostatin and GRH; however, when IL-2 was added to DA, it significantly attenuated both DA-induced somatostatin and GRH release. The results demonstrate the ability of IL-2 to (1) stimulate somatostatin release without affecting GRH release; (2) suppress depolarization induced somatostatin release; (3) suppress depolarization-induced GRH release; and (4) block DA-induced stimulation of both somatostatin and GRH release, which suggests the possible involvement of a dopaminergic pathway in the mecha

ISSN:0028-3835    

DOI:10.1159/000126531

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Alpha-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH), peptides derived from the precursor proopiomelanocortin, share amino acid homology at the aminoterminus of ACTH, occur within the pituitary and the brain and are potent antipyretic compounds in cytokine-mediated fever. Because α-MSH and ACTH act within the hypothalamus to block leukocytic pyrogen- or cytokine-mediated fever, we hypothesized that these compounds might also be capable of blocking the action of interleukin-1 (IL-1) and interleukin-6 (IL-6) to stimulate corticotropin-releasing factor (CRF) release from the hypothalamus. Mediobasal hypothalami (MBH) were incubated in vitro. After 60 min preincubation in Krebs-Ringer bicarbonate buffer (KRB), MBH explants were incubated for 30 min with KRB alone or KRB containing IL-6 (10–13M), IL-1 (10–16–10–10 M) and/or ACTH1–24 (10–15–10–9M) or α-MSH (10–15-10–8M); CRF release into the incubation medium was measured by RIA. None of the ACTH1–24 or α-MSH concentrations changed basal CRF release significantly. As we reported previously, IL-6 (10–13M) increased CRF release; this increase was suppressed, in a dose-dependent fashion, by α-MSH at concentrations of 10–13–10–11M, with the maximal inhibitory effect observed at 10–13M. ACTH1–24 also exerted a dose-dependent inhibitory effect on IL·6-stimulated CRF release but at even lower concentrations (10–15–10–13M) with the maximal inhibitory effect observed with the 10–l4M concentration. Interleukin-1 β (IL-1β) evoked a bell-shaped, concentration-dependent increase in CRF secretion with a maximal effective concentration of 10–15M, 100 times lower than that previously reported for IL·6. IL-1β-induced CRF release was suppressed with a U-shaped concentration-dependent curve by α-MSH, with the maximal inhibitory effect observed with concentrations of 10–13 and 10–14M α-MSH. The results show that α-MSH is a potent inhibitor of IL-1β- and IL·6-induced CRF release from the hypothalamus in vitro and that ACTH1–24 is even more potent than α-MSH (which is ACTH1–13) in the blockade of IL·6-induced CRF release. These findi

ISSN:0028-3835    

DOI:10.1159/000126532

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Immobilization (IMMO) of conscious rats evokes marked increases in release of norepinephrine (NE) in the paraventricular nucleus (PVN) of the hypothalamus, consistent with a role of NE in the PVN release of corticotropin-releasing hormone and therefore in pituitary-adrenocortical activation during stress. The present study examined the effects of surgical hemisection of the brainstem between the locus ceruleus and rostral portion of the medulla on release of NE in the PVN of the hypothalamus in vivo in conscious rats, at baseline and during IMMO. Concentrations of NE, the intraneuronal NE metabolite dihydroxyphenylglycol (DHPG), and the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) were measured in microdialysate samples obtained beginning 24 h after implantation of a microdialysis probe in the PVN either ipsilateral or contralateral to the hemisection. On the lesioned side, baseline levels of NE, DHPG, and DOPAC were significantly lower and IMMO-induced increases were smaller than in sham-operated rats. Contralateral to the hemisection, DOPAC levels were significantly reduced. Neither baseline levels nor IMMO-induced increases in plasma corticosterone levels differed between lesioned and sham-operated animals. The present results indicate that: (1) NE release in the PVN at baseline and during IMMO depends mainly on ascending medullary tracts from ipsilateral brainstem A1 and A2 catecholaminergic areas, with small contributions from the locus ceruleus and from contralateral medullary cells, and (2) brainstem hemisection does not influence IMMO-induced activation of the hypothalamic-pituitary-adrenocortical axis as indicated by plasma corticosterone levels in conscious rats.

ISSN:0028-3835    

DOI:10.1159/000126533

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Intravenous injection of nerve growth factor (NGF) into rats produces a dose-dependent (from 0.1 to 5 nmol/kg) increase in circulating concentrations of adrenocoticotropin (ACTH) and corticosterone. We have investigated whether this effect is produced through a direct action on a component of the hypothalamo-pituitary-adrenocortical axis. NGF (50 and 500 nM), added to the incubation medium of in vitro isolated pituitary segments or dispersed adrenal cells, did not modify either basal and stimulated release of biologically active or immunoreactive ACTH or release of corticosterone, respectively. The presence of NGF in the incubation medium of in vitro isolated hypothalami produced a dose-dependent (from 150 to 600 nM) increase of both release and content of some material with corticotropin-releasing bioactivity. The nature of this corticotropin-releasing bioactivity was determined directly by radioimmunoassays. Results have indicated that NGF induced an increase of both release and content of hypothalamic arginine-vasopressin (AVP), while no changes were observed in the release and content of hypothalamic corticotropin-releasing hormone (CRH). These results suggest that adrenocortical stimulation by NGF in vivo could be mediated by the release of hypothalamic AVP rather than CRH. The finding that in vivo NGF stimulatory effect was not abolished by the specific CRH antagonist α-helical CRH(9–41), while it was accompanied by an increase in circulating AVP levels, supports this interpretation. However, the fact that the hypothalamus is stimulated in vitro by NGF concentrations higher than those expected to reach this structure after systemic injection of active doses raises the possibility that other brain areas such as the hippocampus participate in NGF-induced adrenocortical activati

ISSN:0028-3835    

DOI:10.1159/000126534

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Passive immunization is a common approach used to eliminate the biological activity of an endogenous substance by its binding to a specific antibody (Ab). Surprisingly little information has been gathered on the mechanisms involved. Moreover, the possibility that immunoneutralization could affect also the secretion of the antigen itself has been mostly ignored. To study hypothalamic neuropeptide secretion under the condition of passive immunization, labeled and unlabeled monoclonal antibody (MoAb) against arginine vasopressin (AVP) was injected intravenously. After 2 h a similar amount of 125I-MoAb was found in hypophyseal portal and peripheral (femoral artery) plasma, showing a distribution volume of 73.2 ml/kg. Assessment of the MoAb dilution in the same plasma samples from the binding studies revealed substantially higher dilutions (800–5,700 ml/kg). Such a MoAb dilution (saturation) would be attained by the binding of 130-290 pmol AVP/ml plasma. The calculated amount of plasma AVP decreased by one half within the interval from 2 to 24 h after Ab injection, similarly as did the 125I-MoAb content. Intravenous injection of polyclonal corticotropin-releasing hormone (CRH) Ab resulted in a decrease of plasma adrenocorticotropin and corticosterone levels. After 24 h the dilution of the Ab in portal plasma exceeded two times that in peripheral plasma. CRH concentrations of 0.6-2.5 pmol/ml were found by specific radioimmunoassay after its dissociation from the Ab in plasma. The CRH concentration was higher in portal than in peripheral plasma and was related to the amount of the Ab injected. CRH mRNA levels in the paraventricular nucleus were significantly increased in CRH Ab as compared with normal rabbit serum injected rats. Intravenous injection of the specific antibody results in the binding of a high amount of the respective peptide in plasma, most probably due to an excessive hypothalamic secretion, and may result in an increase of its biosynthesi

ISSN:0028-3835    

DOI:10.1159/000126535

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

A possible inter-relationship between oestrogen, α-melanotrophin (αMSH) and NA in the ventromedial nucleus (VMN) has been studied in ovariectomised-adrenalectomised rats primed with a low dose of oestradiol benzoate (2 or 5 µg OB), which induces receptivity in approximately half the rats. Priming with OB increased NA turnover in the VMN (as assessed by the decline in NA concentration 1 h after 250 mg/kg α-methyl tyrosine αMT) and also enhanced the release of NA from basal medial hypothalamic fragments in vitro. This occurred whether the rats were receptive or non-receptive. Injection of 20 µg/ rat αMSH, 4 h before autopsy in OB-primed rats, reduced NA turnover in the VMN but only in the receptive animals. αMSH had no effect on NA content in the VMN, but prevented the decline normally induced by the αMT, indicating an inhibition of release. Application of 1 µg/ml αMSH to incubated hypothalamic fragments enhanced release of NA in the tissue obtained from untreated controls and the OB-non-receptive group, but had no effect on the tissue of the OB-receptive animals. Perhaps NA release had already occurred in vivo in the latter group. αMSH (100 ng/side/rat) and NA (20, 200 and 2,000 ng/side/rat) were injected into the VMN of ovariectomised-adrenalectomised rats primed with 1 µg OB. Both agents stimulated lordosis in non-receptive animals with a peak activity at 60 min. The effect of αMSH declined over the next 2 h, but the maximum effect of 200 and 2,000 ng NA was maintained until the end of the test at 4 h. Neither agent affected behaviour in receptive animals. Intra-VMN administration of the β-adrenergic antagonists, propranolol and metoprolol (both at 400 ng/side/rat) reduced the effect of αMSH and the former also antagonised the effect of NA, while the α-adrenergic antagonist, phentolamine (200 µg), was ineffective. These results show that αMSH and NA in the VMN stimulate female sexual behaviour and the effect of αMSH may be mediated by NA acting on β-receptors. αMSH may act by enhancing the release of NA, but once receptivity is initiated, αMSH appears instead to reduce NA release and thus to terminate the

ISSN:0028-3835    

DOI:10.1159/000126536

出版商:S. Karger AG    

年代:1993

数据来源: Karger