摘要:

To characterize the short-term ACTH secretion pattern and to investigate factors regulating it, pituitary venous (PV) blood was collected using our nonsurgical method from 8 unperturbed horses every 20 or 30 s for approximately 1 h. In all but 1 horse, sampling occurred during the broad circadian maximum in plasma cortisol concentrations. Concentrations of corticotropin-releasing hormone (CRH; n = 7 horses), arginine vasopressin (AVP), ACTH and cortisol were measured by radioimmunoassay. In all horses, CRH, AVP and ACTH secretion patterns appeared irregular in time and amplitude. The mean (±SEM) numbers of peaks per hour detected by the cluster program were 2.8 ± 1.2, 10.1 ± 1.9 and 10.2 ± 1.4for CRH, AVP and ACTH, respectively. However, when 2- and 5-min sampling frequencies were simulated by meaning consecutive values, significantly fewer peaks were detected in each hormone. There was no correlation between the prevailing cortisol concentration and peak frequencies of CRH, AVP or ACTH. Secretion patterns of ACTH and AVP were closely related in all horses as assessed by cross correlation analysis and coincidence of peaks, although the ratio between PV ACTH and AVP concentrations fluctuated markedly within each horse. In contrast, the relationship between CRH and ACTH secretion was variable. Bivariate spectral analysis showed only a modest degree of underlying periodicity in CRH, AVP and ACTH secretion during the very short term studied. Nevertheless, distinct peaks exceeding the 95% confidence limits of white noise were observed at periods between 2 and 30 min in 5 of 7 CRH, 6 of 8 AVP and 5 of 8 ACTH spectra. Furthermore, the slope of the regression line through each spectrum did not become indistinguishable from zero, i.e. the flat white noise continuum, until mean (±SEM) periods of 2.6 ± 0.8, 1.6 ± 0.2, and 2.0 ± 0.2 min, for CRH, AVP and ACTH spectra, respectively. At the ACTH spectral maximum, the coherence coefficient, which is analogous to the squared correlation coefficient, exceeded 0.5 in comparisons of all ACTH and AVP spectra and of 5 of 7 ACTH and CRH spectra. We conclude that (1) rapid sampling is needed to define short-term CRH, AVP and ACTH secretion patterns accurately: peaks are missed when 2- or 5-min collection regimens are used, and (2) the major components in the ACTH micropulsatile secretion pattern in the horse are regulated by secretagogues. The closeness and consistency of the relationship between AVP and ACTH secretion suggest that AVP may be the primary signal for ACTH micropulses in the unperturbe

ISSN:0028-3835    

DOI:10.1159/000126755

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The most common lesion in Cushing’s disease is an anterior pituitary adenoma. However, normal or hyperplastic corticotropic pituitary tissue has also been found in some cases. In an attempt to distinguish the patterns of ACTH response to oCRH in different forms of anterior pituitary hypersecretion, 17 patients with pituitary adenoma and 17 without pathological evidence of adenoma were studied. These patients underwent transsphenoidal pituitary surgery by the same surgeon and were retrospectively evaluated. The diagnosis of pituitary lesions was confirmed by microscopical and immunohistochemical studies. Patients without pituitary adenoma showed a higher and more prolonged mean plasma ACTH response than that observed in patients with pituitary tumors. In patients with pituitary adenoma, the peak ACTH response was observed within 30 min after oCRH administration, and was followed by a gradual decrease to basal levels in the following 30 min. In those cases in whom no pituitary adenoma was found, oCRH injection produced a marked increase in plasma ACTH levels during the first 60 min with a slower decline at the subsequent time points. The mean response curves of the two groups, analyzed by Beherens-Fischer nonparametric ANOVA, showed significant differences, either when they were compared globally (p < 0.01), or at single time points. Differences in ACTH response to oCRH stimulation support the hypothesis of different pathogenetic mechanisms leading to ACTH hypersecretion in Cushing’s disease with and without pituitary aden

ISSN:0028-3835    

DOI:10.1159/000126756

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The involvement of hypothalamic histaminergic neurons in the mediation of the ACTH and β-endorphin (β-END) response to lipopolysaccharide (LPS) endotoxin was investigated in conscious male rats. LPS stimulated the release of ACTH and β-END dose-dependently and increased the hypothalamic concentration of the histamine (HA) metabolite tele-methylhistamine significantly and that of HA slightly, indicating an increased turnover of neuronal HA. Pretreatment with the HA synthesis inhibitor α-fluoromethyl-histidine administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) inhibited the ACTH and β-END response to LPS about 60%, whereas i.p. administration of the H3 receptor agonist R(α)methylHA, which inhibits HA synthesis and release, decreased the response about 50%. Pretreatment with the H1 receptor antagonist mepyramine (67 µg × 2 i.c.v.) inhibited the hormone response to LPS about 50%, while pretreatment with equimolar doses of the H1 receptor antagonists cimetidine (67 µg × 2 i.c.v.) or ranitidine (83 µg × 2 i.c.v.) had no effect on the LPS-induced release of ACTH and β-END. When the H1 receptor antagonists mepyramine and cetirizine were administered i.p. in doses (10 mg/kg) which penetrate the blood-brain barrier the hormone response to LPS was inhibited 50% and 30%, respectively. Administered i.p. the H2 receptor antagonists had no effect on the hormone response to LPS. We conclude that hypothalamic histaminergic neurons in rats are involved in the mediation of the ACTH and β-END response to LPS stimulation via activation of central postsynaptic H1

ISSN:0028-3835    

DOI:10.1159/000126757

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Possible interactions of ACTH-like peptides with melatonin regulation of central-type benzodiazepine (BNZ) receptors have been studied by means of highaffinity 3H-fiunitrazepam binding to rat cerebral cortex membrane preparations. Intracerebroventricular injections of melatonin produce a dose-dependent increase in Bmax in pinealectomized rats, without changes in KD. Analogous effects were obtained after intracerebroventricular injection of melatonin in adrenalectomized and in adrenalectomized plus pinealectomized rats, which indicated the lack of participation of adrenal steroids in this response. Moreover, intracerebroventricular injection of ACTH1–10 induced a similar dose-dependent increased Bmax in sham-operated animals, whereas pinealectomy, but not adrenalectomy, partially counteracted this effect of ACTH1–10 administration. Besides, simultaneous injection of ACTH1–10 plus melatonin reverses the effects of pinealectomy, resulting in an additive effect of both compounds on Bmax. The response obtained when using ACTH4–10 was somewhat different, because no dose response was obtained in any experiment. Although lack of endogenous melatonin partially reduced the increasing effect of ACTH4–10 on Bmax, there were no additive effects at the different doses used. The results strongly suggest that ACTH-like peptides, in addition to melatonin, play a role in regulating central-type rat BNZ

ISSN:0028-3835    

DOI:10.1159/000126767

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The hippocampus contains a high concentration of the two corticosterone (CT) receptor subtypes, i.e. the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). The endogenous steroid hormone CT has tenfold higher affinity for the MR than the GR. Under physiological conditions the MR is 80-95% occupied; during the daily diurnal surge of CT and following a stressful stimulus, the MR is 100% occupied and the GR 67-80% occupied. Previous studies have shown that CT can alter the synthesis of proteins within 30 min whereas it takes up to 7 days to alter the synthesis of other proteins. The physiological relevance of MR and GR activation is not totally understood. Intracellular recording techniques in hippocampal slices maintained in vitro were used to investigate chronic continuous or short-term effects of CT administration on hippocampal pyramidal cell activity. Rats were adrenalectomized (ADX) with or without CT replacement. The CT pellet used provided continuous plasma corticosterone levels equal to that seen in a normal rat in the morning. On the day of the experiment, slices from ADX animals were perfused with buffer containing no steroid, 1 nM CT or the selective GR agonist RU28362. Slices taken from ADX with CT pellet treated rats were superfused with buffer containing 1 nM CT or no steroid. Short-term and chronic CT treatment increased the membrane time constant, decreased the slow afterhyperpolarization (sAHP) amplitude, and increased the number of action potentials elicited by a depolarizing current pulse. Chronic continuous CT treatment decreased input resistance measured at 300 ms, increased action potential amplitude and duration, and decreased the fast afterhyperpolarization (fAHP) amplitude. The net result of these actions would be to increase pyramidal cell excitability, i.e. increase the probability of action potential generation and action potential firing frequency, and to increase the synaptic output of the CA1 pyramidal cell to its efferent connections. We conclude that chronic continuous low CT concentrations, equal to those plasma concentrations normally present throughout the day, modulate the physiology of the CA1 hippocampal pyramidal cell.

ISSN:0028-3835    

DOI:10.1159/000126758

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The influx of extracellular calcium is a critical step involved in the stimulated release of adrenocorticotropin (ACTH) from pituitary corticotrophs. It has been proposed that the mechanism of early glucocorticoid feedback is mediated through inhibition of stimulus-evoked calcium transients. We tested this hypothesis using corticotrophic mouse pituitary AtT-20 cells by coevaluating secretory dynamics and cytosolic calcium transients. In static monolayer culture and in a dynamic microperifusion system, dexamethasone (DEX, 100 nM, 2 h) significantly inhibited ACTH secretion stimulated by corticotropin-releasing hormone (CRH, 100 nM). When ACTH was stimulated by KC1 (56 mM) depolarization or the voltage-dependent calcium channel agonist, maitotoxin (MTX, 1 ng/ml), DEX did not inhibit secretion. In contrast, CRH-, KC1-, and MTX-stimulated ACTH secretion were significantly inhibited in static monolayer culture when cells were pretreated with the voltage-dependent calcium channel blocker, nifedipine (NIF, 1 µM, 15 min), confirming the requirement for the influx of extracellular calcium. Intracellular calcium was measured under similar culture conditions in populations of cells grown on coverslips, utilizing the fluorescent calcium indicator, fura-2. DEX had no effect on basal, spike, or plateau calcium levels in response to CRH, KC1 or MTX stimulation. For example, CRH stimulation resulted in an increase in intracellular calcium from a basal concentration of 90 ± 3.1 nM (mean ± SE) to a plateau of 222 ± 8.7 nM, whereas the plateau after DEX was 225 ± 4.1 nM. In contrast, NIF significantly lowered the stimulated calcium response to each secretagogue (spike and plateau). These results do not support the hypothesis that glucocorticoids suppress stimulated secretion of ACTH from corticotrophs through an effect on intracellular calcium transients. Instead, the data suggest that early glucocorticoid negative feedback occurs at a step(s) distal to the influx of extracellular cal

ISSN:0028-3835    

DOI:10.1159/000126759

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

We have shown previously that sexual stimulation (copulation with intromission or vaginocervical stimulation) induces c-fos mRNA and Fos-like immunoreactivity (IR) within estrogen-concentrating and nonconcentrating regions of the female rat forebrain, including regions that contain gonadotropin-releasing hormone (GnRH) neurons in septum and anterior preoptic area. The overall induction of Fos-like IR within these regions was specific to afferent sensory stimulation and did not require treatment with estrogen and progesterone. Because vaginocervical stimulation facilitates lordosis and increases the release of luteinizing hormone, the present study examined whether hormone treatment that promotes sexual receptivity, with or without sexual stimulation, increases Fos-like IR specifically within GnRH-containing neurons. Sexually experienced ovariectomized rats were administered estradiol benzoate (10 µg) 48 h and progesterone (500 µg) 4 h before either 1 h of paced copulation with a sexually vigorous male, 50 vaginocervical stimulations with a glass rod distributed over 1 h, or no stimulation. Control rats received injections of the oil vehicle. Fos-like IR was found within a significant number of GnRH-positive neurons in the anterior preoptic area caudal to the organum vasculosum following copulation with intromission or vaginocervical stimulation as compared with no stimulation. Although few GnRH cells coexpressed Fos following hormone treatment alone, this treatment enhanced the number of GnRH neurons that coexpressed Fos following vaginocervical stimulation as compared with the effect of vaginocervical stimulation in oil-treated rats. Together, these data indicate that estrogen and progesterone can augment the responsiveness of certain GnRH neurons to vaginocervical stimulation, consistent with the effects of sexual activity on GnRH releas

ISSN:0028-3835    

DOI:10.1159/000126760

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Corticotropin-releasing hormone (CRH) has been shown capable of inhibiting hypothalamic gonadotropin-releasing hormone (GnRH) release through activation of an endogenous opioid peptide (EOP)-dependent mechanism. Recently, we have shown that prolactin (PRL) stimulates CRH release and inhibits GnRH release by hypothalami explanted from male rats. Thus, the present study was undertaken to investigate whether the inhibitory effect of PRL on GnRH release in vitro is mediated by CRH and/or EOP. To this aim, the release of GnRH in response to PRL was evaluated in presence of CRH9–41 α-helical (CRH9–41), a CRH receptor antagonist, and/or naloxone (NAL), a nonselective opioid receptor antagonist, using a static hypothalamic organ culture system which enabled us to evaluate immunoreactive GnRH (iGnRH) release from individually incubated longitudinally halved hypothalamic. As previously shown, PRL at the concentration of 100nmol/l inhibited basal iGnRH release by about 35%. CRH9–41 or NAL overcame the inhibitory effect of PRL on iGnRH release in a concentration-dependent fashion. The simultaneous co-incubation with both antagonists was not more effective than each single antagonist. CRH9–41 did not have any effect on basal iGnRH release whereas NAL, as previously reported, increased it. In addition, PRL at the concentration of 100 nmol/l stimulated basal hypothalamic β-endorphin (β-EP) release. In conclusion, these data show that antagonism to CRH receptors counteracts the suppressive effects of PRL upon GnRH release and that PRL is able to stimulate hypothalamic β-EP relea

ISSN:0028-3835    

DOI:10.1159/000126761

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The objective of the present study was to examine the role of vasopressin in the regulation of LH secretion in the rhesus monkey. The effect of vasopressin administration on basal LH secretion and vasopressin antagonism on stress-induced inhibition of LH secretion were examined. Intracerebroventricular (i.c.v.) infusion of vasopressin (20 µg/h) to chair restrained ovariectomized rhesus monkeys (n = 5) decreased the area under the LH curve by –51.61 ± 13.73 ng/ml/h compared to –8.35 ± 7.11 ng/ml/h following infusion of artificial CSF (aCSF; p = 0.021). This effect was independent of any change in mean arterial pressure. Subsequently, the role of vasopressin in hypoglycemia-induced suppression of LH was examined. Administration of insulin (1 U/kg BW) to chair-restrained ovariectomized rhesus monkeys decreased the area under the LH curve by –60.88 ± 19.77 ng/ml/h. The decrease in LH was significantly different from that observed in aCSF-infused euglycemic controls which exhibited a slight decrease in LH (–8.35 ± 7.11 ng/ml/h; p = 0.036). In contrast, the area under the LH curve was increased slightly (1.42 ± 11.93 ng/ml/h) when insulin administration was combined with i.c.v. infusion of the vasopressin antagonist [deaminopenicillamine1, O-methyl-tyrosine2, arginine8]-vasopressin (120 µg/h; p = 0.013 vs. insulin only). The demonstration that vasopressin administration inhibits LH secretion whereas vasopressin antagonism prevents hypoglycemia-induced LH suppression suggests that vasopressin is a physiological inhibitor of LH secretion in the

ISSN:0028-3835    

DOI:10.1159/000126762

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The presence of prolactin (PRL) mRNA in the mammary gland of lactating goats and sheep was demonstrated by Northern analysis and RT-PCR. This provides evidence that the PRL gene is transcribed in this tissue. This ectopic expression is not restricted to the lactational period, as PRL transcripts were also found during the last third of pregnancy. Comparison of mammary and pituitary PRL mRNAs showed that they are similar in size but less abundant in mammary gland. In addition, an 847-bp cDNA fragment amplified from mammary retrotranscripts, containing the entire coding region and the major part of the 5’ and 3’ untranslated regions (UTRs), was found to be identical in sequence to its pituitary counterpart. Primer extension analysis, performed to obtain further information on the structure of the mammary PRL mRNA, has shown that the 5’ UTR is 56 nucleotides (nt) long for both species. This is comparable with the size (53 nt) found using the caprine pituitary RNA as template. These results strongly suggest that the PRL gene is not transcribed from a different promoter in mammary gland, as has been demonstrated for placental and lymphocyte cells, but is more likely transcribed from the pituitary-specific promoter. Finally, the presence of PRL mRNA in polysomal fractions suggests that PRL is synthesized in mammary

ISSN:0028-3835    

DOI:10.1159/000126763

出版商:S. Karger AG    

年代:1994

数据来源: Karger