摘要:

We investigated the effects of glucocorticoids and estrogen on the gene expression of growth hormone (GH) and the receptor for growth-hormone-releasing hormone (GHRH) by measuring the mRNA levels of GH and GHRH receptor in pituitary tissues of Sprague-Dawley rats using Northern blot hybridization and specific cDNA probes. Male rats, 6 weeks of age, were either adrenalectomized (or sham-operated) or treated with varying doses of dexamethasone (40, 200, 500 or 1,000 µg/kg/day, i.p.) for 3 days. Female rats, 4 weeks of age, were oophorectomized or sham-operated, and treated with 17β-estradiol benzoate 25 µg/kg/day (or vehicle) s.c. for 5 days starting 10 days after oophorectomy. Adrenalectomy was associated with a reduction in weight gain and decreased GHRH receptor mRNA levels (p < 0.05 and p < 0.0001 versus sham-operated, respectively). Dexamethasone treatment, however, was associated with a dose-dependent reduction in weight gain (p < 0.0001) but dose-dependent increases in GHRH receptor mRNA and GH mRNA levels (p < 0.0001 and p < 0.05, respectively). In the female rats, weight gain was increased by oophorectomy (p < 0.005 vs. sham-operated) and decreased by estrogen treatment (p < 0.05 vs. vehicle-treated). Pituitary GHRH receptor mRNA levels were also increased by oophorectomy (p < 0.05) and decreased by estrogen (p < 0.005). GH mRNA levels were unchanged by oophorectomy but decreased after estrogen treatment (p < 0.05). In conclusion, our findings suggest that endogenous glucocorticoids and estrogen are physiological regulators of pituitary GHRH receptor gene expression. Glucocorticoids and estrogen also regulate GH secretion via effects on GH gene expression. Changes in GHRH receptor and GH mRNA levels cannot explain the growth retardation in dexamethasone-treated ra

ISSN:0028-3835    

DOI:10.1159/000127075

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Reportedly, somatostatin (SS) withdrawal is an effective generator of pulsatile GH release in mammals and it has been proposed that the amplitude of the GH bursts is related to the functional activity of GHRH-producing neurons. Our study was designed to test this hypothesis in the unanesthetized dog, under different conditions of endogenous GHRH function. First, we evaluated the ability of withdrawal of SS infusion to induce a GH secretory burst under basal conditions when GHRH function is thought to be enhanced, i.e. in young (2- to 3-year-old) dogs under sustained (30 days) caloric restriction (CR) or a 2-day fast. Secondly, we performed experiments in aged (11- to 17-year-old) dogs, in which hypothalamic GHRH secretion is thought to be reduced. Old dogs were evaluated under basal conditions, after a 2-day fast and after a 10-day administration of GHRH alone or followed by fasting. Both before and 14 h after the end of each experimental period, young and old dogs underwent a 3-hour (from 10.00 to 13.00 h) intravenous SS infusion (4 µg · kg-1 · h–1)·The secretory profile of GH was generated by 15-min sampling from 09.00 to 15.00 h. Under baseline conditions, SS withdrawal induced a significant burst of GH in young but not in old dogs. After CR, termination of SS infusion was followed in young dogs by a robust GH burst, significantly higher than that observed when dogs were fed ad libitum. In this instance, reduction of plasma IGF-I concentrations was unlikely to be responsible for the higher GH burst; the same pattern was present in the young dogs after a 2-day fast, when circulating IGF-I was unaltered. In old dogs, SS withdrawal did not modify baseline GH levels even after fasting, but induced a significant GH increase after GHRH priming. When GHRH priming was followed by fasting, SS withdrawal resulted in a GH burst higher than that occurring after fasting or GHRH alone. Altogether, these data support the view that the rebound rise in GH induced by withdrawal of SS is related to the endogenous GHRH tone. It is suggested that extrapolation of these findings to humans might permit probing, albeit inferentially, the endogenous GHRH tone under different physiologic or pathologic condi

ISSN:0028-3835    

DOI:10.1159/000127076

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The purpose of the present study was to evaluate the opioid receptor subtype mediating opioid modulation of growth hormone (GH) secretion during ontogeny. The µ-agonist morphine and the Kagonist U50,488 caused a stimulation and inhibition of GH secretion, respectively, on postnatal day 10. Studies on postnatal days 2, 5, 10, 15 and 20 showed that ĸ-inhibition could be observed as early as day 2, but substantial µ-stimulation was not observed until postnatal day 10. Intracerebroventricular (i.c.v.) administration of the µ-selective peptide [D-Ala2-NMe-Phe4-Gly-ol]-enkephalin (DAMGO) elicited a marked rise in GH secretion, while administration of the δ-agonists [D-pen2D)-pen5]-enkephalin (DPDPE) or deltorphin II caused only a minor and non-dose-related rise in GH secretion in neonatal rats. The relative importance of µ- and δ-receptors in stimulating GH secretion was also studied in older pups (day 20). i.c.v. administration of DAMGO stimulated GH secretion, while neither DPDPE nor deltorphin II consistently increased GH secretion. Furthermore, peripheral administration of either morphine or the highly selective µ-agonist sufentanil elicited marked GH secretion on postnatal day 20, but only combined administration of the µ-antagonist β-funaltrexamine (β-FNA) and the δ-antagonist naltrindole substantially diminished these responses. These results suggest that both µ- and ĸ-opioid receptors are involved in the regulation of GH secretion in neonatal rats. While δ-receptors do not play a prominent independent role in this response, they may act synergistically with µ-receptors in produc

ISSN:0028-3835    

DOI:10.1159/000127077

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

In an attempt to examine the effect of prolonged physical activity on the function of the GH/IGF-1 axis during the aging process in man, we have evaluated basal and GHRH (GHRH-29: 1 µg/kg i.v. as a bolus) stimulated GH secretion as well as basal plasma IGF-1 levels in a group of 25 healthy runners (50-60 years, mean age 55.5 ± 0.6) and 24 age-matched relatively sedentary normal controls (mean age 55.8 ± 0.7). The runners had a minimum distance in kilometers of 26 km/week for at least 15 years, and competed in distances ranging from 16 km to the marathon. In runners, GHRH induced an increase of GH which was significantly higher (p < 0.001) than that observed in the age-matched controls. Baseline IGF-1 levels were significantly higher (p < 0.001) in trained runners (171 ± 8.4 µg/l) compared to the controls (91.1 ± 5.5 µg/l). These data show that in middle-age prolonged physical activity increases the function of the GH/IGF-1 axis. To clarify the possible mechanisms underlying the GH/IGF-1 secretory pattern in the runners, the GH responses to both single and combined administration of GHRH and arginine (ARG: 30 g infused over 30 min), a GH secretagogue likely acting via inhibition of hypothalamic somatostatin release, were investigated in 6 runners (mean age 55 ± 1.9 years) and 6 controls (mean age 55 ± 0.9 years). ARG clearly increased the GH response to GHRH in the controls, whereas it was unable to further potentiate the GH-releasing effect of GHRH in runners, thus suggesting that the increased GH responsiveness to GHRH might be due to an exercise-related decrease in endogenous hypothalamic somatostatinergic

ISSN:0028-3835    

DOI:10.1159/000127078

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Secretion of luteinizing hormone is decreased when hens start to incubate their eggs and is increased after nest deprivation or hatching of the eggs. The purpose of this study was to determine whether decreased luteinizing hormone (LH) secretion during incubation in the domestic hen is associated with a decrease in hypothalamic chicken gonadotropin-releasing hormone-I (cGnRH-I) mRNA or peptide. A semiquantitative competitive PCR assay was developed to measure cGnRH-I mRNA. Hypothalamic mRNA was quantified as the amount of GnRH cDNA obtained by reverse transcription of cGnRH-I mRNA. The amount of hypothalamic cGnRH-I mRNA was significantly higher in laying than in incubating hens (38.7 ± 10.3 vs. 7.7 ± 1.6 × 10–17 mol cDNA, p = 0.01, n = 8). The hypothalamic GnRH peptide content was not significantly different between laying and incubating hens in either the preoptic area (286.9 ± 24.01 vs. 269.3 ± 29.3 pg, n = 8) or the basal hypothalamus (1.67 ± 0.19 vs. 1.54 ± 0.21 ng, n = 8). Five days after incubating hens were deprived of their eggs, the resulting increase in LH secretion was associated with a significant increase in hypothalamic content of cGnRH-I mRNA (22.8 ± 2.2 vs. 6.7 ± 1.7 × 10–17 mol cDNAp < 0.001, n = 8). These observations suggest that a decrease in the expression of the cGnRH-I gene is a major factor in maintaining depressed LH secretion in incubating dome

ISSN:0028-3835    

DOI:10.1159/000127079

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

In male rats androgens are involved in the regulation of follicle-stimulating hormone (FSH) synthesis and secretion. Two nonsteroidal antiandrogens, fiutamide and Casodex, were used to study the influence of androgens on the carbohydrate structure of FSH isoforms and the relationship with their bioactivity in prepubertal male rats. Different doses of flutamide or Casodex (vehicle, 1, 5, or 10 mg/rat/day) were administered subcutaneously for 10 days to 23-day-old rats. Immunological FSH was determined by radioimmunoassay and the bioactivity by in vitro Sertoli cell bioassay. Concanavalin A affinity chromatography was used to study the distribution of immunoactive and bioactive pituitary FSH isoforms. A significant depletion of immunological and biological pituitary FSH contents was observed even at the lowest dose of flutamide or Casodex used. The bioactive/immunoactive ratio of pituitary FSH was reduced at the highest dose of flutamide; however, no change was observed in Casodex-treated rats, suggesting a differential effect of the antiandrogens on the FSH bioactivity. Flutamide treatment provoked a significant decrease in proportion and bioactivity of FSH isoforms bearing biantennary and truncated hybrid oligosaccharide side chains and an increase in the proportion but a decrease in bioactivity of FSH isoforms bearing high-mannose oligosaccharides. Conversely, Casodex administration did not modify the proportions of FSH isoforms, although those bearing biantennary and truncated hybrid structures were less bioactive, while those bearing high-mannose oligosaccharides were more bioactive. The highest dose of flutamide decreased the bioactive/immunoactive ratio of FSH isoforms with a high degree of branching in their carbohydrate chains. Our results suggest that androgens, acting directly and indirectly at the pituitary, regulate the selective incorporation of sugar residues to the FSH molecule, thus modulating its biological activity.

ISSN:0028-3835    

DOI:10.1159/000127080

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The presence of multiple monomeric forms has been described for the estrogen receptor (ER) in the pituitary gland. We analyzed ER mRNA forms in male and female rat pituitary. A single 6.2-kb ER mRNA species was detected in the male rat pituitary, whereas the female rat pituitary exhibited two ER mRNA forms of 6.2 and 5.5 kb, respectively. The 6.2-kb mRNA was present throughout the different stages of the estrous cycle, while the 5.5-kb mRNA appeared to be restricted to proestrus, suggesting an acute regulation of ER transcription at this stage. The 5.5-kb ER mRNA could be rapidly induced either by 17β-estradiol replacement in ovariectomized adult female rats or by priming immature rats with pregnant-mare serum gonadotropin. Using enriched cell populations, an inverse and strong correlation was established between the presence of the 5.5-kb ER mRNA form and the number of gonadotropes. Conversely, the localization of the 5.5-kb mRNA form was demonstrated in lactotrope populations. In order to elucidate the structural modifications in the transiently expressed ER mRNA, a series of reverse-transcriptase polymerase chain reaction amplifications was carried out using several pairs of primers corresponding to the entire ER-coding region. The data showed that no alternative splicing was occurring in the ER-coding region involving a potential role of either 3’- or 5’-untranslated regions. Thus, ER presents a 17β-estradiol-dependent transcriptional mechanism triggered on proestrous day and specific to the female lactot

ISSN:0028-3835    

DOI:10.1159/000127081

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

It is known that chronic exposure of F344 rats to diethylstilbestrol (DES) induces prolactin (PRL)-secreting pituitary tumors composed of proliferating mammotropic cells. In the present work, we studied the effects of progesterone (P4) on several parameters stimulated in the pituitary tumors (DES-T), such as nuclear estrogen receptors (NE2R), cytosolic progestin receptors (CP4R) and serum PRL. Additionally, we have measured in hypothalamus the mRNA levels for tyrosine hydroxylase (TH), the rate-limiting enzyme for synthesis of dopamine, the main PRL-inhibitory factor. We found that pellet implantation of P4 during 1 month significantly reduced weight, ligand binding to NE2R and CP4R and serum PRL in the tumorous glands. Reductions in sex steroid receptor binding were due to changes in Bmax without changes in Kd, as observed after Scatchard plot analysis. Receptor binding data, therefore, suggests a pituitary site of action of P4. TH mRNA expression was studied in tuberoinfundibular dopaminergic (TIDA) neurons by in situ hybridization techniques employing a 35S-labeled oligonucleotide probe. Mean number of grains/cell decreased significantly in DES-T, an effect partly reversed by P4 treatment. Frequency histograms were constructed by plotting the number of cells versus the number of grains/cell and examined by χ2 test and analysis of residuals. We found that DES-T presented significantly more cells with less grains whereas in control glands, P4-treated rats and DES-T receiving P4, cells with a higher grain number prevailed. These results suggest that in addition to a direct pituitary effect, P4 may also antagonize DES-induced tumorigenesis acting on mRNA for TH and presumably on the activity of TIDA neurons of the hypothalamus. The use of DES-T as a model for hyperprolactinemia may allow further assessment of P4 effects in pituitary adenomas in humans

ISSN:0028-3835    

DOI:10.1159/000127082

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC)-derived peptides located in the arcuate nucleus (ARC) have been postulated to be good candidates to play a modulatory role during lactation. In the present study, we first quantified, by in situ hybridization, lactation-induced changes in NPY and POMC gene expression throughout the ARC. In a second phase of the study, we attempted to determine whether any relationship exists between neuropeptide gene expression and the suckling stimulus itself. For this, we used experimental groups of animals submitted to suppression of the suckling stimulus by removal of pups and the subsequent restoration of the suckling stimulus by the return of the litter. Since lactation is characterized by an estrogen-deficient status [15], we attempted using ovariectomized (2 or 21 days) diestrous females to describe the changes in NPY gene expression observed during lactation. Since the suckling stimulus induces a strong prolactin (PRL) release, we completed this study by using an intravenous injection of PRL antiserum in order to discriminate the effects of PRL per se on the observed suckling-induced changes in neuropeptide gene expression. Freely nursing lactating females exhibited a large increase in NPY mRNA expression as compared to diestrous females (10.10 ± 0.50 vs. 4.51 ± 0.35). After suppression of the suckling stimulus by removal of pups, this increase intensified during short-term suppression of 16 h (15.37 ± 0.67) and was reversed following long-term suppression of 36 h (12.35 ± 0.61). Ovariectomized diestrous animals showed significant changes in NPY mRNA expression as compared to lactating females (5.25 ± 0.42 vs. 10.10 ± 0.50). Lactating females submitted to PRL immunoneutralization by PRL antiserum showed a slight increase in NPY mRNA expression as compared to non-injected lactating females (13.75 ± 0.51 vs. 12.95 ± 0.59). Freely nursing lactating females showed a decrease in POMC mRNA expression (8.27 ± 0.33) whereas suppression of suckling by removal of the pups (9.52 ± 0.45) resulted in a return to diestrous POMC mRNA levels (10.77 ± 0.36). We showed that restoration of suckling by the return of the litter induced an increase in POMC gene expression (12.55 ± 0.66). By lowering circulating levels of PRL with PRL antiserum after restoration of suckling, we observed a decrease in POMC mRNA expression (9.81 ± 0.46). Results of this study showed that the increase in NPY mRNA in the medial ARC during lactation did not appear to be due either to gonadal steroid-deficient status or to the suckling-induced hyperprolactinemia. If freely nursing lactating females showed a moderate decrease in POMC gene expression, restoration of the suckling stimulus by return of the pups provoked an increase in POMC gene expression which seemed to depend on high endogenous l

ISSN:0028-3835    

DOI:10.1159/000127083

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

We have previously shown that histaminergic neurons participate in mediation of the prolactin (PRL), adrenocorticotropin (ACTH) and oxytocin responses to physiological stimuli such as stress and dehydration. Since suckling is a potent stimulus for the secretion of these three hormones, we investigated the mediating role of neuronal histamine in suckling-induced release of oxytocin, PRL and ACTH in conscious lactating rats. The animals were pretreated with the histamine synthesis inhibitor α-fluoromethylhistidine, the H1 receptor antagonist mepyramine, the H2 receptor antagonist cimetidine or the H3 receptor agonist R(α)methylhistamine, which by binding to H3 autoreceptors inhibits histamine release and synthesis. After the lactating rats were separated from their pups for 240 min, the pups were returned for a suckling period of 20 min. Thereafter the mothers were sacrificed by decapitation and trunk blood was collected for determination of hormones. Lactating rats not exposed to suckling served as controls. Suckling increased oxytocin 2-fold, PRL 50-fold and ACTH 5-fold. Blockade of histamine synthesis by α-fluoromethylhistidine or histamine release by R(α)methylhistamine reduced the suckling-induced secretion of the three hormones significantly. Blockade of postsynaptic H1 receptors by mepyramine inhibited the hormone responses to suckling, while the blockade of postsynaptic H2 receptors by cimetidine decreased the suckling-induced oxytocin and PRL release but did not affect the ACTH release. None of the compounds affected oxytocin, PRL or ACTH secretion in lactating mothers not exposed to suckling. In addition, suckling significantly increased the mRNA of the histamine synthesizing enzyme histidine decarboxylase in the ventrolateral tuberomammillary nucleus by 1.5-fold, indicating that the stimulus of suckling enhances the neuronal histamine synthesis. We conclude that suckling increases neuronal histamine synthesis and that histaminergic neurons by activation of postsynaptic H1 and H2 receptors are involved in the hypothalamic mediation of oxytocin, PRL and ACTH responses to suckling. These findings further substantiate a role of neuronal histamine in the neuroendocrine regulation of pituitary hormones in response to physiological stim

ISSN:0028-3835    

DOI:10.1159/000127084

出版商:S. Karger AG    

年代:1996

数据来源: Karger