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The somatostatin (SST) receptor family controls pituitary hormone secretion, but the distribution and specific roles of these receptors on the excitability and voltage-gated calcium signaling of hormone producing pituitary cells have not been fully characterized. Here we show that the rat pituitary gland expressed Sstr1, Sstr2, Sstr3, and Sstr5 receptor genes in a cell type-specific manner: Sstr1 and Sstr2 in thyrotrophs, Sstr3 in gonadotrophs and lactotrophs, Sstr2, Sstr3, and Sstr5 in somatotrophs, and none in corticotrophs and melanotrophs. Most gonadotrophs and thyrotrophs spontaneously fired high-amplitude single action potentials, which were silenced by SST without affecting intracellular calcium concentrations. In contrast, lactotrophs and somatotrophs spontaneously fired low-amplitude plateau-bursting action potentials in conjunction with calcium transients, both of which were silenced by SST. Moreover, SST inhibited GPCR-induced voltage-gated calcium signaling and hormone secretion in all cell types expressing SST receptors, but the inhibition was more pronounced in somatotrophs. The pattern of inhibition of electrical activity and calcium signaling was consistent with both direct and indirect inhibition of voltage-gated calcium channels, the latter being driven by cell type-specific hyperpolarization. These results indicate that the action of SST in somatotrophs is enhanced by the expression of several types of SST receptors and their slow desensitization, that SST may play a role in the electrical resynchronization of gonadotrophs, thyrotrophs, and lactotrophs, and that the lack of SST receptors in corticotrophs and melanotrophs keeps them excitable and ready to responses to stress., Competing Interests: Declaration of competing interest This is to state that there is no any financial and personal relationships with other people or organizations that could be viewed as inappropriately influencing or bias our work., (Copyright © 2024. Published by Elsevier Ltd.)

Dexamethasone-induced Ras-related protein 1 (Rasd1) is a member of the Ras superfamily of monomeric G proteins that have a regulatory function in signal transduction. Rasd1, also known as Dexras1 or AGS1, is rapidly induced by dexamethasone (Dex). While prior data indicates that Rasd1 is highly expressed in the pituitary and that the gene may function in regulation of corticotroph activity, its exact cellular localization in this tissue has not been delineated. Nor has it been determined which endocrine pituitary cell type(s) are responsive to Dex-induced expression of Rasd1. We hypothesized that Rasd1 is primarily localized in corticotrophs and furthermore, that its expression in these cells would be upregulated in response to exogenous Dex administration. Rasd1 expression in each pituitary cell type both under basal conditions and 1-hour post Dex treatment were examined in adult male mice. While a proportion of all endocrine pituitary cell types expressed Rasd1, a majority of corticotrophs and thyrotrophs expressed Rasd1 under basal condition. In vehicle treated animals, approximately 50–60% of corticotrophs and thyrotrophs cells expressed Rasd1 while the gene was detected in only 15–30% of lactotrophs, somatotrophs, and gonadotrophs. In Dex treated animals, Rasd1 expression was significantly increased in corticotrophs, somatotrophs, lactotrophs, and gonadotrophs but not thyrotrophs. In Dex treated animals, Rasd1 was detected in 80–95% of gonadotrophs and corticotrophs. In contrast, Dex treatment increased Rasd1 expression to a lesser extent (55–60%) in somatotrophs and lactotrophs. Corticotrophs of the pars intermedia, which lack glucocorticoid receptors, failed to display increased Rasd1 expression in Dex treated animals. Rasd1 is highly expressed in corticotrophs under basal conditions and is further increased after Dex treatment, further supporting its role in glucocorticoid negative feedback. In addition, the presence and Dex-induced expression of Rasd1 in endocrine pituitary cell types, other than corticotrophs, may implicate Rasd1 in novel pituitary functions. [ABSTRACT FROM AUTHOR]

1. In this study, geese (Anas cygnoides) embryonic pituitary cells were cultured in vitro to determine if glucocorticoids could induce growth hormone (GH) expression and to investigate the molecular mechanisms involved in this process. 2. On embryonic day 15 (e15) and e20 the pituitary cells were treated with corticosterone (CORT), membrane impermeable bovine serum albumin–conjugate corticosterone (CORT-BSA), dexamethasone (DEX), and a glucocorticoid receptor (GR) antagonist (RU486) to detect responsiveness of somatotrophs to glucocorticoids. 3. Treatment with CORT, CORT-BSA, and DEX for as little as 6 h increased the percentage of GH-positive cells (P < 0.01) and increased GHmRNA expression (P < 0.01) in e15 goose pituitary cells compared to the control. CORT significantly increased the level of GH protein secreted from cultured e15 goose embryonic pituitary cells, and CORT-BSA increased GH secretion from e20 goose embryonic pituitary cells. 4. A significant increase was observed in the glucocorticoid receptor in GR transcription levels (P < 0.01) with CORT, CORT-BSA, and DEX treatment. Furthermore, the CORT-stimulated GHmRNA expression was completely negated by pre-treatment with RU486. 5. These findings demonstrate that glucocorticoids can stimulate somatotroph differentiation in vitro, as characterised by enhanced GH protein secretion andmRNA expression in cultured geese embryonic pituitary cells. The membrane GR was involved in pituitary somatotroph differentiation induced by glucocorticoids during the embryonic development of geese. [ABSTRACT FROM AUTHOR]

Abstract It is well known that stress changes levels of pituitary hormones in the bloodstream and in the pituitary itself. However, almost nothing is known about the impact of stress on histological and stereological parameters of the growth hormone producing cells (somatotrophs-GH cells). The aim of the present study was to investigate the effect of: acute and repeated immobilization; acute and repeated restraint on histological and morphofunctional parameters of somatotrophs in adult Wistar rats. Changes in the pituitary gland volume; the volume density and volume of somatotrophs following acute and repeated immobilization (IMO, R-IMO); acute and repeated restraint (R, R-R) were evaluated using a stereological system (newCAST), while growth hormone level within pituitary was determined by Western blot. Our results demonstrated the decrease (p < 0.05) of the pituitary volume (17%, 19%) in the IMO and R groups, respectively, and the increase in the R-R group. The volume density of GH cells decreased (p < 0.05) in the R-IMO (7%), R (26%) and R-R (18%) group in comparison to the control value. The pituitary GH content was increased (p < 0.05) after the IMO (2-fold), R (2.5-fold) and R-R (2.1-fold) as compared to the control group. These results point out that acute and repeated immobilization and/or restraint lead not only to changes in GH hormone concentration, but also modify the morphological aspects of GH cells within the rat pituitary. [ABSTRACT FROM AUTHOR]

Somatotropinomas are pituitary tumors with a heterogenous clinical behavior. The tumor microenvironment regulates the interaction between tumor cells and the host immune system, potentially modulating tumor behavior. Here, we aimed to investigate the tumor immune infiltration in a cohort of medically naïve acromegaly patients. A retrospective, monocenter study was designed to analyze the presence of CD3+, CD20+, CD138+, CD4+, CD8+, CD68+ immune cells in samples of somatotropinomas and their prognostic significance on tumor behavior and response to first generation somatostatin analogs (fg-SSA). Thirty-six patients (23 females) were included in the study. Macroadenomas were identified in 23 cases: 12 with cavernous sinus invasion. The number of CD8+ lymphocytes positively correlated with CD4+ lymphocytes (p = .05, r:0.245) and with CD68+ macrophages (p = .01, r = 0.291). The CD8+/CD4+ ratio inversely correlated with CD68+/CD8+ ratio (p < .001, r = -0.626). CD68+ macrophages positively correlated with tumor size (maximum diameter p = .003, r = 0.574; volume p = .009, r = 0.566) and were more numerous in somatotropinomas with Ki-67 > 3% (median 65/HPF, IQR:15), compared to cases with Ki67 < 3% (median 50/HPF, IQR:22, p < .001). CD8+ and CD138+ lymphocytes were more numerous in cases responsive to fg-SSA (respectively median 18/HPF IQR:18 and median 8/HPF IQR: 6.5) as compared to fg-SSA nonresponsive cases (median 14.5/HPF IQR:40 p = .03; median 3.5/HPF IQR: 14 p = .03). CD8+ lymphocytes act as single predictor of response to fg-SSA, independently from age, GH and IGF-I levels, tumor dimension and invasion. Our results support that lymphocytes and macrophages generate an immune network in somatotropinomas and the characteristic of the immune infiltrate may predict treatment outcome., (© 2023 British Society for Neuroendocrinology.)

Purpose: Currently, endoscopic transsphenoidal surgery is the main treatment for pituitary neuroendocrine tumors (PitNETs). Excision of the tumor may have positive or negative effects on pituitary endocrine function, and the pituitary function of somatotroph tumors is a point of particular concern after the operation. This study aimed to conduct a meta-analysis on the effect of endoscopic transsphenoidal somatotroph tumor resection on pituitary function., Methods: A systematic literature search was conducted for articles that included the evaluation of pituitary target gland before and after endoscopic transsphenoidal pituitary tumor resection and were published between 1992 and 2022 in PubMed, Cochrane, and Ovid MEDLINE., Results: Sixty-eight studies that included biochemical remission rates in 4524 somatotroph tumors were concluded. According to the 2000 consensus, the biochemical remission rate after transsphenoidal endoscopic surgery was 66.4% (95% CI, 0.622-0.703; P = 0.000), the biochemical remission rate was 56.2% according to the 2010 consensus (95% CI, 0.503-0.620; P = 0.041), and with the rate of biochemical remission ranging from 30.0 to 91.7% with investigator's definition. After endoscopic resection, adrenal axis dysfunction was slightly higher than that before surgery, but the difference was not statistically significant. Hypothyroidism was 0.712 times higher risk than that before surgery (OR = 0.712; 95% CI, 0.527-0.961; P = 0.027). Hypogonadism was 0.541 times higher risk than that before surgery (OR = 0.541; 95% CI, 0.393-0.746; P = 0.000). Hyperprolactinemia was 0.131 times higher risk than that before surgery (OR = 0.131; 95% CI, 0.022-0.783; P = 0.026). The incidence of pituitary insufficiency was 1.344 times the risk before surgery after endoscopic resection of somatotroph tumors, but the difference was not statistically significant., Conclusions: In patients with somatotroph tumors after undergoing endoscopic surgery, the risk of dysfunction and pituitary insufficiency tend to increase, while preoperative thyroid insufficiency, gonadal insufficiency, and hyperprolactinemia will be partially relieved., (© 2023. The Author(s).)

Exposure to alcohol alters many physiological processes, including endocrine status. The present study examined whether prolonged alcohol (A) exposure could modulate selected stereological and hormonal aspects of pituitary somatotrophs (growth hormone-GH cells) and corticotrophs (adrenocorticotropic hormone-ACTH cells) in adult rats. Changes in pituitary gland volume; the volume density, total number and volume of GH and ACTH cells following alcohol exposure were evaluated using a stereological system (newCAST), while peripheral GH and ACTH levels were determined biochemically. Our results demonstrated the reduction (p < 0.05) of the volume density (37%) and volume of GH cells (29%) in the group A. Also, there was a tendency for the total number of GH cells to be smaller in the group A. Serum GH level was significantly decreased (p < 0.05; 70%) in the group A when compared to control values. Moreover, prolonged alcohol exposure induced declines (p < 0.05) in volume density (24%) and volume of ACTH cells (29%). The total number of ACTH cells and ACTH level were higher (p < 0.05; 42%) in the group A than in control rats. Collectively, these results indicate that prolonged alcohol exposure leads not only to changes in GH and ACTH hormone levels, but also to alterations of the morphological aspects of GH and ACTH cells within the pituitary. [ABSTRACT FROM AUTHOR]

All secretory anterior pituitary cells exhibit spontaneous and extracellular calcium-dependent electrical activity, but differ with respect to the patterns of firing and associated calcium signaling and hormone secretion. Thus, somatotrophs and lactotrophs fire plateau-bursting action potentials spontaneously and without coupling to calcium release from intracellular stores, which generate calcium signals of sufficient amplitude to keep steady hormone release. In these cells, both spontaneous electrical activity and basal hormone secretion can be further amplified by activation of Gq/11 and Gs-coupled receptors and inhibited by Gi/o/z-coupled receptors. In contrast, gonadotrophs fire single, high-amplitude spikes with limited ability to promote calcium influx and exocytosis, whereas activated Gq/11-coupled receptors in these cells transform single-action potential spiking into the plateau-bursting type of electrical activity and trigger periodic high-amplitude calcium signals and exocytosis of prestored secretory vesicles. Here, we review biochemical and biophysical aspects of spontaneous and receptor-controlled electrical activity, calcium signaling, and hormone secretion in pituitary cells.

The involvement of L-type Ca2+ channels in both 'basal' and 'stimulated' growth hormone ( GH) secretion is well established; however, knowledge regarding the involvement of non- L-type Ca2+ channels is lacking. We investigated whether non- L-type Ca2+ channels regulate GH secretion from anterior pituitary ( AP) cells. To this end, GH secretion was monitored from dissociated AP cells, which were incubated for 15 min with 2 m m K+ ('basal' secretion) or 60 m m K+ ('stimulated' secretion). The role of non-L-type Ca2+ influx was investigated using specific channel blockers, including ω-agatoxin- IVA, ω-conotoxin GVIA or SNX-482, to block P/Q-, N- or R-type Ca2+ channels, respectively. Our results demonstrate that P/Q-, N- and R-type Ca2+ channels contributed 21.2 ± 1.9%, 20.2 ± 7.6% and 11.4 ± 1.8%, respectively, to 'basal' GH secretion and 18.3 ± 1.0%, 24.4 ± 5.4% and 14.2 ± 4.8%, respectively, to 'stimulated' GH secretion. After treatment with a 'cocktail' that comprised the previously described non-L-type blockers, non-L-type Ca2+ channels contributed 50.9 ± 0.4% and 45.5 ± 2.0% to 'basal' and 'stimulated' GH secretion, respectively. Similarly, based on the effects of nifedipine (10 μM), L-type Ca2+ channels contributed 34.2 ± 3.7% and 54.7 ± 4.1% to 'basal' and 'stimulated' GH secretion, respectively. Interestingly, the relative contributions of L-type/non-L-type Ca2+ channels to 'stimulated' GH secretion were well correlated with the relative contributions of L-type/non-L-type Ca2+ channels to voltage-gated Ca2+ influx in AP cells. Finally, we demonstrated that compartmentalisation of Ca2+ channels is important for GH secretion. Lipid raft disruption (methyl-β-cyclodextrin, 10 m m) abrogated the compartmentalisation of Ca2+ channels and substantially reduced 'basal' and 'stimulated' GH secretion by 43.2 ± 3.4% and 58.4 ± 4.0%, respectively. In summary, we have demonstrated that multiple Ca2+ channel-dependent pathways regulate GH secretion. The proper function of these pathways depends on their compartmentalisation within AP cell membranes. [ABSTRACT FROM AUTHOR]

Nonalcoholic fatty liver disease (NAFLD) can be ameliorated by calorie restriction, which leads to the suppressed somatotroph axis. Paradoxically, the suppressed somatotroph axis is associated with patients with NAFLD and is correlated with the severity of fibrosis. How the somatotroph axis becomes dysregulated and whether the repressed somatotroph axis impacts liver damage during the progression of NAFLD are unclear. Here, we identify a regulatory branch of the hepatic integrated stress response (ISR), which represses the somatotroph axis in hepatocytes through ATF3, resulting in enhanced cell survival and reduced cell proliferation. In mouse models of NAFLD, the ISR represses the somatotroph axis, leading to reduced apoptosis and inflammation but decreased hepatocyte proliferation and exacerbated fibrosis in the liver. NAD + repletion reduces the ISR, rescues the dysregulated somatotroph axis, and alleviates NAFLD. These results establish that the hepatic ISR suppresses the somatotroph axis to control cell fate decisions and liver damage in NAFLD., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

The aim of the present study was to evaluate the effect of antidopaminergic agents on the somatotrophs in the presence of hyperprolactinemia. Adult male Wistar rats were divided into 6 groups: a control group and five groups chronically treated (60 days) with haloperidol, fluphenazine, sulpiride, metoclopramide or estrogen. Somatotrophs and lactotrophs were identified by immunohistochemistry and the data are reported as percent of total anterior pituitary cells counted. The drugs significantly increased the percentage of lactotrophs: control (mean ± SD) 21.3 ± 4.4, haloperidol 27.8 ± 2.2, fluphenazine 34.5 ± 3.6, sulpiride 32.7 ± 3.5, metoclopramide 33.4 ± 5.5 and estrogen 42.4 ± 2.8. A significant reduction in somatotrophs was observed in animals treated with haloperidol (23.1 ± 3.0), fluphenazine (22.1 ± 1.1) and metoclopramide (24.2 ± 3.0) compared to control (27.3 ± 3.8), whereas no difference was observed in the groups treated with sulpiride (25.0 ± 2.2) and estrogen (27.1 ± 2.8). In the groups in which a reduction occurred, this may have simply been due to dilution, secondary to lactotroph hyperplasia. In view of the duplication of the percentage of prolactin-secreting cells, when estrogen was applied, the absence of a reduction in the percent of somatotrophs suggests a replication effect on this cell population. These data provide additional information about the direct or indirect effect of drugs which, in addition to interfering with the dopaminergic system, may act on other pituitary cells as well as on the lactotrophs.

Malathion is one of the organophosphorus insecticides that are widely used in agriculture and have been reported to cause multiple organ damage. Vitamin C has been proposed as an antioxidant because it reduces oxidative stress.This work aimed to study the possible histological, immunohistochemical, and ultrastructural changes of gonadotrophs and somatotrophs of the pars distalis of the anterior pituitary gland associated with chronic sublethal malathion administration and assess the possible beneficial role of vitamin C in ameliorating these possible changes.Forty adult female albino rats were divided into four groups. Group I served as the control group. Group II received vitamin C at a dose of 20 mg/100 g/day. Group III animals were treated with malathion at a dose of 100 mg/kg/day. Groups IV animals received vitamin C and then malathion after 2 h at the previous doses. The treatments were given orally to the rats for 2 months. The rats were then sacrificed and specimens from the anterior pituitary gland were taken for light and electron microscopic examination.Light microscopic examination of rats treated with malathion revealed that gonadotrophs exhibited vacuolated degranulated cytoplasm and pyknotic nuclei, whereas somatotrophs appeared shrunken with dense nuclei. Immunohistochemically, there was a decrease in the immunoreactivity of follicle stimulating hormone, luteinizing hormone, and growth hormone-secreting cells. Ultrastructurally, gonadotrophs and somatotrophs showed disintegration of cellular organelles and apoptosis of the nuclei. Coadministration of malathion with vitamin C showed a slight improvement in some gonadotrophs and somatotrophs that looked normal in both light microscopic and electron microscopic examination; however, still others were markedly affected, showing signs of degeneration and apoptosis.The results showed that malathion in chronic doses induces histological, immunohistochemical, and ultrastructural changes in gonadotrophs and somatotrophs because of oxidative stress, and the use of vitamin C partially improves the malathion-induced toxicity. [ABSTRACT FROM AUTHOR]

Leptin is an adipocyte-derived hormone. The plasma level of leptin is elevated in obesity and decreased in emaciation. It is involved in the neuroendocrine regulation of pituitary gland function.The present work was carried out to study the histological changes in the pars distalis of the pituitary gland after an injection of leptin in female albino rats.Thirty just-weaned immature female albino rats (22 days) were divided into two groups: group I included 10 animals and served as a control group and group II included 20 animals that received a daily subcutaneous injection of 5µg leptin up to the end of the experiment. The females were subjected daily to vaginal smear. After the maturation was established, rats from each group were again subdivided into groups a and b, which were sacrificed 4 and 20 days after puberty, respectively. The pituitary glands were dissected and specimens were prepared for electron microscopic and immunohistochemical assessment.Leptin injection induced various changes in the pars distalis of the pituitary gland. Some cells had deeply stained nuclei and vacuolated cytoplasm. There was a statistically significant increase in the number of positive p53 antibody immunostained cells in the leptin-treated group, especially after 4 days of leptin injection. The most affected cells were somatotrophs, thyrotrophs, and gonadotrophs. They showed features of hyperactivity, with the appearance of some apoptotic cells. Later, necrotic changes such as pyknotic nuclei, ballooned mitochondria with destroyed cristae, and dilated rough endoplasmic reticulum were observed.Prepubertal increase in leptin led to histological changes in some cells of the pars distalis. It is recommended to avoid increase in body weight, especially at a young age. [ABSTRACT FROM AUTHOR]

The anterior pituitary gland (AP) increases growth hormone (GH) secretion in response to resistance exercise (RE), but the nature of AP adaptations to RE is unknown. To that end, we examined the effects of RE on regional AP somatotroph GH release, structure, and relative quantity. Thirty-six Sprague-Dawley rats were assigned to one of four groups: 1) no training or acute exercise (NT-NEX); 2) no training with acute exercise (NT-EX); 3) resistance training without acute exercise (RTNEX); 4) resistance training with acute exercise (RT-EX). RE incorporated 10, 1 m-weighted ladder climbs at an 85° angle. RT groups trained 3 days/wk for 7 wk, progressively. After death, trunk blood was collected, and each AP was divided into quadrants (ventral-dorsal and left-right). We measured: 1) trunk plasma GH; 2) somatotroph GH release; 3) somatotroph size; 4) somatotroph secretory content; and 5) percent of AP cells identified as somatotrophs. Trunk GH differed by group (NT-NEX, 8.9 ± 2.4 μg/l; RT-NEX, 9.2 ± 3.5 μg/l; NT-EX, 15.6 ± 3.4 μg/l; RT-EX, 23.4 ± 4.6 μg/l). RT-EX demonstrated greater somatotroph GH release than all other groups, predominantly in ventral regions (P < 0.05-0.10). Ventral somatotrophs were larger in NT-EX and RT-NEX compared with RT-EX (P < 0.05-0.10). RT-NEX exhibited significantly greater secretory granule content than all other groups but in the ventral-right region only (P < 0.05-0.10). Our findings indicate reproducible patterns of spatially distinct, functionally different somatotroph subpopulations in the rat pituitary gland. RE training appears to induce dynamic adaptations in somatotroph structure and function. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct study of G∝ and GRKs in hormone release from native pituitary cells. • G q/11 subunits are a requisite for GnRH-induced LH and GH release in vitro. • Additional non-G q/11 subunits may participate in GnRH-induced GH secretion. • GRK2/3 proteins mediate GnRH-stimulated LH release. • Active G q/11 is necessary for GnRH-induced ERK signalling in pituitary extracts. In goldfish (Carassius auratus) , two endogenous isoforms of gonadotropin-releasing hormone (GnRH) stimulate luteinizing hormone (LH) and growth hormone (GH) secretion. These isoforms, GnRH2 and GnRH3, act on a shared population of cell-surface GnRH receptors (GnRHRs) expressed on both gonadotrophs and somatotrophs, and can signal through unique, yet partially overlapping, suites of intracellular effectors, in a phenomenon known as functional selectivity or biased signalling. In this study, G-protein alpha (Gα) subunits were targeted with two inhibitors, YM-254890 and BIM-46187, to ascertain the contribution of specific G-protein subunits in GnRH signalling. Results with the Gα q/11 -specific inhibitor YM-254890 on primary cultures of goldfish pituitary cells revealed the use of these subunits in GnRH control of both LH and GH release, as well as GnRH-induced elevations in phospho-ERK levels. Results with the pan-Gα inhibitor BIM-46187 matched those using YM-254890 in LH release but GH responses differed, indicating additional, non-Gα q/11 subunits may be involved in somatotrophs. BIM-46187 also elevated unstimulated LH and GH release suggesting that Gα subunits regulate basal hormone secretion. Furthermore, G-protein-coupled receptor kinase (GRK2/3) inhibition reduced LH responses to GnRH2 and GnRH3, and selectively enhanced GnRH2-stimulated GH release, indicating differential use of GRK2/3 in GnRH actions on gonadotrophs and somatotrophs. These findings in a primary untransformed system provide the first direct evidence to establish Gα q/11 as an obligate driver of GnRH signalling in goldfish pituitary cells, and additionally describe the differential agonist- and cell type-selective involvement of GRK2/3 in this system. [ABSTRACT FROM AUTHOR]

Highlights: [•] LH receptor (LHR) was cloned in grass carp and its 3D protein model was deduced. [•] Expression studies confirmed the ligand specificity and cAMP coupling of carp LHR. [•] LHR gene expression in GH cells could be induced by dopamine (DA) D1 activation. [•] DA D1-induced LHR gene expression could be blocked by local secretion of LH. [•] DA and LH could regulate LHR gene expression via cAMP-dependent mechanisms. [Copyright &y& Elsevier]

The present study demonstrates that a significant proportion of high voltage-activated ( HVA) Ca2+ influx in native rat anterior pituitary cells is carried through non- L-type Ca2+ channels. Using whole-cell patch-clamp recordings and specific Ca2+ channel toxin blockers, we show that approximately 35% of the HVA Ca2+ influx in somatotrophs and lactotrophs is carried through Cav2.1, Cav2.2 and Cav2.3 channels, and that somatotrophs and lactotrophs share similar proportions of these non- L-type Ca2+ channels. Furthermore, experiments on mixed populations of native anterior pituitary cells revealed that the fraction of HVA Ca2+ influx carried through these non- L-type Ca2+ channels might even be higher (approximately 46%), suggesting that non- L-type channels exist in the majority of native anterior pituitary cells. Using western blotting, immunoblots for α1C, α1D, α1A, α1B and α1E Ca2+ channel subunits were identified in native rat anterior pituitary cells. Additionally, using reverse transcriptase-polymerase chain reaction, c DNA transcripts for α1C, α1D, α1A and α1B Ca2+ channel subunits were identified. Transcripts for α1E were nonspecific and transcripts for α1S were not detected at all (control). Taken together, these results clearly demonstrate the existence of multiple HVA Ca2+ channels in the membrane of rat native anterior pituitary cells. Whether these channels are segregated among different membrane compartments was investigated further in flotation assays, demonstrating that Cav2.1, Cav1.2 and caveolin-1 were mostly localised in light fractions of Nycodenz gradients (i.e. in lipid raft domains). Cav1.3 channels were distributed among both light and heavy fractions of the gradients (i.e. among raft and nonraft domains), whereas Cav2.2 and Cav2.3 channels were distributed mostly among nonraft domains. In summary, in the present study, we demonstrate multiple pathways for HVA Ca2+ influx through L-type and non- L-type Ca2+ channels in the membrane of native anterior pituitary cells. The compartmentalisation of these channels among raft and nonraft membrane domains might be essential for their proper regulation by separate receptors and signalling pathways. [ABSTRACT FROM AUTHOR]

Alteration in the cellular composition of the anterior pituitary gland could be involved in both prolactin and growth hormone disturbances in cases of poorly controlled diabetes.This study was conducted to investigate the ultrastructural changes in both somatotrophs and lactotrophs of diabetic rats and to investigate the possible protective effect of α-lipoic acid.Thirty adult male rats were randomly divided into three equal groups: group A (control), group B (alloxan-induced diabetic rats), and group C (alloxan-induced diabetic rats that received α-lipoic acid). In rats of groups B and C, diabetes was induced by a single intraperitoneal injection of alloxan monohydrate. In animals of group C, α-lipoic acid was given intraperitoneally during the period of the experiment. Twelve weeks after induction of diabetes, specimens of the pituitary gland were processed for transmission electron microscopic examination and a morphometric study was conducted.Somatotrophs of diabetic rats showed condensed nuclei, dilated Golgi saccules, and dilated rough endoplasmic reticulum cisternae. Further, some lactotrophs showed corrugated or condensed nuclei, dilated Golgi saccules, and relatively fewer granules. In both somatotrophs and lactotrophs of diabetic rats, the number of cytoplasmic granules was significantly decreased as compared with that of control rats. In addition, a significant increase in the percentage of empty granules to the total number of granules was recorded. However, the total number of granules and the percentage of empty granules to the total number in both somatotrophs and lactotrophs were significantly reduced in diabetic rats treated with α-lipoic acid as compared with untreated diabetic rats.The spectrum of changes in lactotrophs and somatotrophs of uncontrolled diabetic rats was found to be corrected by α-lipoic acid and therefore α-lipoic acid is recommended as a form of adjuvant therapy for diabetes. [ABSTRACT FROM AUTHOR]

Abstract: Growth hormone (GH) is a prominent metabolic factor that is targeted by glucocorticoids; however, their role in GH production remains controversial. This is explained in part by discrepancies between in vitro and in vivo, short-term versus long-term exposure and even species-specific effects. The prevailing view, however, is that glucocorticoids are negative modulators of growth and GH production. An examination of recent findings from elegant avian and gene ablation in mice studies as well as clinical case reports, suggests this is not the case. The evidence suggests that the effect of glucocorticoids on growth and GH production can be uncoupled, and reveals they play a crucial and positive role in maturation of functional somatotrophs, the GH-producing cells of the anterior pituitary. Here, we provide an overview and insights into the possible roles of glucocorticoids in the development of somatotrophs before birth as well as regulation of GH production in infancy (neonatal) and adulthood (postnatal). A fully functional glucocorticoid-signaling pathway appears to be required for establishment of somatotrophs before birth, and glucocorticoids continue to be required for maintenance of GH production in the newborn. There is evidence to suggest progenitor somatotrophs may persist after birth, and perhaps account for the ability of glucocorticoid therapy to correct some cases of GH deficiency as a result of compromised glucocorticoid signaling. Finally, there is support for positive regulation of avian, murine and human GH gene activation and/or expression by glucocorticoids, however, there appears to be no common mechanism and the contribution of direct versus indirect effects remains unclear. Thus, our observations reveal a largely hidden face of glucocorticoids, specifically, a positive role in somatotroph development and GH gene activation/expression, which may enable us to better understand the differential effect of glucocorticoids on growth and GH production in human studies. [Copyright &y& Elsevier]

This study aimed to detect the effects of long term administration of diazepam on the ultrastructure of somatotrophs and thyrotrophs of the anterior pituitary, and the possibility of recovering from its effects after withdrawal. Forty male adult rats used in this study were divided into a control and experimental groups. The latter was divided into two subgroups; first received diazepam intraperitoneally at a daily dose of 0.18 mg/200 gm body weight for 21 days. The second was left for one month after stopping the diazepam, which was given for same period. The pars distalis of the pituitary glands were dissected and processed for light and electron microscopic study. Most of the somatotrophs showed signs of degeneration following administration of diazepam for 21 days. Thyrotrophs showed variable degrees of effect, but to a lesser extent compared to somatotrophs. After withdrawal of diazepam, most of the somatotrophs showed irreversible changes, apart from few cells that appeared intact. Some thyrotrophs recovered from the effects of diazepam while others could not. In conclusion, withdrawal of diazepam did not allow the affected somatotrophs and thyrotrophs to recover from its harmful effect. Therefore, diazepam should be given cautiously, especially when treating children. [ABSTRACT FROM AUTHOR]

Comparative morphological study of the adenohypophysis was conducted in 3-week-old normotensive WAG and hypertensive ISIAH rats (prehypertension period) to elucidate the role of the adenohypophysis in the development of essential hypertension. Morphometric analysis revealed ultrastructural signs of functional activation of somatotrophs, gonadotrophs, and corticotrophs in ISIAH rats. These peculiarities of structural organization of adenohypophysis in hypertensive rats can attest to enhanced response of the hypothalamic-pituitary-adrenal axis in these animals to natural stress associated with their transition to independent feeding. Increased stress sensitivity during the prehypertensive period of postnatal ontogeny contributes to the development of arterial hypertension. [ABSTRACT FROM AUTHOR]

Several receptors linked to the adenylyl cyclase signaling pathway stimulate electrical activity and calcium influx in endocrine pituitary cells, and a role for an unidentified sodium-conducting channel in this process has been proposed. Here we show that forskolin dose-dependently increases cAMP production and facilitates calcium influx in about 30% of rat and mouse pituitary cells at its maximal concentration. The stimulatory effect of forskolin on calcium influx was lost in cells with inhibited PKA (cAMP-dependent protein kinase) and in cells that were haploinsufficient for the main PKA regulatory subunit but was preserved in cells that were also haploinsufficient for the main PKA catalytic subunit. Spontaneous and forskolin-stimulated calcium influx was present in cells with inhibited voltage-gated sodium and hyperpolarization-activated cation channels but not in cells bathed in medium, in which sodium was replaced with organic cations. Consistent with the role of sodium-conducting nonselective cation channels in PKA-stimulated Ca2+ influx, cAMP induced a slowly developing current with a reversal potential of about 0 mV. Two TRP (transient receptor potential) channel blockers, SKF96365 and 2-APB, as well as flufenamic acid, an inhibitor of nonselective cation channels, also inhibited spontaneous and forskolin-stimulated electrical activity and calcium influx. Quantitative RT-PCR analysis indicated the expression of mRNA transcripts for TRPC1 >> TRPC6 > TRPC4 > TRPC5 > TRPC3 in rat pituitary cells. These experiments suggest that in pituitary cells constitutively active cation channels are stimulated further by PKA and contribute to calcium signaling indirectly by controlling the pacemaking depolarization in a sodium-dependent manner and directly by conducting calcium. [ABSTRACT FROM AUTHOR]

Gonadotrophin-releasing hormone (GnRH) is a hypothalamic decapeptide with an undisputed role as a primary regulator of gonadal function. It exerts this regulation by controlling the release of gonadotrophins. However, it is becoming apparent that GnRH may have a variety of other vital roles in normal physiology. A reconsideration of the potential widespread action that this traditional reproductive hormone exerts may lead to the generation of novel therapies and provide insight into seemingly incongruent outcomes from current treatments using GnRH analogues to combat diseases such as prostate cancer. [ABSTRACT FROM AUTHOR]

Abstract: From case studies in humans it is known that primary hypothyroidism (PH) may be associated with morphological and functional changes of the pituitary. There is no insight into the time scale of these changes. In this study, seven beagle dogs were followed up for 3 years after the induction of primary hypothyroidism. Three of these dogs were followed up for another 1.5 years while receiving l-thyroxine. Adenohypophyseal function was investigated at 2-month intervals with the combined intravenous injection of CRH, GHRH, GnRH, and TRH, and measurement of the plasma concentrations of ACTH, GH, LH, PRL, and TSH. In addition, after 2 years of hypothyroidism a single TRH-stimulation test and a somatostatin test were performed, with measurements of the same pituitary hormones. Every 6 months the pituitary gland was visualized by computed tomography (CT). Induction of PH led to high plasma TSH concentrations for a few months, where after concentrations gradually declined to values no longer significantly different from pre-PH values. A blunted response to stimulation of TSH release preceded this decline. Basal plasma GH concentrations increased during PH and there was a paradoxical hyperresponsiveness to TRH stimulation. Basal GH concentrations remained elevated and returned only to low values during l-thyroxine treatment. Basal PRL concentrations decreased significantly during PH and normalized after several months of l-thyroxine treatment. The pituitary gland became enlarged in all dogs. Histomorphology and immunohistochemical studies in 4 dogs, after 3 years of PH, revealed thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and decreased numbers of mammotrophs. Several cells stained for both GH and TSH. In conclusion, with time PH led to a loss of the TSH response to low T4 concentrations, hypersecretion of GH, and hyposecretion of PRL. The enlarged pituitaries were characterized by thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and double-staining cells, which are indicative of transdifferentiation. [Copyright &y& Elsevier]

The elevation in baseline circulating growth hormone (GH) that occurs in pregnant rats is thought to arise from increased pituitary GH secretion, but the underlying mechanism remains unclear. Distribution, Fourier and algorithmic analyses confirmed that the pregnancy-induced increase in circulating GH in 3-week pregnant rats was due to a 13-fold increase in baseline circulating GH (P < 0.01), without any significant alteration in the parameters of episodic secretion. Electron microscopy revealed that pregnancy resulted in a reduction in the proportion of mammosomatotrophs (P < 0.01) and an increase in type II lactotrophs (P < 0.05), without any significant change in the somatotroph population. However, the density of the secretory granules in somatotrophs from 3-week pregnant rats was reduced (P < 0.05), and their distribution markedly polarised; the granules being grouped nearest the vasculature. Pituitary GH content was not increased, but steady-state GH mRNA levels declined progressively during pregnancy (P < 0.05). In situ hybridisation revealed that pregnancy was accompanied by a suppression of GH-releasing hormone mRNA expression in the arcuate nuclei (P < 0.05) and enhanced somatostatin mRNA expression in the periventricular nuclei (P < 0.05), an expression pattern normally associated with increased GH feedback. Although gastric ghrelin mRNA expression was elevated by 50% in 3-week pregnant rats (P < 0.01), circulating ghrelin, GH-secretagogue receptor mRNA expression and the GH response to a bolus i.v. injection of exogenous ghrelin were all largely unaffected during pregnancy. Although trace amounts of ‘pituitary’ GH could be detected in the placenta with radioimmunoassay, significant GH-immunoreactivity could not be observed by immunohistochemistry, indicating that rat placenta itself does not produce ‘pituitary’ GH. Although not excluding the possibility that the pregnancy-associated elevation in baseline circulating GH could arise from alternative extra-pituitary sources (e.g. the ovary), our data indicate that this phenomenon is most likely to result from a direct alteration of somatotroph function. [ABSTRACT FROM AUTHOR]

Recent, compelling evidence indicates that kisspeptins, the products of KiSS-1 gene, and their receptor GPR54, represent key elements in the neuroendocrine control of reproduction, and that they act primarily by regulating gonadotrophin-releasing hormone (GnRH) secretion at the hypothalamus. Conversely, and despite earlier reports showing GPR54 expression in the pituitary, the potential physiological roles of kisspeptins at this gland have remained elusive. To clarify this issue, cultures of rat pituitary cells were used to evaluate expression of KiSS-1 and GPR54, and to monitor the ability of kisspeptin-10 to stimulate Ca2+ responses in gonadotrophs and to elicit luteinising hormone (LH) secretion in vitro. The results obtained show that both GPR54 and KiSS-1 are expressed in the pituitary of peripubertal male and female rats. Moreover, kisspeptin-10 induced a rise in free cytosolic Ca2+ concentration ([Ca2+]i) in approximately 10% of male rat pituitary cells. Intriguingly, kisspeptin-responsive cells included not only gonadotrophs, in which a 62.8 ± 16.0%[Ca2+]i rise was observed, but also somatotrophs, wherein kisspeptin induced a 60.3 ± 5.5%[Ca2+]i increase. Accordingly, challenge of dispersed pituitary cells with increasing kisspeptin-10 concentrations induced dose-related LH and growth hormone (GH) secretory responses, which were nevertheless of lower magnitude than those evoked by the primary regulators GnRH and GH-releasing hormone, respectively. In particular, 10−8 M kisspeptin caused maximal increases in LH release (218.7 ± 23.6% and 180.4 ± 7.2% in male and female rat pituitary cells, respectively), and also stimulated maximally GH secretion (181.9 ± 14.9% and 260.2 ± 15.9% in male and female rat pituitary cells, respectively). Additionally, moderate summation of kisspeptin- and GnRH-induced LH responses was observed after short-term incubation of male rat pituitary cells. In conclusion, our results provide unequivocal evidence that kisspeptins exert direct pituitary effects in peripubertal male and female rats and suggest a possible autocrine/paracrine mode of action. The precise relevance and underlying mechanisms of this potential new actions of kisspeptins (i.e. the direct modulation of gonadotrophic and somatotrophic axis at the pituitary) deserve further analysis. [ABSTRACT FROM AUTHOR]

Somatotrophs were identified and quantified in pituitary pars distalis of male viscachas (Lagostomus maximus maximus) during the annual reproductive cycle, after the administration of melatonin, after castration and in different growth stages by immunohistochemistry and morphometric analysis. In adult male viscachas, the somatotrophs were distributed throughout the pars distalis during the reproductive cycle. They were oval, pyramidal or round in shape with a large round nucleus. The percentage immunopositive area, the major cellular diameter and the number of cells decreased during the gonadal regression period in relation to the values found in the reproductive period. The administration of melatonin did not provoke any variations of the morphometric parameters studied. On the contrary, a significant decrease in the percentage immunopositive area, in the major cellular diameter and in the number of somatotrophs in castrated viscachas was observed. The study of different growth stages showed that these morphometric parameters increased from immature to adult animals in the reproductive period. The results obtained suggested that the variations of the morphometric parameters of somatotrophs are more related to the gonadal development and activity than to a direct effect of melatonin. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

This investigation determined the influence of acute and chronic resistance exercise on responses of growth hormone (GH) molecular variants in women. Seventy-four healthy young women (23 ± 3 yr, 167 ± 7 cm, 63.8 ± 9.3 kg, 26.3 ± 4.0% body fat) performed an acute bout of resistance exercise (6 sets of 10 repetition maximum squat). Blood samples were obtained pre- and postexercise. Resulting plasma was fractionated by molecular mass (fraction A, >60 kDa;fraction B, 30-60 kDa; and fraction C, <30 kDa) using chromatography. Fractionated and unfractionated (UF) plasma was then assayed for GH using three different detection systems (monoclonal immunoassay, polyclonal immunoassay, and rat tibial line in vivo bioassay). Subjects were then matched and randomly placed into one of four resistance exercise training groups or a control group for 24 wk. All experimental procedures were repeated on completion of the 24-wk resistance training programs. After acute exercise, immunoassays showed consistent increases in UF GH samples and fractions B and C; increases in fraction A using immunoassay were seen only in the monoclonal assay. No consistent changes in bioactive GH were found following acute exercise. Conversely, chronic exercise induced no consistent changes in immunoassayable GH of various molecular masses, whereas, in general, bioassayable GH increased. In summary, although acute exercise increased only immunoactive GH, chronic physical training increased the biological activity of circulating GH molecular variants. Increased bioactive GH was observed across all fractions and training regimens, suggesting that chronic resistance exercise increased a spectrum of GH molecules that may be necessary for the multitude of somatogenic and metabolic actions of GH. [ABSTRACT FROM AUTHOR]

Abstract: Growth hormone (GH) is known to play a key role in the regulation of body growth and metabolism. Similar to mammals, GH secretion in fish is under the control of hypothalamic factors. Besides, signals generated within the pituitary and/or from peripheral tissues/organs can also exert a feedback control on GH release by effects acting on both the hypothalamus and/or anterior pituitary. Among these feedback signals, the functional role of IGF is well conserved from fish to mammals. In contrast, the effects of steroids and thyroid hormones are more variable and appear to be species-specific. Recently, a novel intrapituitary feedback loop regulating GH release and GH gene expression has been identified in fish. This feedback loop has three functional components: (i) LH induction of GH release from somatotrophs, (ii) amplification of GH secretion by GH autoregulation in somatotrophs, and (iii) GH feedback inhibition of LH release from neighboring gonadotrophs. In this article, the mechanisms for feedback control of GH synthesis and secretion are reviewed and functional implications of this local feedback loop are discussed. This intrapituitary feedback loop may represent a new facet of pituitary research with potential applications in aquaculture and clinical studies. [Copyright &y& Elsevier]

Ikaros transcription factors play critical functions in the control of lymphohematopoiesis and immune regulation. Family members contain multiple zinc fingers that mediate DNA binding and homooligomerization or heterooligomerization. Ikaros is abundantly expressed in pituitary mammosomatotrophs, where it deacetylates histone 3 sites on the proximal growth hormone (GH) promoter to silence gene expression. lkaros-null mice display stunted growth with reduced circulating levels of the GH target factor insulin-like growth factor I (IGF-l). Ikaros-deficient mice have small anterior pituitary glands with a disproportionately reduced somatotroph population. Systemic administration of GH results in in- creased IGF-l levels and enhanced somatic growth. In contrast. reconstitution with WT lymphocytes was not sufficient to rescue the stunted growth phenotype of Ikaros-deficient mice. Ikaros was identified in mouse hypothalamic arcuate nuclei, where it colocalized with GH-releasing hormone (GHRH); in contrast, Ikaros-null mice lack GHRH immunoreactivity in the hypothalamus. Overexpression of Ikaros enhanced GHRH promoter activity and induced endogenous GHRH gene expression. These findings unmask a wider role for Ikaros in the neuroendocrine system, highlighting a critical contribution to the development of the hypothalamicpituitary somatotrophic axis. [ABSTRACT FROM AUTHOR]

The objective of this immunohistochemical study was to identify the spatial distribution patterns of growth hormone (GH) secreting cells (somatotrophs) in the newborn and prepubertal porcine pituitary. No differences were observed among the total somatotrophs per unit area across the three ages. There were, however, changes in spatial distribution of somatotrophs in porcine pituitary with developmental age. Distinctive characteristics of the pattern included a high population of somatotrophs (44±1.2; mean ± standard error of the mean per 30,495 µm2) in regions 1 and 5 and a low population (22±1.4) in regions 2 and 4 at each level (P<0.05). Somatotrophs increased 55% in region 3 from proximal to distal levels at all ages. With increasing age, however, somatotrophs in region 3 at the proximal level decreased 33%. From these results, we suggest that there may be regional specificity of cellular differentiation and transformation to facilitate GH secretion to meet the need for endocrine regulation as the animal ages. [ABSTRACT FROM AUTHOR]

We reported that corticosterone (CORT) can induce differentiation of growth hormone (GH) cells in vitro and in vivo during chick embryonic development. In the present study, a quantitative in situ hybridization plate assay (ISHPA) for GH mRNA was developed and used to assess the mechanism of glucocorticoid-induced GH gene expression directly in cell culture plates. Embryonic pituitary cells were treated with GH-releasing hormone (GHRH) alone, CORT alone and GHRH and CORT in combination. CORT increased levels of GH mRNA 22-fold, while GHRH acted synergistically with CORT to further augment GH mRNA levels (130-fold relative to control). GHRH alone induced only a 2.5-fold increase in GH mRNA. GH mRNA levels were increased after 8 h but not after 4 h of CORT treatment. In addition, synergistic effects of GHRH on CORT-induced GH mRNA were also observed after 8 h of treatment, however, GHRH alone for up to 24 h failed to increase GH mRNA levels, suggesting that embryonic pituitary cells do not respond substantially to GHRH in the absence of CORT. Cycloheximide (CHX) blocked CORT induction of GH mRNA, indicating that synthesis of some protein(s) is required for CORT induction of GH gene expression. Bypassing the GHRH receptor through treatment with forskolin and 3-isobutyl-1-methylxanthine (IBMX) and phorbol 12-myristate-13-acetate failed to increase GH mRNA levels, suggesting that a lack of GHRH receptors alone cannot account for the lack of GHRH responses in the absence of CORT. Treatment with inhibitors of protein kinase A (PKA; H-89), protein kinase C (PKC; calphostin C) and mitogen activated protein kinase (MAPK; PD098059) did not block induction of GH mRNA by CORT. In contrast, Manumycin, an inhibitor of Ras–GTPase, significantly suppressed the effect of CORT on GH mRNA. These results indicate that glucocorticoid induction of GH gene expression in embryonic pituitary cells requires active protein synthesis. The protein(s) involved in this induction is probably not a component of the PKA, PKC or MAPK signaling cascades but may involve Ras or a Ras-like compound. Current efforts in our laboratory are directed at identifying this intermediary protein(s). [Copyright &y& Elsevier]

We studied the effects of adrenergic agents on the five main cell types of the rat anterior pituitary by monitoring the changes of the cytosolic free [Ca2+] ([Ca2+]i) in single cells that were identified by multiple sequential primary immunocytochemistry at the end of the Ca2+ measurements. Adrenaline (100 nM) increased [Ca2+]i in 30% of the cells. Responses were most prominent in somatotrophs and corticotrophs (40–65% of the cells responded) whereas the other three cell types, lactotrophs, thyrotrophs and gonadotrophs, gave poorer responses. Selective agonists and antagonists revealed the presence of both α1- and β-adrenergic receptors. α1-Receptors dominated in corticotrophs, β-receptors in somatotrophs. The α1-adrenergic responses increased with culture of the cells. The β-adrenergic responses were mediated by cAMP and consisted of stimulation of Ca2+ entry through L-type voltage-gated channels. Stimulation of α1-receptors released Ca2+ from intracellular stores in corticotrophs and induced cAMP-independent Ca2+ entry in somatotrophs. The effects of α1-agonists were additive with those of the releasing factors growth hormone-releasing hormone (GHRH) and corticotropin releasing factor (CRF) whereas those of the β-agonists were not. Our results suggest that direct effects of plasma catecholamines on AP cells may contribute to the hormonal response to stress. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate in monkeys the effects of undernutrition on neurocranial and facial components, correlated with a histometric and ultrastructural analysis of somatotroph (growth hormone, GH) and lactotroph (prolactin, PRL) pituitary populations. Twenty Saimiri sciureus boliviensis (Cebidae) of both sexes were employed. The monkeys were born in captivity and when they reached 1 year of age, they were separated into two groups: control and undernourished animals. They were fed ad libitum a 20% and 10% protein diet, respectively. The monkeys were radiographed when they were 3 years old in order to measure the length, width and height of the anterior, middle and posterior components of the neurocranium, as well as those of the masticatory, respiratory and optic components of the face. The volumetric and morphometric indices were then calculated. After the sacrifice, pituitary glands were processed for light and electron microscopy. The quantitative immunohistochemistry revealed a decrease in the volume density and cell density of both GH and PRL cells from malnourished animals when compared to control ones. The ultrastructural study showed changes suggestive of cellular hyperfunction for both types of cells in the former experimental group. Under nutrition also affected the size of the cranial components, with males being more affected than females; brain weight was, however, nonmodified by stress, with the brain/body ratio difference being the same for both sexes. We conclude that in monkeys, experimental undernutrition produces a decrease in the pituitary GH and PRL cell populations, in some way related to changes in the cranio-facial morphometric patterns.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Growth hormone-releasing hormone (GHRH) is an important regulator of somatotroph development and function. However, GHRH signaling is still not completely understood. Signaling through the mitogen-activated protein kinase (MAPK) pathway has been observed in a wide variety of cell types but has not been explored as a mediator of GHRH action. In this study, we examined the phosphorylation of MAPK pathway intermediates in response to GHRH. After treatment of the GH4 rat somatotroph cell line with rGHRH (10 M) for 2.5 min, there was robust phosphorylation of MAPK not seen in vehicle-treated cells. Treatment of HeLa cells with GHRH resulted in no activation of MAPK, but activation was conferred by transfection with the GHRH receptor cDNA. MAPK activation by GHRH was dose dependent from 1 to 100 n M, was evident at 2.5 min, peaked at 5 min, and returned to baseline by 20 min. Pretreatment of GH4 cells with somatostatin analog BIM23014 or the MEK1 inhibitor PD98095 prevented the activation of MAPK. Finally, treatment with GHRH increased GH4 proliferation in culture, and this response was prevented by pretreatment with BIM 23014 and PD98095. These results indicate that GHRH activates the MAPK pathway. Furthermore, activation of MAPK may mediate, at least in part, the effects of GHRH on somatotroph cell line proliferation. The findings support the concept that multiple pathways mediate the effects of GHRH. [ABSTRACT FROM AUTHOR]

The question of whether thyroxine (T4) and thyrotropin-releasing hormone (TRH) affect mitoses in pituitary thyrotrophs (Tt) and somatotrophs (St) of hypothyroid rats was investigated. Fifteen day thyroidectomized (Tx) rats were used. Groups of Tx animals received T4 or TRH or both. Except 6 and 24 h TRH groups, the animals were sacrificed 12 h after injections. Unoperated euthyroid rats served as controls. In Tx group adenohypophysial mitoses were significantly increased. T4 diminished mitoses in Tx rats. Mitotic counts were decreased in 6 and 24 h Tx groups, but increased in 12 h TRH group. TRH plus T4 in Tx animals had a synergistic effect on adenohypophysial mitoses. In unoperated controls few mitoses were observed in Tt and more mitoses in St. In Tx rats more mitoses were seen in Tt than in St. T4 alone failed to reduce mitoses in Tt but increased them in St. We concluded that T4 affects Tt and St replication. In normal rats mitoses occur mainly in St. In Tx rats mitotic activity increased in Tt. TRH plus T4 have a synergistic motogenic effect on St. T4 but not TRH affects St replication. It appears that the presence, of T4 is necessary for St multiplication. [ABSTRACT FROM AUTHOR]

Pulse-chase experiments utilising(H)leucine have been used to study the effects of colchicine and vinblastine on intracellular transport and secretion of newly synthesised growth hormone from rat anterior pituitary fragments. Growth hormone was isolated from medium and fragments by polyacrylamide gel electrophoresis. When colchicine or vinblastine, which disrupt microtubules, were added immediately after pulse labelling, inhibition of the subsequent secretion of newly synthesised growth hormone was detected throughout the succeeding 5 h. Similar inhibition was seen if the drugs were added after a 1 h delay. However, if colchicine or vinblastine were added only after a 2 h chase incubation, then no significant effect on subsequent release of labelled growth hormone was seen. The results suggest that these agents may inhibit the transport of newly formed growth hormone storage granules from the Golgi complex to the cytoplasmic pool. Microtubules do not appear to be involved in the mechanism of the final secretion of newly synthesised hormone by exocytosis. [ABSTRACT FROM AUTHOR]

An immunocytochemical staining of ultrathin sections using the peroxidase-antiperoxidase complex was employed to localize the somatotrophs in the anterior pituitary of the human fetus. This technique allowed a specific identification of the somatotrophs and a detailed description of their ultrastructure which was well preserved by the fixation employed. They appeared as cells with a dense cytoplasmic matrix, lamellar rough endoplasmic reticulum, and prominent Golgi apparatus. Their secretory granules had a mean diameter of 300 nm. [ABSTRACT FROM AUTHOR]