Somatotroph Pituitary Adenomas Research Articles

Growth hormone-releasing hormone stimulates mitogen-activated protein kinase.

GH-releasing hormone (GHRH) can induce proliferation of somatotroph cells. The pathway involving adenylyl cyclase/cAMP/protein kinase A pathway in its target cells seems to be important for this action, or at least it is deregulated in some somatotroph pituitary adenomas. We studied in this work whether GHRH can also stimulate mitogen-activated protein (MAP) kinase. GHRH can activate MAP kinase both in pituitary cells and in a cell line overexpressing the GHRH receptor. Although both protein kinase A and protein kinase C could activate MAP kinase in the CHO cell line studied, neither protein kinase A nor protein kinase C appears to be required for GHRH activation of MAP kinase in this system. However, sequestration of the betagamma-subunits of the G protein coupled to the receptor inhibits MAP kinase activation mediated by GHRH. This pathway also involves p21ras and a phosphatidylinositol 3-kinase, probably phosphatidylinositol 3-kinase-gamma. Despite the involvement of p21ras, the protein kinase Raf-1 is not hyperphosphorylated in response to GHRH, contrary to what usually occurs when the Ras-Raf-MAP kinase pathway is activated. In summary, this work describes for the first time the activation of MAP kinase by GHRH and outlines a path for this activation that is different from the cAMP-dependent mechanism that has been traditionally described as mediating the mitogenic actions of GHRH.

The epidemiology of endocrine tumours.

The epidemiological study of disease aims to increase our understanding of the aetiology, patterns of occurrence and natural history of clinical conditions by reference to populations and defined sub-populations. One of the potential gains from such an approach is the possibility of drawing inferences regarding the contributions of genetic and specific environmental factors in causation. On a more immediately practical level, the determination of prevalence of disease in defined populations is important for the planning of specialist facilities and the prediction of direct and indirect costs of treatment. Tumours of endocrine glands, although rare in the context of the overall burden of oncological disease, have provided important insights into the mechanisms of sporadic and familial tumour formation, important examples being the primary role of constitutively activated cell membrane G protein-linked mechanisms in determining proliferation in pituitary somatotroph adenomas (Spada et al. 1990), and the recent elucidation of the molecular basis of the multiple endocrine neoplasia (MEN) syndromes (Ponder 1994, Chandrasekharappa et al. 1997). However, it is often difficult to obtain an epidemiological perspective for endocrine tumours, either because of asymptomatic disease which results in incomplete case ascertainment or the rarity of individual tumours (Table 1). The reported incidence of parathyroid adenoma is a classical example of the dependence of incidence data on diagnostic facilities and local policies for routine serum calcium measurements. These problems are magnified by the fact that clinical care of endocrine tumours may occur in a variety of settings (including endocrinology,

Absence of somatostatin receptor type 2 A mutations and gip oncogene in pituitary somatotroph adenomas.

Somatostatin, acting via specific receptors in the anterior pituitary, tonically inhibits pituitary growth hormone secretion and somatotroph proliferation. Reduction of growth hormone secretion and tumour regression in GH-secreting pituitary adenomas treated with long-acting somatostatin analogues varies widely. In 30-40% of these tumours dominant somatic mutations of the Gsalpha gene (gsp) have been demonstrated leading to constitutive adenylyl cyclase induction. A relationship between somatostatin sensitivity and tumour pathogenesis in some tumours has been suggested. Changes in the function of the somatostatin receptor or intracellular signal elements may be of relevance. Somatostatin receptor type 2 A (sst2A) and Gi2 are proposed to mediate selectively the inhibition of GH release in the somatotroph. We therefore investigated the presence of sst2A mutations and gip oncogene in somatotrophic pituitary adenomas. Tumour samples from 15 patients with pituitary somatotroph adenomas were obtained. RNA was isolated and used for reverse transcription and subsequent polymerase chain reaction. All samples were screened for the presence of sst2A mutations and of the gip oncogene by SSCP analysis and sequencing. For comparison, the gsp oncogene was examined. The relationship between clinical data and molecular analysis results was investigated. Seven of the tumours harboured a gsp mutation. No mutations affecting the sst2A protein were found in any of the tumours analysed. Furthermore, gip oncogene was absent in all tumours. Mutations of the somatostatin receptor type 2 A and the gip oncogene are unlikely to be involved in the pathogenesis of acromegaly.

Octreotide Effect on Growth Hormone and Somatostatin Subtype 2 Receptor mRNAs of the Human Pituitary Somatotroph Adenomas.

Octreotide, a somatostatin analog used to treat acromegalic patients harboring a pituitary tumor, acts via somatostatin subtype 2 receptor (SSTR2) and causes significant decrease of circulating GH levels and sometimes mild to moderate tumor shrinkage. To further elucidate the mechanism of octreotide action, we studied GH and SSTR2 mRNAs by in situ hybridization in densely and sparsely granulated somatotroph adenomas removed by surgery from 14 treated and 14 untreated patients. Only in densely granulated adenomas were the GH and SSTR2 mRNA signals mildly decreased relative to untreated matched adenomas. The decrease of GH mRNA in densely granulated somatotroph adenomas suggests that they may have a more favorable response to octreotide therapy than sparsely granulated tumors.

Detection of a silent pituitary somatotroph adenoma in a patient with amenorrhea and/or galactorrhea: paradoxical response of GH in TRH or GnRH provocation test.

Detection of a silent pituitary somatotroph adenoma in a patient with amenorrhea and/or galactorrhea: paradoxical response of GH in TRH or GnRH provocation test.

Mutation analysis of protein kinase A catalytic subunit in thyroid adenomas and pituitary tumours.

The adenylyl cyclase system plays an important role in the control of both thyroid follicular and anterior pituitary cell function. Activating mutations affecting important pathway components such as the TSH receptor and Gsalpha occur in the majority of autonomously functioning thyroid nodules. Only a small proportion of other types of thyroid tumours, however, have been reported to harbour these mutations. Activating mutations of Gsalpha have been reported to occur in up to 40% of pituitary somatotroph adenomas. As the majority of cold thyroid nodules and pituitary tumours are unaffected by these mutations, we have investigated the possibility of activating mutations occurring in protein kinase A (PKA), which is another key component of the adenylyl cyclase pathway. Genomic DNA and cDNA were analysed for the presence of PKA Calpha mutations by allele-specific oligonucleotide hybridisation and single strand conformation polymorphism analysis. A total of 171 tissue samples were investigated. These comprised 66 benign and 24 malignant thyroid neoplasms, 21 somatotroph adenomas, 35 non-functioning pituitary adenomas, 2 corticotroph adenomas, 1 malignant prolactinoma, and 22 normal pituitary tissue samples. No mutations of PKA Calpha were identified using either allele-specific oligonucleotide hybridisation or single strand conformation polymorphism analysis. It appears that PKA Calpha mutations at the codons investigated do not represent an oncogenetic mechanism in the development of thyroid and pituitary neoplasms.

Pituitary Somatotroph Adenoma Producing Growth Hormone (GH)-Releasing Hormone (GHRH) with an Elevated Plasma GHRH Concentration: A Model Case for Autocrine and Paracrine Regulation of GH Secretion by GHRH

Pituitary Somatotroph Adenoma Producing Growth Hormone (GH)-Releasing Hormone (GHRH) with an Elevated Plasma GHRH Concentration: A Model Case for Autocrine and Paracrine Regulation of GH Secretion by GHRH

Pronostic and therapeutic consequences of Gs alpha mutations in somatotroph adenomas.

Human pituitary somatotroph adenomas can be associated with mutations of the s alpha-subunit of G proteins. However, the impact of the gsp mutations on the tumoral phenotype is not well understood at present. This study aims to determine whether the detection of this mutation could impact on the management of acromegalic patients. We examined 30 acromegalic patients; 8 were gsp positive, and 22 were gsp negative. The gsp-positive adenomas appeared to secrete significantly more when the ratio of basal GH level/tumor size was considered. A better octreotide sensitivity of mutated adenomas was clearly shown under in vivo (short and long term) and in vitro conditions. During the acute octreotide test, the GH nadir was significantly lower in the gsp-positive adenomas (85% of maximal inhibition vs. 52%). Eighteen patients were treated with octreotide (300 micrograms/day) for at least 3 months before surgery: the percent inhibition of GH hypersecretion was higher in gsp-positive adenomas (76% vs. 47%). In cell culture, the octreotide-induced inhibition of GH release was significantly higher in gsp-positive adenomas (71% vs. 30%). Finally, during 2 yr of postoperative follow-up, GH hypersecretion was controlled in all patients with gsp mutation even in those in whom tumoral tissue remained after surgery. On the contrary, in the gsp-negative group, octreotide treatment was unable to control hypersecretion in 4 patients bearing tumoral remnants. The Gs alpha mutation could, therefore, be a new marker to foresee the susceptibility of the tumor to be controlled by somatostatin analogs, which improves prognosis.

Pit-1 gene expression in human lactotroph and somatotroph pituitary adenomas is correlated to D2 receptor gene expression.

The expression of the pituitary-specific transcription factor Pit-1 gene was analyzed in a series of 30 human lactotroph and somatotroph pituitary tumors. Northern blot analysis failed to reveal any quantitative differences in Pit-1 gene expression between somatotroph and lactotroph tumors, and reverse transcription-PCR analysis showed similar patterns of Pit-1 isoforms expression in both populations of tumors. The expression of the D2 receptor gene was subsequently analyzed in the same adenomas. In the prolactinomas, which presented with a variable sensitivity to dopamine agonist treatment, the intensity of the D2 receptor transcripts (2.8 kilobases) was variable and was related to the sensitivity to the dopamine agonist treatment. Notably, the individual D2 receptor messenger ribonucleic acid (mRNA) levels were highly correlated to the Pit-1 mRNA levels measured in the same tumors (r = 0.90; P < 0.0001). In the GH-secreting tumors, a significant expression of the D2 receptor gene was evidenced by Northern blot in all mixed somato-lactotroph adenomas and in some of the pure somatotroph adenomas; again, a positive correlation was found between D2 mRNA and Pit-1 mRNA levels (r = 0.68; P < 0.01). These results suggest the existence of mechanisms responsible for a coordinate control of Pit-1 and D2 receptor genes that remain to be determined.

Pit-1 gene expression in human lactotroph and somatotroph pituitary adenomas is correlated to D2 receptor gene expression

Pit-1 gene expression in human lactotroph and somatotroph pituitary adenomas is correlated to D2 receptor gene expression

Interphase Analysis of Chromosome 11 in Human Pituitary Somatotroph Adenomas by Direct Fluorescence In Situ Hybridization.

Chromosome 11 numerical abnormalities were detected by fluorescence in situ hybridization (FISH) technique in four surgically removed pituitary somatotroph adenomas from patients clinically associated with acromegaly. The tumors were diagnosed by histology. immunocytochemistry, and electron microscopy, and included two densely granulated somatotroph (DG-SM) and two sparsely granulated somatotroph (SG-SM) adenomas. For demonstration of chromosome 11, the direct FISH technique was applied on imprints from fresh adenoma tissue fixed in acetone using an a-satellite specific centromeric probe. The slides were studied with a fluorescence microscope and the percentages of positive nuclei with aberrant fluorescent signals were counted. All tumors exhibited numerical chromosomal abnormalities in 8-23% of their cell population and included nuclei containing 1-3 extra chromosome 11 copies. The SC-SM adenomas exhibited more prominent abnormalities compared with the DG-SM adenomas. We conclude that numerical chromosome 11 abnormalities represent a frequent event among somatotroph adenomas with a tendency for higher frequency in SC-SM adenomas.

G s protein mutations and the pathogenesis and function of pituitary tumors

Hypothalamic growth hormone-releasing hormone (GHRH) stimulates growth hormone (GH) production and somatotroph proliferation by binding to a seven transmembrane-domain receptor, linked to G s. G s stimulates production of cyclic adenosine 3′–5′-monophosphate (cAMP) and hence activation of protein kinase A (PKA). A subgroup of pituitary somatotroph adenomas has been demonstrated, which has constitutive activation of G s, with reduced in vitro responsiveness to agents that stimulate G s. Subsequently, somatotroph adenomas have been identified, which have activating mutations of G s ( gsp). However, there are no clear clinical or biochemical phenotypic characteristics that enable gsp-positive and gsp-negative tumors to be differentiated from one another. Gsp mutations occur in 35% to 40% of somatotroph adenomas in caucasians, but have a much lower reported prevalence of 4% to 9% in the Japanese population. G-protein mutations also occur in clinically nonfunctioning pituitary tumors and, rarely, in corticotroph adenomas. There is little direct evidence at present to suggest that the gsp mutation has a primary oncogenic role in the pathogenesis and function of pituitary tumors. Further functional studies are needed. The gsp mutation is probably one of several oncogenic mutations required for pituitary tumor development.

A Case of pituitary somatotroph adenoma with concomitant secretion of growth hormone, prolactin, and adrenocorticotropic hormone ? an adenoma derived from primordial stem cell, studied by immunohistochemistry, in situ hybridization, and cell culture

Somatotroph adenomas often secrete prolactin (PRL) besides growth hormone (GH) and are sometimes immunostained for other anterior pituitary hormones or their subunits, such as thyroid-stimulating hormone (TSH) beta-subunit and glycoprotein hormone alpha-subunit (alpha SU). However, somatotroph adenomas showing hypersecretion of adrenocorticotropic hormone (ACTH) are extremely rare. There have been, to our knowledge, only five published reports on somatotroph adenomas accompanied by excessive ACTH secretion. Here we report a case of intracavernously invading somatotroph macro-adenoma with high serum GH, PRL, and ACTH levels. We examined the case using immunohistochemistry (IHC), in situ hybridization (ISH), and cell culture, and confirmed GH, PRL, and ACTH, as well as alpha SU, production, and the expression of Pit-1 protein by the adenoma, which is known as a transcriptional factor for GH, PRL, and TSH, not for ACTH. Therefore, the presence of unknown transcriptional factor other than Pit-1, common to GH, PRL, and ACTH, may be speculated to be expressed in this adenoma. In our previous study, we had found plurihormonal mRNA expression, especially for ACTH, the beta-subunit of follicle-stimulating hormone and luteinizing hormone in some somatotroph adenomas, using non-radio-isotopic ISH, and suggested that these adenomas might be derived from plurihormonal primordial stem cells. Our present case is significant from the viewpoint of histogenesis of pituitary adenomas, because it further supports the cell origin of somatotroph adenomas from plurihormonal primordial stem cells, and moreover it suggests the presence of unknown transcriptional factor other than Pit-1, common to GH, PRL, and ACTH.

Production of alpha-subunit of glycoprotein hormones by pituitary somatotroph adenomas in vitro.

Somatotroph adenomas of the pituitary secrete growth hormone in excess and are associated with acromegaly. Morphologically, they can be separated into two entities, densely and sparsely granulated variants. It has been shown that a number of somatotroph adenomas produce alpha-subunit of glycoprotein hormones; however, it is not clear whether alpha-subunit production correlates with tumor cell morphology. We studied 32 surgically removed pituitary somatotroph adenomas in tissue culture to determine structure-function correlations of growth hormone and alpha-subunit production. All tumors were classified on the basis of detailed histological, immunocytochemical and electron-microscopic studies. Fifteen tumors were densely granulated and 17 were sparsely granulated. In addition to growth hormone, all 15 densely granulated tumors released alpha-subunit in vitro, whereas of the 17 sparsely granulated tumors only 4 released alpha-subunit; moreover, the mean baseline levels of alpha-subunit were significantly higher in densely granulated adenomas than in sparsely granulated adenomas. Parallel response of release of both hormones was found during stimulation with growth hormone-releasing hormone or thyrotropin-releasing hormone and during suppression with somatostatin or bromocriptine in densely granulated tumors. alpha-subunit response to stimulation or suppression could not be determined with significance in sparsely granulated tumors because of low basal levels. The results indicate that alpha-subunit production and release is characteristic of densely granulated somatotroph adenomas and that alpha-subunit is coregulated with growth hormone by adenohypophysiotropic substances; in contrast, alpha-subunit production, by sparsely granulated somatotroph adenomas is rare and, when present, much lower in quantity.(ABSTRACT TRUNCATED AT 250 WORDS)

Coexisting acromegaly and a unilateral cortisol-producing adrenal adenoma: a possible variant of multiple endocrine neoplasia type I.

An unusual case of coexisting acromegaly and Cushing's syndrome is reported in a 34-yr-old female. There was no biochemical or morphological evidence to suggest the presence of other endocrinopathies. She did not have any family history to suggest a hereditary tendency to endocrine disorders. Her acromegaly and Cushing's syndrome were proven to be due to a pituitary somatotroph adenoma and a cortisol-producing adenoma in the right adrenocortex, respectively. Surgical removal of both tumors led to a marked biochemical improvement of the two endocrinopathies. To account for the simultaneous occurrence of the two endocrine tumors, at least two endocrine syndromes may be considered. One of them is Carney's complex. However, Cushing's syndrome in this complex is unexceptionally due to primary pigmented nodular adrenocortical disease, differing from the adrenal pathology of our patient. In addition, a lack in this case of any other characteristic suggestive of this syndrome appears to speak against this possibility. A second possibility is multiple endocrine neoplasia type 1. The absence of a parathyroid or pancreatic islet cell tumor does not strongly support this possibility, but adrenocortical lesions are not rare in this syndrome although they are only rarely functional. However, existence of similar case reports, although very few, in the literature leaves the possibility that she represents another rare variant of sporadic multiple endocrine neoplasia type I syndrome.

Colon Polyps in Acromegaly

Acromegaly results from unrestrained secretion of growth hormone and insulin-like growth factor 1 (IGF-1), usually occurring as a result of a pituitary somatotroph adenoma (1). Of 283 acromegalic p...

INOSITOL PHOSPHOLIPID TURNOVER AND INTRACELLULAR Ca2+ RESPONSES TO THYROTROPHIN‐RELEASING HORMONE, GONADOTROPHIN‐RELEASING HORMONE AND ARGININE VASOPRESSIN IN PITUITARY CORTICOTROPH AND SOMATOTROPH ADENOMAS

We have studied the inositol phospholipid turnover response to thyrotrophin-releasing hormone (TRH) gonadotrophin-releasing hormone (GnRH) and arginine vasopressin (AVP) in five corticotroph and six somatotroph pituitary adenomas. GnRH (100 nM) increased inositol phospholipid turnover in five of five somatotroph adenomas tested by an average of 36.4 +/- 9.4% (mean +/- SE). In a fifth, which was too small to allow inositol phospholipid turnover to be assessed, GnRH produced a rapid increase in mean intracellular calcium ion concentration. Only one of five corticotroph adenomas responded to GnRH with an increase in inositol phospholipid turnover of 19%. In contrast, all the somatotroph and corticotroph adenomas tested (four of four and five of five respectively) increased inositol phospholipid turnover in response to AVP (100 nM), by an average of 61 +/- 11.8% and 415 +/- 186% respectively. The finding of an inositol phospholipid or intracellular Ca2+ response to thyrotrophin-releasing hormone (TRH) (100 nM) in three of five somatotroph adenomas (Ca2+ increasing from 50 to 175 nM in one and inositol phospholipid turnover increasing by 172 +/- 1.9% and 49 +/- 5.2% in two) and to GnRH in all five somatotroph adenomas concurs with the common clinical finding of paradoxical growth hormone responses to these releasing factors in patients with acromegaly. The lack of such a response in three of the four corticotroph adenomas suggests that the appearance of GnRH and TRH receptors on adenomatous pituitary cells is not common to all cells.

Human pituitary somatotroph adenoma and prolactinoma: An ultrastructural and immunoelectron microscopical study

17 cases of pituitary somatotroph adenoma and 38 cases of prolactinoma were studied with electron microscopy and immunoelectron microscopy using protein A-gold complex. 4 adenomas were shown by immunoelectron microscopy to contain simultaneously growth hormone (GH)-producing and prolactin (PRL)-producing cells. 6 cases were classified as densely granulated GH adenomas and 11 as sparsely granulated variant, whereas only 3 adenomas out of 38 prolactinomas were identified as densely granulated adenomas. The present study showed that not all cells with fibrous bodies possessed secretory granules positive for GH, and in some cells with fibrous bodies PRL-producing granules were also detected. Misplaced exocytosis was found frequently in the sparsely granulated prolactinomas. From these findings it may be suggested that fibrous bodies are not a morphological feature characteristic of pituitary somatotroph adenomas.

Phorbol ester and phospholipase C-induced growth hormone secretion from pituitary somatotroph adenoma cells in culture: effects of somatostatin, bromocriptine, and pertussis toxin.

To clarify the role of the breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2) in GH secretion in human somatotrophs and the effects of inhibitors of GH secretion on this mechanism, we studied the effects of 12-tetradecanoylphorbol-13-acetate (TPA) and phospholipase C (Plase C) on GH secretion and the interactions of somatostatin (SRIH), bromocriptine, and pertussis toxin (IAP) with TPA or Plase C, using human GH-secreting pituitary adenoma cells in culture. SRIH (10(-9)-10(-7) M) inhibited and TPA (10(-10)-10(-8) M) and Plase C (0.125-1.0 U/mL) stimulated GH secretion. SRIH (10(-9)-10(-7) M) inhibited GH release induced by TPA (10(-8) M) or Plase C (1.0 U/mL). Bromocriptine (10(-8) M) also inhibited 10(-8) M TPA-induced GH secretion. When adenoma cells were treated with 100 ng/mL IAP for 24 h, basal and TPA-induced GH secretion rates did not change. However, the inhibitory effects of SRIH (10(-8) M) or bromocriptine (10(-8) M) on basal and 10(-8) M TPA-stimulated GH secretion were attenuated. In addition, IAP reduced GH secretion induced by 0.5 U/mL Plase C, while SRIH inhibition of Plase C-evoked GH release was diminished by IAP. We conclude that the hydrolysis of PIP2 by Plase C, which causes activation of protein kinase C by 1,2-diacylglycerol and Ca2+ mobilization by inositol 1,4,5-triphosphate, is a physiological intracellular mechanism leading to GH secretion in human somatotrophs; SRIH inhibits GH secretion mediated by this mechanism, and bromocriptine blocks at least protein kinase C-mediated GH release; the inhibitory guanine nucleotide-binding protein (Ni) is involved in these inhibitory effects of SRIH and bromocriptine; and Ni modulates the breakdown of PIP2 by Plase C.