Neuropeptide Y (NPY) actions on the corticotroph cell of the anterior pituitary gland are not mediated by a direct effect
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Corticotropic cell
Corticotropin-releasing hormone
Hypothalamic–pituitary–adrenal axis
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Somatostatin (SRIF), originally described as a hypothalamic hormone that inhibits the release of growth hormone was subsequently shown to inhibit the secretion of multiple pituitary hormones. Five genes encoding six different SRIF receptors (sst1,2A,2B,3,4 and 5) have been cloned and mRNAs for all five are expressed in the anterior pituitary. We used double immunostaining to determine which cells in the anterior pituitary bear sst2A and sst5 receptors. Our results show that these two receptors are widely distributed in the pituitary gland and are both present in a large percentage of GH cells. In addition, sst5 occurs in a small population of corticotrophs and a large percentage of lactotrophs whereas sst2A is found in only a few lactotrophs but a large number of corticotrophs. The sst2A receptor is also expressed in about a third of the gonadotrophs and thyrotrophs. Interestingly, sst2A and sst5 receptors colocalize in a small percentage of cells, most likely somatotrophs demonstrating that the same cells can contain multiple sst receptor subtypes. These results indicate that sst subtype specific analogs are likely to be useful for the selective regulation of individual pituitary hormones.
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Somatostatin (SRIF), originally described as a hypothalamic hormone that inhibits the release of growth hormone was subsequently shown to inhibit the secretion of multiple pituitary hormones. Five genes encoding six different SRIF receptors (sst1,2A,2B,3,4 and 5) have been cloned and mRNAs for all five are expressed in the anterior pituitary. We used double immunostaining to determine which cells in the anterior pituitary bear sst2A and sst5 receptors. Our results show that these two receptors are widely distributed in the pituitary gland and are both present in a large percentage of GH cells. In addition, sst5 occurs in a small population of corticotrophs and a large percentage of lactotrophs whereas sst2A is found in only a few lactotrophs but a large number of corticotrophs. The sst2A receptor is also expressed in about a third of the gonadotrophs and thyrotrophs. Interestingly, sst2A and sst5 receptors colocalize in a small percentage of cells, most likely somatotrophs demonstrating that the same cells can contain multiple sst receptor subtypes. These results indicate that sst subtype specific analogs are likely to be useful for the selective regulation of individual pituitary hormones.
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Abstract A morphometric analysis of the cell types within the adenohypophysis of the female rat was conducted with an emphasis on regional variations. Type I and type II gonadotropes and corticotropes had the largest volumes, mammotropes and somatotropes were of medium size, and thyrotropes and chromophobes were the smallest cells. There was no regional variation in the volumes of the respective cell types. Somatotropes and mammotropes were most numerous, followed by the gonadotropes, chromophobes, corticotropes, and thyrotropes. There was no significant regional localization of the somatotropes, mammotropes, corticotropes, and thyrotropes. Gonadotropes were best defined as two populations with type I cells being localized in the central regions and type II cells being distributed throughout the gland. Chromophobes were the only cells with a significant distribution in the anterior regions and were most numerous in the anterior peripheral regions. These fine‐structural morphometric findings are discussed in relation to other studies of the adenohypophysis that utilize immunocytochemistry.
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Silent Corticotroph and Somatotroph Double Pituitary Adenoma: A Case Report and Review of Literature
Introduction: Clinically silent double pituitary adenomas consisting of corticotroph and somatotroph cells are exceedingly rare clinical findings. In this report, we present the case of a double adenoma with sparsely granulated somatotroph and densely granulated corticotroph cells, the latter of which exhibited an elevated Ki-67 labeling index.
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Pituitary adenomas can express and secrete different hormones. Expression of pituitary hormones in nonneoplastic pituitary cells is regulated by different transcription factors. Some pituitary adenomas show plurihormonal expression. The most commonly reported plurihormonal adenomas are composed of somatotrophs, lactotrophs, thyrotrophs and gonadotrophs. Pituitary adenomas composed of both corticotroph and somatolactotroph secreting cells are not common because transcription factors regulating the expression of these hormones are different. We report a rare case of pituitary adenoma with concomitant corticotroph, prolactin, and growth hormone staining cells, review literature on similar cases, and discuss possible biological mechanisms underlying these plurihormonal tumors.
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The cell types of the mature adenohypophysis are derived embryologically from somatic ectoderm associated with Rathke' s pouch. Highly specific trophic factors determine a precise temporal and spatial development of cells expressing unique gene products. The six hormones of the anterior pituitary gland are expressed by at least five distinct hormone-producing cell populations, including corticotrophs (pro-opiomelanocortin, POMC), somatotrophs (growth hormone, GH), lactotrophs (prolactin, PRL), thyrotrophs (thyroid-stimulating hormone, TSH), and gonadotrophs (follicle-stimulating hormone, FSH, and luteinizing hormone, LH) (Table 48-1). Each of these cells are identified by specific assays of polypeptide gene expression, including single-cell mRNA, immunoelectron microscopy, and immunocytochemical assays. The temporal ontogeny of these gene products is initially adrenocorticotropic hormone (ACTH) and α-subunit. After the appearance of Pit-1, apou-domain transcription factor, mixed mammosomatroph products appear. Distinct GH- and PRL-expressing cells PRL-expressing cells follow and TSH, LH, and FSH are the final IPII types to mature at 12 weeks.
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We have investigated the possibility that local production of GHRH within the adenohypophysis could be an aetiological factor in the development of human pituitary somatotroph and other tumours. We examined 51 human pituitary adenomas for GHRH transcripts using in situ hybridization histochemistry. GHRH transcripts were identified in 13 of 17 somatotroph adenomas, 4 of 10 corticotrophs, 1 of 6 lactotrophs and 1 of 18 endocrinologically inactive adenomas. In 11 GHRH-expressing somatotroph adenomas, SRIH transcripts were also identified. In all cases except one (a corticotroph adenoma) the average number of GHRH transcripts exceeded that found in the arcuate nucleus of simultaneously hybridized rat brain sections. In some pituitary adenomas, GHRH transcripts were clearly localized to a discrete subpopulation of cells and in these, the amount of GHRH mRNA per cell was comparable to that found in the GHRH-expressing cells of the rat arcuate nucleus. Although we have not directly demonstrated an association between the two, the identification of localized, high level GHRH gene expression in somatotroph adenomas suggests that GHRH may have a role in pituitary adenoma formation.
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