pancreastatin and Pituitary-Neoplasms

Pancreastatin, derived from chromogranin A, inhibits insulin and stimulates glucagon secretion in rodents. Immunohistochemistry localised pancreastatin in human pancreatic islet cells and gonadotroph pituitary cells. Nonsecreting pituitary adenomas, frequently associated with diabetes mellitus, arise quasi-constantly from gonadotroph cells. We evaluated the possible involvement of pancreastatin in the physiopathology of diabetes mellitus associated with nonsecreting pituitary adenomas. Plasma pancreastatin levels were measured by radioimmunoassay in 5 groups of subjects: 10 patients with nonsecreting pituitary adenomas associated with diabetes mellitus (group I), 10 patients with nonsecreting pituitary adenomas without diabetes (Group II), 10 patients with ACTH or GH-secreting pituitary adenomas and diabetes mellitus (Group III), 10 diabetic patients without pituitary adenomas (Group IV), and 10 healthy controls (Group V). Kidney and liver functions were normal in all of them and no patient was treated with a proton pump inhibitor. All pituitary adenomas were trans-sphenoidally removed. Immunohistochemistry against pancreastatin was performed in 5 patients of each of the 3 groups of pituitary adenomas. Plasma pancreastatin levels were not different between the different groups: 182±46 pg/ml (Group I), 195±57 pg/ml (Group II), 239±42 pg/ml (Group III), 134±31 pg/ml, (Group IV), and 122±29 pg/ml (Group V). In contrast, they were significantly (p<0.05) higher before (391±65 pg/ml) than after trans-sphenoidal surgery (149±18 pg/ml) without post-surgical change in diabetes. An immunostaining against pancreastatin was found in a majority of pituitary adenomas, associated or not with diabetes mellitus. These results argue against a role of pancreastatin in the pathogenesis of diabetes mellitus associated with nonsecreting pituitary adenomas.

Topics: Aged; Aged, 80 and over; Chromogranin A; Diabetes Complications; Female; Humans; Male; Middle Aged; Pancreatic Hormones; Pituitary Neoplasms

Leptin is a circulating hormone secreted by adipose and a few other tissues. The leptin receptor consists of a single transmembrane-spanning polypeptide that is present as a long physiologically important form as well as in several short isoforms. Recent studies have suggested that the anterior pituitary may have a role in the regulatory effects of leptin in animal models. To test this possibility in human pituitaries, we examined the expression of leptin and OB-R in normal and neoplastic pituitaries, and the possible functions of leptin in the pituitary were also analyzed. Leptin was present in 20-25% of anterior pituitary cells and was expressed in most normal anterior pituitary cells, including ACTH (70% of ACTH cells), GH (21%), FSH (33%), LH (29%), TSH (32%), and folliculo-stellate cells (64%), but was colocalized with very few PRL cells (3%), as detected by double labeling immunohistochemistry with two different antileptin antibodies. In addition, leptin expression was detected by RT-PCR in some pituitary tumors, including ACTH (three of four), GH (one of four), null cells (two of four), and gonadotroph (one of four) tumors as well as in normal pituitary. Immunohistochemical staining showed greater immunoreactivity for leptin in normal pituitaries compared to adenomas. Treatment of an immortalized cultured anterior pituitary cell line, HP75, with leptin stimulated pancreastatin secretion in vitro. Leptin also inhibited cell growth in the human HP75 and in the rat pituitary GH3 cell lines. Both long (OB-Rb) and common (OB-Ra) forms of the leptin receptor messenger ribonucleic acid and leptin receptor protein were expressed in normal and neoplastic anterior pituitary cells. These findings show for the first time that leptin is expressed by most human anterior pituitary cell types and that there is decreased leptin protein immunoreactivity in pituitary adenomas compared to that in normal pituitary tissues. We also show that OB-Rb is widely expressed by normal and neoplastic anterior pituitary cells, implicating an autocrine/paracrine loop in the production and regulation of leptin in the pituitary.

Topics: Animals; Carrier Proteins; Cell Division; Chromogranin A; Human Growth Hormone; Humans; Immunohistochemistry; In Situ Hybridization; Leptin; Pancreatic Hormones; Pituitary Gland; Pituitary Neoplasms; Proteins; Rats; Receptors, Cell Surface; Receptors, Leptin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured

Pituitary adenomas are members of the family of neuroendocrine cells and tumors which have secretory granules containing chromogranins/secretogranins and other proteins. Pituitary adenomas express the neuroendocrine specific proconvertases PC1 (also known as PC3) and PC2, which are important for the proteolytic processing of chromogranins/secretogranins molecules. We examined the distribution of PC1 and PC2 in primary cultures of 20 pituitary adenomas and analyzed the regulation of the proconvertase mRNAs and proteins by various secretagogues including hypothalamic hormones and phorbol ester to determine the role of PC1 and PC2 in CgA processing in pituitary adenomas. Although PC2 was present in all adenomas, there was a differential distribution of PC1 with PRL adenomas expressing lower levels of PC1 compared to other adenoma types by RT-PCR analysis, in situ hybridization and immunostaining. Treatment of primary cultures of pituitary adenomas with phorbol 12-myristrate 13-acetate (PMA) resulted in an increase in pancreastatin (PST) secretion in most pituitary adenomas and increased PC1 mRNA and protein expression in gonadotroph adenomas, but not in other types of adenomas. Analysis of a human pituitary adenoma cell line, immortalized by recombinant defective adenovirus (HP75), which expressed chromogranin A, FSH, PC1 and PC2 showed that PST was secreted by these immortalized cells. Treatment with TGF beta 1 resulted in an increase in PST secretion and in PC1 mRNA and protein. These results indicate that a) there is a differential distribution of PC1 in human pituitary adenomas with PRL adenomas expressing very little PC1 mRNA and protein and b) that PC1 expression in gonadotropin hormone-producing adenomas is regulated by PMA and TGF beta 1. These findings support the observation that chromogranin A is a substrate for the endoproteinase PC1 in human pituitary adenoma cells.

Topics: Adenoma; Aspartic Acid Endopeptidases; Base Sequence; Chromogranin A; Chromogranins; DNA Primers; Humans; Immunohistochemistry; In Situ Hybridization; Pancreatic Hormones; Pituitary Hormones; Pituitary Neoplasms; Proprotein Convertase 2; Proprotein Convertases; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; RNA, Neoplasm; Subtilisins; Tumor Cells, Cultured

Pancreastatin, a carboxyl-terminal amidated peptide derived from chromogranin (Cg)A, inhibits secretion of insulin and parathyroid hormone. Our recent studies found significant amounts of immunoreactive pancreastatin in all pituitary adenomas except prolactin adenomas. To analyze the effects of pancreastatin on pituitary cell function, 17 cultured pituitary adenomas were examined for immunoreactive pancreastatin and pancreastatin secretion by the tumors. The effects of pancreastatin on pituitary hormone secretion and on pituitary hormone (follicle-stimulating hormone and prolactin), CgA, and CgB mRNA levels were also examined. Immunoreactive pancreastatin and CgA were present diffusely in gonadotroph and null cell adenomas, but only a few prolactin adenoma cells expressed pancreastatin or CgA. When cells were treated with hypothalamic peptides, gonadotroph adenomas were the only group that released increased amounts of pancreastatin in response to gonadotropin-releasing hormone (10(-7) mol/L). Pancreastatin (10(-7) mol/L) treatment did not stimulate pituitary hormone secretion significantly. In situ hybridization analyses showed that gonadotropin-releasing hormone and pancreastatin treatment led to significant increases in CgB and follicle-stimulating hormone mRNAs in gonadotroph adenomas, whereas CgA mRNA levels did not change significantly. These results show that there is a differential distribution of pancreastatin secretion in pituitary adenomas and that the hypothalamic hormone gonadotropin-releasing hormone and the CgA-derived peptide pancreastatin can regulate CgB mRNA in gonadotroph adenomas, suggesting an autocrine effect of pancreastatin on pituitary tumor function.

Topics: Adenoma; Adult; Aged; Child; Chromogranin A; Chromogranin B; Chromogranins; Female; Humans; Hypothalamic Hormones; Immunohistochemistry; In Situ Hybridization; Male; Middle Aged; Pancreatic Hormones; Pituitary Hormones; Pituitary Neoplasms; Prolactinoma; RNA, Messenger; Tumor Cells, Cultured