Kovács, Kálmán

Rab3B, is a low molecular weight GTP binding protein implicated in the regulation of exocytosis. To shed light on its presence in the pituitary, an immunohistochemical study of 130 surgically removed human pituitary adenomas was undertaken, including 23 somatotroph, 32 lactotroph, 19 functioning corticotroph, 10 silent subtype 1 and 8 silent subtype 2 corticotroph, 12 gonadotroph, 10 thyrotroph, 7 subtype 3, and 9 null cell adenomas. Ten lactotroph adenomas were pretreated with bromocriptine, a dopamine agonist and 10 somatotroph adenomas with octreotide, a somatostatin analog. Ten autopsy obtained nontumorous adenohypophyses were also examined. The tumors were classified on the basis of their histologic, immunohistochemical and ultrastructural characteristics. Rab3B immunopositivity was strongest in corticotrophs followed by thyrotroph, lactotroph, gonadotroph, Subtype 3, null cell and somatotroph adenomas. No difference was noted between endocrinologically active and silent corticotroph adenomas. Bromocriptine therapy was associated with decreased Rab3B immunoexpression, whereas pretreatment with octreotide induced no significant reduction. Immunopositivity was cytoplasmic and evenly distributed. No staining was noted in the nontumorous adenohypophyses. Our results add new information to the view that Rab3B is involved in the regulation of pituitary hormone secretion.

The aim of our work was to investigate immunohistochemical expression of nestin, a member of the intermediate filament family, in the adenohypophysial vasculature during the development and progression of pituitary infarction. Non‐tumorous adenohypopheses (45 cases) and pituitary adenomas (34 cases) of various types, all exhibiting acute or healing infarcts were examined. The streptavidin‐biotin‐peroxidase complex method was applied. In areas of adenohypophyses and pituitary adenomas with no infarction, nestin was expressed in scattered capillaries and endothelial cells. In acute infarcts, no nestin was demonstrable in the necrotic capillaries (50 cases). Where newly formed capillaries spread into necrotic zones, nestin expression was noted in all capillaries (25 cases). In the hypocellular, fibrotic scar phase, only few vessels were apparent and immunoreactivity was focal and mild (4 cases). In conclusion, nestin is strongly expressed in newly formed capillaries and is downregulated when infarcts transform to fibrous tissue. Nestin expression may provide valuable insight into the process of pituitary angiogenesis.

Ghrelin, a 28 amino acid‐containing orexigenic peptide, is an endogenous ligand of the GH secretagogue receptor. It was extracted from the rat stomach, but is present in other organs. The aim of this work was to localize ghrelin by immunohistochemistry in autopsy‐derived non‐tumorous human pituitaries. Immunohistochemistry was performed using the streptavidin‐biotin‐peroxidase complex method and the results were analyzed independently by 3 of the authors. Double Immunostaining was also undertaken to determine which cell type was expressing both the adenohypophysial hormone and ghrelin. Results showed that ghrelin can be localized in the adenohypophysis. It's immunoexpression being cytoplasmic, weak to moderate, and present in only a subset of cells. The neurohypophysis is immunonegative. Double immunostaining showed that ghrelin is co‐localized with GH, ACTH and LH and is present to 51–90% of such cells. PRL, TSH and FSH cells are consistently non‐reactive. The role of ghrelin in adenohypophysial endocrine activity is not clear. It may well be that ghrelin exerts an autocrine‐paracrine effect and can modulate hormone synthesis and release.

Ghrelin, an orexigenic hormone occurs mainly in stomach, and in several tumor types. We investigated ghrelin immunopositivity using the streptavidin‐biotin‐peroxidase complex method in the full spectrum of pituitary adenoma subtypes. Quantification was undertaken by analyzing both the percentage of tumor cells stained for ghrelin and the staining intensity. Cytoplasmic ghrelin immunopositivity was identified in several adenoma subtypes. Not every cell was immunopositive; the intensity of staining differed among cells within the given lesion and among the various tumors. The highest scores were noted in GH adenomas exposed to somatostatin analogues. In decreasing order, lower scores were encountered in ACTH‐producing, silent subtype 1 and 2 adenomas in Cushing disease, silent subtype 3 adenomas, untreated GH adenomas, dopamine agonist‐treated PRL adenomas, gonadotroph adenomas, and ACTH adenomas in Nelson syndrome. No immunoreactivity was found in TSH, untreated PRL‐producing, and null cell adenomas. The high immunoexpression of ghrelin in GH adenomas exposed to somatostatin analogues, may be due to increased ghrelin synthesis or to suppression of its release.

Previous studies showed that in pregnancy the pituitary enlarges and increases in weight due to lactotroph hyperplasia. We demonstrated that in pituitaries of pregnant women, microvessel density is significantly increased compared to those of age– matched non pregnant women. Vascular endothelial growth factor (VEGF) stimulates new vessel formation in several tissues and neoplasms. The aim of the present study was to reveal whether VEGF is involved in the causation of increased vascularity in the pituitaries of pregnant women. We assessed VEGF immunoexpression in 20 autopsy obtained pituitaries of pregnant women and compared the results with 20 controls. Slides were immunostained for VEGF and pituitary hormones using the streptavidin‐biotin‐peroxidase complex method. VEGF immunoexpression was evaluated in 10 random high‐power fields using an image analyzer and the results compared by chi‐square or Fisher exact tests. Immunoexpression of VEGF was not increased in the adenohypophyses of pregnant women compared with the controls indicating that VEGF plays no major role in the causation of increased vascularity. The cause remains to be investigated.

Objective MGMT expression in brain and pituitary tumors has been correlated with temozolomide treatment. Few medical therapies are available in patients with Nelson Syndrome. The aim of the present study was to assess immunohistochemical expression of MGMT in ACTH‐secreting pituitary adenomas in patients with Nelson Syndrome. Methods Our material consisted of specimens from ACTH‐secreting pituitary adenomas from patients with Nelson Syndrome. Immunohistochemical staining for MGMT was performed using the streptavidin‐biotin‐peroxidase complex method. MGMT immunoreactivity was assessed microscopically and recorded as an estimated percentage of nuclear MGMT immunopositivity. (0=none, 1=<10%, 3=<50%, 4=>50%) Results Male:Female ratio was 3:5, with average patient age being 62 (range 57–66). Five of the eight specimens (65%) exhibited no MGMT immunoreactivity, with two out of eight cases (25%) showing slight MGMT immunopositivity and one out of eight cases (12%) demonstrating moderate MGMT immunopositivity (<25%). Conclusions Temozolomide therapy may be useful in patients with Nelson Syndrome. Absent or low MGMT staining in brain and other neoplasms has been shown to correlate with successful treatment with temozolomide, and recent reports assessing aggressive pituitary adenomas suggest similar outcome.

Following traumatic brain injury (TBI) approximately 25% of patients develop partial or complete hypopituitarism (HP). In our previous histologic study we found no changes in the pituitaries of patients who died instantly after TBI (Group I). In 43% of patients who survived 1‐7 days acute pituitary infarcts were apparent (Group II). In the present work, 3 group I and 7 group II pituitaries with infarcts were selected for histological and immunohistochemistry (IH) evaluation. IH was performed for adenohypophyseal hormones by the streptavidin‐biotin‐peroxidase method. In group I pituitaries, no histological changes were found and IH showed normal distribution and intensity for GH, PRL, ACTH, TSH, FSH, LH and α‐subunit (α‐SU). In group II pituitaries acute infarct (size range: 10% to 80%) was evident. IH in the non‐necrotic areas revealed no significant change. In the area of early necrosis the dying cells were still immunopositive (IP) for GH, PRL, ACTH, TSH, FSH, LS, and α‐SU. Even in the necrotic cells with loss of cell membrane, nuclear pyknosis, rhexis and lysis IP cytoplasms were still apparent indicating that hormone release is affected by ischemia. Subsequently the intensity of IP cells gradually decreased and IP granules leaked out from the necrotic cells and were seen extracellularly. In conclusion infarction and loss of adenohypophyseal cells may contribute to HP but other factors should also be considered.

AbstractWe examined the specific cell types in normal human pituitaries that expressed PRL receptor (PRL-R) messenger ribonucleic acid (mRNA) by combined in situ hybridization and immunohistochemistry. The distribution of PRL-R mRNA in 28 pituitary adenomas was examined by in situ hybridization and reverse transcription-PCR in 12 cases of adenomas. In another set of experiments, 34 PRL adenomas from men, women, and bromocriptine-treated patients were analyzed for PRL-R by in situ hybridization.In the normal pituitary, PRL- and LH-producing cells had significantly more mean grain counts per cell and higher percentages of cells positive for PRL-R than GH and TSH cells. PRL-R mRNA was present in all groups of adenomas by in situ hybridization and reverse transcription-PCR. PRL adenomas had a significantly higher density of labeling compared to other adenoma types. Although there was no difference in the levels of PRL-R mRNA in PRL adenomas from men and premenopausal and postmenopausal women, patients treated with bromocriptine before pituitary surgery had significantly lower levels of PRL-R compared to all other groups. These results indicate that in the normal pituitary, PRL and LH cells have the highest level of PRL-R mRNA, whereas PRL adenomas have significantly higher levels of PRL-R mRNA than other types of adenomas, and bromocriptine treatment decreases the levels of PRL-R mRNA in PRL adenomas.