Light bodies in human pituitary adenomas

Summary Light bodies are large cytoplasmic granules originally described in the gonadotrophic cells of the rat pituitary gland. In order to determine whether similar bodies occur in the human anterior pituitary gland, 89 pituitary adenomas and periadenomatous tissue from 20 cases were examined by transmission electron microscopy. Double membrane bound bodies with filamentous internal structure identical to rodent light bodies were identified in 10 hormone-producing adenomas: 5 PRL, 1 PRL-GH, 2 GH, and 2 ACTH-producing tumours. No light bodies were found in the remaining 79 tumours nor in the pituitary cells in periadenomatous tissue from 20 cases. These results show that some human pituitary adenomas may contain light bodies identical to those seen in gonadotrophs of rat pituitary.Abbreviations PRL prolactin - GH growth hormone - ACTH adenocorticotropic hormone - FSH follicle-stimulating hormone - LH luteinizing hormone     

Incidental adenomas of the human pituitary gland

Using conventional histological technique, we investigated 44 adenomas (31 men, 13 women) incidentally found in 36 pituitaries (25 men, 11 women) obtained from 1,117 unselected autopsies. The overall incidence of adenomas was 3.2% (men, 3.8%; women, 2.4%) without any significant sex predominance. Size, age distribution, and histological appearances of these adenomas were similar to those previously reported by others. Statistical analysis showed that the adenomas had a predilection for occurrence at the anterior margin of the gland. We further investigated 33 available adenomas with immunohistochemistry using antibodies for various adenohypophyseal hormones, S-100 protein, and glial fibrillary acidic protein, of which 6 contained growth hormone, 3 contained growth hormone and prolactin, 7 contained prolactin, 6 contained follicle-stimulating hormone, 3 contained follicle-stimulating and luteinizing hormones, 2 contained thyroid-stimulating and adrenocorticotrophic hormones (separately), and 6 contained no adenohypophyseal hormones. None of adenomas revealed neoplastic proliferation of folliculostellate cells. To investigate tumor proliferation, nucleolar organizer regions were studied in 9 adenomas using the argyrophil method. The mean number per nucleus was slightly higher than that of corresponding, nontumorous adenohypophysis at a statistically significant level. No adenoma caused symptoms of adenohypophyseal hormone abnormalities.     

In vitro studies of human pituitary adenomas

The application of morphologic and tissue culture techniques to the study of human pituitary adenomas allows further investigation of structure-function correlations. Using these methods, we have documented morphometric differences between densely and sparsely granulated somatotroph adenomas but the release of growth hormone in vitro and responses to adenohypophysial hormones/drugs do not correlate with tumor type. The morphologic and functional alterations in somatotroph adenomas exposed to SMS 201-995 appear to be reversible in vitro. Incubation of lactotroph adenomas with bromocriptine for 3 days directly reduces tumor cell size, cytoplasmic volume and cytoplasmic volume densities of endoplasmic reticulum and Golgi regions; these changes are similar to the effects of longterm bromocriptine therapy in vivo. Tissue culture studies of gonadotroph adenomas of men confirm that gonadotropin-releasing hormone (GnRH) stimulates gonadotropin release by tumor cells and yields morphologic evidence of increased hormone synthesis whereas these tumors have variable sensitivity to gonadal steroids; structural changes in tumor cells correlate with hormone release after stimulation, suggesting that morphologic parameters may reflect the hormonal milieu of these adenomas. Null cell adenomas and oncocytomas release small quantities of glycoprotein hormones, predominantly gonadotropins in vitro and there are no functional differences between these 2 tumor types; gonadotropin release responds to GnRH stimulation and, paradoxically, to other adenohypophysiotropic hormones, but such stimulation does not result in secretion of other adenohypophysial hormones by these tumors.     

The neurofibromatosis gene in human pituitary adenomas

The neurofibromatosis 1 (NF1) gene encodes a protein neurofibromin, which contains a glutamyl transpeptidase (GTP)-activating protein (GAP)-related domain: NF1 GRD. This domain is able to down-regulate P^21ras by stimulating its intrinsic GTPase. Because P^2lras has an important role in regulating growth and differentiation, somatic mutations in the NF1 gene may result in mutant neurofibromins that might interfere with the Ras signaling pathway and contribute to the development of tumors. In this study, we used polymerase chain reaction (PCR)-coupled single-stranded conformational polymorphism (SSCP) and DNA sequencing to examine possible mutations in the NF1 GRD in human pituitary tumors. We screened 36 nonfunctioning and 20 growth hormone—secreting adenomas. No mutation was detected in these tumors. Our results indicate that inactivation of neurofibromin may not have a primary role in the formation of pituitary adenomas.     

Immunohistochemical studies of human FSH producing pituitary adenomas

Summary Ten FSH producing pituitary adenomas were studied immunohistochemically. 9 cases were in males, and 7 showed elevated serum FSH levels. Immunohistochemically, all cases showed the presence of -subunit and FSH- subunits in many tumour cells. These two subunits were frequently colocalized in the same cells. However, the expression of LH- subunit was extremely low (1 of 10 cases exhibiting occasional LH- positive tumour cells), although it has been reported that FSH- and LH- subunits are colocalized in the same cells of the normal adult pituitary gland. Immunoelectron microscopically, -subunits and FSH- were present in the secretory granules and suggested the co-release of subunits or secretion of combined form of FSH. In 7 cases, TSH- was positive, and in some cases, TSH- was colocalized in the same tumour cells which contained -subunit and FSH- subunit. A few cases also demonstrated immunoreactivity for PRL and ACTH. Our immunohistochemical studies suggest that FSH adenomas are multihormonal and that there is abnormal gene expression in FSH cells with loss of LH- appearance and co-expression of TSH-.     

Immunocytochemistry of folliculo-stellate cells of normal and neoplastic human pituitary gland.

Five normal human pituitaries and 20 pituitary neoplasms were investigated by immunocytochemical methods. Glial fibrillary acidic protein and S100 have been shown in the anterior lobe of the pituitary. Both these markers were present in the folliculo-stellate cell. Evidence is presented for the presence of a transitional folliculo-stellate cell which is immunoreactive for S100. The role of the folliculo-stellate cell is discussed.     

The TSH secretion in the human pituitary adenomas

TSH secretion by a pituitary tumor is very rare (2%) and it is often associated with another hormone: GH or PRL essentially. We present here nine tumors in which the TSH secretion was proved by immunocytochemistry (ICC) and by RIA in the tumor extracts, in the serum and in the culture medium. Four tumors secreted TSH only. Five tumors secreted TSH and GH predominantly. In 3 of them traces of other hormones (PRL and FSH) were also detected. The "pure" TSH adenomas were monomorphous with typical ultrastructural and immunocytochemical features. Plurihormonal TSH adenomas were bimorphous with different cells secreting GH and TSH or monomorphous with one type of cell which secreted TSH or GH or both TSH and GH. In a majority of the cases, the tumoral TSH secretion induced hyperthyroidism but in 2 patients with TSH adenoma there was euthyroidism and in another with TSH-GH adenoma there was no sign of acromegaly and GH serum levels were normal.     

垂体ACTH细胞腺瘤的免疫电镜研究

5 cases of pituitary adenomas associated with Cushing's disease or Nelson's syndrome were studied with electron microscopy and immunoelectron microscopy by using protein A--gold complex. Diversified ultrastructure was displayed in these tumors, among which 4 revealed presence of ACTH positive secretory granules. These granules were round or polyhedric in shape, varied in number, size and electronic density. Bundles of microfilaments could be seen in the tumor cells frequently, which were of the highest diagnostic value. There was no significant difference found in ultrastructure and immunocytochemical reaction of adenomas in Cushing's disease and Nelson's syndrome.     

Pathology of prolactin cell adenomas of the human pituitary

Prolactin (PRL) cell adenoma is the most common tumor type in the human pituitary. It accounts for 30% of surgically removed adenomas, while its prevalence is even higher (45%) among incidental pituitary tumors observed at autopsy. Most PRL cell adenomas are highly differentiated with a characteristic ultrastructure. Administration of bromocriptine, a dopaminergic agonist, evokes profound morphologic changes in responsive PRL cell adenomas, while it leaves the fine structure of unresponsive tumors unchanged. The importance of immunocytochemical and electron microscopic investigation of pituitary biopsies is emphasized as tumors with different cell derivation, biological behavior, and therapeutic responsiveness may mimic PRL cell adenomas clinically.     

Plurihormonal pituitary adenomas

Plurihormonal adenomas of the pituitary, ie, tumors that engage in the production of unusual combinations of hormones, represent approximately 10% to 15% of all adenomas. Such tumors comprise in excess of 50% of adenomas in the setting of acromegaly and occur with somewhat greater frequency in childhood and adolescence than in adulthood. Eight percent are associated with multiple endocrine neoplasia, type I. The most common variant of plurihormonal adenoma produces growth hormone, prolactin, and one or more glycoprotein hormones, the most common being TSH. Clinical effects most often reflect the presence of growth hormone, and to a lesser extent, prolactin cells; expression of glycoprotein hormone production is rare. The tumors are more often macroadenomas (80%) than microadenomas (20%) and demonstrate gross invasion in 50% of cases. Plurihormonal adenomas may be ultrastructurally monomorphous, bimorphous, or trimorphous; thus, one morphologic cell type may elaborate several hormones.     

Structure-function correlations of human pituitary gonadotroph adenomas in vitro

Two pituitary gonadotroph adenomas were studied in vitro to characterize structure-function correlations. Both tumors were from men, aged 63 and 69 years, who had elevated blood levels of follicle-stimulating hormone (FSH) and normal blood luteinizing hormone (LH) and testosterone values. The surgically resected adenomas contained diffuse immunohistochemical positivity for beta-FSH, beta-LH, and alpha-subunit of glycoprotein hormones; by electron microscopy they were composed of well-differentiated gonadotrophs. In vitro, both tumors released FSH, LH, and alpha-subunit. Morphometric studies were performed on surgically resected and cultured adenoma cells. Compared with the surgical specimens, the cultured cells had decreased cytoplasmic volume densities of endoplasmic reticulum and Golgi apparatus and slightly increased cytoplasmic volume densities of secretory granules. Incubation with gonadotropin-releasing hormone (GnRH) for 2 and 24 hours increased FSH, LH, and alpha-subunit release by both tumors; morphometry after 2 consecutive days of exposure confirmed significant increases in cytoplasmic volume densities of endoplasmic reticulum and Golgi regions and marked decreases in that of secretory granules. There was no significant change in cell size, nuclear/cytoplasmic ratio, or secretory granule diameter. The two tumors differed in their response to gonadal steroids. Estradiol, testosterone, and progesterone stimulated release of FSH, LH, and alpha-subunit by one tumor and the morphologic changes paralleled the biochemical response; addition of testosterone suppressed the secretory and morphologic response to GnRH. The other tumor showed no significant response to estradiol or testosterone and addition of these steroids did not alter the response to GnRH. The results are consistent with the interpretation that GnRH stimulates not only release but also synthesis of gonadotropins by gonadotroph adenomas of men. The data also indicate variable sensitivity of these tumors to gonadal steroids with paradoxical stimulation alone and inhibition of response to GnRH. The structural changes correlate with the hormone release response in vitro.     

Alpha-subunit-producing pituitary adenomas

Summary Immunohistological techniques demonstrate the alpha-subunit of glycoprotein hormones in the majority of endocrine-inactive, undifferentiated pituitary adenomas and pituitary oncocytomas. In about one-fifth of endocrine-active adenomas, the alpha-subunit is produced in combination with either adrenocorticotropic hormone or prolactin, and it is found in combination with growth hormone in about half of those adenomas causing acromegaly.Pure alpha-subunit-producing, endocrine-inactive adenomas characteristically have small secretory granules that are destroyed by direct osmium fixation, but are well preserved after prefixation with glutaraldehyde. As only a few atypical prolactinomas show similar secretory granules, and as they display a positive reaction for the alpha-subunit only exceptionally, this ultrastructural feature can serve as a guide to differentiate such adenomas.     

Heterogeneous pituitary adenomas

Summary The combined use of several histological procedures (i.e. conventional light microscopy, immunohistochemistry and electron microscopy) among 45 unselected pituitary adenomas demonstrated the existence of 9 tumors (20%) containing several identifiable adenohypophy seal cell types. Thecellular associations were between 2 or 3 identifiable cell types. Mammosomatotrophic tumors were the most frequent but not the only mixed type (somatomammocorticotrophic, somatocorticotrophic tumors were also found). The cellular components varied in size but the cells appeared randomly distributed in the tumors. In all the adenomas there was an unidentified cell component (no reactivity with antisera used) varying from sparse to numerous elements. On adjacent sections the adenomatous cells reacted with a single specific antiserum, but in two cases the immunohistochemistry on contiguous paraffin embedded sections did not confirm this with certainty. These results confirm those of others and a new term is purposed to designate these tumors: heterogeneous pituitary adenomas. According to the nature and the proportions of the cell components the heterogeneous adenomas were subdivided into two groups: a group A which comprised adenomas formed by a major identifiable cellular type associated with one or two other less frequent cell types, and a group B formed by a predominant unidentifiable (no reactivity with immunochemical stainings) cell type associated with one or two other identified cell types. The present morphofunctional classifications of pituitary adenomas should be modified to include homogeneous adenomas with a single cell type and heterogeneous adenomas with several cell types.     

Unusual configurations of endoplasmic reticulum in human pituitary adenomas

Electron microscopic study of 435 surgically-removed human pituitary adenomas and 43 nontumorous adenohypophyses revealed unusual configurations of endoplasmic reticulum in 102 adenohypophysial tumors (23%) and in 12 nontumorous adenohypophyses (28%). These configurations classified as paired reticulum, annulate lamellae and ribosome-lamellar complexes were noted in various adenomatous and nontumorous adenohypophysial cells, indicating that they could not be used as specific markers for pituitary adenomas or for a particular adenohypophysial cell type. Paired reticulum was a common finding, whereas annulate lamellae and ribosome-lamellar complexes were rarely encountered. Whether or not these endoplasmic reticulum configurations could be considered as normal constituents of adenohypophysial cells was difficult to assess, since nontumorous cells studied were from patients who had various diseases and who had been treated with different hormones. The presence of endoplasmic reticulum configurations was neither related to age, sex of the patients nor degree of differentiation or endocrine activity of pituitary adenomas.     

Coexpression of galanin and adrenocorticotropic hormone in human pituitary and pituitary adenomas.

Galanin is a neuropeptide that regulates the secretion of several pituitary hormones, including prolactin (PRL) and growth hormone (GH). Galaninlike immunoreactivity (Gal-IR) and galanin mRNA in the rat anterior pituitary is cell lineage specific, with predominant expression in lactotrophs and somatotrophs. The authors examined the cellular distribution of human Gal-IR in seven normal postmortem pituitaries and 62 pituitary tumors by immunoperoxidase staining. In contrast to the rat, Gal-IR in human anterior pituitaries was present in corticotrophs scattered throughout the gland, but not in lactotrophs, somatotrophs, thyrotrophs, or gonadotrophs. Distinct Gal-IR also was present in hyperplastic and neoplastic corticotrophs in 19 of 22 patients with Cushing's disease. In noncorticotroph cell tumors, unequivocal Gal-IR was present in 5 of 11 GH-secreting tumors associated with clinical acromegaly, 9 of 18 nonfunctioning pituitary adenomas, and 2 of 14 prolactinomas. Of these galanin-positive tumors, four of the five GH-secreting adenomas, six of the nine nonfunctioning adenomas, and both of the prolactinomas also contained adrenocorticotropic hormone immunoreactivity (ACTH-IR). Immunostaining and in situ hybridization on adjacent sections using an 35S-labeled probe complementary to human galanin mRNA demonstrated predominant galanin expression in normal corticotrophs. Immunoelectron microscopy confirmed the presence of Gal-IR in pituitary cells characteristic of corticotrophs in both normal and neoplastic pituitaries. Thus, as in the rat, galanin gene expression in the human pituitary is cell-type specific. Unlike the rat, however, human galanin gene expression is restricted to the corticotroph lineage. Studies of tumors confirmed the observed coexpression of galanin and adrenocorticotropic hormone. The divergent cell type specificity of galanin production in human and rat pituitaries reflects different patterns of gene activation in these two species. In addition, these results suggest that galanin in the human pituitary may participate locally in the regulation of the hypothalamic-pituitary-adrenal axis.     

Invasiveness of pituitary adenomas

528 biopsies from 396 pituitary adenomas were re-examined by light microscopy and checked for invasion of neighbouring tissues. The overall invasion rate was 41.9%. Highly differentiated ACTH-cell adenomas were invasive in 24.1%, undifferentiated mucoid-cell adenomas in 66.7%. The histological type of invasion was influenced by the adenoma type and by the invaded tissue. There was no obvious correlation between the adenoma type and the invaded tissue.