Pure alpha subunit-secreting pituitary tumors

Alpha subunit in clinically non-functioning pituitary adenomas: An immunohistochemical study

Pituitary adenomas may be classified as either functioning or non-functioning, depending on whether excess hormone secretion can be clinically identified. Of the six hormones produced in the anterior pituitary, TSH, FSH and LH are known as glycoproteins and contain two subunits (α and β). While α-subunit is identical within all of them, each β-subunit is unique and biologically specific. Independently, the α- and β-subunits are inactive and only induce a hormonal response when they are non-covalently associated. Studies have shown that in certain cases, pituitary adenomas may abnormally secrete only α-subunit, detectable in the serum or through immunohistochemical analysis. In the present study, we examined α-subunit immunoexpression in surgically removed non-functioning pituitary adenomas and analyzed its prognostic value. Results showed that expression of α-subunit in clinically non-functioning pituitary adenomas is not a rare occurrence. While there were no age/gender differences between tumors that expressed α-subunit and those that did not, α-subunit immunonegative adenomas presented with suprasellar extension more frequently and had an Ki67 proliferation greater than 3%. The use of immunohistochemical techniques to determine the presence of α-subunit may provide information on tumor cell proliferation and biologic behavior. To fully understand the role of α-subunit in pituitary adenomas more work is needed.

A functioning FSH-secreting pituitary macroadenoma causing an ovarian hyperstimulation syndrome with multiple cysts resected and relapsed after leuprolide in a reproductive-aged woman

Bioactive gonadotropin-secreting pituitary adenomas are very rare in fertile women and can cause an ovarian hyperstimulation syndrome (OHSS). A 31-year-old woman with oligo-amenorrhea, severe ovarian cystic swelling and high serum estradiol was submitted to the resection of ovarian cysts and then treated with long-acting leuprolide 11.25 mg. Two months later, the ovarian multicystic hyperplasia relapsed, thus a pituitary MRI was performed and a pituitary macroadenoma was detected. In January 2010, she was referred to our Endocrinology Department where her hormonal evaluation showed high serum estradiol, FSH, α-subunit and inhibin with low LH. In April 2010, she underwent a trans-sphenoidal pituitary adenomectomy, which rapidly regularized the hormonal profile, the ovary and pituitary morphology and the menses. The case presented confirms that gonadotrophinomas occurring in reproductive-aged women frequently produce symptoms of ovarian hyperstimulation and proves that the use of GnRH analogs is not indicated in this condition.

Ovarian hyperstimulation without elevated serum estradiol associated with pure follicle-stimulating hormone-secreting pituitary adenoma

We report a unique case of a 28-yr-old woman with a gonadotroph adenoma secreting FSH, presented with ovarian hyperstimulation, without elevation of serum estradiol. She presented with abdominal pain and large ovaries (both 10 cm in diameter) with multiple follicular cysts shortly after discontinuing oral contraceptive pills. She had a supranormal PRL level of 71 microg/liter (normal, <20), FSH of 8.4-9.2 IU/liter (normal for follicular phase, 2.4-10), LH of 0.01 IU/liter (normal, 1.6-9.3), estradiol of 108 pmol/liter (normal for follicular phase, 80-790), and free alpha-subunit level of 0.11 microg/liter (normal, <1.8). A nuclear magnetic resonance study revealed invasive pituitary macroadenoma, 30 mm in diameter. Dopamine agonist (cabergoline) treatment normalized serum PRL but had no affect on FSH levels. A transsphenoidal surgery was performed, and most of the adenoma was resected. One month after surgery the patient resumed menstruation, and the hormonal profile included serum FSH of 6.3 IU/liter, LH of 2.1 IU/liter, estradiol of 156 pmol/liter, and PRL of 10 microg/liter. The excised adenoma tissue exhibited intense immunostaining for FSH and secreted this hormone to culture medium. Stimulation with TRH (both in vivo preoperatively and in vitro study of the excised tumor) had no effect on FSH secretion from the adenoma. Estradiol did not suppress FSH release from cultured adenoma cells. Patient serum samples showed significant FSH bioactivity when tested in a human granulosa cell line. This case is remarkable because the ovarian hyperstimulation related to the FSH-secreting adenoma was not associated with high levels of serum estradiol, probably due to insufficient LH production by the normal pituitary. Thus, it supports the two-cell, two-gonadotropin theory, that both FSH and LH are necessary for normal ovarian estrogen production.

Pituitary adenomas in acromegaly: Comparison of different adenoma types with clinical data

Adenoma tissues from 309 patients with active acromegaly was examined by routine light microscopy and immunohistochemistry, and selectively by electron microscopy. All adenomas were immunoreactive for growth hormone. Eighty-seven adenomas were monohormonal (28%), 58 were bihormonal (immunoreactive for growth hormone and prolactin) (19%), and 157 adenomas were plurihormonal (51%), with positivity for glyco-proteins and/or their α-subunit as well. The mean tumor size was significantly greater in monohormonal adenomas than in other adenoma types. There was no difference in invasiveness among the various adenoma types. Younger patients showed invasive tumor growth more often. Patients with densely granulated GH cell adenomas had a significantly longer duration of symptoms compared to patients with other adenoma types. More than half of the patients with sparsely granulated GH cell adenomas had a duration of less than 5 yr. There was no correlation between duration of symptoms and tumor size. The preoperative mean GH level was significantly higher in patients with sparsely granulated GH cell adenomas than in those with mixed GH/PRL cell adenomas. The preoperative mean PRL level was significantly higher in patients with bihormonal adenomas than in those with plurihormonal adenomas. There was an inverse correlation between age and preoperative GH and PRL levels. No linear correlation was found between preoperative basal GH and PRL levels. Monohormonal adenomas presented more often with suprasellar and/or parasellar extension than other adenoma types. Our data suggest a positive correlation between tumor extension and preoperative GH and PRL levels. Patients with plurihormonal adenomas were significantly older than patients with sparsely granulated GH cell adenomas and mixed GH/PRL cell adenomas. No significant difference was found between the various adenoma types and the extent of surgical removal, which depends on the degree of invasiveness, tumor size, and extrasellar tumor extension.

Production and characterization of specific anti-peptide antiserum against free alpha-subunit of rat pituitary glycoprotein hormones

To obtain an antibody specific for the alpha-subunit of rat pituitary glycoprotein hormones, we synthesized a peptide corresponding to the sequence 37-53 (ST-7: Phe-Ser-Arg-Ala-Tyr-Pro-Thr-Pro-Ala-Arg-Ser-Lys-Lys-Thr-Met-Leu-Val) of the rat alpha-subunit. The polyclonal antiserum against this peptide was generated in rabbits. This region is hydrophilic and highly conserved among several mammalian species. Noncompetitive binding tests showed that the ST-7 antiserum had specific affinity for the rat free alpha-subunit, but not for rat intact LH, FSH, and TSH. The ST-7 antiserum immunostained two types of cells in the rat anterior pituitary, i.e., gonadotrophs and thyrotrophs. This was also the case in mouse, cattle, sheep, and pig, which have an identical sequence of ST-7 in their alpha-subunit. The pituitary cells of horse (Arg substituted for Lys as residue 48 of the rat alpha-subunit), human, and eel (Leu for Ala at residue 45), chicken (Met for Ala at residue 45), and bullfrog (Tyr for Phe at residue 37 and Met for Ala at residue 45) were not stained with the ST-7 antiserum. This study indicated that the ST-7 antiserum is sequence-specific for the alpha-subunit and is therefore useful for immunohistochemical studies on the secretory pathway of the free alpha-subunit.

Secretory and nonsecretory pituitary adenomas are distinguishable by 1/T1 magnetic relaxation rates at very low magnetic fields in vitro

RATIONALE AND OBJECTIVES

The authors investigated whether hormonally active and inactive pituitary adenomas can be discriminated in vitro by magnetic resonance (MR) imaging-related data.

METHODS

1/T1 nuclear magnetic relaxation dispersion profiles were measured for 39 fresh surgical specimens of secreting and nonsecreting adenomas, classified using clinical criteria or preoperative serum hormone levels. Nonsecreting adenomas were subdivided into hormone-producing and nonhormone-producing by immunostains. At five fields (0.00024 to 1.2 tesla [T]), mean 1/T1 was analyzed for statistically significant differences among these three tumor categories.

RESULTS

Mean 1/T1 was significantly higher (P < 0.02) for hormone-secreting than for nonsecreting adenomas at fields below 0.24 T; no significant difference existed at typical MR imaging fields (0.5 to 1.5 T). Mean 1/T1 for hormone-producing and nonhormone-producing, nonsecreting adenomas were not significantly different at any field.

CONCLUSIONS

Because 1/T1 at low fields is related to 1/T2 at imaging fields, it may be possible to detect hormone secretion of pituitary adenomas noninvasively by MR imaging.

Gonadotropic pituitary carcinoma: case report

A 37-year-old man developed multiple intracranial, intraspinal, and general metastases from an invasive nonfunctioning pituitary adenoma after surgery and radiation therapy. This is the first gonadotropic pituitary carcinoma reported in literature.

Large pituitary adenoma of the sphenoid sinus and the nasopharynx: report of a case with ultrastructural evaluations

A unique case of nonfunctioning pituitary adenoma exclusively involving the sphenoid sinus and the nasopharynx is reported. The computed tomography and magnetic resonance imaging (MRI) clearly depicted the presence of a large, soft mass in the sphenoid sinus and its extensive invasion to the sphenoid wing and the clivus. In particular MRI was found useful in delineating precise anatomic relationships between this sphenoid sinus tumor and the pituitary fossa. The sphenoid sinus tumor was partially resected by sublabial transnasal approach, and the intact dura mater of the base of the pituitary fossa was confirmed. Pathologic examinations including immunocytochemical and ultrastructural studies showed that the tumor was classified as a nonfunctioning acidophilic pituitary adenoma. Despite the endocrine-inactive tumor, the presence of small secretory granules in the cytoplasm demonstrated by electron microscopic studies was of significant importance in establishing the diagnosis. This rare tumor is reviewed in the literature in the context of nasopharyngeal extension of pituitary adenomas, and a possibility of ectopic occurrence and growth is also discussed in the presented case.

Immunohistochemical expression of human chorionic gonadotropin and P-glycoprotein in human pituitary glands and craniopharyngiomas

In order to clarify the cellular origin of craniopharyngiomas, the authors examined the distribution of P-glycoprotein (PGP) and human chorionic gonadotropin (HCG) in five normal adenohypophyses and in 23 craniopharyngiomas using peroxidase immunohistochemistry. The correlation between the expression of PGP in craniopharyngiomas and the recurrence of these tumors was also investigated. A number of pars intermedia cyst-lining cells immunostained positively for anti-PGP antibodies. A small number of adenohypophysial cells were also positive for PGP, but squamous epithelial nests were negative in all samples. However, HCG-beta was consistently demonstrated in adenohypophysial cells, pars intermedia cyst-lining cells, and squamous epithelial nests. In 11 craniopharyngiomas, the apical portion of cuboidal cells and some polygonal cells immunostained positively with anti-PGP antibodies. In four HCG-producing craniopharyngiomas, a large number of tumor cells were immunostained with anti-PGP antibodies, three of which showed a recurrence of cystic tumors. By double labeling, the coexpression of HCG-beta and PGP was demonstrated in these recurrent tumors. Accordingly, it is suggested that craniopharyngiomas produce HCG-like peptides and that craniopharyngiomas are unique squamous neoplasms arising in the sellar region from progenitor cells of a neuroendocrine lineage.

Null cell adenomas, oncocytomas, and gonadotroph adenomas of the human pituitary: An immunocytochemical and ultrastructural anafysis of 300 cases

The immunocytochemical profile of 300 clinically nonsecreting pituitary adenomas was investigated. All tumors were diagnosed, classified, and separated into null cell adenomas, oncocytomas, and gonadotroph adenomas according to their ultrastructural morphology. The immunocytochemical analysis was based on the semiquantitative proportional estimates of positive cells immunostained for all known peptide and glycoprotein pituitary hormones including alpha-subunit. The majority of tumors (87%) were to some extent immunopositive for various hormones. Glycoprotein hormones were most frequently encountered. Usually, particularly in males, more than one subunit was present in the same tumor. In 97 tumors (32%) more than 25% of adenoma cells were immunoreactive for gfycoprotein hormones. Fifty-five tumors (18%) contained occasional cells immunopositive for growth hormone (GH), prolactin (PRL), and adenocorticotropin (ACTH) in addition to glycoprotein hormones. Given the significant proportion of immunoreactive cells for gonadotropins and alpha-subunit, in tumors characterizedas null cell adenomas and oncocytomas, imrnunocytochemistry may provide valuable information to the pathologist and clinical endocrinologist contributing to the evaluation of this heterogeneous group of tumors.

An aetiological profile of optic atrophy

484 cases of optic atrophy were studied for the distribution pattern and significance of various etiological factors in different age groups of both sexes. Bilateral optic atrophy was found to be two and a half times as common as unilateral optic atrophy. Intracranial neoplasm (29.5%) was the most frequent known cause of bilateral optic atrophy in either sex and the most common tumor was chromophobe adenoma (48% of intracranial tumors) with highest incidence over 20 years of age. Craniopharyngioma was the most frequent tumor responsible for bilateral optic atrophy before 20 years of age. Intracranial glioma also emerged as an important cause of bilateral optic atrophy. Head injury due to road accidents and periocular trauma were the most common causes of unilateral optic atrophy in males, whereas no definite factor could be elucidated in unilateral optic atrophy in females. Vascular factors were the usual cause of optic atrophy after 40 years of age, highlighting the significance of thorough systemic evaluation.

The alpha-subunit of glycoprotein hormones exists in the prolactin secretory granules of the bullfrog (Rana catesbeiana) pituitary gland

Our recent finding that the number of immunoreactive alpha-subunit cells was invariably greater than the total number of immunoreactive gonadotropin (GTH) and thyrotropin (TSH) cells in the bullfrog (Rana catesbeiana) pituitary gland raises the possibility that the alpha-subunit also exists in pituitary cells other than GTH and TSH cells. The present study demonstrates that there are a considerable number of immunoreactive prolactin (PRL) cells that are also stained with antibody against the alpha-subunit when adjacent sections are immunocytochemically examined. Neither immunoreactive growth hormone nor adrenocorticotropin cells are stained with the antibody against the alpha-subunit. The specificity of the antibody against the alpha-subunit and of that against PRL was demonstrated by preabsorption test, non-competitive binding test, and immunoblot analysis. Double-immunolabeling with gold particles of different sizes for the alpha-subunit and PRL revealed that most of the immunolabeled PRL-secretory granules are also labeled with the alpha-subunit antibody. The gold particles indicating the presence of the alpha-subunit were mostly found in the peripheral zone of the secretory granules.

Differential appearance of the subunits of glycoprotein hormones (LH, FSH, and TSH) in the pituitary of bullfrog (Rana catesbeiana) larvae during metamorphosis

The ontogeny of gonadotrophs and thyrotrophs in the bullfrog pituitary was examined immunohistochemically using monoclonal antibodies against bullfrog lutropin beta-subunit (LH beta), follitropin beta-subunit (FSH beta) and its alpha-subunit, and polyclonal anti-human thyrotropin beta-subunit (TSH beta) serum. Immunoreactive alpha-subunit- and TSH beta-, but not FSH beta- and LH beta-containing cells were observed at embryonic stage 24 (Shumway's classification). Immunoreactive FSH beta cells first appeared at Taylor-Korllos stage V, and immunoreactive LH beta cells at stage X. Throughout metamorphosis, several gonadotrophs containing both FSH and LH were found in the ventrocaudal region, but most gonadotrophs contained only FSH. Immunoreactive alpha-subunit cells were always more frequent than the sum of immunoreactive beta-subunit cells, which was confirmed by quantitative studies using immunohistochemical and RIA techniques.

HGH, PRL and beta HCG/beta LH gene expression in clinically inactive pituitary adenomas detected by in situ hybridization

Within our surgical collection clinically inactive pituitary adenomas represent 30.7% of all pituitary tumours. To characterize their endocrine activity we studied 40 clinically inactive pituitary adenomas with in situ hybridization (ISH) using cRNA probes labelled with 35S encoding growth hormone (GH), prolactin (PRL) and chorionic gonadotrophin (beta HCG). No tumour was associated with clinical evidence of elevated hormone secretion. A mild hyperprolactinaemia not correlated with hormone or the mRNA content of the cells was interpreted to be incidental in 11 patients. By histological analysis, immunohistochemistry (IH) and electron microscopy the adenomas were diagnosed as small cell chromophobic (n = 16) and large cell chromophobic (n = 8) adenomas, and oncocytomas (n = 16). Gene expression of one or more hormones was identified by ISH in 18 of 40 adenomas in few cells. GH and PRL gene expression was rare (GH mRNA in 3 of 40 tumours and PRL mRNA in 8 of 40 tumours) whereas in 14 of 40 adenomas beta HCG/beta LH gene expression was identified in scattered cells. Five of 40 adenomas lacking hybridization signals revealed hormones by IH. The detection of mRNA was accompanied by positive immunostaining for the respective hormones in 72%. The combination of ISH and IH reveals good evidence that the hormones are synthesized in the tumours and not taken up from the serum and stored in the cells. The two methods used together permit a more precise analysis of tumour biology than each alone.

Clinically nonfunctioning pituitary tumors are monoclonal in origin

Clinically nonfunctioning pituitary adenomas are benign neoplasms comprising approximately 25-30% of pituitary tumors. Little is known about the pathogenesis of pituitary neoplasia. Clonal analysis allows one to make the important distinction between a polyclonal proliferation in response to a stimulatory factor versus a monoclonal expansion of a genetically aberrant cell. We investigated the clonal origin of pituitary tumors using X-linked restriction fragment length polymorphisms at the phosphoglycerate kinase and hypoxanthine phosphoribosyl-transferase genes. Restriction enzymes were used to distinguish maternal and paternal X-chromosomes, and combined with a methylation-sensitive restriction enzyme to analyze allelic X-inactivation patterns in six pituitary adenomas. All six tumors showed a monoclonal pattern of X-inactivation. These data indicate that nonfunctioning pituitary adenomas are unicellular in origin, a result consistent with the hypothesis that this tumor type is due to somatic mutation.

Pro-opiomelanocortin gene expression in silent corticotroph-cell adenoma and Cushing's disease

The silent corticotroph-cell adenoma (SCCA) is characterized by the presence of immunoreactive adrenocorticotropic hormone (ACTH) in the tumor tissue in patients without symptoms of Cushing's disease. To elucidate the pathophysiology of SCCA, the expression of pro-opiomelanocortin (a ACTH precursor) genes was studied in a patient with SCCA and in three patients with Cushing's disease. Pro-opiomelanocortin messenger ribonucleic acid (mRNA) was found in the SCCA tissue to a greater degree than in the adenomas of the patients with Cushing's disease. Northern blot analysis revealed that the size of pro-opiomelanocortin mRNA present in the SCCA tissue was indistinguishable from that in the adenomas associated with Cushing's disease. A ribonuclease mapping study indicated that there were no point mutations in the coding sequence of pro-opiomelanocortin mRNA present in the SCCA tissue. Because of the presence of pro-opiomelanocortin mRNA and immunoreactive ACTH in the adenoma tissue, it is proposed that translation of the mRNA and subsequent accumulation of ACTH precursor occurred in the SCCA. Thus, the absence of Cushing's disease symptoms in this SCCA could not be caused by abnormality in the coding sequence of the pro-opiomelanocortin gene or in ribonucleic acid processing. The occurrence of abnormality at or after the translational steps was strongly suggested.

Confounding factors in the interpretation of gonadotropin and gonadotropin-subunit release from cultured human pituitary adenomas

Culture data of 31 human pituitary non-functioning adenomas and effects of cross-reactivity and in vitro culturing conditions on immunoreactivity of gonadotropins and subunits were investigated. Using immunoradiometric assays for FSH and LH and radioimmunoassays for alpha-subunit and LH beta-subunit crossreactivities were reduced to a minimum. Repeated freezing and thawing had no effect on immunoreactivity of hormones and subunits tested. Incubation at 37 degrees C did not affect the immunoreactivity of purified subunit preparations and no recombination of alpha-subunit and LH beta into intact LH could be demonstrated after coincubation of the subunits. FSH immunoreactivity in culture media from 3 pituitary tumors was not affected by incubation at 37 degrees C. LH from a purified preparation and LH in culture media from 3 pituitary adenomas showed a rapid decrease of LH immunoreactivity when left at 37 degrees C. Concomitant with decreasing LH levels at 37 degrees C, a rise in the concentration of alpha-subunit occurred. A direct correlation between gain in alpha-subunit and loss of LH was found. LH beta levels remained stable while LH decreased. This observation may be attributed to an increase in LH beta levels which is compensated by the loss of LH, which has a relatively high crossreactivity in the LH beta immunoassay. LH, FSH, alpha-subunit, LH beta or a combination of these glycoproteins could be demonstrated in 26 out of 31 cultured tumours from patients operated upon because of a clinically non-functioning adenoma. In none of the media of 15 adenomas in which both alpha-subunit and LH were detected, could alpha-subunit levels have been caused by dissociation of LH at 37 degrees C. In two cases, measured LH levels could have been caused by crossreactivity of alpha-subunit and FSH. It was concluded that: (1) in research of non-functioning pituitary adenomas data on gonadotropin and gonadotropin-subunit secretion may suffer from bias caused by crossreactivity; (2) that dissociation of LH into subunits at 37 degrees C is relatively unimportant in in vitro research of non-functioning adenomas; (3) that virtually all non-functioning pituitary adenomas contain or release gonadotropins and/or subunits.

Detection of mRNA of prolactin and ACTH in clinically nonfunctioning pituitary adenomas

Clinically nonfunctioning pituitary adenomas have been thought to synthesize some pituitary hormones as shown by studies involving cell culture, immunocytochemistry, or measurement of hormone levels in tumor homogenates. Nevertheless, they are not associated with hypersecretion of pituitary hormones. To further clarify hormone synthesis in such pituitary adenomas, the presence of messenger ribonucleic acid (mRNA) of prolactin (PRL) growth hormone, and adrenocorticotropic hormone (ACTH) in the cytoplasm of 16 nonfunctioning adenomas was determined by means of a hybridization technique, and compared to the immunocytochemical findings. In three adenomas (19%) PRL mRNA was detected and in one case (6%) ACTH mRNA was detected. The hybridization technique appears to be more sensitive than immunohistochemistry for detection of specific mRNA's in assigning the hormone synthesis potential to clinically nonfunctioning tumors. The results suggest that PRL and ACTH are synthesized in some cases of clinically nonfunctioning pituitary adenomas and that hybridization techniques are useful to investigate hormone synthesis in pituitary adenomas. The ability to demonstrate PRL mRNA in tumor tissues allowed differentiation between hyperprolactinemia caused by synthesis of PRL in the tumor and that due to hypersecretion from the adjacent normal pituitary.

Simultaneous production of the alpha-subunit of glycoprotein hormones and other hormones in pituitary adenomas

The immunohistological classification of 97 pituitary adenomas revealed in 34 cases alpha-subunit (a-su) positive cells in the tumor tissue. In 15 cases a-su was the only hormone found, in 11 cases the beta-subunits of the glycoprotein hormones could also be detected (10 cases with LH/FSH and 1 case with TSH). In 8 cases a-su was found simultaneously together with other hormones of the pituitary (ACTH and a-su in 1 case, GH and a-su in 4 cases, prolactin and a-su in 2 cases, prolactin, GH and a-su in 1 case). A-su could be demonstrated to be partly simultaneously produced together with these hormones in identical cells and secretory granules. Next to prolactin, the a-su was the second most frequently occurring hormone that could be detected immunohistologically in our material.

Production of the alpha-subunit of glycoprotein hormones by pituitary adenomas

Positive immunoreactions with alpha-subunit antibodies were present in 43% of biopsy samples obtained from 147 subsequently operated pituitary adenomas representing all major endocrine types (57 endocrine inactive adenomas, 43 prolactinomas, 30 adenomas causing acromegaly, and 17 adenomas causing Cushing's disease or Nelson's syndrome). Marked variations of the incidence, however, were found among the individual endocrine groups. Positive reactions were present in 63% of endocrine inactive adenomas, 57% of adenomas causing acromegaly, 35% of ACTH-secreting adenomas, and 9% of prolactinomas. A positive alpha-subunit reaction was accompanied in a minority of cases only with positive glycoprotein hormone-beta-subunit reactions. There were 21 pure alpha-subunit adenomas in the group of endocrine inactive adenomas.

Hormone production in clinically nonfunctioning pituitary adenomas

Pituitary tumors in which no excess hormone secretion can be identified clinically have been considered as nonfunctioning or null-cell adenomas. Immunocytochemical data presented here suggest that many of these tumors contain subunits of the glycoprotein hormones. Of 160 patients referred for pituitary surgery, 37 (23%) had no evidence of excess hormone secretion on preoperative endocrine evaluation. Immunocytochemical staining of these tumors was carried out using antibodies specific for prolactin, growth hormone, adrenocorticotropic hormone, the beta subunits of luteinizing hormone (beta-LH), follicle-stimulating hormone (beta-FSH), and thyroid-stimulating hormone (beta-TSH), and the alpha subunit. One or more of these pituitary hormones were detected in 73% of cases. The alpha and beta subunits were detected most frequently, being found in 68% of cases; 27% had staining for one or more beta subunits and 37.9% had staining for both alpha and beta subunits. The incidence was: beta-FSH in 58%, beta-LH in 47%, beta-TSH in 33%, and the alpha subunit in 42%. Staining for multiple glycoprotein hormones was common (52%), and mixed glycoprotein hormones and prolactin cell types were found in 16% of cases. These data suggest that most apparently nonfunctioning pituitary tumors contain immunoreactive hormones and the majority of these are subunits of the glycoprotein hormones. Since the glycoprotein hormone beta subunits must combine with the alpha subunit to produce biologically active hormones, the production of the subunits alone may not have endocrine manifestations.

Immunohistochemical colocalization of growth hormone (GH) and alpha subunit in human GH secreting pituitary adenomas

This immunohistochemical study disclosed that 9 of 15 GH secreting pituitary adenomas contained alpha subunit positive cells. These cases also contained PRL positive adenoma cells, but LH beta was negative. Of these 9 cases, 4 cases showed occasional FSH beta containing cells, 2 of these also contained a few TSH beta positive cells. By mirror section technique, variable numbers of adenoma cells were found to contain both GH and alpha subunit. Immunoelectron microscopically, both GH and alpha subunit were localized in secretory granules which suggested their co-release from the tumour cells. The presence of GH and alpha subunit in rough endoplasmic reticulum indicated their active production in the tumour. In the normal adult anterior pituitary gland, about 10% of GH cells contain FSH alpha, beta and LH beta subunits and had appearances suggesting the co-production of GH and FSH as well as LH. The colocalization of GH and FSH alpha is considered to be associated with the neoplastic transformation GH cells which possess the intrinsic potentiality of differentiation toward alpha subunit. However, the mechanism for the lack or deficiency of beta subunits in the neoplastic condition remains to be further investigated.

Alpha-subunit-producing pituitary adenomas. Immunocytochemical and ultrastructural studies

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.