Biological Aspects of Pituitary Tumors Induced by Synthetic Salmon Calcitonin (TZ–CT) in Sprague-Dawley Rats

Rat pituitary tumors induced by synthetic salmon calcitonin (TZ–CT) were studied by the indirect peroxidase-labeled antibody method, together with ultrastructure and serum hormone measurement. Immunohistochemically, TZ–CT-induced pituitary tumors showed staining for only rLHα subunit, and were negative for other peptide hormones including GH, PRL, αMSH and ACTH, and the α subunit of glycoprotein hormones. Electron microscopic examination showed that the majority of tumor cells possessed numerous small secretory granules, 100 to 200 nm in diameter. The serum PRL concentrations of rats with TZ–CT induced pituitary tumors were markedly elevated, but not beyond 130 ng/ml. From our data, TZ–CT-induced pituitary tumors are considered to be endocrinologically inactive and to produce α subunit. Furthermore, these tumors are thought to be potentially useful models of α subunit producing pituitary tumors in humans. This is the first report to document the tumorigenesis of α subunit producing pituitary tumors in rats after long-term treatment with calcitonin.     

Glycoprotein hormone alpha-subunit-producing pituitary adenomas in rats treated for one year with calcitonin.

Calcitonin, a calcium-lowering hormone, has been associated with an increased incidence of nonfunctioning pituitary tumors in rats. In this study, rats were treated with calcitonin (80 IU/kg/d) for 52 weeks. After treatment with calcitonin, immunohistochemistry and in situ hybridization analyses demonstrated that most pituitary tumors expressed the glycoprotein hormone alpha-subunit. Expression of the alpha-subunit was identified rarely in hyperplastic lesions of control animals. Serum levels of GH, PRL, ACTH, LH, and FSH were unchanged in calcitonin-treated rats relative to controls. However, TSH levels were increased 2.1 fold after chronic treatment with calcitonin in both male and female rats (P less than 0.001). The level of glycoprotein hormone alpha-subunit was markedly increased (20-fold) in male rats with smaller elevations in female rats. Time course studies demonstrated that increases in serum alpha-subunit levels could be detected by 24 weeks of treatment and that elevations in alpha-subunit were present in the majority of animals by 40 weeks of treatment with calcitonin. The authors conclude that high doses of calcitonin, administered to rats for 6 months or longer, increases the incidence of alpha-subunit-producing pituitary tumors.     

Studies on prolactin-secreting cells in aging rats of different strains. I. Alterations in pituitary histology and serum prolactin levels as related to aging

Serum PRL levels and histologically tumor-free pituitary glands of 91 aging rats of the BN/BiRij strain, the WAG/Rij strain and their F1 hybrid were studied. In rats with pituitary glands without signs of hyperplasia, serum PRL levels were, in comparison to rats of 15-24 months, increased 25-29-month-old female BN/BiRij rats and showed a decline with further aging. This rise and decline during aging correlated with changes in the PRL cell volume density and in ultrastructural signs of their synthetic activity. Rats with hyperplastic pituitaries showed similar age-related changes in serum PRL levels, but these levels were higher. Concerning the hyperplasia, some strain differences were found. In BN/BiRij rats anti-r-PRL positive hyperplasia, and in WAG/Rij and F1 rats, anti-r-PRL negative and anti-r-PRL positive hyperplasia were present. All foci of hyperplasia were negative for anti-ACTH and anti-h-GH. In male rats no age-related changes of serum PRL levels could be established, although a decline of PRL cell volume density in the oldest rats is indicated. We conclude that the absence of a continuous age-related rise of serum PRL levels in our animals is caused by exclusion of animals with pituitary tumors.     

Heterogeneity of the MtTW15 mammosomatotropic tumor. I. Light microscopic evaluation of cell types by means of immunocytochemistry, morphometric quantitation, fluorescence cytophotometry and radioimmunoassay.

Large MtTW15 pituitary tumors produced 200- to 800-fold elevations in serum growth hormone (GH) and prolactin (PRL) levels. Female tumor hosts showed doubling in body weight, milk secretion, and a 2-fold hepatosplenomegaly. Pituitaries of host animals were reduced by about 50% in both weight and concentrations of GH and PRL. Large tumors were well-encapsulated, multinodular and showed variable amounts of necrosis and hemorrhage. Cytofluorometric analysis revealed a range of 100-fold in nuclear DNA content of tumor parenchymal cells which were chromophobic, pleomorphic and frequently mitotic. Concentrations of hormones in tumors were less than in normal pituitaries and highly variable with the ratio of GH/PRL ranging up to 30-fold within the same tumor. Immunostaining and linear scanning quantitation showed that about 50% of the tumor cells contained immunodetectable hormones. Comparison of immunostained adjacent sections showed that hormone-containing tumor cells were pleomorphic, unequally distributed within nodules, lacking in distinctive identifying morphological characteristics and that they contained GH or PRL but not both hormones simultaneously. Collectively our results show that large MtTW15 tumors are comprised of a markedly heterogeneous population of tumor cells and they suggest that the hormone-containing cells are monohormonal secreting tumor cells which can produce GH or PRL but not both hormones.     

Pure alpha-secreting pituitary adenomas

Isolated hypersecretion of the alpha subunit of the glycoprotein hormones occurred in two men with previously diagnosed "nonfunctioning chromophobe adenomas." The alpha hypersecretion was unresponsive to hypothalamic releasing hormone, thyroid hormone, and sex-steroid hormones. After trans-sphenoidal surgery and conventional pituitary irradiation, alpha secretion was decreased. Increased quantities of immunologically active and biologically inactive luteinizing hormone (LH) material were detected in serum and in tumor homogenate. Immunologic and gel-chromatographic studies determined that only the alpha subunit was present and that it was cross-reacting in the LH immunoassay. These studies suggest that the alpha subunit may be a useful marker of pituitary tumors, particularly in patients without clinical evidence of hormonal hypersecretion.     

Heterogeneity of the MtTW15 mammosomatotropic tumor. I. Light microscopic evaluation of cell types by means of immunocytochemistry,morphometric quantitation,fluorescence cytophotometry and radioimmunoassay

Large MtTW₁₅ pituitary tumors produced 200- to 800-fold elevations in serum growth hormone (GH) and prolactin (PRL) levels. Female tumor hosts showed doubling in body weight, milk secretion, and a 2-fold hepatosplenomegaly. Pituitaries of host animals were reduced by about 50% in both weight and concentrations of GH and PRL. Large tumors were well-encapsulated, multinodular and showed variable amounts of necrosis and hemorrhage. Cytofluorometric analysis revealed a range of 100-fold in nuclear DNA content of tumor parenchymal cells which were chromophobic, pleomorphic and frequently mitotic. Concentrations of hormones in tumors were less than in normal pituitaries and highly variable with the ratio of GH/PRL ranging up to 30-fold within the same tumor. Immunostaining and linear scanning quantitation showed that about 50% of the tumor cells contained immunodetectable hormones. Comparison of immunostained adjacent sections showed that hormone-containing tumor cells were pleomorphic, unequally distributed within nodules, lacking in distinctive identifying morphological characteristics and that they contained GH or PRL but not both hormones simultaneously. Collectively our results show that large MtTW₁₅ tumors are comprised of a markedly heterogeneous population of tumor cells and they suggest that the hormone-containing cells are monohormonal secreting tumor cells which can produce GH or PRL but not both hormones.     

Morphologic effects of bromocriptine on spontaneously occurring pituitary prolactin-cell hyperplasia in old Long-Evans rats.

The effect of bromocriptine (BEC), a dopaminergic agonist, on nontumorous pituitary prolactin (PRL) cells of aging female Long-Evans rats, was studied histologically, immunocytologically, electron-microscopically, and morphometrically. Rats were arbitrarily divided into two control groups, one with normal (less than 20 ng/ml) and one with elevated serum PRL concentrations, and into four BEC-treated groups, all of which had increased serum PRL levels prior to commencement of BEC administration. In hyperprolactinemic control rats, compared with normoprolactinemic control rats, pituitary weight and percentage of pituitary PRL cells were increased. The morphologic features of PRL cells in these two groups did not differ markedly, which suggested that hyperprolactinemia was due to increased PRL-cell number and not increased PRL-cell function. Compared with age-matched hyperprolactinemic control rats, hyperprolactinemic rats treated with BEC showed a reversible decrease in serum PRL levels, pituitary weight as well as percentage of pituitary PRL cells, and by ultrastructural morphometry an increase in the volume density of lysosomes. BEC caused no striking changes in nuclear and cytoplasmic areas, volume densities of RER, Golgi regions, mitochondria, lipid droplets, and size and volume densities of forming and storage granules. Since spontaneously hyperplastic PRL cells show less conspicuous morphologic changes following BEC treatment than PRL cells rendered hyperplastic by estrogen administration or pituitary transplantation, it is suggested that PRL cells with no increased endocrine function respond less markedly to dopaminergic suppression than endocrinologically hyperactive PRL cells. It can be concluded that BEC suppresses spontaneous proliferation of PRL cells which occurs with aging.     

Estrogen-induced hyperplasia and neoplasia in the rat anterior pituitary gland. An immunohistochemical study

Diethylstilbestrol (DES) treatment of weanling F344 female rats resulted in enlarged pituitary glands and diffuse pituitary prolactin (PRL) cell hyperplasia in all animals after 9 and 12 weeks of treatment. Serum PRL was significantly greater than in control rats (P less than 0.001). Immunohistochemical studies showed that most of the pituitary gland cells consisted of PRL cells. Ultrastructural studies showed increased numbers of PRL cells with hyperplasia of the rough endoplasmic reticulum and decreased numbers of secretory granules. There was a decrease in the relative number of growth hormone (GH) and other cell types in the anterior pituitary. Pituitary tumors and normal pituitary glands were dissociated with trypsin and maintained in culture for 3 weeks. The numbers of PRL and GH cells decreased with time in both groups, and there was an increase in the number of fibroblasts. Staining of the culture cells with neuron-specific enolase showed that the anterior pituitary cells were positive for this enzyme, while the fibroblastic cells were negative. When dissociated pituitary cells were cultured in the presence of 10(-9) M DES for 7 days, there was a 42% increase in the number of immunoreactive PRL cells. These results indicate that DES-treated rats provide an excellent model for study of the in vivo and in vitro regulation of pituitary hyperplasia and neoplasia.     

Free alpha subunit of the pituitary glycoprotein hormones. Measurement in serum and tissue of patients with pituitary tumors.

A solid-phase radioimmunoassay was developed that measures the free alpha subunits of pituitary glycoprotein hormones (alpha PGpHs) and has negligible cross-reactivity with the intact hormones (less than 0.014% for thyroid-stimulating hormone [TSH], less than 0.1% for human chorionic gonadotropin [hCG], 0.8% for luteinizing hormone [LH], and 2.0% for follicle-stimulating hormone [FSH]). The assay is standardized with the alpha subunit of hCG but also reacts well with the alpha subunits of the other glycoprotein hormones (84% for alpha TSH, 77% for alpha FSH, and 64% for alpha LH). Concentrations as low as 0.3 micrograms/L can be reliably measured, and the 97.5% reference range in 27 healthy adults, including postmenopausal females, is less than or equal to 1.2 micrograms/L. Elevated preoperative alpha PGpH concentrations were found in 45 (9.4%) of 479 sera from patients with pituitary adenoma and 3 (4.5%) of 66 patients with nonadenomatous sellar lesions. Postoperative alpha PGpH levels were lower in 30 of 39 adenoma patients and 2 of 3 nonadenoma patients. In five (1%) of the patients with pituitary adenomas, alpha PGpH was the only elevated serum hormone marker. Serum values of alpha PGpH correlate weakly with alpha subunit immunocytochemical staining--95% of those with negative staining have normal alpha PGpH values, but only 18% of those with positive staining have elevated alpha PGpH values.     

Endocrinologic milieu and susceptibility of the rat mammary gland to carcinogenesis.

The incidence of DMBA-induced mammary carcinomas in Sprague-Dawley rats depends upon their previous reproductive histories. Young virgin rats (YV) are highly susceptible to the carcinogen, while old virgin rats (OV) are less susceptible, and parous rats (P) are resistant. The authors performed endocrinologic studies in these three groups of rats in order to determine whether the different susceptibility to carcinogenesis, according to the reproductive history, is or is not related to the hormonal milieu. The pituitary, the ovaries, the adrenals, and the mammary glands were processed for light microscopy. Pituitary prolactin (PRL), follicle-stimulating hormone, and luteinizing hormone cells were immunostained by peroxidase-antiperoxidase and quantitated with an image analyzer. Radioimmunoassays of serum and pituitary PRL and serum estradiol were also done. The results showed no differences in the hormonal milieu of YV, OV, and P rats at the time of carcinogen treatment. Several changes were observed after DMBA administration, the most conspicuous being 1) hyperplasia of pituitary PRL cells, 2) high serum PRL levels, 3) nodular hyperplasia of the adrenal cortex, 4) high serum estradiol levels, and 5) lack of adrenal necrosis in P rats and some OV rats. These modifications did not correlate with the degree of susceptibility of YV, OV, and P rats to carcinogenesis, supporting the concept of the importance of the mammary gland differentiation at the moment of carcinogen administration. (Am J Pathol 1982, 109:47-56).     

Immunohistochemical detection of somatostatin receptor subtypes in “clinically nonfunctioning” pituitary adenomas

Pituitary tumors diagnosed before surgery as “non-functioning” in fact represent a heterogenous group, the majority of which express glycoprotein hormones or their free subunits. It is known that some of them expresses somatostatin receptors, but the data available until now rarely refer to the receptor subtype. Five different subtypes of somatostatin receptors (sst1-5) have been cloned. We studied 18 pituitary tumors diagnosed before surgery as “non-functioning”. After the surgery the tumors were immunostained with antibodies against pituitary hormones and alpha subunit as well as with antibodies against the somatostatin receptor proteins 1–5. Thirteen adenomas expressed immunoreactivity for FSH, LH, and/or alpha subunit and were classified as gonadotroph adenomas. The remaining five adenomas were immunonegative for all the examined pituitary hormones and were diagnosed as null cell adenomas. All the adenomas of both the groups showed immunopositivity for at least three receptor subtypes. The strongest immunopositivity was found in both groups with anti-sst1 and anti-sst5 antibodies. The marked immunopositivity was also revealed in both groups with anti-sst2B antibody. On the other hand, the sst2A immunopositivity was weak or absent in a majority of tumors. The main difference between two groups was in the sst4 receptor subtype which was absent in all but two gonadotroph adenomas but present in all but one null cell adenoma. These findings suggest that “non-functioning” pituitary adenomas are potential candidates for therapy with somatostatin analogs targeted mainly to the receptor subtypes 1 and 5.     

Alpha-subunit immunoreactivity in plurihormonal pituitary adenomas of patients with acromegaly.

Twelve plurihormonal pituitary adenomas, removed surgically from 11 of 20 patients with acromegaly, were investigated. The mean age of the 11 patients was 45 yr. Seven patients with eight tumors were men. The tumors were immunostained for all known adenohypophysial hormones by the avidin-biotin-peroxidase complex (ABC) technique. All 12 adenomas were immunoreactive for growth hormone (GH) and alpha-subunit; prolactin (PRL) was detected in five tumors. Stains for the beta-subunits of glycoprotein hormones [thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH)] revealed immunopositivity for specific beta-subunits in ten adenomas. The close association between GH and alpha-subunit in pituitary tumors of acromegalic patients remains to be explained.     

The effects of ad libitum overfeeding and moderate and marked dietary restriction on age-related spontaneous pituitary gland pathology in Sprague-Dawley rats

This study compared the effects of ad libitum (AL) overfeeding and moderate or marked dietary restriction (DR) on the pathogenesis of aged-related pituitary gland changes in Sprague-Dawley (SD) rats. SD rats were fed Purina Certified Rodent Diet AL (group 1), DR at 72-79% of AL (group 2), DR at 68-72% of AL (group 3) or DR at 47-48% of AL (group 4) for 106 weeks. Interim necropsies were performed at 13, 26, and 53 weeks, after a 7-day 5-bromo-2-deoxyuridine (BrdU)-filled minipump implantation. Body weights, organ weights and insulin-like growth factor 1 (IGF-1) serum levels were measured at interim and final necropsies. Serum levels of prolactin (PRL), progesterone, estradiol, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured at 53 and/or 106 weeks. In addition to the routine histopathologic examination, determination of 7 stereologic parameters after pituitary immunohistochemistry of PRL, growth hormone (GH) and BrdU was done in both sexes at 13, 26, and 53 weeks. Body and pituitary weights were proportional to the food intake. In AL-fed rats, hyperplastic and neoplastic changes developed early and progressed with age, affecting almost all animals by 106 weeks. These changes were associated with high PRL serum levels. Pituitary adenomas were the most common cause of death in both sexes. In DR rats, a delayed onset and a decreased incidence of pituitary tumors were observed in association with decreased serum IGF-1, PRL, estradiol, and LH levels. The results of the stereological analysis demonstrated that, compared to AL-fed rats, pituitary glands from DR rats contained lower PRL and GH secreting cell volumes, and a lower epithelial cell BrdU labeling index, which correlated with a lower incidence of pituitary tumors at study termination. Moderate and marked degrees of DR delayed the onset of pituitary tumors in a temporal- and dose-related manner. In contrast to marked DR, which dramatically reduced the incidence of hyperplastic and neoplastic pituitary gland changes, moderate DR delayed the onset but did not prevent the development of pituitary tumors.     

Ageing and melatonin influence on in vitro gonadotropins and prolactin secretion from pituitary and median eminence

The effect of ageing and/or melatonin (MEL) on in vitro gonadotropins, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) release and tissue content from pituitary and median eminence (ME) were investigated. Gonadotropins and PRL basal release (I-1) from hemipituitaries of young cyclic-rats was decreased by MEL to levels shown in old acyclic rats. Pituitary tissue content of LH and PRL were not affected by ageing or MEL treatment. However, pituitary FSH tissue content was decreased by ageing and MEL, suggesting a different regulatory mechanism. MEL inhibitory influence on pituitary hormones is mainly exerted on the secretory process. This effect is only exerted in young rats. ME LH and PRL release and content were significantly lower than in pituitary. However, FSH release and content in ME showed values similar to those found in the pituitary. This study confirms that the functional capacities of pituitary gland and ME are maintained during reproductive senescence.     

Regulation of prolactin gene expression in a DMBA-estrogen-induced transplantable rat pituitary tumor.

A new transplantable rat pituitary tumor was induced in F344 female rats with dimethylbenz(a)anthracene and estrogen (MtT/F-DMBA) and studied for 20 serial transplant generations. The tumor grew without estrogen supplements in female rats by the second transplant generation. Sensitivity to estrogens, as indicated by a prolonged latency period for tumor development, was seen at the 20th, but not the 5th transplant generation. MtT/F-DMBA tumors expressed prolactin (PRL), growth hormone (GH), and adrenocorticotropin (ACTH) mRNAs. A decrease in the percentage of cells expressing PRL mRNA, PRL protein, and in the number of secretory granules per cell occurred with serial transplantation. S-100 protein-positive folliculostellate cells were present in the hyperplastic pituitary but not in the transplantable tumors. Estrogen treatment at the 20th transplant generation prolonged the tumor latency period, increased the number of cells expressing PRL mRNA greater than 5-fold by in situ hybridization analysis (14 +/- 2% versus 77 +/- 5%), increased PRL secretion (132 +/- 40 ng/ml versus 3762 +/- 890 ng/ml), and increased the number of cytoplasmic secretory granules per cell. These results indicate that hyperplastic pituitary and true pituitary neoplasms differ in their ability to grow readily after transplantation. The presence of S-100 protein-positive folliculostellate cells, which are present in hyperplastic but not in neoplastic pituitary tissues, may serve as a morphologic marker to separate hyperplastic and neoplastic rat pituitary tissues. Transplantable tumors remained responsive to estrogen with expression of a more differentiated phenotype, including an increased number of cells expressing PRL mRNA and increased numbers of PRL secretory granules.     

Analysis of S-100 protein positive folliculo-stellate cells in rat pituitary tissues.

The effects of diethylstilbestrol (DES) treatment and withdrawal on the folliculo-stellate (FS) cells in hyperplastic pituitaries were examined in Fischer 344 (F344) and Wistar Furth (W/F) rats by immunochemistry and electron microscopy. The presence of S-100 protein positive cells was examined by immunostaining in spontaneous and in transplantable rat pituitary tumors. The pituitaries of F344 rats showed a fivefold greater increase in weight in response to 5 weeks of DES treatment compared to pituitaries from W/F rats. S-100 protein (S-100) positive cells were significantly increased in both strains with hyperplastic pituitaries (P less than 0.05) 2 days after DES withdrawal. Ultrastructural studies revealed increased phagocytic activity in FS cells. S-100 positive cells were absent in both MtT/W15 and MtT/F4 transplantable tumors even after treatment with DES. Some spontaneous pituitary tumors in aged female rats had S-100 positive cells within the tumors at the periphery of the tumor nodules (3 of 12 cases), while most of these neoplasms did not contain S-100 positive cells. Incubation of normal dissociated pituitary cells with S-100 protein increased PRL secretion in vitro. The effectiveness of S-100 protein in increasing PRL secretion in vitro was less than thyrotropin releasing hormone (TRH). These results indicate that S-100 positive cells are present in normal and hyperplastic pituitaries, but not in spontaneous or in transplantable rat pituitary tumors and also suggest that the FS cells may exert a paracrine type regulation on PRL secretion.     

An immunocytochemical study of pituitary adenomas and focal hyperplasia in old Sprague-Dawley and Fischer 344 rats

Spontaneous pituitary tumors occurring in groups of 100 Sprague-Dawley (SD) and 100 Fischer 344 (F344) rats of each sex on a 2-year aging study were characterized by immunocytochemistry. The SD strain had a total of 75 tumors with 10% in males and 65% in females. Tumors immunoreactive for prolactin (PRL) alone were the most common tumor (64%) with the immunonegative tumor being the second most common (17.3%). F344 rats had a total of 62 tumors with 26% in males and 36% in females. The majority of the tumors were reactive for prolactin alone (56.5%) and tumors reactive for both growth hormone (GH) and PRL were the second most common (21%). Most tumors were immunoreactive for only 1 hormone; however, both strains had tumors that expressed multiple hormones in unusual combinations.     

Changes in serum concentrations and pituitary content of the two prolactins and growth hormone during the reproductive cycle in female tilapia, Oreochromis mossambicus, compared with changes during fasting

Patterns of change in serum concentrations and pituitary content of GH and two tilapia prolactins (PRL177 and PRL188) were examined during the reproductive cycle of female tilapia, Oreochromis mossambicus, adapted to fresh water and to seawater. Changes in these hormones during fasting were examined to elucidate whether changes observed during brooding could be attributed to a reduction in feeding during brooding. Serum concentrations of GH increased prior to pituitary content during the brooding phase of the reproductive cycle. In contrast, pituitary content of GH increased prior to serum concentrations during fasting. There was no consistent pattern of change in serum or pituitary PRL levels during the reproductive cycle, among experiments. Serum concentrations of PRL177 were elevated in all fasted fish, whereas PRL188 was elevated during fasting in males but not females. The increases in the serum concentration of PRLs and GH, and in the pituitary content of GH in response to fasting support the notion that these hormones are involved in the regulation of the use of metabolic substrates in tilapia. We conclude that reduced food intake during brooding may contribute to changes in serum and pituitary levels of the PRLs and GH observed during the reproductive cycle. Nevertheless, differences between changes in serum and pituitary GH during brooding and fasting suggest GH has actions in reproduction, and changes in GH during brooding are not only in response to fasting.     

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.