Neoplastic Pituitary Tissues Research Articles

Apoptosis: its role in pituitary development and neoplastic pituitary tissue

Apoptosis, also known as programmed cell death, is a phenomenon in which different stimuli trigger cellular mechanisms that culminate in death, in the absence of inflammatory cell response. Two different activation pathways are known, the intrinsic pathway (or mitochondrial) and extrinsic (or death-receptor pathway), both pathways trigger enzymatic reactions that lead cells to break up and be phagocytized by neighboring cells. This process is a common occurrence in physiological and pathological states, participating in the control of cell proliferation, differentiation and remodeling of organs. In the early steps of pituitary gland formation, numerous apoptotic cells are detected in the separation of Rathke's pouch from the roof of oral ectoderm. In the distal part of the gland, which will form the adenohypophysis, the ratio of apoptosis was significantly lower. However, there is evidence that neoplastic pituitary cells undergo unbalance in genes that control apoptosis leading to uncontrolled cell growth. No direct evidence of apoptosis was found in the drugs used for tumors producing prolactin and growth hormone. In conclusion, an unbalancing in the apoptosis process is the boundary between development and tumor growth.

Analysis of IMP3 Expression in Normal and Neoplastic Human Pituitary Tissues

Insulin-like growth factor II mRNA-binding protein 3 (IMP3) is an oncofetal protein highly expressed in fetal tissue and malignant tumors but rarely found in adult benign tissues. In various tumors, IMP3 expression is correlated with increased tumor aggressiveness and reduced overall survival. To our knowledge, IMP3 expression has not been investigated in pituitary tumors. We analyzed the immunohistochemical expression of IMP3 in five normal pituitary tissues and 75 pituitary tumors (64 adenomas and 11 carcinomas) to determine if specific tumor types expressed IMP3 and if there were differences in IMP3 expression between adenomas and carcinomas. Immunohistochemical analysis showed that IMP3 was positive in four (80%) normal pituitaries with focal stain in a subset of normal anterior pituitary cells. IMP3 was expressed in 31% (20/64) of adenomas and in 36% (4/11) of carcinomas. A slightly higher level of IMP3 expression was observed in PRL-GH-TSH adenomas compared to the other types of pituitary adenomas. Expression of IMP3 was not significantly higher in carcinomas than in adenomas (p = 0.737). RT-PCR and Western Blotting supported the heterogeneous expression of IMP3. These results indicate that IMP3 is expressed both in normal and in neoplastic pituitary gland tissues without significant differences in expression levels in pituitary carcinomas.

Euclidean and fractal geometry of microvascular networks in normal and neoplastic pituitary tissue

In geometrical terms, tumour vascularity is an exemplary anatomical system that irregularly fills a three-dimensional Euclidean space. This physical characteristic and the highly variable shapes of the vessels lead to considerable spatial and temporal heterogeneity in the delivery of oxygen, nutrients and drugs, and the removal of metabolites. Although these biological characteristics are well known, quantitative analyses of newly formed vessels in two-dimensional histological sections still fail to view their architecture as a non-Euclidean geometrical entity, thus leading to errors in visual interpretation and discordant results from different laboratories concerning the same tumour. We here review the literature concerning microvessel density estimates (a Euclidean-based approach quantifying vascularity in normal and neoplastic pituitary tissues) and compare the results. We also discuss the limitations of Euclidean quantitative analyses of vascularity and the helpfulness of a fractal geometry-based approach as a better means of quantifying normal and neoplastic pituitary microvasculature.

Advances in pituitary pathology: use of novel techniques.

Many new techniques are rapidly being developed and applied to the study of normal and neoplastic pituitary tissues. These range from techniques used for the past few decades such as in situ hybridization to more recent developments such as comparative genomic hybridization, laser capture microdissection, DNA and tissue arrays, proteomics, and RNA interference technology. These approaches have been applied to answer many challenging questions about pituitary function and pathophysiology. This chapter reviews many of these recent developments and shows their applications to pituitary biology in order to demonstrate how these new techniques are providing insights about basic aspects, clinical, and pharmacologic knowledge of the pituitary gland and of pituitary tumors.

Abnormal expression of 11 beta-hydroxysteroid dehydrogenase type 2 in human pituitary adenomas: a prereceptor determinant of pituitary cell proliferation.

The physiological effects of glucocorticoids (GCs) are, at least in part, mediated by inhibition of cell proliferation. Two isozymes of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) interconvert cortisol (F) and inactive cortisone (E), and are thus able to modulate GC action at an autocrine level. Previously, we have demonstrated absent expression of 11 beta-HSD2 in normal pituitaries; however, in a small number of pituitary tumors analysed, 11 beta-HSD2 was readily demonstrable. Here we have used real-time RT-PCR to quantify expression of mRNA for 11 beta-HSD1 and 2 in 105 human pituitary tumors and have performed enzyme expression and activity studies in primary pituitary cultures. Overall, pituitary tumors expressed lower levels of 11 beta-HSDl mRNA compared with normals (0.2-fold, P<0.05). In contrast, expression of 11 beta-HSD2 mRNA was 9.8-fold greater in tumors than in normals (P<0.001). Enzyme assays showed significant 11 beta-HSD2 activity (71.9+/-22.3 pmol/h/mg protein (mean+/-s.d.)) but no detectable 11 beta-HSDl activity. Proliferation assays showed that addition of glycyrrhetinic acid (an 11 beta-HSD2 inhibitor) resulted in a 30.3+/-7.7% inhibition of cell proliferation. In summary, we describe a switch in expression from 11 beta-HSDl to 11 beta-HSD2 in neoplastic pituitary tissue. We propose that abnormal expression of 11 beta-HSD2 acts as a proproliferative prereceptor determinant of pituitary cell growth, and may provide a novel target for future tumor therapy.

Expression of Growth Factors in Normal and Neoplastic Pituitary Tissues

Many growth factors are expressed in normal pituitary cells and pituitary tumors. They are involved in gene expression for pituitary hormones and in cell proliferation. Some appear to be important for prognosis or treatment. Strong overexpression of some growth factors may indicate a more rapid growth. The significance of the different growth factors for pituitary function and pathology is discussed.

Expression of prolactin-releasing peptide and its receptor messenger ribonucleic acid in normal human pituitary and pituitary adenomas.

The recently identified PRL-releasing peptide (PrRP) is the first hypothalamic peptide hormone that specifically stimulates PRL production from the pituitary gland. Similar to other hypothalamic regulatory hormones, it acts through its specific seven-transmembrane domain, G protein-coupled receptor. Using RT-PCR, we examined messenger ribonucleic acid (mRNA) expression of PrRP and its receptor in normal human pituitary tissue and in pituitary tumors. PrRP mRNA was expressed in all five normal pituitary glands examined. In contrast, PrRP mRNA was detected in only 5 of 11 of the human prolactinomas. All 5 prolactinomas expressing PrRP were responsive to dopamine agonist treatment, whereas PrRP-negative prolactinomas were non- or partially responsive. PrRP mRNA was also detected in 6 of 13 GH-secreting tumors and 5 of 10 clinically nonfunctioning tumors investigated. PrRP receptor mRNA was found in all the normal and neoplastic human pituitary samples studied. The production of PrRP and its receptor by normal and neoplastic pituitary tissue raises the question of whether it may regulate PRL production in an autocrine/paracrine manner in pituitary tissue. Further investigation of PrRP and its receptor expression and function will be needed to clarify its potential role in regulating PRL secretion in normal human lactotrophs and pituitary tumors.

Apoptosis in Nontumorous and Neoplastic Human Pituitaries: Expression of the Bcl-2 Family of Proteins

Analyses of apoptosis and of the apoptosis regulatory proteins Bcl-2, Bax, Bcl-X, and Bad were done in 95 nontumorous and neoplastic pituitary tissues by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL), immunohistochemistry, and Western blotting. The apoptotic index was relatively low in all groups but was at least fourfold higher in pituitary carcinomas compared with any other groups. Pituitaries from pregnant and postpartum women had a fivefold higher apoptotic index compared with matched controls from nonpregnant females. Preoperative treatment of adenomas with octreotide or dopamine agonists did not change the apoptotic index significantly. The lowest levels of Bcl-2, Bax, and Bcl-X expression were in pituitary carcinomas as detected by immunostaining. An immortalized human pituitary adenoma cell line, HP75, developed in our laboratory using a replication-defective recombinant human adenovirus with an early large T-antigen, had a much higher level of apoptosis than nontumorous and neoplastic pituitaries. Treatment with transforming growth factor (TGF)-beta1 and protein kinase C (PKC) inhibitors increased apoptosis in this cell line. Analysis of the Bcl-2 family of proteins after treatment with TGF-beta1 and PKC inhibitors showed a 20% to 30% decrease in Bcl-X in the treated groups compared with controls. These results, which represent the first study of apoptosis in pituitaries from pregnant and postpartum cases and in pituitary carcinomas, indicate that 1) the apoptotic rate is low in nontumorous and neoplastic pituitary tissues but is relatively higher in pituitary carcinomas, 2) there are alterations in the expression of the Bcl-2 family of proteins in pituitary neoplasms with a decrease in Bcl-2 expression in pituitary carcinomas that may contribute to pituitary tumor pathogenesis and/or proliferation, and 3) cultured pituitary tumor cells respond to TGF-beta1 and PKC inhibitors by undergoing apoptotic cell death.

Transcription factors in normal and neoplastic pituitary tissues.

Transcription factors are proteins that bind to regulatory elements in DNA and have critical roles in gene regulation during development, in cellular growth and differentiation. The four major groups of transcription factors have been classified according to the motif in the DNA-binding domains and include: (1) the helix-turn-helix group, which includes the Pit-1/GHF-1 (Pit-1) transcription factor; (2) the zing finger group, which includes estrogen and other steroid hormone receptors; (3) the leucine zipper group, which includes c-fos protooncogene, and (4) the helix-loop-helix group, which includes the c-myc oncogene. Members of all four groups have been described in normal and neoplastic anterior pituitary gland tissues. Pit-1 has been shown to regulate prolactin (PRL), growth hormone (GH), and thyroid-stimulating hormone (TSH) cells during development and differentiation. Genetic defects in this transcription factor have led to specific diseases in rodents and humans such as dwarfism and cretinism. Estrogen receptor (ER) protein plays a critical role in the regulation of gene expression in some anterior pituitary cells. There is a differential distribution of ER in anterior pituitary cells and tumors; PRL, gonadotroph, and null cell tumors are the principal adenomas expressing ER. The protooncogene c-fos is regulated by estrogen in various tissues, linking the regulation of one transcription factor by another transcription factor with a different motif. The c-myc oncogene has been detected in the pituitary gland and in some pituitary tumors, although the exact role of this oncogene in pituitary tumor development is uncertain. Because of the critical role that transcription factors play in pituitary cell development and differentiation, we can anticipate many more studies to elucidate their many functions in normal and neoplastic pituitary tissues.

Gonadotropin-releasing hormone and gonadotropin-releasing hormone receptor messenger ribonucleic acids expression in nontumorous and neoplastic pituitaries.

In the nontumorous pituitary, GnRH stimulates the release and synthesis of LH and FSH by gonadotroph cells via the GnRH receptor (GnRH-R). Little is known, however, about expression of GnRH and GnRH-R messenger RNAs (mRNAs) in nontumorous pituitary tissue and in adenomas. To learn more about the distribution and regulatory roles of GnRH and its receptor, we investigated the expression of both GnRH and GnRH-R mRNAs in nontumorous human pituitary and in various types of pituitary adenomas using the RT-PCR, in situ hybridization, and in situ hybridization in combination with RT-PCR (in situ RT-PCR). Using RT-PCR, GnRH mRNA was found to be expressed in normal human pituitaries and in all types of adenomas. Similarly, GnRH-R mRNA was expressed in nontumorous human pituitaries and in most, but not all, adenomas. These included 5 gonadotroph adenomas, 6 null cell adenomas, 1 of 2 GH-producing tumors, and 1 of 2 ACTH-producing adenomas, but not in the 2 PRL-producing adenomas examined. In situ hybridization studies showed GnRH and GnRH-R mRNAs in all 3 nontumorous pituitaries and in 12 of 33 (36.4%) and 10 of 33 adenomas (30.3%), respectively. Using an indirect in situ RT-PCR technique to increase the sensitivity of the in situ localization, GnRH and GnRH-R mRNAs were detected in 29 (87.9%) and 25 (75.8%) of 33 adenomas, respectively. This is the first report of the localization of GnRH and GnRH-R mRNAs in individual pituitary adenoma cells using in situ RT-PCR. The frequent expression of GnRH and GnRH-R mRNAs in pituitary cells suggests that GnRH has autocrine/paracrine functions in nontumorous and neoplastic pituitary tissues.

Prolactin Receptor Messenger Ribonucleic Acid in Normal and Neoplastic Human Pituitary Tissues

Prolactin Receptor Messenger Ribonucleic Acid in Normal and Neoplastic Human Pituitary Tissues

Human pituitary adenomas express endogenous inhibin subunit and follistatin messenger ribonucleic acids.

Specific factors involved in the pathogenesis of tumors that stimulate clonal human pituitary adenoma cell proliferation remain unknown. An important question regarding the pathogenesis of human pituitary tumors is whether they synthesize autocrine regulatory factors that regulate both hormone biosynthesis and neoplastic growth. Activin and inhibin are both comprised of inhibin subunits and have diverse regulatory roles as growth and differentiation factors in normal and neoplastic tissue. Activin stimulates FSH beta messenger ribonucleic acid (mRNA) biosynthesis and FSH secretion, and these effects are down-regulated in normal gonadotrophs by the endogenous glycoprotein follistatin. In addition to its effects on gonadotrophs, activin modulates hormone secretion by somatotroph and corticotroph cell lines. It is not known whether human neoplastic pituitary tissue synthesizes inhibin subunits or follistatin or whether their expression is cell type specific. We investigated whether alpha-, beta A-, and beta B-inhibin subunit and follistatin mRNAs could be detected in 27 human pituitary adenomas [clinically nonfunctioning (n = 11), somatotroph (n = 5), corticotroph (n = 5), and lactotroph (n = 6)] using reverse transcriptase-polymerase chain reaction techniques. Twenty-six of the tumors contained mRNAs encoding one or more inhibin subunits. beta B-Inhibin mRNA was the most prevalent (81% of tumors), followed by beta A-inhibin (59% of tumors) and alpha-inhibin (52% of tumors). Endogenous alpha-, beta A-, and beta B-inhibin subunit mRNA synthesis was also examined in normal human pituitary and testicular complementary DNA libraries, and all subunit mRNAs were detected. In contrast to the widespread expression of inhibin subunits in pituitary tumors, follistatin mRNA was detected in a subset of nonfunctioning tumors (54%) as well as in control normal human pituitary and testicular complementary DNA libraries. Tumor-specific follistatin biosynthesis was not observed in other pituitary tumor subtypes. These data are the first to demonstrate that 1) endogenous inhibin subunits are synthesized in human pituitary adenomas of all known secretory phenotypes as well as normal pituitary tissue; and 2) follistatin gene expression in pituitary adenomas is specific to clinically nonfunctioning or gonadotropin subunit-producing tumors. The characterization of inhibin subunit and follistatin biosynthesis by human pituitary tumors will be important in investigating their potential roles in regulating both tumor phenotype and cell proliferation.

Neural cell adhesion molecule (NCAM) in normal and neoplastic human pituitary tissues: Analysis by immunohistochemistry and in situ hybridization.

The expression of the neural cell adhesion molecule (NCAM) in 6 normal human pituitaries and 25 pituitary adenomas was investigated by immunohistochemistry and in situ hybridization. NCAM protein and mRNA were present in all normal and neoplastic human pituitary tissues. There were tumor type-specific differences in the distribution of NCAM in various pituitary adenomas. Growth hormone adenomas and prolactin-producing adenomas usually expressed lower levels of NCAM, compared to null cell and gonadotroph adenomas. Adreno-corticotropic hormone adenomas expressed the highest levels of NCAM mRNA. Six freshly dissociated pituitary adenomas were cultured in serum-free medium for 7 days to analyze the regulation of NCAM mRNA by in situ hybridization. The lower levels of NCAM expression in growth hormone and prolactin adenomas were not present in cells cultured for 7 days in serum-free medium on extracellular matrix. Phorbol 12-myristate 13-acetate (PMA) stimulated NCAM mRNA expression in 5 of 6 tumors. Gonadotropin-releasing hormone and growth hormone-releasing hormone increased NCAM expression in some adenomas. This study demonstrates that there is a variable expression of NCAM in pituitary adenomas and that hypotha-lamic hormones and PMA can regulate NCAM mRNA levels in neoplastic pituitary cells.

Imbalanced follicle-stimulating hormone beta-subunit hormone biosynthesis in human pituitary adenomas.

Clinically nonfunctioning pituitary adenomas represent approximately 25% of all pituitary tumors. Recent studies using a number of in vitro techniques show that the majority of such tumors produce gonadotropins. Hypersecretion of uncombined gonadotropin subunits by these tumors has also been identified raising the possibility that gonadotropin biosynthetic alterations may occur in neoplastic pituitary tissue. To determine whether underlying intracellular biosynthetic alterations lead to imbalanced secretion of the gonadotropin subunits by such tumors, we investigated 1) steady state gonadotropin-subunit messenger ribonucleic acid (mRNA) levels in tumor tissue from 49 patients with clinically nonfunctioning adenomas, 2) secretion of gonadotropins in dispersed pituitary tumor cultures, and 3) serum concentrations of gonadotropins and free subunits. Northern blots of RNA extracted from surgically obtained pituitary tumor tissue were hybridized with complementary DNA probes for FSH beta, LH beta, and alpha-subunit, and quantitative analysis was done to compare alpha- and beta-subunit biosynthesis in individual tumors. Of these tumors, 47 contained sufficient RNA for Northern analysis and 77% of these tumors contained one or more of the gonadotropin-subunit mRNAs. Steady state alpha-subunit mRNA was detected in 57% of tumors, FSH beta mRNA in 49%, and LH beta in 1 (2%). We found FSH beta mRNA in excess of alpha-subunit mRNA in one-third of tumors, including 9 tumors where alpha-subunit mRNA was undetectable. In cultured cells, FSH beta was secreted in excess of alpha-subunit in 41% of tumors. For those tumors in which both mRNA and culture data were available, FSH beta mRNA and secreted subunit levels were in excess of alpha-subunit in 64% of tumors. We conclude that clinically nonfunctioning pituitary adenomas frequently synthesize excess FSH beta subunit relative to alpha-subunit. This finding is in contrast to previous data in normal pituitary or placental tissue where alpha-subunit is present in excess of beta-subunits at both the mRNA and protein levels. The free-beta-subunit hypersecretion identified in pituitary adenomas may be due to biosynthetic abnormalities intrinsic to neoplastic gonadotrophs.

Mammosomatotropes: Presence and Functions in Normal and Neoplastic Pituitary Tissue*

I. Introduction MORE than a half century has passed since Romeis first proposed the “one cell-one hormone” theory which holds that each of the major pituitary hormones is produced by a separate and distinct cell type (1). Consistent with this idea, the acidophilic staining cells (termed acidophils) of the adenohypophysis have been traditionally subdivided into two categories, those that secrete only GH and others that produce just PRL. This view was supported by considerable tinctorial evidence available at the time of Romeis' hypothesis and generated in the subsequent three decades (1–5). Moreover, data produced throughout the 1970s and early 1980s by the use of light microscopic immunocytochemistry (ICC) and immunofluorescence were generally consonant with the one cell-one hormone theory, except in the case of certain pituitary tumors (6–8). The presence of bihormonal acidophils in this latter situation was attributed to aberrant mechanisms attendant to the neoplastic condition. However, as will be disc...

Regulation of estrogen receptor mRNA in normal and neoplastic rat pituitary tissues.

The effects of estradiol 17β (E2) on the regulation of estrogen receptor (ER) mRNA amounts in normal and neoplastic rat pituitary tissues were analyzed by in situ hybridization with an oligonucleotide probe. E2 treatment produced a significant increase in ER mRNA amounts in two transplantable pituitary tumors (MtT/Wl5 and MtT/F4) and in the GH3 cell line. ER mRNA amounts were also increased In normal pituitaries after 6 weeks of E2 treatment, but the differences were not significant. Biochemical assay of ER proteins confirmed the presence of ER protein in MtT/Wl 5 and MtT/F4 tumors. "Cytoplasmic" ER proteins were decreased by E2 in the MtT/Wl5 tumor.These results indicate that ER mRNA is present in normal pituitaries and in pituitary tumors and can be regulated by estrogen treatment in vivo and in vitro. The inhibitory effects of high estrogen concentration on proliferation of transplantable pituitary tumors in vivo and GH3 cells in vitro is not explained by the absence of ER mRNAs in these tumors.

Analysis of mammosomatotropic cells in normal and neoplastic human pituitaries

The reverse hemolytic plaque assay (RHPA) was used to analyze hormone secretion in normal and neoplastic human pituitary cells. Immunocytochemical (ICC) staining for PRL and GH with the peroxidase method and ultrastructural ICC with colloidal gold labeling were used along with the RHPA to analyze for mammosomatotropic (MS) cells in these dissociated and cultured pituitary cells. MS cells were identified in both normal and neoplastic pituitary tissues. Quantitation of plaque areas, showed that PRL cells from normal pituitaries had significantly larger plaque areas than PRL cells from PRL-producing adenomas or from mixed PRL-GH producing adenomas.

Gonadotropin and thyrotropin alpha- and beta-subunit gene expression in normal and neoplastic tissues characterized using specific messenger ribonucleic acid hybridization probes.

The glycoprotein hormones consist of a common alpha-subunit and distinct, but structurally related, beta-subunits which confer biological specificity. To study glycoprotein hormone gene expression, we prepared specific oligonucleotides complementary to nonhomologous regions of the alpha-subunit and each of the beta-subunit mRNAs encoding human LH, CG, TSH, and FSH. beta-Subunit mRNAs were expressed at relatively low levels in normal pituitary tissue, but were found in greater amounts in pituitary gonadotroph and thyrotroph adenomas. The lengths of the glycoprotein hormone alpha- and beta-subunit mRNAs in normal and neoplastic pituitary tissue were indistinguishable. Expression of different members of the closely related LH beta/CG beta gene family were examined in normal and neoplastic pituitary and placenta using short oligonucleotides complementary to nonhomologous regions of the genes. Although CG beta mRNA was found previously in a pituitary adenoma, none was detected in normal pituitary tissue. In placenta, there was abundant expression of the CG beta gene, but no expression of the LH beta gene, consistent with the acquisition of tissue-specific regulatory sequences in the recently evolved upstream promoter recognition site of the CG beta gene. Primer extension analysis of CG beta mRNA indicated that the same CG beta gene promoter site was used in both normal placenta and JEG-3 choriocarcinoma cells. Of the two CG beta genes that have been reported to be functional, CG beta gene 5 was preferentially expressed in both normal placenta and the neoplastic JEG-3 cell line. CG beta gene 3 expression accounted for only about 5% of the total CG beta mRNA. The previously uncharacterized human TSH beta and FSH beta mRNAs were studied in normal and neoplastic pituitary tissue. At least two species of FSH beta mRNA were found on Northern blots. Oligonucleotide-primed extension of pituitary mRNA demonstrated that FSH beta mRNA heterogeneity resulted from transcription from distinct promoter sites, encoding 5'-untranslated tracts of 48 and 83 bases. These studies demonstrate that specific oligonucleotide probes distinguish expression of the structurally related glycoprotein hormone beta-subunit mRNAs, allowing analyses of tissue-specific gene expression under different physiological conditions as well as in normal and neoplastic tissues.

Hormone Secretion by Human Somatotrophic, Lactotrophic, and Mixed Pituitary Adenomas in Culture*

Hormone secretion by short and long term explant cultures from needle aspiration biopsies of human pituitary adenomas was measured. The results were compared with similarly studied specimens obtained by transsphenoidal hypophysectomy and related to tumor immunocytochemistry and the clinical presentation. There was a high degree of correlation between the pattern of hormone secretion from the pituitary biopsies, the hormones found in the tissue, and the clinical presentation of the patient. In the five aspiration biopsies studied, evidence was obtained that two adenomas secreted solely PRL, one secreted only GH, and two secreted a mixture (one with a preponderance of GH over PRL, and one with a preponderance of PRL over GH). In the latter, the GH and PRL were secreted by separate cells. The three specimens from transsphenoidal hypophysectomies secreted PRL, GH, LH, FSH, and TSH and contained both neoplastic and normal pituitary tissue. In long term culture, GH, LH, FSH, and TSH secretion declined rapidly. ...

Fluorescamine fluorescence detection of growth hormone-producing cells in human pituitary adenomas.

Formalin-fixed and paraplast-embedded tissue specimens of human pituitary, thyroid, and pancreas were investigated using fluorescamine fluorescence and immunohistochemical methods. Growth hormone-producing cells present in normal and neoplastic pituitary tissue exhibited fluorescamine fluorescence. The other tissues examined showed no fluorescamine binding.