Cellular and molecular specificity of pituitary gland physiology.

The anterior pituitary gland has the ability to respond to complex signals derived from central and peripheral systems. Perception of these signals and their integration are mediated by cell interactions and cross-talk of multiple signaling transduction pathways and transcriptional regulatory networks that cooperate for hormone secretion, cell plasticity, and ultimately specific pituitary responses that are essential for an appropriate physiological response. We discuss the physiopathological and molecular mechanisms related to this integrative regulatory system of the anterior pituitary gland and how it contributes to modulate the gland functions and impacts on body homeostasis.

KISS1 receptor is preferentially expressed in clinically non-functioning pituitary tumors.

OBJECTIVE: KISS1 is a metastasis suppressor gene involved in cancer biology. Given the high expression levels of KISS1 and KISS1R in the hypothalamus and the pituitary respectively, we hypothesized that this system could possibly affect tumor invasiveness and clinical behavior of pituitary tumors. METHODS: Expression levels of KISS1 and KISS1R mRNA were evaluated by RT-PCR. Clinical information pertaining tumor characteristics was extracted from patients' charts. RESULTS: Tumors from 39 patients (21 females, mean age 47.5 years) were examined. KISS1R was expressed in 26 (67%) of samples (94% of NFPA, 42% of GH-, 67% of ACTH-, and 25% of PRL-secreting adenomas) and was found more often in female patients (81 vs. 50% males, p < 0.05); and in NFPA (94 vs. 45.5% in secreting tumors; p = 0.003). Patients expressing KISS1R were older at presentation (50.5 ± 1.4 vs. 38.1 ± 1.3 years; p = 0.008). In the multivariate analysis, factors significantly associated with KISS1R expression included female gender (OR 13.8, 95 % CI 1.22-155.9; p = 0.03) and having a NFPA (OR 24.7, 95% CI 1.50-406.4; p = 0.02). Tumor size, invasiveness and age at presentation were not independently associated with KISS1R expression. Pituitary tumors and normal pituitary were negative for KISS1 mRNA expression. CONCLUSIONS: The majority of human NFPA expressed KISS1R with lower rates of expression in other types of pituitary tumors. KISS1R expression did not impart a clinical beneficial tumor phenotype, as it was not associated with tumor size or invasiveness. Additional studies are required to elucidate the role of KISS1 receptor in pituitary gland physiology and pathology.

Curcumin inhibits the growth, induces apoptosis and modulates the function of pituitary folliculostellate cells.

The polyphenol curcumin (diferuloylmethane) is the active componenet of the spice plant Curcuma longa and has been shown to exert multiple actions on mammalian cells. We have studied its effect on folliculostellate (FS) TtT/GF mouse pituitary cells, representative of a multifunctional, endocrine inactive cell type of the anterior pituitary. Proliferation of TtT/GF cells was inhibited by curcumin in a monolayer cell culture and in the colony formation assay in soft agar. Fluorescence-activated cell-sorting (FACS) analysis demonstrated curcumin-induced cell cycle arrest at G(2)/M accompanied by inhibition of cyclin D(1) protein expression. Curcumin had a small effect on necrosis of TtT/GF cells, but it mainly stimulated apoptosis as demonstrated by FACS analysis (Annexin V-fluorescein isothiocyannate/7-aminoactinomycin D staining). Curcumin-induced apoptosis involved suppression of Bcl-2, stimulation of cleaved caspase-3 and induction of DNA fragmentation. Functional studies on FS cell-derived compounds showed that curcumin inhibited mRNA synthesis and release of angiogenic vascular endothelial growth factor-A (VEGF-A). Immune-like functions of FS cells were impaired since curcumin downregulated Toll-like receptor 4, reduced nuclear factor-kappaB expression and suppressed bacterial endotoxin-induced interleukin-6 (IL-6) secretion. The inhibitory action of curcumin on VEGF-A and IL-6 production was also found in primary rat pituitary cell cultures, in which FS cells are the only source of these proteins. The observed effects of curcumin on FS cell growth, apoptosis and functions may have therapeutic consequences for the intrapituitary regulation of hormone production and release as well as for pituitary tumor pathogenesis.

Hypoxia and the hypoxia inducible factor 1α activate protein kinase A by repressing RII beta subunit transcription.

Overactivation of the cAMP signal transduction pathway plays a central role in the pathogenesis of endocrine tumors. Genetic aberrations leading to increased intracellular cAMP or directly affecting PKA subunit expression have been identified in inherited and sporadic endocrine tumors, but are rare indicating the presence of nongenomic pathological PKA activation. In the present study, we examined the impact of hypoxia on PKA activation using human growth hormone (GH)-secreting pituitary tumors as a model of an endocrine disease displaying PKA-CREB overactivation. We show that hypoxia activates PKA and enhances CREB transcriptional activity and subsequently GH oversecretion. This is due to a previously uncharacterized ability of HIF-1α to suppress the transcription of the PKA regulatory subunit 2B (PRKAR2B) by sequestering Sp1 from the PRKAR2B promoter. The present study reveals a novel mechanism through which the transcription factor HIF-1α transduces environmental signals directly onto PKA activity, without affecting intracellular cAMP concentrations. By identifying a point of interaction between the cellular microenvironment and intracellular enzyme activation, neoplastic, and nonneoplastic diseases involving overactivated PKA pathway may be more efficiently targeted.

GEOFFREY HARRIS AWARD 2019: Translational research in pituitary tumours.

Although effective treatment regimens (surgical resection, drug treatment with dopamine agonists or somatostatin analogues, radiotherapy) have been established for the therapy of most pituitary tumours, a considerable proportion of affected patients cannot completely cured due to incomplete resection or drug resistance. Moreover, even if hormone levels have been normalized, patients with hormone-secreting tumours still show persistent pathophysiological alterations in metabolic, cardiovascular or neuropsychiatric parameters and have an impaired quality of life. In this review reasons for the discrepancy between biochemical cure and incomplete recovery from tumour-associated comorbidities are discussed and the clinical management is delineated exemplarily for patients with acromegaly and Cushing's disease. In view of the development of additional treatment concepts for the treatment of pituitary adenomas we speculate about the relevance of RSUME as a potential target for the development of an anti-angiogenic therapy. Moreover, the role of BMP-4 which stimulates prolactinoma development through the Smad signalling cascade is described and its role as putative drug target for the treatment of prolactinomas is discussed. Regarding the well-known resistance of a part of somatotropinomas to somatostatin analogue treatment, recently identified mechanisms responsible for the drug resistance are summarized and ways to overcome them in future treatment concepts are presented. Concerning novel therapeutic options for patients with Cushing's disease the impact of retinoic acid, which is currently tested in clinical studies, is shown, and the action and putative therapeutic impact of silibinin to resolve glucocorticoid resistance in these patients is critically discussed.

Modulation of growth hormone and prolactin secretion in Trypanosoma cruzi-infected mammosomatotrophic cells.

OBJECTIVE: In a previous study, we reported an imbalance in the hypothalamus-pituitary-adrenal axis of mice acutely infected with the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. METHODS: Possible effects of this parasitic infection on the endocrine function of other pituitary cell types were studied, in particular regarding the production of prolactin (PRL) and growth hormone (GH). RESULTS: In the mammosomatotrophic cell line GH3, both GH and PRL secretion were decreased, reflecting the diminished PRL concentrations in the pituitary glands of infected mice. Additionally, expression of extracellular matrix proteins, e.g. laminin, was increased in T. cruzi-infected GH3 cells, which may be related to the diminished secretory function of these cells. Lastly, the expression of Pit-1, a major transcription factor for the PRL and GH genes, is also decreased in T. cruzi-infected cultures. CONCLUSION: T. cruzi infection downregulates PRL and GH production. Combined with our previous data showing increased glucocorticoid levels following T. cruzi infection, the immunosuppression induced by T. cruzi infection may be partially related to multiple endocrine changes involving the hypothalamus-pituitary axis and corresponding target endocrine glands.

Regulation of pituitary function by cytokines.

Research performed on the pituitary has proven that cytokines play an important role in maintaining pituitary physiology, affecting not only cell proliferation but also hormone secretion. The effects of cytokines can be autocrine or paracrine. This review gives an overview on the effects of the most studied cytokines in the pituitary. Special interest is focused on interleukin-6 (IL-6) because it has the distinctive characteristic of stimulating pituitary tumor cell growth, but has the opposite effect on normal pituitary cells. On the other hand, IL-6 is a cytokine of interest in the pituitary because recent work has shown that it promotes and maintains senescence in certain types of tumors. Given that the majority of pituitary adenomas are microadenomas and the fact that clinically inapparent pituitary tumors are quite common, senescence, perhaps mediated by IL-6, is an attractive mechanism for explaining the benign nature of pituitary tumors.

Toll-like receptor-4 is expressed in meningiomas and mediates the antiproliferative action of paclitaxel.

Meningiomas are the second most common type of brain and CNS tumors by histology. Surgery and radiotherapy are main treatment options, but meningiomas may be impossible to adequately resect or may regrow after surgery. In spite of many experimental attempts, there is no generally accepted chemotherapeutic approach. We have studied in a series of meningiomas the expression of the Toll-like receptor 4 (TLR4), which apart from its major role as a key factor of the innate immune system, is believed to play a role in tumorigenesis. All meningiomas studied expressed TLR4 mRNA and protein at variable degree. Paclitaxel, a ligand of TLR4, exhibited a dose- and time-dependent growth suppression in both monolayer and spheroid meningioma cell cultures. The knockdown of TLR4 with siRNA in meningioma cell cultures abrogated the inhibitory effect of paclitaxel. The suppressive action of paclitaxel on meningioma cell growth was enhanced in the presence of fluvastatin or the mitogen-actvated protein kinase (ERK1/2) inhibitor PD98059. At least part of the growth suppressive effect was mediated by the induction of apoptosis in meningioma cells by paclitaxel alone or in combination with fluvastatin. In conclusion, our in vitro results suggest that paclitaxel alone or in combination with other inhibitors of cell growth (statins, MAPK inhibitors) could provide a potential tool for the treatment of TLR4 expressing meningiomas.

Recent advances in understanding corticotroph pituitary tumor initiation and progression.

Cushing's disease is the most frequent form of hypercortisolism and is caused by hypophyseal corticotroph adenomas secreting excessive amounts of adrenocorticotropic hormone. Most of the tumors develop sporadically and only a limited number of corticotroph adenomas have been found to be associated with different neuroendocrine syndromes or with familial isolated pituitary adenomas. The pathogenic mechanisms of corticotroph adenomas are largely unknown, but the discovered aberrant chaperoning activity of heat shock protein 90 on the one hand and the presence of ubiquitin-specific protease 8 mutations on the other hand partially explained the causes of their development. Corticotroph tumors arise initially as benign microadenomas but with time form invasively growing aggressive macroadenomas which can switch to corticotroph carcinomas in extremely rare cases. The mechanisms through which corticotroph tumors escape from glucocorticoid negative feedback are still poorly understood, as are the processes that trigger the progression of benign corticotroph adenomas toward aggressive and malignant phenotypes. This review summarizes recent findings regarding initiation and progression of corticotroph pituitary tumors.

Physical Exercise and Spatial Training: A Longitudinal Study of Effects on Cognition, Growth Factors, and Hippocampal Plasticity.

Physical exercise has been suggested to improve cognitive performance through various neurobiological mechanisms, mediated by growth factors such as BDNF, IGF-I, and VEGF. Moreover, animal research has demonstrated that combined physical and cognitive stimulation leads to increased adult neurogenesis as compared to either experimental condition alone. In the present study, we therefore investigated whether a sequential combination of physical and spatial training in young, healthy adults elicits an additive effect on training and transfer gains. To this end, we compared the effects of (i) eight 20-minute sessions of cycling, (ii) sixteen 30-minute sessions of spatial training, (iii) a combination of both, and included (iv) a passive control cohort. We assessed longitudinal changes in cognitive performance, growth factor levels, and T1 relaxation of hippocampal subfields (acquired with 7 T MRI). While substantial physical and spatial training gains were elicited in all trained groups, longitudinal transfer changes did not differ between these groups. Notably, we found no evidence for an additive effect of sequential physical and spatial training. These results challenge the extrapolation from the findings reported in animals to young, healthy adults.

Advances in understanding hypopituitarism.

The understanding of hypopituitarism has increased over the last three years. This review provides an overview of the most important recent findings. Most of the recent research in hypopituitarism has focused on genetics. New diagnostic techniques like next-generation sequencing have led to the description of different genetic mutations causative for congenital dysfunction of the pituitary gland while new molecular mechanisms underlying pituitary ontogenesis have also been described. Furthermore, hypopituitarism may occur because of an impairment of the distinctive vascularization of the pituitary gland, especially by disruption of the long vessel connection between the hypothalamus and the pituitary. Controversial findings have been published on post-traumatic hypopituitarism. Moreover, autoimmunity has been discussed in recent years as a possible reason for hypopituitarism. With the use of new drugs such as ipilimumab, hypopituitarism as a side effect of pharmaceuticals has come into focus. Besides new findings on the pathomechanism of hypopituitarism, there are new diagnostic tools in development, such as new growth hormone stimulants that are currently being tested in clinical trials. Moreover, cortisol measurement in scalp hair is a promising tool for monitoring cortisol levels over time.

Bone morphogenetic protein-4 inhibits corticotroph tumor cells: involvement in the retinoic acid inhibitory action.

The molecular mechanisms governing the pathogenesis of ACTH-secreting pituitary adenomas are still obscure. Furthermore, the pharmacological treatment of these tumors is limited. In this study, we report that bone morphogenetic protein-4 (BMP-4) is expressed in the corticotrophs of human normal adenohypophysis and its expression is reduced in corticotrophinomas obtained from Cushing's patients compared with the normal pituitary. BMP-4 treatment of AtT-20 mouse corticotrophinoma cells has an inhibitory effect on ACTH secretion and cell proliferation. AtT-20 cells stably transfected with a dominant-negative form of the BMP-4 signal cotransducer Smad-4 or the BMP-4 inhibitor noggin have increased tumorigenicity in nude mice, showing that BMP-4 has an inhibitory role on corticotroph tumorigenesis in vivo. Because the activation of the retinoic acid receptor has an inhibitory action on Cushing's disease progression, we analyzed the putative interaction of these two pathways. Indeed, retinoic acid induces both BMP-4 transcription and expression and its antiproliferative action is blocked in Smad-4dn- and noggin-transfected Att-20 cells that do not respond to BMP-4. Therefore, retinoic acid induces BMP-4, which participates in the antiproliferative effects of retinoic acid. This new mechanism is a potential target for therapeutic approaches for Cushing's disease.

Temazepam triggers the release of vasopressin into the rat hypothalamic paraventricular nucleus: novel insight into benzodiazepine action on hypothalamic-pituitary-adrenocortical system activity during stress.

We investigated the influence of a representative classical benzodiazepine on the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis activity both under basal conditions and stress. Adult male Wistar rats were intravenously administered with temazepam (0.5, 1, and 3 mg/kg body weight) and plasma concentrations of corticotropin (ACTH) and vasopressin (AVP) were measured in blood samples collected via chronically implanted jugular venous catheters. Simultaneously, the release of AVP within the hypothalamic paraventricular nucleus (PVN) was monitored via microdialysis. Plasma AVP levels remained unaffected by the different treatment conditions. Temazepam blunted the stressor exposure-induced secretion of ACTH in a dose-dependent manner. Concurrently, and also in a dose-dependent manner temazepam enhanced the intra-PVN release of AVP, known to originate from magnocellular neurons of the hypothalamic neurohypophyseal system. Furthermore, temazepam did not affect the in vitro secretion of ACTH from the adenohypophyseal cells. Taken together, the results of this study suggest that temazepam modulates the central nervous regulation of the HPA axis by altering intra-PVN AVP release. An increasingly released AVP of magnocellular origin seems to provide a negative tonus on ACTH secretion most probably via inhibiting the release of ACTH secretagogues from the median eminence into hypophyseal portal blood.

Hypothalamus-pituitary-adrenal axis during Trypanosoma cruzi acute infection in mice.

Functional interactions between neuroendocrine and immune systems are mediated by similar ligands and receptors, which establish a bi-directional communication that is relevant for homeostasis. We investigated herein the hypothalamus-pituitary-adrenal (HPA) axis in mice acutely infected by Trypanosoma cruzi, the causative agent of Chagas' disease. Parasites were seen in the adrenal gland, whereas T. cruzi specific PCR gene amplification product was found in both adrenal and pituitary glands of infected mice. Histological and immunohistochemical analyses of pituitary and adrenal glands of infected animals revealed several alterations including vascular stasis, upregulation of the extracellular matrix proteins fibronectin and laminin, as well as T cell and macrophage infiltration. Functionally, we detected a decrease in CRH and an increase in corticosterone contents, in hypothalamus and serum respectively. In contrast, we did not find significant changes in the amounts of ACTH in sera of infected animals, whereas the serum levels of the glucocorticoid-stimulating cytokine, IL-6 (interleukin-6), were increased as compared to controls. When we analyzed the effects of T. cruzi in ACTH-producing AtT-20 cell line, infected cultures presented lower levels of ACTH and pro-opiomelanocortin production when compared to controls. In these cells we observed a strong phosphorylation of STAT-3, together with an increased synthesis of IL-6, suppressor of cytokine signaling 3 (SOCS-3) and inhibitor of activated STAT-3 (PIAS-3), which could explain the partial blockage of ACTH production. In conclusion, our data reveal that the HPA axis is altered during acute T. cruzi infection, suggesting direct and indirect influences of the parasite in the endocrine homeostasis.

Localization of vascular endothelial growth factor (VEGF) receptors in normal and adenomatous pituitaries: detection of a non-endothelial function of VEGF in pituitary tumours.

As for any solid tumour, pituitary adenoma expansion is dependent on neovascularization through angiogenesis. In this process, vascular endothelial growth factor (VEGF) and its receptors VEGFR-1, VEGFR-2 and neuropilin-1 (NRP-1) may play an outstanding role. The intention of this work was to study the expression/localization and possible function of VEGF receptors in pituitary adenomas. VEGF receptor mRNA and protein expression was studied by in situ hybridization, immunohistochemistry and RT-PCR in 6 normal human pituitaries, 39 human pituitary adenomas and 4 rodent pituitary adenoma cell lines. VEGFR-1 expressing somatotroph MtT-S cells were used as a model to study the role of VEGF on cell proliferation and to elucidate the underlying mechanism of action. In normal pituitaries, VEGFR-1 was detected in endocrine cells, whereas VEGFR-2 and NRP-1 were exclusively expressed in endothelial cells. In pituitary tumours, a heterogeneous VEGFR expression pattern was observed by IHC. VEGFR-1, VEGFR-2 and NRP-1 were detected in 24, 18 and 17 adenomas respectively. In the adenomas, VEGFR-1 was expressed in epithelial tumour cells and VEGFR-2/NRP-1 in vessel endothelial cells. Functional studies in VEGFR-1-positive MtT-S cells showed that the ligands of VEGFR-1 significantly stimulated cell proliferation. This effect was mediated through the phosphatidylinositol-3-kinase-signalling pathway and involves induction of cyclin D1 and Bcl-2. Based on our results, we speculate that the ligands of VEGF receptors, such as VEGF-A and placenta growth factor, not only play a role in angiogenesis in pituitary adenomas, but also affect the growth of pituitary tumour cells through VEGFR-1.

Bone morphogenetic protein-4 control of pituitary pathophysiology.

Bone morphogenetic protein-4 (BMP-4), a member of the transforming growth factor-Beta(TGF-Beta) family, is overexpressed in different prolactinoma models and induces the development of these lineage adenomas. SMAD proteins activated by growth factors of the TGF-Beta and BMP family interact with estrogen receptors to stimulate the proliferation of prolactin and growth hormone-secreting cells. Furthermore, BMP-4 presents differential expression in normal and adenomatous corticotropes and inhibitory action on corticotropinoma cell proliferation. Moreover, BMP-4 mediates the antiproliferative action of retinoic acid in these cells. The present review highlights not only the crucial and opposite role of BMP-4 in the progression of pituitary adenomas but also that BMP-4 and retinoic acid interaction might serve as a potential new mechanism target for therapeutic approaches for Cushing disease.

RSUME is implicated in tumorigenesis and metastasis of pancreatic neuroendocrine tumors.

The factors triggering pancreatic neuroendocrine tumor (PanNET) progression are largely unknown. Here we investigated the role and mechanisms of the sumoylation enhancing protein RSUME in PanNET tumorigenesis. Immunohistochemical studies showed that RSUME is strongly expressed in normal human pancreas, in particular in ß-cells. RSUME expression is reduced in insulinomas and is nearly absent in other types of PanNETs suggesting a role in PanNET tumorigenesis. In human pancreatic neuroendocrine BON1 cells, RSUME stimulates hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor-A (VEGF-A), which are key components of tumor neovascularisation. In contrast, RSUME suppresses nuclear factor-κB (NF-κB) and its target interleukin-8 (IL-8). Correspondingly, PanNET cells with RSUME knockdown showed decreased HIF-1α activity and increased NF-κB and IL-8 production leading to a moderate reduction of VEGF-A release as reduced HIF-1α/VEGF-A production is partly compensated by NF-κB/IL-8-induced VEGF-A. Notably, RSUME stabilizes the tumor suppressor PTEN, which is frequently lost in PanNETs and whose absence is associated with metastasis formation. In vivo orthotopic transplantation of PanNET cells with or without RSUME expression into nude mice showed that PanNETs without RSUME have reduced PTEN expression, grow faster and form multiple liver metastases. In sum, RSUME differentially regulates key components of PanNET formation suggesting that the observed loss of RSUME in advanced PanNETs is critically involved in PanNET tumorigenesis, particularly in metastasis formation.

The role of poly (adenosine 5'-diphosphate-ribose) polymerase in the response of pituitary tumor cells to reactive oxygen species.

As an enzyme implicated in the stress response, we investigated poly(ADP-ribose) polymerase (PARP) in the response of GH3 rat pituitary tumor cells to oxidants. These cells are unusual in that they undergo rapid cell death (90 min) with low doses of the prooxidant, H2O2 (50-200 microm), whereas at higher doses (1 mm), death occurs some hours later (4-5 h). Measurement of PARP activity shows that low doses of H2O2 (50-200 microm) fail to increase the activity of PARP, whereas at 0.5 and 1 mm, the enzyme becomes activated. In parallel with the activation of PARP, cellular ATP concentrations fall at high H2O2 doses and the PARP inhibitors, 3-aminobenzamide and nicotinamide (NIC) partially prevent this fall. Using NIC to inhibit PARP activity, we show that treatment of cells with NIC before the addition of H2O2 (0.5-1 mm), results in rapid cell death (90 min). In contrast, prior exposure to H2O2 (0.5-1 mm) for 1 h, before withdrawal and exposure to 1 mm NIC, allows cell survival for many hours. These data suggest that PARP is involved in blocking rapid death of GH3 cells in response to oxidants. In contrast to other cell types tested here, in which inhibitor studies show that PARP is activated at low H2O2 doses and this decreases the extent of apoptosis, GH3 cells are unable to sufficiently activate PARP to prevent rapid cell death.

Expression and function of sonic hedgehog pathway components in pituitary adenomas: evidence for a direct role in hormone secretion and cell proliferation.

CONTEXT: Sonic hedgehog (Shh) belongs to a family of signaling proteins involved in development and has been recently implicated in cancer. Shh signaling is active in the corticotrophs of the adult pituitary gland, where it cross-talks with the CRH pathway and regulates ACTH secretion. Because developmental pathways are involved in pituitary tumorigenesis, we hypothesized that Shh may be important in pituitary tumors. OBJECTIVE: The objective of this study was to examine the expression and function of Shh-pathway components in pituitary adenomas. METHODS: Using immunohistochemistry, we determined the expression of Shh and its receptors Patched 1 (Ptc1) and Patched 2 (Ptc2) in 55 human pituitary adenomas compared with the normal pituitary gland. The AtT-20 and GH3 pituitary tumor cell lines were used as models for studying the role of Shh on cell proliferation and hormone secretion. The effect of Shh on hormone secretion was confirmed in primary cultures of normal rat pituitaries and human pituitary tumors. RESULTS: Ptc1 and Ptc2 were present, whereas Shh was down-regulated in pituitary adenomas and completely absent in Cushing tumors. Shh inhibited cell proliferation in AtT-20 corticotrophinoma cells and the Shh-specific inhibitor cyclopamine increased proliferation in GH3 mammosomatotrophinoma cells. On the other hand, exogenous administration of Shh increased hormone secretion from normal rat pituitaries, pituitary cell lines, and 10 different pituitary tumors. CONCLUSIONS: Our results suggest that Shh might maintain pituitary cells in a nonproliferative state. We conclude that Shh is a newly described hypophysiotropic cytokine and its down-regulation may be involved in the pathogenesis of pituitary adenomas.