Intrahypophyseal Immune-Endocrine Interactions: Endocrine Integration of the Inflammatory Inputs.

Endotoxin (lipopolysaccharide, LPS) of gram-negative bacteria has been recognized for more than 40 years as a modulator of anterior pituitary hormone production. The action of LPS was thought to be predominantly mediated through LPS-stimulated immune cell-derived cytokines, and is part of the concept of immune-endocrine crosstalk, which regulates bidirectional adaptive processes between the endocrine and immune systems during inflammatory or infectious processes. With the detection of innate immune system components in the normal and tumoral pituitary, including the Toll-like receptor 4, the target of LPS, it has become evident that LPS can directly modify the physiology and pathophysiology of the anterior pituitary. LPS-induced intrapituitary mechanisms involve the stimulation of intrapituitary cytokines, and also directly act on hormone synthesis, growth, and apoptosis of endocrine cells. This review focuses on the effects of LPS on pituitary physiology, its interaction with pro- and anti-inflammatory factors, and the molecular mechanisms involved in these processes.

RSUME inhibits VHL and regulates its tumor suppressor function.

Somatic mutations or loss of von Hippel-Lindau (pVHL) happen in the majority of VHL disease tumors, which present a constitutively active Hypoxia Inducible Factor (HIF), essential for tumor growth. Recently described mechanisms for pVHL modulation shed light on the open question of the HIF/pVHL pathway regulation. The aim of the present study was to determine the molecular mechanism by which RSUME stabilizes HIFs, by studying RSUME effect on pVHL function and to determine the role of RSUME on pVHL-related tumor progression. We determined that RSUME sumoylates and physically interacts with pVHL and negatively regulates the assembly of the complex between pVHL, Elongins and Cullins (ECV), inhibiting HIF-1 and 2α ubiquitination and degradation. We found that RSUME is expressed in human VHL tumors (renal clear-cell carcinoma (RCC), pheochromocytoma and hemangioblastoma) and by overexpressing or silencing RSUME in a pVHL-HIF-oxygen-dependent degradation stability reporter assay, we determined that RSUME is necessary for the loss of function of type 2 pVHL mutants. The functional RSUME/pVHL interaction in VHL-related tumor progression was further confirmed using a xenograft assay in nude mice. RCC clones, in which RSUME was knocked down and express either pVHL wt or type 2 mutation, have an impaired tumor growth, as well as HIF-2α, vascular endothelial growth factor A and tumor vascularization diminution. This work shows a novel mechanism for VHL tumor progression and presents a new mechanism and factor for targeting tumor-related pathologies with pVHL/HIF altered function.

Hypoxia inducible factor-1 is involved in growth factor, glucocorticoid and hypoxia mediated regulation of vascular endothelial growth factor-A in human meningiomas.

In meningiomas, neovascularization through angiogenesis is essential for tumor expansion. As the vascular endothelial growth factor-A (VEGF-A) plays an outstanding role in this process, we have studied basal VEGF-A release and some aspects of its regulation in 46 meningiomas and in Ben-Men-1 cells in vitro. Among two putative VEGF-A stimulating growth factors tested, TGF-1ß was more potent than TGF-α in enhancing VEGF-A secretion. Hypoxia-mimicking conditions induced by CoCl2 treatment also strongly increased VEGF-A secretion. The synthetic glucocorticoid dexamethasone (DEX) potently suppressed both basal and growth factor or CoCl2-induced VEGF-A release. All these effects were also seen in the Ben-Men-1 cell line in which studies on the role of HIF-1 in the regulation of VEGF-A showed that not only hypoxia but also the growth factors induced HIF-1α and DEX suppressed HIF-1α induction. Therefore, in Ben-Men-1 cells with HIF-1α knock-down the effects of hypoxia, growth factors and DEX on VEGF-A production were strongly impaired. This clearly indicates that HIF-1 not only regulates hypoxia-induced VEGF-A production but also mediates at least in part the effects of growth factors and DEX on VEGF-A synthesis and release. Our findings show the complexity of VEGF-A regulation in meningiomas and point to new options for the pharmacological treatment of these tumors.

Curcumin acts anti-proliferative and pro-apoptotic in human meningiomas.

Meningiomas, the most frequent benign intracranial and intraspinal types of tumors are normally removed by surgery. Complications can occur when the tumor is critically localized and cannot be completely removed or when comorbidities of the mostly elder patients increase the general surgical risk. Thus, alternate medical treatment concepts for the therapy of meningiomas would be desirable. Curcumin, the active ingredient of the spice plant Curcuma longa has shown anti-tumorigenic actions in many different types of tumors and therefore, its effect on growth and apoptosis of meningioma cells was studied in the present paper. In vitro, treatment of the human Ben-Men-1 meningioma cell line and of a series of 21 primary human meningioma cell cultures with curcumin (1-20 µM) strongly reduced the proliferation in all cases in a dose dependent manner. Cell cycle analysis by fluorescence-activated cell sorting showed growth arrest at G2/M phase, which was confirmed by demonstrating the corresponding modulation of proteins involved in G2/M arrest by immunoblotting and/or confocal laser microscopy. High dosages (20, 50 µM) of curcumin induced a significant increase of apoptosis in Ben-Men-1 and primary meningioma cell cultures as demonstrated by morphological changes of cell nuclei, DNA fragmentation, translocation of cell membrane associated phosphatidyl serine and the induction of apoptotic-acting cleaved caspase-3. Our results suggest that the multi-targeting drug curcumin has potent anti-tumorigenic actions in meningioma cells and might therefore be a putative candidate for the pharmacological treatment of meningiomas.

Curcumin suppresses HIF1A synthesis and VEGFA release in pituitary adenomas.

Curcumin (diferuloylmethane), a polyphenolic compound derived from the spice plant Curcuma longa, displays multiple actions on solid tumours including anti-angiogenic effects. Here we have studied in rodent and human pituitary tumour cells the influence of curcumin on the production of hypoxia inducible factor 1α (HIF1A) and vascular endothelial growth factor A (VEGFA), two key components involved in tumour neovascularisation through angiogenesis. Curcumin dose-dependently inhibited basal VEGFA secretion in corticotroph AtT20 mouse and lactosomatotroph GH3 rat pituitary tumour cells as well as in all human pituitary adenoma cell cultures (n=32) studied. Under hypoxia-mimicking conditions (CoCl(2) treatment) in AtT20 and GH3 cells as well as in all human pituitary adenoma cell cultures (n=8) studied, curcumin strongly suppressed the induction of mRNA synthesis and protein production of HIF1A, the regulated subunit of the hypoxia-induced transcription factor HIF1. Curcumin also blocked hypoxia-induced mRNA synthesis and secretion of VEGFA in GH3 cells and in all human pituitary adenoma cell cultures investigated (n=18). Thus, curcumin may inhibit pituitary adenoma progression not only through previously demonstrated anti-proliferative and pro-apoptotic actions but also by its suppressive effects on pituitary tumour neovascularisation.

RSUME is implicated in HIF-1-induced VEGF-A production in pituitary tumour cells.

The recently cloned small RWD-domain containing protein RSUME was shown to increase protein levels of hypoxia-inducible factor-1α (HIF-1α). The latter is the oxygen-regulated subunit of HIF-1, the most important transcription factor of the cellular adaptive processes to hypoxic conditions. It is also a major regulator of vascular endothelial growth factor-A (VEGF-A), which is critically involved in the complex process of tumour neovascularisation. In this study, the expression and role of RSUME in pituitary tumours was studied. We found that RSUME mRNA was up-regulated in pituitary adenomas and significantly correlated with HIF-1α mRNA levels. Hypoxia (1% O(2)) or treatment with hypoxia-mimicking CoCl(2) enhanced RSUME and HIF-1α expression, induced translocation of HIF-1α to the nuclei and stimulated VEGF-A production both in pituitary tumour cell lines and primary human pituitary adenoma cell cultures. When RSUME expression was specifically down-regulated by siRNA, the CoCl(2)-induced increase VEGF-A secretion was strongly reduced which was shown to be a consequence of the RSUME knockdown-associated reduction of HIF-1α synthesis. Thus, RSUME plays an important role in initiating pituitary tumour neovascularisation through regulating HIF-1α levels and subsequent VEGF-A production and may therefore be critically involved in pituitary adenoma progression.

Novel medical therapies for pituitary tumors.

Despite considerable progress, there is still no medical treatment available for some kinds of pituitary tumors, in particular hormone inactive adenomas and corticotroph pituitary tumors. Surgical removal or at least debulking of the tumor is the only option to treat these kinds of tumors apart from rarely applied radiotherapy. Moreover, treatment resistance is present in a considerable proportion of patients bearing pituitary tumors, for which medical treatment regimens are already available (prolactinomas, somatotroph adenomas). Thus, novel or improved medical treatment strategies would be desirable. Here, we summarize preclinical and clinical findings about the hormone and growth-suppressive action of various drugs, which will probably lead to novel future medical treatment concepts for pituitary tumors.

Platelet-derived growth factor (PDGF) and PDGF receptor expression and function in folliculostellate pituitary cells.

Homo- and heterodimers of platelet-derived growth factor-A (PDGF-A) and PDGF-B chains are involved through PDGF alpha- and beta-receptors in the growth regulation of multiple normal and tumoural cell types as well as in tumour neovascularization. Since little information is available on the impact of PDGF/PDGF receptors in normal and adenomatous pituitary, we studied the expression and action of this growth factor system in a variety of pituitary tumour cell lines and in rat anterior pituitary cell cultures. By RT-PCR, mRNA expression of PDGF-A and -B chains and of both receptors was found in rat pituitary and mouse folliculostellate TtT/GF pituitary tumour cells. Rat somatotroph MtT-S and mouse corticotroph AtT20 tumor cells expressed only a part of the PDGF/PDGF receptor components whereas mouse gonadotroph alphaT3-1 and rat lactosomatotroph GH3 pituitary tumour cells contained neither PDGF nor PDGF receptors. To further characterize the role of PDGF in TtT/GF cells, the effect of PDGF-AB and -BB on growth and vascular endothelial growth factor-A (VEGF-A) release was studied. Proliferation of TtT/GF cells was weakly but significantly stimulated by PDGF. Both in rat pituitary cell cultures and in TtT/GF cells, PDGF-AB and -BB strongly enhanced VEGF-A secretion. The PI3 kinase inhibitor LY 294002 blocked the increase in VEGF-A. Western immunoblotting confirmed the participation of key components of the PI3 kinase/Akt signal pathway (PDK1, Akt-Ser476) in PDGF-stimulated VEGF production. Thus the PDGF/PDGF receptor system is expressed in folliculostellate cells and is involved in VEGF regulation. Its role in endocrine pituitary tumour cell lines and pituitary adenomas need to be clarified in future studies.

Curcumin acts as anti-tumorigenic and hormone-suppressive agent in murine and human pituitary tumour cells in vitro and in vivo.

Curcumin (diferuloylmethane) is the active ingredient of the spice plant Curcuma longa and has been shown to act anti-tumorigenic in different types of tumours. Therefore, we have studied its effect in pituitary tumour cell lines and adenomas. Proliferation of lactosomatotroph GH3 and somatotroph MtT/S rat pituitary cells as well as of corticotroph AtT20 mouse pituitary cells was inhibited by curcumin in monolayer cell culture and in colony formation assay in soft agar. Fluorescence-activated cell sorting (FACS) analysis demonstrated curcumin-induced cell cycle arrest at G2/M. Analysis of cell cycle proteins by immunoblotting showed reduction in cyclin D(1), cyclin-dependent kinase 4 and no change in p27(kip). FACS analysis with Annexin V-FITC/7-aminoactinomycin D staining demonstrated curcumin-induced early apoptosis after 3, 6, 12 and 24 h treatment and nearly no necrosis. Induction of DNA fragmentation, reduction of Bcl-2 and enhancement of cleaved caspase-3 further confirmed induction of apoptosis by curcumin. Growth of GH3 tumours in athymic nude mice was suppressed by curcumin in vivo. In endocrine pituitary tumour cell lines, GH, ACTH and prolactin production were inhibited by curcumin. Studies in 25 human pituitary adenoma cell cultures have confirmed the anti-tumorigenic and hormone-suppressive effects of curcumin. Altogether, the results described in this report suggest this natural compound as a good candidate for therapeutic use on pituitary tumours.

Immunohistochemical analysis of VEGF-C/VEGFR-3 system and lymphatic vessel extent in normal and adenomatous human pituitary tissues.

The angiogenic growth factor Vascular Endothelial Growth Factor-C (VEGF-C) and its receptor VEGFR-3 are also known to be implicated in the development of lymphatic vessels. We assessed the expression of VEGF-C and VEGFR-3, together with blood and lymphatic vessel extents and proliferation index (PI) values, by immunohistochemistry (IHC) in 6 normal human pituitary glands and 53 pituitary adenomas of different tumour grade, on consecutive tissue sections. VEGF-C was detected in around 10% of the endocrine cells in normal pituitary tissue, while this gland was devoid of lymphatic vascularization and showed very few vessels positive for VEGFR-3. Concerning tumour tissue, most of the adenomas showing VEGF-C immunoreactivity (21/47) were positive in 60% of the tumour cells and the ones positive for VEGFR-3 showed a number of immunostained vessels higher than those observed in the normal pituitary. Most of the tumours positive for VEGFR-3 did not show any LYVE-1 positive vessels (18/53), suggesting that at least in these cases, VEGFR-3 is expressed on blood vessels. Nevertheless, we observed a significant association between low expression of VEGFR-3 and low lymphatic vessel number, suggesting that VEGFR-3 might be involved in the starting of DE NOVO lymphangiogenesis in this tumour type. Moreover, tumours bearing lymphatic vessels showed the tendency to shift towards a more aggressive behaviour (high tumour grade and high PI). In conclusion, the VEGF-C/VEGFR-3 system might be involved in controlling tumour angiogenesis in the pituitary adenomas lacking lymphatic vessels, but may also play a role in starting the process of tumour lymphangiogenesis.

Endocrine disturbances in depression.

Depression is one of the most common psychiatric disorders. For a long time, clinicians suspected a causal link between depression and the endocrine system. The most frequently occurring endocrine abnormality in depressed subjects is hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. CRH and AVP are likely to play a substantial role in the pathophysiology of this disorder, and their receptors appear to be a specific target for future antidepressant drugs. Depression also affects the hypothalamic-pituitary-GH (HPGH) and -thyroid (HPT) axes. Alterations in the reproductive system may also play a role in the pathology of depression. In addition, there is increasing evidence that leptin and neurosteroids, such as DHEA, are implicated in mood disorders.

Bacterial endotoxin (lipopolysaccharide) stimulates interleukin-6 production and inhibits growth of pituitary tumour cells expressing the toll-like receptor 4.

Members of the Toll receptor (Tlr) family have a crucial role in the innate immune response following bacterial infection. The effects of Gram-negative bacteria-derived endotoxins (lipopolysaccharide, LPS) are predominantly mediated by Tlr4, and we have recently shown that pituitary folliculostellate cells express functional Tlr4. In the present study, we investigated whether Tlr4 is also present in normal and transformed endocrine epithelial pituitary cell types. By reverse transcriptase-polymerase chain reaction, Tlr4 mRNA expression was found in some pituitary epithelial tumour cell lines (AtT20, HP75), whereas others were negative (GH3, alphaT3-1). Tlr4 protein was detected by immunohistochemistry in a few epithelial cells in normal human anterior pituitaries and in 26 out of 67 human pituitary tumours analysed. LPS had no effect on adrenocorticotropic hormone secretion in Tlr4-positive AtT20 cells, but it suppressed the growth of these cells in a dose-dependent manner. As expected, neither hormone secretion, nor growth of Tlr4-negative GH3 cells was affected by LPS. In cell cultures of Tlr4-positive pituitary adenomas, LPS dose-dependently stimulated the production of interleukin (IL)-6, which is known to induce growth and hormone production in pituitary tumours. The LPS-induced IL-6 production was blocked by the specific p38alphaMAP kinase inhibitor, SB203580, and by the synthetic glucocorticoid, dexamethasone. The data suggest that, during Gram-negative bacteria-induced infections or inflammatory processes, LPS could affect pituitary tumour pathophysiology and progression in the subset of Tlr4-expressing pituitary adenomas.

Accidental busulfan overdose during conditioning for stem cell transplantation.

High dose busulfan is widely used in preparative regimens for bone marrow transplantation. We describe three cases of accidental busulfan overdosing. Two adults received a single dose of 8 and 18 mg/kg busulfan, respectively. Doses of 9 x 4 mg/kg were ingested by a 14-year-old girl, who experienced seizures. In all cases, no severe liver toxicity including veno-occlusive disease was observed. Plasma samples were obtained from two patients. Busulfan plasma concentrations were far above published values after high-dose busulfan treatment. Busulfan was eliminated by a first-order process. All patients survived these high doses of busulfan and successful transplantation was possible. Two patients died from refractory GvHD on days 91 and 80 after transplantation. One patient is alive in remission after an observation time of 18 months. These cases show that busulfan overdosing may occur and pharmacokinetic evaluation is warranted to estimate risk of early and late toxicity.

Determination of neomycin by LC-tandem mass spectrometry using hydrophilic interaction chromatography.

A specific, and automated method was developed to quantitate neomycin in human serum. Samples were prepared with an automated solid phase extraction (SPE). The hydrophilic interaction chromatography (HILIC) was used for additional sample cleanup and baseline separation. The analyte neomycin was detected with electrospray ionisation tandem mass spectrometry (ESI-MS-MS). Using a volume of 500 microl biological sample the lower limit of quantification was 100 ng/ml. The described HILIC-MS-MS method is suitable for clinical and pharmcokinetical investigations of neomycin.

Estradiol stimulates vascular endothelial growth factor and interleukin-6 in human lactotroph and lactosomatotroph pituitary adenomas.

Estrogens are considered to be critically involved in lactotroph and lactosomatotroph pituitary tumor development. In addition to direct effects, estradiol-induced tumor formation may involve alterations in growth factor and cytokine production. We have studied whether estradiol stimulates the production of the angiogenic vascular endothelial growth factor and the potential tumor progression factor interleukin-6 in 5 lactotroph (LA) and 5 lactosomatotroph (LSA) human pituitary adenoma cell cultures. All tumors secreted heterogenous basal amounts of VEGF (18.0 +/- 1.4 to 425 +/- 26 pg/ml per 24 h) and IL-6 (18.1 +/- 1.5 to 604 +/- 17 pg/ml per 24 h). Estradiol (100 nM) significantly enhanced VEGF release in all LA and LSA cell cultures (47 to 168 % above basal). IL-6 secretion was stimulated in 3 out of 5 LA and in all LSA cell cultures (31 to 287 % above basal). In cell cultures obtained from tumors from which sufficient cells could be isolated, a dose-dependent effect of estradiol (1 to 100 nM) on VEGF and IL-6 production was observed. Stimulation of IL-6 and/or VEGF secretion by estradiol in the majority of human lactotroph and lactosomatotroph adenoma cell cultures studied, suggests that estrogens may contribute to adenoma expansion through the stimulation of these auto-/paracrine-acting adenoma progression factors.

Liquid chromatographic method for detection and quantitation of STI-571 and its main metabolite N-desmethyl-STI in plasma, urine, cerebrospinal fluid, culture medium and cell preparations.

An isocratic online-enrichment HPLC-assay was developed allowing for the simple and fast separation and quantitation of STI-571 and its main metabolite N-desmethyl-STI (N-DesM-STI) in plasma, urine, cerebrospinal fluid (CSF), culture media and cell preparations in various concentrations using UV-detection at 260 nm. The analytical procedure consists of an online concentration of STI-571 and N-DesM-STI in the HPLC system followed by the elution on a ZirChrom-PBD analytical column. Time of analysis is 40 min including the enrichment time of 5 min. The detection limit is 10 ng/ml in plasma, CSF, culture medium (RPMI) and 25 ng/ml in urine for both STI-571 and N-DesM-STI. The intra-day precision, as expressed by the coefficient of variation (CV), in plasma samples ranges between 1.74 and 8.60% for STI-571 and 1.45 and 8.87% for N-DesM-STI. The corresponding values for urine measurements are 2.17-7.54% (STI-571) and 1.31-9.51% (N-DesM-STI). The inter-day precision analyzed over a 7-month time period was 8.31% (STI-571) or 6.88% (N-DesM-STI) and 16.45% (STI-571) or 14.83% (N-DesM-STI) for a concentration of 1000 ng/ml in plasma and 750 ng/ml in urine, respectively. Moreover, we demonstrate that with an alternative, but more time and labor consuming sample preparation and the implementation of electrochemical detection, a detection limit < 10 ng/ml can be achieved. The method described was used to perform pharmacokinetic measurements of STI-571 and N-desmethyl-STI in patient samples and for kinetic measurements of intracellular STI-571 and N-DesM-STI following in vitro incubation.

Laminin inhibits lactotroph proliferation and is reduced in early prolactinoma development.

Laminin is a component of the extracellular matrix (ECM) that regulates cell proliferation and hormone secretion. Here we describe the effects of laminin on prolactin secretion in normal and tumor cells and analyze laminin expression pattern during prolactinoma development. Prolactin secretion and cell proliferation were inhibited by laminin in GH3 cells. In contrast, no effect was observed in normal pituitary cells. Laminin showed a dynamic expression pattern during prolactinoma development, which was: (a) strong in normal pituitaries from wild type or dopamine D2 receptor deficient mice, (b) lower in pituitary hyperplasia and (c) markedly reduced in prolactinomas from D2R -/- mice. A similar gradual decrease in laminin was found by comparing normal human pituitaries, human pituitary hyperplasia and human prolactinomas. These results show dynamic changes of laminin expression during prolactinoma formation which, due to laminin action on PRL production and cell proliferation, indicate a possible role for laminin in prolactinoma development.

Transforming growth factor-beta stimulates vascular endothelial growth factor production by folliculostellate pituitary cells.

TGF-beta isoforms are expressed in the anterior pituitary and modulate the growth and function of endocrine pituitary cells. Recently, TGF-beta has been shown to stimulate growth and basic fibroblast growth factor secretion in nonendocrine folliculostellate (FS) pituitary cells. We therefore studied whether the production of FS cell-derived vascular endothelial growth factor (VEGF), the most important regulator of vascular permeability and angiogenesis, is affected by TGF-beta. We observed by RT-PCR that TtT/GF cells, which are FS mouse pituitary tumor cells, synthesize TGF-beta1, -beta2, and -beta3. They also express TGF-beta receptors types 1 and 2, as well as Smad2, Smad3, and Smad4 proteins, which are essential for TGF-betabinding and signaling. Stimulation of TtT/GF cells with either TGF-beta1 or TGF-beta3 induced a rapid translocation of Smad2 into the cell nuclei. Both TGF-beta isoforms dose dependently stimulated VEGF production in TtT/GF cells, but not in lactosomatotroph GH3 cells. Time-course studies and suppression of TGF-beta-induced VEGF production by cycloheximide suggest that TGF-beta induces de novo synthesis of VEGF in folliculostellate cells, which is completely blocked by dexamethasone. In primary rat pituitary cell cultures, TGF-beta1 and -beta3 stimulated VEGF production. TGF-beta stimulation of VEGF production by folliculostellate cells could modulate intrapituitary vascular permeability and integrity as well as angiogenesis in an auto-/paracrine manner.

The role of endothelins in the regulation of pituitary function.

The different members of the endothelin peptide family exhibit potent, long-lasting vasoconstrictive effects and thus play a central role in blood pressure regulation. However, endothelins have also been shown to modulate renal, cardiac and immune functions under physiological and pathophysiological conditions. In addition, endothelins are thought to be involved in the progression of some types of tumours. Soon after their discovery in 1988, it was shown that endothelins affect hormone release in the pituitary. Moreover, the intrapituitary production and expression of both endothelins and endothelin receptors have been described. This review summarises the present day knowledge concerning the expression and regulation of intrapituitary endothelins and their receptors. In addition, the effects of endothelins on hormone production by anterior, intermediate and posterior pituitary cell types are reviewed and their importance for pituitary physiology and pathophysiology is discussed.

The intrapituitary stimulatory effect of lipopolysaccharide on ACTH secretion is mediated by paracrine-acting IL-6.

During infection/inflammation bacterial lipopolysaccharide (LPS) activates the immune system and thus enhances the level of circulating cytokines. These circulating cytokines induce adaptive processes within the endocrine system and in particular stimulate the HPA axis to increase the level of anti-inflammatory-acting glucocorticoids in the circulation. We have shown recently that LPS stimulates intrapituitary IL-6 production in folliculostellate cells via specific receptors and the p38a mitogen-activated protein kinase/nuclear factor-kappa B pathway. To test the physiological relevance of these findings, we studied whether LPS could enhance ACTH secretion via paracrine-acting intrapituitary IL-6. Lipopolysaccharide stimulated IL-6 secretion both in monolayer and aggregate mouse pituitary cell cultures, but only in aggregates, ACTH secretion was significantly enhanced by LPS. Other hormones, such as GH or PRL, were less stimulated by LPS. My4, an antibody that blocks the interaction of LPS with the LPS receptor CD14, suppressed both LPS-induced IL-6 and ACTH secretion in aggregate cultures. A neutralizing antibody against mouse IL-6 also inhibited LPS-induced ACTH secretion in aggregates. In mouse pituitary fragments, LPS-induced ACTH secretion was blocked by My4 and IL-6 antibodies, identically to re-aggregate cell cultures. LPS-induced ACTH secretion, mediated by intrapituitary IL-6, may represent a pituitary-specific mechanism that stimulates the HPA axis during infection/inflammation.