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      Regulation of pituitary function by cytokines.

      Hormone research
      Adenoma, etiology, Animals, Cell Aging, physiology, Cytokines, metabolism, Humans, Interleukin-6, Models, Biological, Pituitary Gland, growth & development, pathology, Pituitary Neoplasms

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          Abstract

          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. Copyright 2009 S. Karger AG, Basel.

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          Most cited references52

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          MIF is a pituitary-derived cytokine that potentiates lethal endotoxaemia.

          Cytokines are critical in the often fatal cascade of events that cause septic shock. One regulatory system that is likely to be important in controlling inflammatory responses is the neuroendocrine axis. The pituitary, for example, is ideally situated to integrate central and peripheral stimuli, and initiates the increase in systemic glucocorticoids that accompanies host stress responses. To assess further the contribution of the pituitary to systemic inflammatory processes, we examined the secretory profile of cultured pituitary cells and whole pituitaries in vivo after stimulation with bacterial lipopolysaccharide (LPS). Here we identify macrophage migration inhibitory factor (MIF) as a major secreted protein release by anterior pituitary cells in response to LPS stimulation. Serum analysis of control, hypophysectomized and T-cell-deficient (nude) mice suggests that pituitary-derived MIF contributes to circulating MIF present in the post-acute phase of endotoxaemia. Recombinant murine MIF greatly enhances lethality when co-injected with LPS and anti-MIF antibody confers full protection against lethal endotoxaemia. We conclude that MIF plays a central role in the toxic response to endotoxaemia and possibly septic shock.
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            Early involvement of estrogen-induced pituitary tumor transforming gene and fibroblast growth factor expression in prolactinoma pathogenesis.

            Pituitary tumors are commonly encountered, and result from clonal expansion of a single mutated cell. Hypothalamic hormones, local growth factors and circulating sex steroid hormones promote pituitary tumor growth and expansion into large invasive tumors. Estrogen acting directly through its receptor and by stimulation of fibroblast growth factor regulates prolactin synthesis and secretion. Fibroblast growth factor-2 (bFGF) modulates angiogenesis, tumor formation and progression in many tissues, including the anterior pituitary. A pituitary tumor-derived transforming gene (PTTG) has been isolated, which is tumorigenic in vivo, regulates bFGF secretion, and inhibits chromatid separation. The human PTTG family consists of at least three homologous genes, of which PTTG1 is located on chromosome 5q33 and is expressed at low levels in most normal human tissues but is highly expressed in malignant human cell lines and in pituitary tumors. We report here that pituitary pttg is regulated in vivo and in vitro by estrogen. Maximal induction of rat pituitary pttg mRNA in vivo occurred early in pituitary transformation (normal cell to hypertrophic/hyperplastic cell), coincident with bFGF and vascular endothelial growth factor induction and pituitary angiogenesis. We also demonstrate that pttg expression is induced by bFGF, and show concordant pttg and bFGF expression in experimental and human pituitary adenomas. As bFGF and estrogen both induce pttg, and pttg expression coincides with the early lactotrophic hyperplastic response, angiogenesis and prolactinoma development, we propose a previously unknown paracrine growth factor-mediated mechanism for pituitary tumor pathogenesis and potentially other estrogen-regulated tumors.
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              Release of multiple hormones by a direct action of interleukin-1 on pituitary cells.

              Exposure to bacterial endotoxins has long been known to stimulate the release of anterior pituitary hormones; administration of endotoxin was at one time a common clinical test of anterior pituitary function. Endotoxin is a potent stimulus for production of the endogenous pyrogenic protein, interleukin-1 (IL-1), by macrophages and monocytes. The possibility that IL-1 has a direct effect on the secretion of hormones by rat pituitary cells in a monolayer culture was investigated. Recombinant human IL-1 beta stimulated the secretion of adrenocorticotropic hormone, luteinizing hormone, growth hormone, and thyroid-stimulating hormone. Increased hormone secretion into culture supernatants was found with IL-1 concentrations ranging from 10(-9) M to 10(-12) M. Prolactin secretion by the monolayers was inhibited by similar doses. These concentrations of IL-1 are within the range reported for IL-1 in serum, suggesting that IL-1 generated peripherally by mononuclear immune cells may act directly on anterior pituitary cells to modulate hormone secretion in vivo. Incubation of IL-1 solutions with antibody to IL-1 neutralized these actions. These pituitary effects of IL-1 suggest that this monokine may be an important regulator of the metabolic adaptations to infectious stressors.
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