Increased interleukin-2 levels during standard TRH test in man

Diagnosis of hypoprolactinemia

Prolactin is a polypeptide hormone composed of 199 amino acids, synthesized by lactotroph cells. Its primary effects are on the mammary gland and gonadal axes, but it also influences different organs and systems, particularly metabolic functions. Current literature has mainly focused on the diagnosis, monitoring, and treatment of hyperprolactinemia. Due to the lack of a well-established effective treatment for hypoprolactinemia, it is not clinically emphasized. Therefore, data on its diagnosis is limited. Hypoprolactinemia has been associated with metabolic dysfunctions such as type 2 diabetes mellitus, fatty liver, dyslipidemia, fertility problems, sexual dysfunction, and increased cardiovascular disease. While often seen as a part of combined hormone deficiencies due to pituitary damage, isolated prolactin deficiency is rare. Hypoprolactinemia can serve as a marker for extensive pituitary gland damage and dysfunction.Low or undetectable serum prolactin levels and the absence of a sufficient prolactin peak in the thyrotropin-releasing hormone (TRH) stimulation test are considered diagnostic for hypoprolactinemia. Gender appears to influence both basal prolactin levels and TRH stimulation test responses. Basal prolactin levels of, at least, 5 ng/mL for males and 7 ng/mL for females can be used as cut-off levels for normal prolactin reserve. Minimum peak prolactin responses of 18 ng/mL for males and 41 ng/mL for females to TRH stimulation can exclude hypoprolactinemia. However, larger population studies across different age groups and sexes are needed to better define normal basal prolactin levels and prolactin responses to the TRH stimulation test.

The thyrotropin-releasing hormone (TRH)-immune system homeostatic hypothesis

Decades of research have established that the biological functions of thyrotropin-releasing hormone (TRH) extend far beyond its role as a regulator of the hypothalamic-pituitary-thyroid axis. Gary et al. [Gary, K.A., Sevarino, K.A., Yarbrough, G.G., Prange, A.J. Jr., Winokur, A. (2003). The thyrotropin-releasing hormone (TRH) hypothesis of homeostatic regulation: implications for TRH-based therapeutics. J Pharmacol Exp Ther 305(2):410-416.] and Yarbrough et al. [Yarbrough, G.G., Kamath, J., Winokur, A., Prange, A.J. Jr. (2007). Thyrotropin-releasing hormone (TRH) in the neuroaxis: therapeutic effects reflect physiological functions and molecular actions. Med Hypotheses 69(6):1249-1256.] provided a functional framework, predicated on its global homeostatic influences, to conceptualize the numerous interactions of TRH with the central nervous system (CNS) and endocrine system. Herein, we profer a similar analysis to interactions of TRH with the immune system. Autocrine/paracrine cellular signaling motifs of TRH and TRH receptors are expressed in several tissues and organs of the immune system. Consistent with this functional distribution, in vitro and in vivo evidence suggests a critical role for TRH during the developmental stages of the immune system as well as its numerous interactions with the fully developed immune system. Considerable evidence supports a pivotal role for TRH in the pathophysiology of the inflammatory process with specific relevance to the "cytokine-induced sickness behavior" paradigm. These findings, combined with a number of documented clinical actions of TRH strongly support a potential utility of TRH-based therapeutics in select inflammatory disorders. Similar to its global role in behavioral and energy homeostasis a homeostatic role for TRH in its interactions with the immune system is consonant with the large body of available data. Recent advances in the field of immunology provide a significant opportunity for investigation of the TRH-immune system homeostatic hypothesis. Moreover, this hypothesis may provide a foundation for the development of TRH-based therapeutics for certain medical and psychiatric disorders involving immune dysfunction.

Increased pro-thyrotropin-releasing hormone transcription in hypophysiotropic neurons of Lewis rats

The expression of pro-thyrotropin-releasing hormone (pro-TRH) mRNA was analyzed in the hypothalamus of inflammatory susceptible LEW/N and resistant F344/N rats at baseline and in adrenalectomized and lipopolysaccharide-treated animals. In saline-treated control animals, increased pro-TRH transcription was detected in LEW/N with respect to F344/N rats. This increased LEW/N pro-TRH expression was stable regardless of condition in contrast to F344/N increased pro-TRH transcription post-adrenalectomy and decreased pro-TRH after lipopolysaccharide administration. The LEW/N increase in pro-TRH mRNA was independent of changes in hormonal status suggesting alteration of the thyroid axis at the central level in this strain.

Effect of thyroliberin on the course of experimental candidosis in mice

Thyroliberin (TRH) is one of the hormones, which affect immunologic processes. This hormone was studied in experimental subacute candidosis in mice. BALB/c males were given intraperitoneally single dose of Candida albicans cells (1 x 10(7) to 1 x 10(9) cfu of strain no. 244-33 ATCC). The animals from the experimental groups were injected subcutaneously, after 24 h from inoculation, dose of 10 microg TRH in 0.2 ml 0.9% NaCl, seven times at 24 h intervals. The control animals were given respectively 0.2 ml of physiologic NaCl solution. We have found that the examined hormone significantly decreases mortality in these animals (LD50 C. albicans for mice treated with TRH was three times higher than that in the control groups), prolongs mean survival time for mice and decreases the intensity of fungal invasion of the animal organs.

The effect of LHRH and TRH on human interferon-gamma production in vivo and in vitro

Accumulating evidence suggests that hypothalamic luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) are two hypophysiotropic factors which modulate the immune response. The aim of the present study was to determine the in vivo effects of an intravenous bolus of LHRH and TRH on plasma interferon (IFN)-gamma production in five normoprolactinemic women with irregular menstrual cycles. We also determined prolactin (PRL), thyrotropin (TSH), follicle stimulating hormone (FSH), and luteinizing hormone (LH) levels before and after intravenous administration of LHRH and TRH. The results demonstrate that intravenous bolus of LHRH/TRH increases plasma IFN-gamma levels, with the maximum response 45 min after in vivo administration of hypothalamic peptides and after peak levels of adenohypophyseal hormones (PRL: 15 min; TSH: 30 min; FSH: 30 min; LH: 30 min). In order to investigate a possible direct action of hypothalamic hormones on immune cells, we also evaluated, in the same subjects, the influence of LHRH and TRH on IFN-gamma production by human peripheral blood mononuclear cells (PBMCs), collected before the intravenous administration of the peptides and stimulated in vitro with bacterial superantigen staphylococcal enterotoxin A (SEA) and concanavalin A (Con A). LHRH and TRH, separately and together, significantly enhanced in vitro IFN-gamma production by SEA- and ConA-activated PBMCs. The present results suggest that hypothalamic peptides (LHRH and TRH) directly, and/or indirectly pituitary hormones (PRL, TSH, FSH, and LH) or IL-2, have stimulatory effect on IFN-gamma producing cells and are further evidence of interactions between the neuroendocrine and immune systems.

Effects of hCG and beta-hCG on IL-2 and sIL-2R secretion from human peripheral blood mononuclear cells: a dose-response study in vitro

The effects of human chorionic gonadotropin (hCG) as well as beta-subunit of hCG (B-hCG) in concentrations of: 80,000/25,000; 500; 50; 5 mIU/ml on in vitro release of interleukin-2 (IL-2) and soluble interleukin-2 receptor (sIL-2R) from resting or phytohemagglutinin (PHA) activated human peripheral blood mononuclear cells (PBMC) were studied. Both the interleukins were measured in supernatants of human PBMC by quantitative sandwich enzyme immunoassay method (ELISA). We found that hCG in the dilutions of 80,000 mIU/ml (P < 0.01) and 5 mIU/ml (P < 0.05) diminished IL-2 secretion only from PHA activated PBMC. beta-hCG in concentrations of 5 mIU/ml (P < 0.05), 500 mIU/ml (P < 0.01) and 25,000 mIU/ml (P < 0.05) also diminished IL-2 secretion from PHA activated PBMC, and only in a dilution of 25,000 mIU/ml (P < 0.05) from resting PBMC. Simultaneously, hCG in concentration of 80,000 mIU/ml (P < 0.01) potentiated the release of sIL-2R into supernatants from resting and PHA activated PBMC, but in concentration of 50 mIU/ml (P < 0.05) slightly depressed the secretion of IL-2 from PHA activated PBMC cultures. beta-hCG in dilution of 25,000 mIU/ml (P < 0.001) stimulated the release of sIL-2R from resting or PHA activated PBMC. beta-hCG had also inhibitory effect on sIL-2R secretion from resting (in a dilution of 50 mIU/ml; P < 0.05) and PHA activated (500 mIU/ml; P < 0.01) PBMC. The inhibitory effect of very high concentrations of hCG and beta-hCG on IL-2 secretion together with their stimulatory effect on sIL-2R release from PBMC may be an important event during the human pregnancy and various cancers.

The immune effects of neuropeptides

Current evidence indicates that the neuroendocrine system is the highest regulator of immune/inflammatory reactions. Prolactin and growth hormone stimulate the production of leukocytes, including lymphocytes, and maintain immunocompetence. The hypothalamus-pituitary-adrenal axis constitutes the most powerful circuit regulating the immune system. The neuropeptides constituting this axis, namely corticotrophin releasing factor, adrenocorticotrophic hormone, alpha-melanocyte stimulating hormone, and beta-endorphin are powerful immunoregulators, which have a direct regulatory effect on lymphoid cells, regulating immune reactions by the stimulation of immunoregulatory hormones (glucocorticoids) and also by acting on the central nervous system which in turn generates immunoregulatory nerve impulses. Peptidergic nerves are major regulators of the inflammatory response. Substance P and calcitonin gene-related peptide are pro-inflammatory mediators and somatostatin is anti-inflammatory. The neuroendocrine regulation of the inflammatory response is of major significance from the point of view of immune homeostasis. Malfunction of this circuit leads to disease and often is life-threatening. The immune system emits signals towards the neuroendocrine system by cytokine mediators which reach significant blood levels (cytokine-hormones) during systemic immune/inflammatory reactions. Interleukin-1, -6, and TNF-alpha are the major cytokine hormones mediating the acute phase response. These cytokines induce profound neuroendocrine and metabolic changes by interacting with the central nervous system and with many other organs and tissues in the body. Corticotrophin releasing factor functions under these conditions as a major co-ordinator of the response and is responsible for activating the ACTH-adrenal axis for regulating fever and for other CNS effects leading to a sympathetic outflow. Increased ACTH secretion leads to glucocorticoid production. alpha-melanocyte stimulating hormone functions under these conditions as a cytokine antagonist and an anti-pyretic hormone. The sympathetic outflow, in conjunction with increased adrenal activity. leads to the elevation of catecholamines in the bloodstream and in tissues. Current evidence suggests that neuroimmune mechanisms are essential in normal physiology, such as tissue turnover, involution, atrophy, intestinal function, and reproduction. Host defence against infection, trauma and shock relies heavily on the neuroimmunoregulatory network. Moreover, abnormalities of neuroimmunoregulation contribute to the aetiology of autoimmune disease, chronic inflammatory disease, immunodeficiency, allergy, and asthma. Finally, neuroimmune mechanisms play an important role in regeneration and healing.

Immunomodulation of peripheral lymphocytes by hormones of the hypothalamus-pituitary-thyroid axis

The aim of this review is to provide a comprehensive examination of the current literature describing the immunoregulatory effects on the peripheral immune system by the hormones that comprise the hypothalamic-pituitary-thyroid (HPT) axis. This article discusses the effects of the HPT axis hormones on the peripheral lymphoid tissues and the immune responses mediated by the cells that comprise these lymphoid tissues. Neuroendocrine dysfunction in the HPT axis, either naturally or experimentally induced, and the resulting immune dysfunction are also discussed. Emphasis in this article is placed on the most recent study findings and those that provide a unique or novel way of evaluating HPT hormone effects on the immune system. Our knowledge of the immunoregulatory effects of the hormones that comprise the HPT axis has grown tremendously in the last 10 years. As can be seen in this review, the immunoregulatory effects of the HPT axis hormones are quite diverse and influence most, if not all, aspects of immune system physiology. The continued exploration of the bidirectional circuitry between the immune and neuroendocrine systems may allow for development of appropriate prophylactic procedures that prevent dysfunction in both systems.

TRH receptor on immune cells: in vitro and in vivo stimulation of human lymphocyte and rat splenocyte DNA synthesis by TRH

This work examined whether (1) immune cells express thyrotrophin releasing hormone (TRH) receptor mRNA and (2) TRH modulates lymphocyte activation. By Northern blot of RNA extracted from human peripheral blood mononuclear cells (PBMC) and rat splenocytes, a single TRH receptor mRNA band of about 3.8 kb (identical to that obtained from pituitary cells) was obtained, under both basal and stimulated conditions. A significant increase in DNA synthesis was observed in phytohemagglutinin-stimulated PBMC and concanavalin A (Con A) stimulated splenocytes when TRH (10(-6) M-10(-12) M) was added. After 5, 30, 60, 180 min and 24 h of TRH administration in vivo, a significant increase in the rat splenocyte proliferative response to Con A was observed. In vivo administration of anti-rat TSH antibody (1/1000) blocked the increase observed after 30 min of TRH administration on the Con A stimulated splenocyte response. TRH possess immunostimulatory functions directly via its receptor and indirectly via release of other immunostimulatory factors such as thyrotrophin.

Somatostatin (SRIF) stimulates the release of interleukin-6 (IL-6) from human peripheral blood monocytes (PBM) in vitro

Recent evidence has revealed that various neuropeptides appear to have distinct roles as immunomodulators. The aim of this study was to evaluate the role of hypothalamic neuropeptides (thyreoliberin [TRH], somatostatin [SRIF], and gonadoliberin [LH-RH]) on the secretion of interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) from lipopolysaccharide (LPS) activated human peripheral blood monocytes (PM) cultured in vitro. LPS in concentration 1.5 micrograms/ml stimulated PBM to release IL-1 beta or IL-6 into the supernatants. SRIF in concentrations from 10(-8)M to 10(-10)M (but neither RH nor LH-RH in the same concentrations) potentiated the release of IL-6 from PBM. None of the tested neuropeptides stimulated the release of IL-1 beta from LPS activated human monocytes. These data indicate that SRIF in physiological or pharmacological concentrations which activate the release of IL-6 from PBM may be one of the regulators of immune response in humans.