Distribution of thyrotropin-releasing hormone receptor mRNA in rat peripheral tissues

Thyrotropin-Releasing Hormone (TRH) and Somatostatin (SST), but not Growth Hormone-Releasing Hormone (GHRH) nor Ghrelin (GHRL), Regulate Expression and Release of Immune Growth Hormone (GH) from Chicken Bursal B-Lymphocyte Cultures

It is known that growth hormone (GH) is expressed in immune cells, where it exerts immunomodulatory effects. However, the mechanisms of expression and release of GH in the immune system remain unclear. We analyzed the effect of growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), ghrelin (GHRL), and somatostatin (SST) upon GH mRNA expression, intracellular and released GH, Ser133-phosphorylation of CREB (pCREB^S133), intracellular Ca²⁺ levels, as well as B-cell activating factor (BAFF) mRNA expression in bursal B-lymphocytes (BBLs) cell cultures since several GH secretagogues, as well as their corresponding receptors (-R), are expressed in B-lymphocytes of several species. The expression of TRH/TRH-R, ghrelin/GHS-R1a, and SST/SST-Rs (Subtypes 1 to 5) was observed in BBLs by RT-PCR and immunocytochemistry (ICC), whereas GHRH/GHRH-R were absent in these cells. We found that TRH treatment significantly increased local GH mRNA expression and CREB phosphorylation. Conversely, SST decreased GH mRNA expression. Additionally, when added together, SST prevented TRH-induced GH mRNA expression, but no changes were observed in pCREB^S133 levels. Furthermore, TRH stimulated GH release to the culture media, while SST increased the intracellular content of this hormone. Interestingly, SST inhibited TRH-induced GH release in a dose-dependent manner. The coaddition of TRH and SST decreased the intracellular content of GH. After 10 min. of incubation with either TRH or SST, the intracellular calcium levels significantly decreased, but they were increased at 60 min. However, the combined treatment with both peptides maintained the Ca²⁺ levels reduced up to 60-min. of incubation. On the other hand, BAFF cytokine mRNA expression was significantly increased by TRH administration. Altogether, our results suggest that TRH and SST are implicated in the regulation of GH expression and release in BBL cultures, which also involve changes in pCREB^S133 and intracellular Ca²⁺ concentration. It is likely that TRH, SST, and GH exert autocrine/paracrine immunomodulatory actions and participate in the maturation of chicken BBLs.

The forgotten effects of thyrotropin-releasing hormone: Metabolic functions and medical applications

Thyrotropin-releasing hormone (TRH) causes a variety of thyroidal and non-thyroidal effects, the best known being the feedback regulation of thyroid hormone levels. This was employed in the TRH stimulation test, which is currently little used. The role of TRH as a cancer biomarker is minor, but exaggerated responses to TSH and prolactin levels in breast cancer led to the hypothesis of a potential role for TRH in the pathogenesis of this disease. TRH is a rapidly degraded peptide with multiple targets, limiting its suitability as a biomarker and drug candidate. Although some studies reported efficacy in neural diseases (depression, spinal cord injury, amyotrophic lateral sclerosis, etc.), therapeutic use of TRH is presently restricted to spinocerebellar degenerative disease. Regulation of TRH production in the hypothalamus, patterns of expression of TRH and its receptor in the body, its role in energy metabolism and in prolactin secretion are addressed in this review.

Increased TRH and TRH-like peptide release in rat brain and peripheral tissues during proestrus/estrus

Women are at greater risk for major depression, PTSD, and other anxiety disorders. ERβ-selective agonists for the treatment of these disorders are the focus of pharmacologic development and clinical testing. Estradiol and its metabolites contribute to the neuroprotective effects of this steroid class, particularly in men, due to local conversion of testosterone to estiradiol in key brain regions which are predisposed to neurodegenerative diseases. We have used young adult female Sprague-Dawley rats to assess the role of TRH and TRH-like peptides, with the general structure pGlu-X-Pro-NH2 where "X" can be any amino acid residue, as mediators of the neurobiochemical effects of estradiol. The neuroprotective TRH and TRH-like peptides are coreleased with excitotoxic glutamate by glutamatergic neurons which contribute importantly to the regulation of the estrus cycle. The levels of TRH and TRH-like peptides during proestrus and/or estrus in the 12 brain regions analyzed were significantly decreased (due to accelerated release) 106 times but increased only 25 times when compared to the corresponding levels during diestrus days 1 and 2. These changes, listed by brain region in the order of decreasing number of significant decreases (↓) and/or increases (↑), were: striatum (20↓,1↑), medulla oblongata (16↓,2↑), amygdala (14↓,1↑), cerebellum (13↓,1↑), hypothalamus (12↓,1↑), entorhinal cortex (6↓,6↑), posterior cingulate (10↓,1↑), frontal cortex (3↓,5↑), nucleus accumbens (5↓,3↑), hippocampus (5↓,2↑), anterior cingulate (2↓,1↑), and piriform cortex (1↑). In peripheral tissues the corresponding changes were: ovaries (23↓), uterus (16↓,1↑), adrenals (11↓,3↑), and pancreas (1↓,6↑). We conclude that these peptides may be downstream mediators of some of the therapeutic effects of estrogen.

Hypothalamic neurohormones and immune responses

The aim of this review is to provide a comprehensive examination of the current literature describing the neural-immune interactions, with emphasis on the most recent findings of the effects of neurohormones on immune system. Particularly, the role of hypothalamic hormones such as Thyrotropin-releasing hormone (TRH), Corticotropin-releasing hormone (CRH) and Gonadotropin-releasing hormone (GnRH). In the past few years, interest has been raised in extrapituitary actions of these neurohormones due to their receptors have been found in many non-pituitary tissues. Also, the receptors are present in immune cells, suggesting an autocrine or paracrine role within the immune system. In general, these neurohormones have been reported to exert immunomodulatory effects on cell proliferation, immune mediators release and cell function. The implications of these findings in understanding the network of hypothalamic neuropeptides and immune system are discussed.

TRH-like peptides

TRH-like peptides are characterized by substitution of basic amino acid histidine (related to authentic TRH) with neutral or acidic amino acid, like glutamic acid, phenylalanine, glutamine, tyrosine, leucin, valin, aspartic acid and asparagine. The presence of extrahypothalamic TRH-like peptides was reported in peripheral tissues including gastrointestinal tract, placenta, neural tissues, male reproductive system and certain endocrine tissues. Work deals with the biological function of TRH-like peptides in different parts of organisms where various mechanisms may serve for realisation of biological function of TRH-like peptides as negative feedback to the pituitary exerted by the TRH-like peptides, the role of pEEPam such as fertilization-promoting peptide, the mechanism influencing the proliferative ability of prostatic tissues, the neuroprotective and antidepressant function of TRH-like peptides in brain and the regulation of thyroid status by TRH-like peptides.

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.

Ontogeny of prolyl endopeptidase and pyroglutamyl peptidase I in rat tissues

Prolyl endopeptidase and pyroglutamyl peptidase I are enzymes which participate in the degradation of thyrotropin-releasing hormone (TRH), a hormone which is thought to play an important role in the development of organs and tissues. Here, we have characterized the ontogeny of TRH degrading enzyme activity in the brain cortex, lung, heart, kidney and liver. Overall, prolyl endopeptidase activity was found to be 2 to 5 fold higher in newborn vs. adult rat tissues, with the exception of the soluble form in the liver and the particulate form in the lung. In contrast, the developmental profile of pyroglutamyl peptidase I activity was found to be more variable and tissue dependent. These results corroborate the idea that both enzymes play important, tissue-specific roles during the development and maturation of rat organs.

Ontogeny of prolyl endopeptidase and pyroglutamyl peptidase I in rat tissues

Prolyl endopeptidase and pyroglutamyl peptidase I are enzymes which participate in the degradation of thyrotropin-releasing hormone (TRH), a hormone which is thought to play an important role in the development of organs and tissues. Here, we have characterized the ontogeny of TRH degrading enzyme activity in the brain cortex, lung, heart, kidney and liver. Overall, prolyl endopeptidase activity was found to be 2 to 5 fold higher in newborn vs. adult rat tissues, with the exception of the soluble form in the liver and the particulate form in the lung. In contrast, the developmental profile of pyroglutamyl peptidase I activity was found to be more variable and tissue dependent. These results corroborate the idea that both enzymes play important, tissue-specific roles during the development and maturation of rat organs.

Gene and protein expression in the myometrium in pregnancy and labor

Microarray technologies widen our comprehension of the major structural and metabolic transformations which affect the myometrium from the very beginning of pregnancy until parturition. The results are coherent with the mass of information which was accumulated previously, primarily on the basis of studies of selected critical factors. They highlight the activation of precise signaling pathways, some of which may have been previously under evaluated. The remodelling and maturation processes that the myometrium undergoes in pregnancy appear clearly as phenomena which last during the full course of gestation. Comparatively, the onset of labor is perhaps the phenomenon which remains the least well described by these methods of analysis. Nevertheless, genomic studies constitute a necessary first step of orientation and help establishing new links between the generic signaling pathways that are activated during the normal or pathological gestation. These studies also represent an indicative step that will have to be paralleled, in the future, with the results of the systematic proteomic analysis of the myometrium.

Effects of thyrotropin-releasing hormone on human myometrium and umbilical vasculature in vitro

OBJECTIVE

The purpose of this study was to investigate the direct effects of thyrotropin-releasing hormone on isolated human myometrium that was obtained during pregnancy and on human umbilical vasculature in vitro.

STUDY DESIGN

Isolated human myometrial strips were dissected from biopsy specimens that were obtained at elective cesarean delivery and suspended for isometric recording under physiologic conditions. The effects of cumulative additions of thyrotropin-releasing hormone (10(-9)-10(-4) mol/L) on oxytocin-induced myometrial contractility were evaluated. The effects of thyrotropin-releasing hormone (10(-9)-10(-4) mol/L) on umbilical vessel (artery and vein) resistance in vitro were investigated with the use of isolated ring preparations.

RESULTS

Thyrotropin-releasing hormone exerted a significant concentration-dependent relaxant effect on pregnant human myometrial tissue, which ranged from 3.54% (10(-9) mol/L, P=.935) to a net cumulative total of 21.06% (10(-4) mol/L, P<.001). Thyrotropin-releasing hormone also exerted a concentration-dependent relaxant effect on human umbilical vasculature that ranged from 12.51% (10(-9) mol/L, P=.994) to a net cumulative total of 23.27%+/-4.87% (SEM, 10(-4) mol/L, P<.01) in umbilical artery. For umbilical vein, the relaxant effect ranged from 1.80% (10(-9) mol/L, P=.998) to a net cumulative total of 14.64% (10(-4) mol/L, P<.009).

CONCLUSION

Thyrotropin-releasing hormone exerts a significant relaxant effect in human myometrium and in human umbilical vasculature and highlights a potential physiologic role for this neuropeptide in these tissues. These findings have clinical implications for the therapeutic use of thyrotropin-releasing hormone antenatally.

Mice lacking the thyrotropin-releasing hormone gene: what do they tell us?

Thyrotropin-releasing hormone (TRH) is localized in the brain hypothalamus and stimulates the secretion and synthesis of pituitary thyrotropin (TSH). Although TRH deficiency caused by artificial hypothalamic destructions has been reported to result in significant decreases in TSH secretion in rodents, clinical observations from the patients with possible TRH deficiency did not entirely agree with these animal results. Because of its ubiquitous distribution throughout the brain and in the peripheral tissues, TRH has been suggested to possess a wide variety of functions in these regions. However, the neurobehavioral and peripheral actions of TRH still remains to be established. It has been, therefore, anticipated that detailed analysis of TRH-knockout mice might provide insight into the physiological significance of endogenous TRH. The present review focuses on the phenotypic findings of mice deficient in TRH.

The human neuroendocrine thyrotropin-releasing hormone receptor promoter is activated by the haematopoietic transcription factor c-Myb

Thyrotropin-releasing hormone (TRH) receptor (TRHR) is a G-protein-coupled receptor playing a crucial role in the anterior pituitary where it controls the synthesis and secretion of thyroid-stimulating hormone and prolactin. Its widespread presence not only in the central nervous system, but also in peripheral tissues, including thymus, indicates other important, but unknown, functions. One hypothesis is that the neuropeptide TRH could play a role in the immune system. We report here that the human TRHR promoter contains 11 putative response elements for the haematopoietic transcription factor c-Myb and is highly Myb-responsive in transfection assays. Analysis of Myb binding to putative response elements revealed one preferred binding site in intron 1 of the receptor gene. Transfection studies of promoter deletions confirmed that this high-affinity element is necessary for efficient Myb-dependent transactivation of reporter plasmids in CV-1 cells. The Myb-dependent activation of the TRHR promoter was strongly suppressed by expression of a dominant negative Myb-Engrailed fusion. In line with these observations, reverse transcriptase PCR analysis of rat tissues showed that the TRHR gene is expressed both in thymocytes and bone marrow. Furthermore, specific, high-affinity TRH agonist binding to cell-surface receptors was demonstrated in thymocytes and a haematopoietic cell line. Our findings imply a novel functional link between the neuroendocrine and the immune systems at the level of promoter regulation.

A functional genomic study to identify differential gene expression in the preterm and term human myometrium

The mechanisms that lead to the onset of human parturition are still unknown, although selected critical factors have been identified. To investigate the changes in myometrial gene expression associated with parturition, we used two macroarrays each containing 1176 different complementary human cDNA clones. Methods involving hierarchical clustering and conventional statistical analysis allowed us to generate a profile of genes expression at three stages of late pregnancy: preterm (29 wk amenorrhea); full term, not in labor (38 wk amenorrhea); and full term in labor (39 wk amenorrhea). Only 4% of the genes investigated were differentially expressed between the preterm and term groups (P < 0.05). These genes could be clustered as groups of either down-regulated or up-regulated transcripts. The changes in transcript abundance were particularly marked between the preterm and term stages of gestation, whereas the differences between term not in labor and term in labor were less pronounced. The parturition was characterized by a massive down-regulation of a large panel of developmental, cell adhesion molecule and proliferation-related genes, along with the up-regulation of inflammatory, contraction and apoptosis associated genes. We propose that the mechanisms of parturition consist primarily in the arrest of the processes of myometrial development, a step that might be essential to allow the uterus to recover appropriate contractile function before delivery.

Thyrotropin-releasing hormone and its receptor in glia

The presence of thyrotropin-releasing hormone (Thyroliberin, TRH) and its receptor (TRH-R) in frozen coronal sections of the adult rat spinal cord and neonatal rat astroglial cultures was investigated by means of immunocytochemistry and Western blot using polyclonal antibodies generated against the hormone and monoclonal antibodies originated against discrete sequences of the type 1 rat TRH receptor (TRH-R1). TRH-R1 and TRH are present both in astroglial cells from adult rats and in cultured cells from newborn animals. The localization of TRH and TRH-R1 in nonneuronal cells in the central nervous system may reflect that some of the neurotrophic actions of TRH upon the central nervous system are mediated by glial cells.

Thyrotropin-releasing hormone interacts with vasoactive intestinal peptide-specific receptor in guinea pig cecal circular smooth muscle cells

The relationship between thyrotropin-releasing hormone (TRH) binding sites and vasoactive intestinal peptide (VIP) receptors in circular muscle cells obtained from the guinea pig cecum was investigated using antagonists of VIP receptors and a selective receptor protection method. Both VIP10-28, a VIP antagonist, and atrial natriuretic peptide1-11 (ANP1-11), a VIP-specific receptor antagonist, completely inhibited 10(-5) M TRH-induced relaxation in a concentration-dependent manner. The muscle cells where cholecystokinin octapeptide (CCK-8) and TRH binding sites were protected completely preserved the inhibitory responses to TRH and ANP (a VIP-specific receptor agonist), and partially the inhibitory response to VIP. Peptide histidine isoleucine (PHI: a VIP-preferring receptor agonist) had no inhibitory effect on these cells. The muscle cells where CCK-8 and ANP (VIP-specific) receptors were protected completely preserved the inhibitory responses to TRH and ANP and partially the inhibitory response to VIP. PHI had no inhibitory effect on these cells. The muscle cells where CCK-8 and VIP receptors (both VIP-specific and VIP-preferring receptors) were protected preserved completely the inhibitory responses to TRH, VIP, ANP, and PHI. The muscle cells where CCK-8 and PHI (VIP-preferring) receptors were protected completely preserved the inhibitory response to PHI and partially the inhibitory response to VIP. TRH and ANP had no inhibitory effect on these cells. This study first demonstrates that TRH interacts with VIP-specific receptor in guinea pig cecal circular smooth muscle cells.

Cerebrovascular effects of the TRH analogues pGlu-3-methyl-His-Pro amide and pGlu-Glu-Pro amide: a comparison with TRH

The goal of the study was to assess whether TRH analogues possess cerebrovascular effects similar to the native peptide. The neuropeptide thyrotropin releasing hormone (TRH) elicits cerebrovasodilation in several species under various conditions. The laser-Doppler method was employed to study the effects of TRH and the analogues pGlu-3-methyl-His-Pro amid (M-TRH) and pGlu-Glu-Pro amide. Intravenous (i.v.) injection of 300 microg kg(-1) of TRH elicited cerebrovasodilation and a 62% increase in blood flow within 1 minute. M-TRH, in a dose of 300 microg kg(-1) i.v., elicited a 80% increase in cerebral blood flow. Even a minute dose of M-TRH (625 ng kg(-1)) caused an increase in cerebral blood flow. No clear difference in effects on the cerebral blood flow was observed between spontaneously and mechanically ventilated animals, pGlu-Glu-Pro amide had no cerebrovascular effect.

Tissue distribution of prolactin-releasing peptide (PrRP) and its receptor

Prolactin-releasing peptide (PrRP) is a novel bioactive peptide, originally isolated from bovine hypothalamus by utilizing an orphan seven-transmembrane-domain receptor expressed in the human pituitary gland. In this paper, we analyzed the tissue distribution of rat and human PrRP and their receptor mRNAs by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Northern blotting. In RT-PCR analysis, rat PrRP receptor mRNA was detected in the central nervous system, and the highest expression was detected in the pituitary gland. In addition, in situ hybridization revealed that rat PrRP receptor mRNA was highly expressed in the anterior lobe of the pituitary. On the other hand, rat PrRP mRNA was most abundantly expressed in the medulla oblongata, while significant levels of expression were widely detected in other tissues. In Northern blot analyses, human PrRP receptor mRNA was detected only in the pituitary gland among tissues examined. Human PrRP mRNA was detected in the medulla oblongata and in the pancreas. In contrast to the pattern of mRNA expression, the highest content of bioactive PrRP was found in the hypothalamus rather than the medulla oblongata in the rat brain, indicating that PrRP mRNA does not always parallel with mature PrRP in tissue distribution. The wide distribution of PrRP and its receptor suggests that they have various functions not only in the pituitary gland but also in the other tissues.

Cloning of thyrotropin-releasing hormone precursor and receptor in rat thymus, adrenal gland, and testis

TRH is a hypophysiotropic peptide that acts mainly via the hypothalamic-pituitary-thyroid axis, but TRH immunoreactivity is also detected in several peripheral tissues. PCR with two pairs of primers enabling amplification of three fragments of TRH complementary DNA (cDNA) was used to demonstrate local production of TRH. Products of the expected size were detected in the testis, adrenal gland, lymphoid organs, thymus, and spleen. The amplified cDNA fragments were cloned and sequenced to show that the TRH gene is expressed in the thymus, spleen, and adrenal gland. Competitive RT-PCR showed that the TRH messenger RNA content of the testis was about one third that of the hypothalamus, whereas the adrenal gland contained 2% and the thymus 6%. HPLC analysis of thymus and spleen extracts showed small amounts of TRH, with a particular processing pattern of pro-TRH in lymphoid organs. The expression of the TRH receptor gene in peripheral organs was investigated to determine whether TRH had an autocrine or a paracrine action. cDNA fragments that encompassed the coding region of the receptor were identified in the testis, adrenal gland and thymus. No signal was detected in the spleen. These findings indicate that TRH may have a biological activity in extrapituitary organs and may act locally in the testis, adrenal gland, and thymus.

Structural and functional organization of the gene encoding the human thyrotropin-releasing hormone receptor

The thyrotropin-releasing hormone (TRH) receptor (TRHR) is widely distributed throughout the central and peripheral nervous systems. In addition to its role in controlling the synthesis and secretion of thyroid-stimulating hormone and prolactin from the anterior pituitary, TRH is believed to act as a neurotransmitter as well as a neuromodulator. We have isolated genomic lambda and P1-derived artificial chromosome clones encoding the human TRHR. The gene was found to be 35 kb with three exons and two introns. A 541-bp intron 1 (-629 to -89 relative to the translation start site) is conserved between human and mouse. A large intron 2 of 31 kb disrupts the open reading frame (starting in position +790) in the sequence encoding the supposed junction between the third intracellular loop and the putative sixth transmembrane domain. A similar intron was found in chimpanzee and sheep but not in rat and mouse. Promoter analysis of upstream regions demonstrated cell type-specific reporter activation, and sequencing of 2.5 kb of the promoter revealed putative cis-acting regulatory elements for several transcription factors that may contribute to the regulation of the TRHR gene expression. Functional analysis of potential response elements for the anterior pituitary-specific transcription factor Pit-1 revealed cell type-specific binding that was competed out with a Pit-1 response element from the GH gene promoter.

Cloning and characterization of a cDNA encoding a novel subtype of rat thyrotropin-releasing hormone receptor

A cDNA encoding a thyrotropin-releasing hormone (TRH) receptor expressed in the pituitary was previously cloned (De La Pena, P., Delgado, L. M., Del Camino, D., and Barros, F. (1992) Biochem. J. 284, 891-899; De La Pena, P., Delgado, L. M., Del Camino, D., and Barros, F. (1992) J. Biol. Chem. 267, 25703-25708; Duthie, S. M., Taylor, P. L., Anderson, J., Cook, J., and Eidne, K. A. (1993) Mol. Cell Endocrinol. 95, R11-R15). We now describe the isolation of a rat cDNA encoding a novel subtype of TRH receptor (termed TRHR2) displaying an overall homology of 50% to the pituitary TRH receptor. Introduction of TRHR2 cDNA in HEK-293 cells resulted in expression of high affinity TRH binding with a different pharmacological profile than the pituitary TRH receptor. De novo expressed receptors were functional and resulted in stimulation of calcium transient as assessed by fluorometric imaging plate reader analysis. The message for TRHR2 was exclusive to central nervous system tissues as judged by Northern blot analysis. Studies of the expression of TRHR-2 message by in situ hybridization revealed a pattern of expression remarkably distinct (present in spinothalamic tract, spinal cord dorsal horn) from that of the pituitary TRH receptor (present in hypothalamus, and ventral horn of the spinal cord, anterior pituitary). Therefore, we have identified a novel, pharmacologically distinct receptor for thyrotropin-releasing hormone that appears to be more restricted to the central nervous system particularly to the sensory neurons of spinothalamic tract and spinal cord dorsal horn, which may account for the sensory antinociceptive actions of TRH.

Thyrotropin-releasing hormone immunoreactivity in rat adrenal tissue is localized in mast cells

Pro-thyrotropin-releasing hormone (pro-TRH) has been shown to be present throughout the central nervous system and in several peripheral tissues. In adrenals, TRH immunoreactivity has been reported but not characterized. We show here that two rat pro-TRH-derived peptides, TRH and prepro-TRH[160-169] (Ps4), were detected in extracts of rat adrenal glands by enzyme immunoassay. Endogenous TRH and Ps4 were purified by gel exclusion chromatography and reverse-phase HPLC. Structural identification of each peptide was achieved by chromatographic comparison with synthetic standards. By using the indirect immunofluorescence technique, TRH-immunoreactive cell bodies were found rather widely scattered outside the adrenal, in the brown adipose tissue in which the gland is embedded. These immunofluorescent cells have the typical appearance of mast cells and are metachromatic after histological staining with acidic Toluidine Blue. Our findings suggest that pro-TRH-derived peptides exist in rat mast cells.

Genomic organization and promoter function of the human thyrotropin-releasing hormone receptor gene

We isolated and characterized the gene for the human thyrotropin-releasing hormone receptor. The gene spanned more than 30 kilobases and contained three exons and two introns. Intron 1 exists in the 5'-untranslated region, and intron 2 is more than 25 kilobases in length which interrupts the coding region before the beginning of the putative sixth transmembrane domain. Exon 3 encodes the rest of the coding region and the entire 3'-untranslated region. The 3'-flanking region contains four potential polyadenylation signals, and 3'-rapid amplification of cDNA ends studies showed that only a signal at 2076 base pairs downstream of the stop codon was functional in the anterior pituitary. Primer extension and anchor-polymerase chain reaction studies indicated a transcriptional start site at 344 base pairs upstream of the translational start site. The promoter region does not contain either a TATA box or a CAAT box in the appropriate location. Transient transfection study revealed significant activity of the promoter in GH4C1 cells, and the region between -338 and -933 bp from the transcriptional start site worked as a negative regulator. Knowledge of the genomic organization and the promoter region of thyrotropin-releasing hormone (TRH) receptor gene will allow further studies of possible disorders of the TRH receptor, as well as facilitate elucidation of transcriptional control of the human TRH receptor gene.