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, Jackson 1989 ) and characterized the Trh gene ( Lee et al . 1989 ). The Trh -gene proximal promoter contains response elements (RE) to transcription factors whose binding was revealed by chromatin immunoprecipitation assays; for example, receptors for
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secretion ( De Groef et al. 2003 b ). The stimulating effects of TRH on thyrotropes are mediated through the type 1 TRH receptor (TRH-R1) ( De Groef et al. 2003 a ). Changes in the sensitivity of the thyrotropes to the above
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Laboratory of Endocrine Physiology, Laboratory of Neurophysiology, Carlos Chagas Filho Biophysic Institute, Biology Institute, State University of Rio de Janeiro, Rio de Janeiro 20551‐030, Brazil
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& Seitz 1994 , St Germain et al . 2009 ). Most of actions of TH occur through the nuclear TH receptors (TR), which are encoded by two distinct genes, TRα and TRβ, located on mouse chromosomes 11 and 14. The molecular mechanism of TH action involves TR
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regulate TRH gene expression via activation of intracellular signal-transducer-and-activator-of transcription 3 (STAT-3) proteins in TRH neurons, with evidence that the STAT-3 binding site on the leptin receptor is also required for the effect on TRH
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understanding regarding the degree of hypothyroidism previously reported in EO animal models. Because circulating thyrotropin (TSH) was unaltered in adult small litter (SL) rats, we evaluated the thyrotropin release hormone (TRH) in the hypothalamus, the TSH in
Neurofisiología Molecular, Escuela de Dietética y Nutrición, Dirección de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz (INPRFM), Calzada México-Xochimilco 101, Col. San Lorenzo Huipulco, C.P. 14370, México, Distrito Federal, México
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thyroxine (T 4 ) – as well as their degrading effects on fuel reservoirs. TRH is the hypophysiotropic factor that controls HPT axis function. This peptide is synthesized in the medial PVN (mPVN) of the hypothalamus and released into the portal blood to
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Introduction Melanocortin receptor accessory protein (MRAP) and its paralogue MRAP2 are a recently identified class of small, single-pass transmembrane domain accessory proteins ( Chan et al . 2009 , Novoselova et al . 2013 ). Both MRAP and
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Thyrotropin-releasing hormone (TRH), a hypothalamic tripeptide, is expressed in pancreatic islets at peak levels during the late gestation and early neonate period. TRH increases insulin production in cultured beta-cells, suggesting that it might play a role in regulating pancreatic beta-cell function. However, there is limited information on TRH receptor expression in the pancreas. The aim of the present study was to explore the distribution of the TRH receptor in the pancreas and its function in pancreatic beta-cells. TRH receptor type 1 (TRHR1) gene expression was detected by RT-PCR and verified by Northern blotting and immunoblotting in the beta-cell lines, INS-1 and betaTC-6, and the rat pancreatic organ. The absence of TRH receptor type 2 expression in the tissue and cells indicated the tissue specificity of TRH receptor expression in the pancreas. The TRHR1 signals (detected by in situ hybridization) were distributed not only in islets but also in the surrounding areas of the pancreatic ductal and vasal epithelia. The apparent dissociation constant value for the affinity of [(3)H]3-methyl-histidine TRH (MeTRH) is 4.19 in INS-1 and 3.09 nM in betaTC-6. In addition, TRH induced epidermal growth factor (EGF) receptor phosphorylation with a half-maximum concentration of approximately 50 nM, whereas the high affinity analogue of TRH, MeTRH, was 1 nM. This suggested that the affinity of TRH ligands for the TRH receptor influences the activation of EGF receptor phosphorylation in betaTC-6 cells. Our observations suggested that the biological role of TRH in pancreatic beta-cells is via the activation of TRHR1. Further research is required to identify the role of TRHR1 in the pancreas aside from the islets.
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Substance P (SP) may participate as a paracrine and/or autocrine factor in the regulation of anterior pituitary function. This project studied the effect of TRH on SP content and release from anterior pituitary and the role of SP in TRH-induced prolactin release. TRH (10(-7) M), but not vasoactive intestinal polypeptide (VIP), increased immunoreactive-SP (ir-SP) content and release from male rat anterior pituitary in vitro. An anti-prolactin serum also increased ir-SP release and content. In order to determine whether intrapituitary SP participates in TRH-induced prolactin release, anterior pituitaries were incubated with TRH (10(-7) M) and either WIN 62,577, a specific antagonist of the NK1 receptor, or a specific anti-SP serum. Both WIN 62,577 (10(-8) and 10(-7) M) and the anti-SP serum (1:250) blocked TRH-induced prolactin release. In order to study the interaction between TRH and SP on prolactin release, anterior pituitaries were incubated with either TRH (10(-7) M) or SP, or with both peptides. SP (10(-7) and 10(-6) M) by itself stimulated prolactin release. While 10(-7) M SP did not modify the TRH effect, 10(-6) M SP reduced TRH-stimulated prolactin release. SP (10(-5) M) alone failed to stimulate prolactin release and markedly decreased TRH-induced prolactin release. The present study shows that TRH stimulates ir-SP release and increases ir-SP content in the anterior pituitary. Our data also suggest that SP may act as a modulator of TRH effect on prolactin secretion by a paracrine mechanism.
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ABSTRACT
Pyroglutamylglutamylprolineamide (pGlu-Glu-ProNH2) is a tripeptide with structural and immunological similarities to thyrotrophin-releasing hormone (TRH; pGlu-His-ProNH2). Since TRH stimulates GH secretion in domestic fowl, the possibility that pGlu-Glu-ProNH2 may also provoke GH release was investigated. Unlike TRH, pGlu-Glu-ProNH2 alone had no effect on GH release from incubated chicken pituitary glands and did not down-regulate pituitary TRH receptors. However, pGlu-Glu-ProNH2 suppressed TRH-induced GH release from pituitary glands incubated in vitro and competitively displaced [3H]methyl3-histidine2-TRH from pituitary membranes. Systemic injections of pGlu-Glu-ProNH2 had no significant effect on basal GH concentrations in conscious birds, but promptly lowered circulating GH levels in sodiumpentobarbitone anaesthetized fowl. Submaximal GH responses of conscious and anaesthetized birds to systemic TRH challenge were, however, potentiated by prior or concomitant administration of pGlu-Glu-ProNH2. These results demonstrate, for the first time, that pGlu-Glu-ProNH2 has biological activity, with inhibitory and stimulatory actions within the avian hypothalamo-pituitary axis. These results indicate that pGlu-Glu-ProNH2 may act as a TRH receptor antagonist within this axis.
Journal of Endocrinology (1993) 138, 137–147
