Role of corticotropin-releasing hormone as a thyrotropin-releasing factor in non-mammalian vertebrates.

Laboratory of Comparative Endocrinology, K.U. Leuven, B3000 Leuven, Belgium.
General and Comparative Endocrinology (Impact Factor: 2.82). 04/2006; 146(1):62-8. DOI: 10.1016/j.ygcen.2005.10.014
Source: PubMed

ABSTRACT The finding that thyrotropin-releasing hormone does not always act as a thyrotropin (TSH)-releasing factor in non-mammalian vertebrates has led researchers to believe that another hypothalamic factor may exhibit this function. In representatives of all non-mammalian vertebrate classes, corticotropin-releasing hormone (CRH) appears to be a potent stimulator of hypophyseal TSH secretion, and might therefore function as a common regulator of both the thyroidal and adrenal/interrenal axes. CRH exerts its dual hypophysiotropic action through two different types of CRH receptors. Thyrotropes express type 2 CRH receptors, while CRH-induced corticotropin (ACTH) secretion is mediated by type 1 CRH receptors on the corticotropic pituitary cells. The stimulating effect of CRH on both TSH and ACTH release has profound consequences for the peripheral action of both hormonal axes. The simultaneous stimulation of the thyroidal and adrenal/interrenal axes by CRH, possibly fine-tuned by differential regulation of the expression of the different CRH receptor isoforms, provides a potential mechanism for developmental plasticity.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study attempted to determine the effect of a 1800 MHz electromagnetic field (EMF) (only carrier frequency) on thyroxine (T4), triiodothyronine (T3) and corticosterone (CORT) concentrations in the blood plasma of chick embryos, and to investigate the effect of electromagnetic field (EMF) exposure during embryogenesis on the level of these hormones in birds that are ready for slaughter. Throughout the incubation period, embryos from the experimental group were exposed to a 1800 MHz EMF with power density of 0.1 W/m(2), 10 times during 24 h for 4 min. Blood samples were collected to determine T4, T3 and CORT concentrations on the 12th (E12) and 18th (E18) day of incubation, from newly hatched chicks (D1) and from birds ready for slaughter (D42). The experiment showed that T4 and T3 concentrations decreased markedly and CORT levels increased in the embryos and in the newly hatched chicks exposed to EMF during embryogenesis. However, no changes were found in the level of the analyzed hormones in the birds ready for slaughter. Differences in T4 and T3 plasma concentrations between the EMF-exposed group and the embryos incubated without additional EMF were the highest in the newly hatched chicks, which may be indicative of the cumulative effect of electromagnetic field on the hypothalamo-pituitary-thyroid axis (HPT). The obtained results suggest that additional 1800 MHz radio frequency electromagnetic field inhibits function of HPT axis, however, it stimulates hypothalamo-pituitary-adrenal axis by inducing adrenal steroidogenic cells to synthesize corticosterone. Further investigations are needed to elucidate the mechanisms by which radio EMFs affect HPT and HPA axis function in the chicken embryos.
    International Journal of Occupational Medicine and Environmental Health 01/2014; · 1.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Thyroid hormones are involved in modulating the immune system in mammals. In contrast, there is no information on the role played by these hormones in the immune system of teleost fish. Here we provide initial evidence for the presence of active thyroid signaling in immune organs and cells of teleosts. We demonstrate that immune organs (head kidney and spleen) and isolated leukocytes (from head kidney and peripheral blood) of the rainbow trout (Oncorhynchus mykiss) express both thyroid receptor α (THRA) and β (THRB). Absolute mRNA levels of THRA were significantly higher than those of THRB. THRA showed higher expression in immune organs and isolated immune cells compared to the reference organ, liver, while THRB showed the opposite. In vivo exposure of trout to triiodothryronine (T3) or the anti-thyroid agent propylthiouracil (PTU) altered THR expression in immune organs and cells. Effect of T3 and PTU over the relative expression of selected marker genes of immune cell subpopulations was also studied. Treatments changed the relative expression of markers of cytotoxic, helper and total T cells (cd4, cd8a, trb), B lymphocytes (mIgM) and macrophages (csf1r). These findings suggest that the immune system of rainbow trout is responsive to thyroid hormones.
    Fish &amp Shellfish Immunology 01/2014; · 2.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cadmium is a heavy metal abundant in the environment that can induce endocrine disorder and toxicity in aquatic organisms at low levels. However, its effects on the thyroid system in fish are still unclear. In this study, the thyroid hormones (THs) levels and the expression profiles of genes related to hypothalamic– pituitary–thyroid (HPT) axis, including corticotropin-releasing hormone (crh), thyroid stimulating hormone beta (tshβ), solute carrier family 5 (sodium iodide symporter) member 5 (slc5a5), thyroglobulin (tg), thyroid hormone receptor alpha (trα) and thyroid hormone receptor beta (trβ), were determined in whole body of Chinese rare minnow (Gobiocypris rarus) larvae after exposure to different levels of Cd2 + (0, 0.5 and 2.5 mg/L) for 4 days. And the 96-h lethal concentration of Cd2 + on rare minnow larvae was determined as 2.59 mg/L. The results showed that crh, slc5a5, tg and tshβ mRNA levels were significantly up-regulated in the larvae, but the gene expression of trα and trβ were down-regulated in a concentration-dependent manner. Besides, the THs levels decreased in the whole-body of fish, especially the thyroxine (T4) level. The above results indicated that Cd2 + could alter gene expression in the HPT axis that might subsequently contribute to thyroid disruption.
    Comparative Biochemistry and Physiology Part C Toxicology & Pharmacology 01/2014; · 2.71 Impact Factor


Available from
May 21, 2014