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Percorrer por autor "Jacinto, R."

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  • Disruption of the thyroid system by diethylstilbestrol and ioxynil in the sea bream (Sparus aurata)
    Publication . Morgado, Isabel; Campinho, Marco António; Costa, Rita; Jacinto, R.; Power, Deborah
    Some environmental contaminants are thought to cause disruption of the thyroid system in vertebrates acting as endocrine disrupting chemicals (EDCs). Such chemicals may affect synthesis, transport and metabolism of thyroid hormones (THs). Ioxynil (IOX) and diethylstilbestrol (DES) are potential EDCs with strong affinity in vitro for sea bream transthyretin (TTR), a TH distributor protein (THDP). The aim of the present study was to establish how such chemicals influence the thyroid axis in sea bream (Sparus aurata). DES, IOX and propilthyouracil (PTU, a goitrogen) were administered in the diet to sea bream juveniles at 1 mg/kg fish (n = 14/treatment) for 21 days. After exposure plasma TH levels, quantified by RIA, were similar to those of control fish (p > 0.05) in all treatment groups. Analysis by quantitative PCR revealed that all treatments down-regulated TSH gene transcription (p < 0.05) in the brain and pituitary and deiodinase II and III transcription in the brain (p < 0.001). In contrast, PTU caused DII up-regulation in the liver (p < 0.05). Thyroid receptor beta (TR ) transcription was down-regulated in the pituitary by PTU (p < 0.001) and DES (p < 0.05). TTR plasma levels, quantified by ELISA, were elevated by all the chemicals including PTU (p < 0.001) which also increased TTR gene transcription in the liver (p < 0.05). Thyroid histology indicated follicular hyperstimulation in all treatments with marked hyperplasia, hypertrophy and colloid depletion in the PTU group. It appears therefore, that in vitro TTR-binders, IOX and DES, can strongly influence several components of the fish thyroid system in vivo but that the thyroid axis may have the ability to maintain or re-establish plasma TH homeostasis.
    2009Artigo científico Acesso restrito Ver mais
  • Regulation of transthyretin by thyroid hormones in Wsh
    Publication . Morgado, Isabel; Santos, C. R. A.; Jacinto, R.; Power, Deborah
    Transthyretin (TTR) is a thyroid hormone-binding protein (THBP) which in its tetrameric form transports thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3) in the blood of vertebrates. The principal site of production of TTR is the liver but in the sea bream TTR mRNA is also present in the heart, intestine and brain. The regulation of TTR is unstudied in Wsh and the normal circulating level of this THBP is unknown. The aim of the present study was to establish factors which regulate TTR production in Wsh. As a Wrst step a number of tools were generated; sea bream recombinant TTR (sbrTTR) and speciWc sbrTTR antisera which were used to establish an ELISA (enzyme-linked immunosorbent assay) for measuring TTR plasma levels. Subsequently, an experiment was conducted to determine the inXuence of THs on TTR production. Circulating physiological levels of TTR in sea bream determined by ELISA are approximately 3.8 gml¡1. Administration of T3 and T4 to sea bream signiWcantly increased (p< 0.001 and p<0.005, respectively) the concentration of circulating TTR (V11.5 gml¡1) in relation to control Wsh, but did not change gene transcription in the liver. Methimazol (MMI) an antithyroid agent, failed to signiWcantly reduce circulating THs below control levels but signiWcantly increased (p < 0.005) plasma TTR levels (approximately 10.8 gml¡1) and decreased (p< 0.05) transcription in the liver. Future studies will aim to elucidate in more detail these regulatory pathways.
    2007Artigo científico Acesso restrito Ver mais