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Page de résumé pour ULgetd-03072011-163944

Auteur : Schnitzler, Joseph
E-mail de l'auteur : Joseph.Schnitzler@ulg.ac.be
URN : ULgetd-03072011-163944
Langue : Anglais/English
Titre : Approaches for assessing the presence and impact of thyroid hormone disrupting chemicals in sea bass (Dicentrarchus labrax) from European coasts
Intitulé du diplôme : Doctorat en sciences
Département : FS - Département des sciences et gestion de l'environnement
Jury :
Nom : Titre :
Balthazart, Jacques Membre du jury/Committee Member
Blust, R. Membre du jury/Committee Member
Klaren, P. Membre du jury/Committee Member
Silvestre, F. Membre du jury/Committee Member
Thome, Jean-Pierre Membre du jury/Committee Member
Poncin, Pascal Président du jury/Committee Chair
Bouquegneau, Jean-Marie Promoteur/Director
Das, Krishna Promoteur/Director
Mots-clés :
  • Endocrine disruption/thyroid/sea bass
Date de soutenance : 2011-03-09
Type d'accès : Public/Internet
Résumé :

Thyroid functional status of wild fish in relation with the contamination of their environment

deserves further investigation. Polychlorinated biphenyls (PCBs) and organochlorine pesticides

like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), aldrin,

dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg) were analysed in the muscle of sea

bass (Dicentrarchus labrax) sampled in coastal regions near several important European river

mouths (Gironde, Charente, Loire, Seine and Scheldt). We applied a multi-level approach of

thyroid function assessment. Thyroxine (T4) and triiodothyronine (T3) concentrations in

muscle were analyzed by radioimmunoassay. The activity of hepatic enzymes involved in

extrathyroidal pathways of thyroid hormone metabolism, viz. deiodination, glucuronidation

and sulfation were analyzed. Last, follicle diameter and epithelial cell heights were measured.

We observed changes that lead to an increased conversion of T4 to T3 and lowered thyroid

hormone excretion. The changes in the metabolic pathways of thyroid hormones can be

interpreted as a pathway to maintain thyroid hormone homeostasis. The higher chlorinated

PCBs seemed to be the most implicated in this perturbation. To gain a more integrated

insight, we examined the effect of subchronic exposure to a mixture of Aroclor standards on

thyroid hormone physiology and metabolism in juvenile sea bass. After 120 days of exposure,

histomorphometry of thyroid tissue, muscular thyroid hormone concentration and activity of

enzymes involved in metabolism of thyroid hormones were assessed. The results show that the

effects of PCB exposures on the thyroid system are dose-dependent. Exposure to

environmentally relevant doses of PCB (0.3 to 1.0 μg Σ7PCBs per g food pellets) increases

thyroid hormone synthesis and stimulates hepatic T4 outer ring deiodinase and T4 sulfation.

Thyroid hormone tissue levels were preserved thanks to the PCB induced changes in T4

dynamics. At 10 times higher concentrations (10 μg Σ7PCBs per g food pellets) an important

depression of T3 and T4 levels could be observed which are apparently caused by degenerative

histological changes in the thyroid tissue. We propose accurate interpretations, by reviewing

the different stages of teleost thyroid function and regulation.

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