Polychlorinated Biphenyls affect Histological Appearance of European sea bass (Dicentrarchus labrax) Thyroids

Polychlorobiphenyls (PCBs) are well-described endocrine disrupters and of particular interest are effects on thyroid function. We propose here a thorough approach to assess effects of these compounds on the thyroid function of European sea bass (Dicentrarchus labrax). An experimental exposure of sea bass to commercial PCB mixtures has been designed to understand underlying toxicity mechanisms and effects on the thyroid system. After 120 days of exposure histological appearance of thyroid tissue was assessed by light and electron microscopy. The follicle area, perimeter, diameter, length and with of every follicle cross section were interactively measured. The shape of the follicles was described with three dimensionless shape descriptors: roundness, form factor and aspect ratio. The histomorphometrical analysis showed a greater heterogeneity of thyroid follicle diameter and especially higher epithelial cell heights in sea bass exposed to environmental relevant doses of PCB (from 0.3 to 0.9 μg g-1 [7 ICES PCB]). Ultrastructural histological investigations showed that the epithelial cells surrounding the bigger follicles present an higher accumulation of colloid droplets. This was interpreted to be the result of increased stimulation of follicular cells. No differences in shape could be identified among the different treatment groups The size of the follicles and the form of the follicular cells gives an indication of the secretary activity of the gland. These observations support the hypothesis that the contamination of PCB mixtures can induce a hyperactivity of the thyroid tissue. These observations were confirmed by measurements of muscular thyroid hormone concentrations and activity thyroid hormone metabolism.