Abstract
In the past, various approaches have been developed to detect adverse effects of pollutants on the thyroid of vertebrates, most of these with special emphasis on the South African clawed frog, Xenopus laevis. Although fish are primarily affected by thyroid-disrupting chemicals, studies into alterations of the thyroid of fish are scarce. Therefore, effects of the reference compound propylthiouracil on histopathology of the thyroid axis were analyzed in a modified early life-stage test with zebrafish (Danio rerio) exposed to propylthiouracil. The test substance induced dose-dependent alterations of thyroidal tissue concomitant with increases in the number of surrounding blood vessels. Despite this massive proliferation of the thyroid, zebrafish were not able to maintain thyroxin concentrations. The pituitary was affected displaying significant alterations in thyroid-stimulating hormone cell counts. Quantitative evaluation of pituitary surface areas revealed a dose-dependent increase of adenohypophyseal tissue. Distinct histopathological effects may contribute to a more easy identification and interpretation of alterations induced by thyroid-disrupting chemicals.
Highlights
Over the past 20 years, the potency of endocrine-disrupting chemicals (EDCs) has attracted attention in numerous toxicological and ecotoxicological studies [1,2,3,4,5,6,7,8,9]
Effects of the reference compound propylthiouracil on histopathology of the thyroid axis were analyzed in a modified early life-stage test with zebrafish (Danio rerio) exposed to propylthiouracil
Quantitative evaluation of pituitary surface areas revealed a dose-dependent increase of adenohypophyseal tissue
Summary
Over the past 20 years, the potency of endocrine-disrupting chemicals (EDCs) has attracted attention in numerous toxicological and ecotoxicological studies [1,2,3,4,5,6,7,8,9]. The main focus of EDCs was clearly on effects on reproductive biology [10,11,12], but the awareness of potential risks by thyroid system-disrupting chemicals is increasing [13,14,15,16,17,18]. Fish form the most versatile and heterogeneous vertebrate group with regard to anatomy, physiology, reproduction, behavior, and ecology [24,25,26]— approx. Perchlorates as a group of water-soluble goitrogens have attracted some interest because of their potency to contaminate drinking water [47]
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