Standardization of the perchlorate discharge assay for thyroid toxicity testing in rats.
The perchlorate discharge assay (PDA) is potentially of high diagnostic value to distinguish between direct and indirect thyroid toxicity mechanisms, provided that standard treatment times are established and positive controls yield reproducible results. Therefore the PDA was evaluated after 2 and/or 4 weeks of treatment with positive control compounds in rats. Phenobarbital, Aroclor 1254 and beta-naphthoflavone (indirect toxic mechanism) enhanced thyroidal radioiodide accumulation, and the administration of potassium perchlorate had no effect on thyroid: blood (125)I ratio. Phenobarbital caused follicular cell hypertrophy and hyperplasia in the thyroid and centrilobular hypertrophy in the liver, without effects on serum triiodotyronine (T(3)), thyroxine (T(4)) levels. Thyroid-stimulating hormone (TSH) levels were moderately increased. Propylthiouracil (direct toxic mechanism) caused severe thyroid follicular cell hypertrophy and hyperplasia, reduced serum T(3) and T(4) levels and increased serum TSH levels, and reduced thyroidal radioiodide accumulation; perchlorate administration significantly reduced thyroid: blood (125)I ratio, demonstrating an iodide organification block. Potassium iodide (direct toxic mechanism) virtually blocked thyroidal radioiodide accumulation, without significant effects on serum T(3), T(4), and TSH levels and a microscopic correlate for higher thyroid weights. Thus, positive controls yielded reproducible results and we conclude that both the 2- and 4-week PDA is suitable to distinguish between direct and indirect thyroid toxicity mechanisms.
Coelho-Palermo Cunha
G
G
BASF Aktiengesellschaft, Experimental Toxicology and Ecology, Z 470 D-67056 Ludwigshafen, Germany.
van Ravenzwaay
B
B
D000818:Animals; D020111:Chlorodiphenyl (54% Chlorine) / Q000633:toxicity; D006965:Hyperplasia; D006984:Hypertrophy; D007457:Iodine Radioisotopes; D008297:Male; D010472:Perchlorates; D010634:Phenobarbital / Q000633:toxicity; D017680:Potassium Compounds; D011193:Potassium Iodide / Q000633:toxicity; D011441:Propylthiouracil / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013960:Thyroid Function Tests / Q000592:standards*; D013961:Thyroid Gland / Q000187:drug effects*; D013972:Thyrotropin / Q000097:blood / Q000187:drug effects; D013974:Thyroxine / Q000097:blood / Q000187:drug effects; D018675:Toxicity Tests / Q000592:standards*; D014284:Triiodothyronine / Q000097:blood / Q000187:drug effects; D019324:beta-Naphthoflavone / Q000633:toxicity
D007457:Iodine Radioisotopes; D010472:Perchlorates; D017680:Potassium Compounds; D014284:Triiodothyronine; D020111:Chlorodiphenyl (54% Chlorine); D011193:Potassium Iodide; C009006:potassium perchlorate; D019324:beta-Naphthoflavone; D011441:Propylthiouracil; D013972:Thyrotropin; D013974:Thyroxine; D010634:Phenobarbital