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- Title
Endocrine toxicology. Inhibition of thyroid iodine uptake and organification in rats treated with kojic acid.
- Authors
Tamura, Toru; Mitsumori, Kunitoshi; Onodera, Hiroshi; Fujimoto, Nariaki; Yasuhara, Kazuo; Takegawa, Kiyoshi; Takahashi, Michihito
- Abstract
In order to elucidate the mechanism of reduction of serum thyroid hormones caused by continuous administration of kojic acid (KA) and its thyroid tumor-promotion effects, male F344 rats were given pulverized basal diet containing 0.008%, 0.03%, 0.125%, 0.5%, or 2% KA for 4 weeks. As an untreated control group, additional rats were given basal diet alone for the same period. The thyroid 125I uptake was significantly decreased in the groups receiving 0.03% or more. In addition, significant reduction of organic formation of iodine and serum T3 and T4 levels were observed in the 2% KA group along with pronounced elevation of serum (TSH). Both absolute and relative thyroid weights were significantly increased in the groups receiving 0.5% of KA or more. Histopathologically, decreased colloid in the thyroid follicles and follicular cell hypertrophy in the thyroid were apparent at high incidences in the groups given 0.03% or more. In addition, thyroid capsular fibrosis was evident in all rats of the 2% KA group. In quantitative morphometrical analysis, the ratio of the area of follicular epithelial cells to the area of colloids was significantly increased in the groups given 0.03% KA or more. The results suggest that KA alteration of thyroid-related hormone levels in the 2% KA group are due to inhibition of iodide uptake and iodine organification in the thyroid proliferative lesions, probably secondary to prolonged serum TSH stimulation resulting from negative feedback through the pituitary-thyroid axis.
- Subjects
THYROID hormones; SERUM; IODINE; ACIDS; LABORATORY rats
- Publication
Toxicological Sciences, 1999, Vol 47, Issue 2, p170
- ISSN
1096-6080
- Publication type
Article
- DOI
10.1093/toxsci/47.2.170