Background and objectives: Pesticides play an essential role in crop protection, but their overuse caused environmental pollution and harmful effect on different animal body systems, including the endocrine system. The thyroid gland is one of the homeostatic regulators of metabolic activities, which is affected by the elements of the external environment. There are very limited studies on the effect of indoxacarb on the histological architecture and functions of thyroid gland. Therefore, this study was conducted with the aim of examining functionally and histologically of the thyroid gland exposed to indoxacarb. Method: 24 Swiss albino mice male and female were randomly divided into two groups, each group male and female; group I is a control group given orally with 1ml of distilled water and group II orally treated with 120 mg/kg Bw. of indoxacarb daily for 3 weeks. Blood samples were collected from each mouse under anesthetic to determine the thyroid-stimulating hormone (TSH), thyroxine (T4) levels. Thyroid gland histopathology was attained for the evaluation of the indoxacarb effect. Results: The treated mice showed non-significant increase in T4 levels and a significant decrease in TSH levels but there was no significant difference recorded in T4 and TSH levels between sexes. Histologically, the sections of the thyroid gland of the treated group showed empty and irregular follicles, degeneration of the follicular epithelial tissue, and hyperplasia in the lining of some follicles, the capsule with congestion blood vessels. Conclusion: This study concluded that indoxacarb may act as a thyroid gland toxicant.

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