Background: Fipronil has also become a widespread environmental contaminant detected in both soil and water. Zinc retards oxidative processes on a long-term basis by inducing the expression of metalbinding cysteine-rich proteins called metallothioneins, and in mammals In mammals, the thyroid is an endocrine gland of critical importance for the regulation of the metabolism in general. Objective: to study protective effect of zinc on thyroid toxicity induced by fipronil in adult male albino rats through biochemical , histopathological and genotoxic studies. MAterials and methods: In the present study, forty adult healthy male albino rats weighing 180 - 200 gm, were used. They were divided into 4 groups as following:Group I(control group): It was subdivided into 2 groups each of 8 rats; Group IA (negative control group) 8 rats: Rats received no medication, only regular diet and water to measure the basic parameters for 6 weeks, Group IB (positive control group) 8 rats: Each rat treated with 1 ml distilled water (the vehicle of fipronil and zinc) by oral gavage once daily for 6 weeks. Group II (zinc group) 8 rats: Each rat was gavaged orally with 2mg/kg bw zinc as powder dissolved in 1 ml distilled water once daily for 6 weeks.Group III (fipronil group) 8 rats: Each rat was gavaged orally with 9.7 mg/kg bw fipronil dissolved in 1 ml distilled water once daily for 6 weeks which equals 1/10 of LD50.Group IV (zinc+fipronil) 8 rats: Each rat was gavaged orally with 2mg/kg bw zinc as powder dissolved in 1 ml distilled water. An hour later; Fipronil was gavaged orally with 9.7mg/kg bw fipronil dissolved in 1 ml distilled water once daily for 6 weeks. At the end of 6 weeks, all rats were anesthetized then subjected to blood samples collection for estimation of serum biomarkers of thyroid functions (TSH, T3 & T4), oxidative stress (MDA) and Antioxidant biomarkers SOD &GPX). Results: The present findings showed that zinc administration significantly decreased thyroid function tests (T3 ,T4 ) & increased TSH in Zinc with fipronil trated group when compared with FPN treated group. that zinc administration with FPN resulted in a very highly significant decrease in the mean values of serum (MDA , GPX &SOD) of Zinc with fipronil group when compared with FPN treated group. Comet assay performed on thyroid specimens of zinc with fipronil treated group revealed a significant decrease in % of tailed nuclei, tail length, tail DNA % and unit tail moment and a significant increase in % of untailed nuclei when compared with those of the negative control group. Conclusion: Zinc plays an important role in protection against fipronil thyroid toxicity evidenced by improving the biochemical, histopathological and comet assay results in groups treated with zinc and fipronil

Zinc, Fipronil, Thyroid