Effects of in ovo exposure to imazalil and atrazine on sexual differentiation in chick gonads.
We examined the effects of atrazine and imazalil, 2 commonly used pesticides, on sexual differentiation in chickens. Atrazine and imazalil were injected into fertile eggs on d 0. At hatching, sex genotype and phenotype were determined. Gonads were stereomicroscopically and histologically observed. In ovo exposure of atrazine (0.01 to 3 mg/egg) did not influence hatchability, whereas imazalil exposure (2 mg/egg) inhibited hatchability. The sex genotype matched the sex phenotype in controls, atrazine, and imazalil-exposed groups. In control females, the right gonad was regressed at hatching. Regression of the right gonad, however, was inhibited following atrazine and imazalil exposure. In atrazine-exposed female chicks, the left gonads had normal ovary structures, and the remaining right gonads had ovary medulla-like structures. In imazalil-exposed females, some left gonads had an ovary medulla-like structure without the cortex as well as tubules, and the right gonad had testis-like structures. There was no change in male gonads at hatching following atrazine and imazalil exposure. Aromatase activity of the left gonad from female chicks was not changed by any concentration of atrazine exposure. These results suggest that atrazine and imazalil inhibit regression of the right gonad in female chicks, although it is not clear whether the remaining right gonad has aromatase activity. In ovo exposure to atrazine influences sexual differentiation of the ovary by different mechanisms from imazalil, possibly by the induction of aromatase in the right gonad, whereas it is confirmed that imazalil inhibits in vitro aromatase activity in the chick ovary. The results indicated that in ovo exposure to imazalil inhibits sexual differentiation of the ovary by inhibiting aromatase activity.