Dienhart et al. investigated the impact of single low-level exposures to the most powerful form of dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (or TCDD) on development of the reproductive tract in fetal rats. It had been found previously that female rats exposed to TCDD on a specific day during gestation (Day 15) showed delayed puberty, reduced ovarian weight, and malformations in the external genitalia (Gray and Ostby 1995, Flaws et al. 1997). Dienhart et al. were interested in when and how the malformation occurs to gain insight into the ways that dioxin causes developmental damage.

They found that the defect begins to be observable within 4 days of dioxin ingestion by the mother rat. The effects are profound and readily visible, and involve at least two different aspects of female reproductive tract development: regression of the Wolffian ducts and fusion of the Mullerian ducts.

They conclude by drawing attention to the importance of considering non-cancer endpoints of dioxin: "In conclusion, although dioxin is a recognized human carcinogen, these studies demonstrate that prenatal exposure to TCDD, in some species, can have subtle yet profound noncarcinogenic effects on the development of the female reproductive system. The fact that TCDD can alter prenatal development of the rat vagina raises concerns that TCDD may elicit other changes in these tissues, changes that may not become apparent until later in development or during reproductive life."

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