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
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.
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.
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."