The aryl hydrocarbon receptor (AhR) regulates the toxicity of environmental
contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As the ph
ysiological role of the AhR in the ovary is unknown, the purpose of this st
udy was to test the hypothesis that the AhR regulates the appearance and nu
mbers of ovarian follicles. Ovaries were harvested from AhR-deficient (AhRK
O) and wild-type mice on gestational day 18 (GD 18) and postnatal days (PND
) 2-3, 8, 32-35, and 53. Complete serial sections of ovaries were evaluated
histologically for the presence of germ cells and follicles. On GD 18, the
re was no difference in the number of germ cells per ovary between AhRKO an
d wild-type fetuses. However, by PND 2-3, AhRKO mice had significantly more
fully formed primordial follicles (AhRKO = 38,440 +/- 3632 versus wild-typ
e = 21,120 +/- 2688) and fewer single germ cells than wild-type mice (AhRKO
= 12,696 +/- 1192 vs. wild-type = 18,160 +/- 720). On PND 8 and 32-35, the
re was no difference in the number of follicles between AhRKO and wild-type
mice but by PND 53, AhRKO mice had significantly fewer antral follicles th
an wild-type (AhRKO = 3416 +/- 480 vs, wild-type = 6776 +/- 1024). Taken to
gether, these results suggest that the AhR may play a role in the formation
of primordial follicles and the regulation of antral follicle numbers.