Mercury vapor and female reproductive toxicity

Epidemiological studies finding menstrual cycle abnormalities among women o ccupationally exposed to Hg degrees prompted us to investigate the mechanis ms of reproductive toxicity of Hg degrees in the female rat. Nose-only Hg d egrees vapor inhalation exposures were conducted on regularly cycling rats 80-90 days of age in dose-response and acute time-course studies, which hav e previously proven useful as a model to identify ovarian toxicants. Vagina l smears were evaluated daily and serum hormone levels were correlated with cycle and with ovarian morphology at necropsy. Exposure concentration-rela ted effects of Hg degrees were evaluated by exposing rats to 0, 1, 2, or 4 mg/m(3) Hg degrees vapor 2 h/day for 11 consecutive days. Tissue Hg levels correlated with exposure concentration and duration. Exposure of rats to 4 mg/m(3) (but not 1 or 2 mg/m(3)) Hg vapor for II days resulted in significa nt decreases in body weights relative to controls. Estrous cycles were slig htly prolonged in the 2 and 4 mg/m(3) dose groups, and serum estradiol and progesterone levels were significantly different in the 4 mg/m3 group compa red to controls. The alterations in cycle and hormones at the 4 mg/m(3) exp osure concentration were attributed to body weight loss and generalized tox icity. In the time-course study, rats were exposed to 2 mg/m3 Hg degrees or air beginning in metestrus and evaluated daily for 8 days. A lengthening o f the cycle was detected and morphological changes were observed in the cor pora lutea (CL) after exposure for 6 days. To determine if changes in the C L and cyclicity correlated with a functional defect, rats were exposed to H g degrees vapor and evaluated for pregnancy outcome. There were no signific ant effects on pregnancy rate or numbers of implantation sites when rats we re exposed to I or 2 mg/m(3) Hg degrees for 8 days prior to breeding, or wh en exposed for 8 days after breeding. These studies indicate that exposure to Hg degrees vapor altered estrous cyclicity, but had no significant effec t on ovulation, implantation, or maintenance of first pregnancy during expo sure of short duration in female rats.