Objective To explore the effects of simultaneous inhalation exposure to nitrates, thiocyanates, and perchlorates on thyroid function in pregnant SD rats.

Methods A total of 40 sexually mature, SPF-grade SD rats were randomly assigned to a control group, and a low, medium, or high concentration aerosol exposure group. After one week of adaptive feeding, the rats were mated. After pregnancy, the rats were exposed to a mixed aerosol solution of sodium nitrate, sodium thiocyanate, and sodium perchlorate hydrate for 3 hours per day. In each group, exposure was continued until day 19 of pregnancy for the first 5 rats and until day 15 of pregnancy for the last 5 rats. At the end of exposure, the arterial blood of pregnant rats was collected. Parameters analyzed included maternal weight gain, thyroid weight and organ coefficients. Serum levels of free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) in female rats were measured. Pathological changes in the thyroid of female rats were observed using hematoxylin-eosin (HE) staining.

Results Maternal weight gain showed no significant differences between groups at 15 days of pregnancy (P>0.05), but was significantly lower in the high concentration group compared to the control group at 19 days of pregnancy (P < 0.05). The thyroid weight and organ coefficients of female rats were significantly higher in the medium and high concentration groups compared to the control group at both 15 and 19 days of pregnancy (P < 0.05). At 15 days of pregnancy, FT3 levels were significantly reduced in the medium and high concentration groups (P < 0.05), FT4 levels were significantly reduced across all exposure groups (P < 0.05), and TSH levels were significantly increased in the high concentration group compared with the control group (P < 0.05). At 19 days of pregnancy, no significant differences in FT3 levels were noted across all exposure groups (P>0.05), FT4 levels were significantly reduced in the low and high concentration groups (P < 0.05), and TSH levels were significantly increased in the high concentration group compared with the control group (P < 0.05). Morphology observation and HE staining showed significant swelling trends in the thyroid of female rats as exposure concentration increased at 15 and 19 days of pregnancy, with diffuse proliferation and lamination in thyroid epithelial cells from the low concentration, which intensified with exposure concentration.

Conclusion Simultaneous inhalation exposure to nitrates, thiocyanates, and perchlorates in pregnant rats causes significant fluctuations in FT3, FT4, and TSH levels, and leads to mild thyroid swelling and significant pathological changes in the thyroid, resulting in thyroid dysfunction.