Influence of high iodine during gestation on thyroid function and cerebral cortical ultrastructure in offspring rats

Objective To establish a model of gestational iodine overdose to observe the changes in thyroid function and cerebral cortical morphology in offspring rats, and to explore the influence of iodine overdose during gestation on thyroid and brain development in offspring rats.

Methods A total of 90 specific pathogen-free female Wistar rats weaned for two weeks were selected and randomly divided into normal iodine (NI) group, mild iodine excess (MIE) group, and severe iodine excess (SIE) group according to body weight, with 30 rats in each group. All rats were fed with a low-iodine diet, and different iodine intake models were established by drinking deionized water containing different concentrations of potassium iodide (KI) (183, 2 283, and 11 617 μg/L, respectively). After 3 months of intervention, the rats were mated and conceived. Blood samples were collected from the abdominal aorta of the offspring rats on day 21 to measure the levels of free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH). Meanwhile, the cerebral cortex was collected from 7 offspring rats of each group to observe neuronal ultrastructure by transmission electron microscopy.

Results The levels of urinary iodine in SIE and MIE groups were 2 368.7 and 644.2 μg/L, respectively, which were significantly higher than that in NI group (286.8 μg/L) (P < 0.05). There was a significant difference in the serum level of FT3 between the offspring rats of SIE group and the NI group (P < 0.05), and there were significant differences in the serum levels of FT4 and TSH between the offspring rats of SIE/MIE groups and the NI group (P < 0.05). The result of transmission electron microscopy showed that both the MIE group and the SIE group offspring rats had varying degrees of damage in cerebral cortical neurons. There were pathological changes including swelling and expansion of neuronal nuclei, severe hydrolysis and vacuolation of the mitochondria, swelling of the rough endoplasmic reticulum vesicles, delamination of the myelin sheath of myelinated nerve, incomplete and narrowed synaptic vesicle segments, and edema of axons.

Conclusion Excessive iodine intake can affect the thyroid function of offspring rats, and both mild and severe iodine overdose during gestation can cause pathological damage to the cerebral cortex of offspring rats, which in turn affects the brain development and function of the offspring.