Iodide-induced hypothyroidism: a potential hazard during perinatal life

Area of Science:

• Endocrinology
• Developmental Biology
• Toxicology

Background:

• Iodide administration during pregnancy can induce hypothyroidism in newborns.
• Thyroid hormone synthesis is crucial for fetal and neonatal development.
• Understanding iodide's effects is vital for managing neonatal thyroid dysfunction.

Purpose of the Study:

• To investigate the effects of iodide administration on thyroid hormone levels in developing rats.
• To determine the age at which rats develop resistance to iodide-induced hypothyroidism.
• To establish a perinatal rat model for studying iodide-induced thyroid dysfunction in human newborns.

Main Methods:

• Pregnant and nursing rats were administered iodide.
• Serum concentrations of thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3) were measured in offspring.
• Measurements were taken at various ages from term fetus through 60 days.

Main Results:

• Iodide administration induced hypothyroidism in fetuses and neonates up to 10 days of age, evidenced by increased TSH and decreased T4/T3.
• Thyroid function normalized in rats from 18 to 60 days of age despite continued iodide exposure.
• This suggests the development of resistance to iodide's inhibitory effects on thyroid hormone synthesis around 18 days of age.

Conclusions:

• A perinatal rat model effectively replicates iodide-induced hypothyroidism observed in human newborns.
• Developing resistance to iodide's goitrogenic effects is a key feature of this rat model.
• This model provides a valuable tool for elucidating the mechanisms of iodide-induced hypothyroidism and goiter.