Radioactive Iodine-induced hypothyroidism interferes with the maturation of reproductive organs during puberty in immature female rats

Animal and human studies suggest that thyroid hormone may have critical roles in the development of the ovary. For example, thyroid deficiency disrupts the ovarian microarchitecture and menstrual cycle in neonate and adult women, respectively. Therefore, it is conceivable that thyroid deficiency might disrupt sexual maturation during the peri-pubertal period. To investigate the impact of radioactive iodine-induced thyroid deficiency on reproductive organs throughout puberty, immature female rats were given water containing radioactive iodine (0.37 MBq/g body weight) twice, on postnatal days 22 and 29. Radioactive iodine-induced hypothyroidism was revealed by low free thyroxin levels. Thyroid deficiency delayed the onset of vaginal opening, reduced ovarian weight and the number of medium-sized follicles and led to elongated uteri. However, there was no effect on the estrous cycle or absolute uterus weight. We conclude that radioactive iodine-induced thyroid deficiency delays sexual maturation and alters normal ovarian growth in peri-pubertal rats.