The influence of low doses 131I-induced maternal hypothyroidism on the development of rat embryos

The aim of our research was to create and verify a model for studying the effects of a low dose of I-131 and I-131-induced maternal hypothyroidism on the development of the embryo's thyroid gland and brain. The given dose (150 mu Ci) corresponds to the absorbed dose of 0.5 Gy. This dose is similar to that dose received by large numbers of the popu lation of the C.I.S. regions polluted by radioactive isotopes of iodine as a result of the Chernobyl accident in 1985. Thirty-five female Wistar rats and their 168 newborn pups were used for observation. The females were divided into a control group and four experimental groups (each distinguished by the time of I-131 injection: group I - no less than 12 days before mating; groups II, III and IV - on 5(th), 10(th) and 16(th) days of gestation, respectively). In all the experimental female groups the incorporate dose of I-131 led to hypothyroidism accompanied by a 43 % reduction in the thyroxin level and by a nearly 8-fold increase in the TSH level. However, the influence of maternal hypothyroidism on the development of the thyroid gland and brain of embryos depends on the time when I-131 took effect. There is a reduction in the weight of the newborns' brain and thyroid gland, total body mass. The hormonal status of the newborns' thyroid gland also changes. The proposed model will allow us to study many aspects of induced changes in the brain and thyroid gland of the embryos which develop under conditions of maternal hypothyroidism resulting from a low dose of I-131, administered at the critical times of development.