THE EFFECT OF MATERNAL AND FETAL THYROIDECTOMY ON FETAL BRAIN DEVELOPMENT IN THE SHEEP

Abstract

Combination of maternal and fetal thyroidectomy had a significant influence on brain development in the fetal sheep at 140 days. There was reduced body weight (36%), brain weight (23%), DNA (26%) and protein (34%) content in 5 fetuses of ewes, subjected to thyroidectomy 6 wk before mating and fetal thyroidectomy at 98 days gestation, compared with 6 sham operated controls. Cholesterol content was also reduced (36%) and water content increased (2.4%). The cerebellum was most severely affected and showed histologically an increased cell density associated with a significant reduction in the ratio of the molecular to granular cell layer area. The cell density was also significantly increased in the CA1 region of the hippocampus, but not in the CA4 region. It was also increased in the parietal layer of the cerebral cortex but not in the motor region. There was a significant reduction in the weight of heart (28.6%) and lungs (33.4%), while the kidneys and pituitary were enlarged (20.5 and 48.5%, respectively) as a result of double thyroidectomy. Combined thyroidectomy was similar to iodine deficiency in its effect on fetal brain development. Apparently, iodine deficiency has its effects in the sheep by a combination of maternal and fetal hypothyroidism.