The effects of fetal thyroidectomy in the ovine fetus.

Cerebral function and metabolism, morphology and histology of the nervous system, and lung maturity in terms of surfactant production were studied at term in five sheep fetuses thyroidectomized at gestational ages ranging from 104 to 111 days. Compared to age-matched controls, body weight (thyroidectomized animals, 2.8 +/- 0.11 kilograms; controls, 3.9 +/- 0.2 kilograms; P less than 0.0005) and brain weight (thyroidectomized animals, 43.51 +/- 1.38 grams; controls, 48.49 +/- 1.75 grams; P less than 0.05) were significantly reduced. In the nervous system, morphology, histology, brain function, and metabolism were not significantly different from those of the controls. Lung weight was less, but not significantly, and surfactant production was not deficient as compared to that of age-matched controls. The failure to find any disturbance of maturation in the brain and lungs of fetuses thyroidectomized at 104 to 111 days may be related to the relative maturity of the sheep fetus at this age.