[Changes in the concentration of triiodothyronine and thyroxine in rabbit fetuses following encephalectomy]

Triiodothyronine (T3) and thyroxin (T4) were detected by radioimmunoassay in the thyroid gland and serum of encephalectomized and intact rabbit fetuses. Encephalectomy performed on the 22-23d day of development did not produce any effect on thyroid hormone concentrations in 29-day-old fetuses. However, on the 30th day the concentrations of T2 and T4 in the thyroid gland were significantly lower in the encephalectomized fetuses than in the intact ones. These findings were consistent with changes in the morphological structure of the thyroid gland. The results obtained indicate that the hypothalamus begins to control thyroid function in the rabbit fetuses apparently from the 30th day of prenatal life.