Studies on the hypothalamic control of thyroid function in the rabbit fetuses.

Abstract

In order to reveal the onset in ontogenesis of hypothalamic control of thyroid function 22-23-day-old fetuses of rabbits were encephalectomized. The concentrations of T3 and T4 in thyroid glands and blood serum were measured radioimmunologically on the 29th and 30th day of prenatal life. Significant differences of T3 and T4 concentrations are revealed only in thyroid glands of 30-day-old encephalectomized fetuses. Treatment of encephalectomized fetuses by TRH 30 min prior to fixation removed the effect of encephalectomy on hormone concentration and on thyroid structure. The represented data are considered as a proof of the establishment of hypothalamic cotrol of hormone synthesis in thyroid gland beginning from the 30th day of prenatal life. The regulation of hormone release from the gland is probably established at a later stage of maturation.