Experimental studies on perinatal development of adrenal and thyroid glands in the rat

In the rat, as regards the adrenal gland, (1) during the fetal period, the adrenal cortex first begins to develop autonomically, (2) subsequently, the cortex comes under the control of the hypophysis, (3) later, the hypophysial-adrenal system comes under hypothalamic regulation, (4) after birth, the adrenal gland becomes shrunken temporarily, accompanied by an abrupt rise and a subsequent decline of the plasma corticosterone concentrations (PCC) just before and after birth. The rise and decline of PCC is probably responsible for the temporary hiatus of the hypothalamic-hypophysial activity, and (5) a preventive therapy of the abrupt rise of PCC allows the adrenal gland to escape neonatal shrinkage. As to the thyroid gland, (1) the initial formation of thyroid follicles is independent of thyroid-stimulating hormone (TSH), (2) follicles, once developed, are capable of responding to TSH, (3) the fetal hypophysial-thyroid function is independent of the hypothalamic regulation, (4) the early neonatal thyroid gland does not seem to undergo hyperfunctioning, and (5) hypothalamic regulation of the thyroid gland seems to begin 5 or more days after birth.