Hypothyroidism and the maturation of the hypothalamo-hypophyseal-adrenal axis

Rats were made hypothyroid by feeding .25% thiouracil in a semipurified casein diet to mothers from the first day of pregnancy through lactation. At 15 days of age, concentrations of adrenal and serum corticosterone were comparable in euthyroid and hypothyroid young, suggesting a basal ACTH release. Ether stress, however, failed to elicit an increased synthesis and release of corticosterone in the hypothyroid rat, but was effective in the euthyroid animal. Exogenous ACTH, on the other hand, did induce corticosterone synthesis and release in hypothyroid and euthyroid rats, indicating a functional adrenal gland. Thus, neonatal hypothyroidism appears to influence the hypothalamus. The retarded maturation of this axis may play a role in behavioral deficiencies seen in hypothyroid animals.