ALTERATIONS OF SERUM THYROXINE, TRIIODOTHYRONINE, AND THYROTROPIN IN THE PROGENY OF HYPOTHYROID RATS

Thyroid function in the progeny of hypothyroid rats was studied from 19 days of gestation until adulthood. Total T4 [thyroxine], T3 [triiodothyronine] and TSH [thyrotropin] were measured by radioimmunoassay in the sera of control, surgically thyroidectomized (Tx), and GH[growth hormone]-treated Tx pregnant rats and their progeny from the late fetal period through adulthood. By the 22nd day of gestation, the fetuses of Tx mothers had T4 and TSH levels significantly above those of their controls. This condition, whereby fetal serum T4 and TSH levels were elevated, was aggravated by GH treatment of the Tx mothers. The progeny of Tx- and Tx and GH-treated mothers also showed alterations in serum T4, T3 and TSH. While the T4 levels of the progeny of Tx mothers were significantly below those of the control progeny only at 30 days of age, T3 levels were significantly depressed at 1, 5 and 30 days of age. The same animals had lower serum TSH levels than the control progeny at 1 and 5 days of age and higher TSH levels at 30 and 75 days of age. Prenatal GH treatment of the mother did not consistently correct thyroid functions of the progeny. As adults, the progeny of the Tx mothers had normal serum concentrations of T4 and T3 but TSH was high. High serum TSH values were not seen in the progeny of Tx plus GH-treated mothers. Maternal hypothyroidism during pregnancy may result in permanent alterations in the thyroidal response to TSH in their progeny.