Observations on the untreated progeny of hypothyroid male rats

The untreated progeny (F1) of hypothyroid male rats that were either radiothyroidectomized (Tx) or had the neo-T4 syndrome (an endocrine disorder produced by large doses of thyroxine (T4) injected during the neonatal period) were studied. The mother rats were all normal. The fathers never had any contact with their progeny. Unexpectedly, the progeny usually showed delayed eye opening, decreased weaning weights, and increased final body weight. The thyroid glands from F1 offspring of both Tx and neo-T4 fathers were enlarged significantly in all but F1 males of Tx fathers. The F1 of Tx fathers had significantly smaller uteri, both absolutely and relatively. The ovaries were significantly larger, whereas the testes were significantly smaller. Pituitary TSH, stalk-median eminence (SME) TSH, and serum TSH were all normal with the exception of an increase in SME TSH in F1 males born of neo-T4 fathers. The response to thyrotropin releasing hormone (TRH) stimulation of the F1 adult progeny of neo-T4 fathers was significantly blunted in the males, whereas the response was normal in offspring of Tx fathers. The mechanisms by which hypothyroid fathers caused changes in their progeny is not known.