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 the offspring of Tx fathers. The mechanisms by which hypothyroid fathers caused changes in their progeny is not known.