Thyroid hormone-induced precocious growth and maturation of the embryonic chicken liver

: The effects of thyroid hormones thyroxine (T4) or triiodothyronine (T3) on the ontogeny of chicken embryonic liver were studied. Two micrograms of T4 administered to chicken embryos, prior to day 11 of incubation, was found to be least toxic and effective in increasing liver weights, total protein and DNA and RNA, over those of controls. A non-toxic dose of T4 (0.1 microgram) had no effect on embryonic chicken liver. Injection of 125I-labelled T4 or T3 into chick embryos showed that T4 was taken up in greater amounts by the liver than was T3. Uptake of both hormones by the liver increased dramatically around day 9 of incubation. Induction of hypothyroidism by methimazole (a goitrogen) suppressed the natural increase in liver weight.