The influence of thyroid hormones on the growth of the lungs in perinatal rats.

The growth and rates of protein turnover in the perinatal lung have been studied in the rat during normal development between late gestation and weaning, and after altering their thyroid status. The aim was to establish what influence thyroid hormones have on the early stages of growth in the lungs. Perinatal hypothyroidism was induced by administering propylthiouracil (PTU) via the mothers' drinking water from late gestation and throughout lactation. A precocious and elevated surge of thyroid hormones was induced by daily injections of T4 from day 3 postpartum onwards. Hypothyroidism in the neonate, but not the fetus, significantly retarded the growth of the animal and its lungs. This was attributable to a decrease in both the pulmonary rates of protein synthesis and protein degradation; the effect on the former rate exceeding that on the latter. Neonatal hyperthyroidism did not significantly alter protein turnover or the growth of the lungs, compared with euthyroid control tissues. This contrasts with the accelerated growth of some other body tissues in the presence of excess thyroid hormones.