Postnatal development of pulmonary alveoli: modulation in rats by thyroid hormones.

We studied the effect of thyroid hormones on the postnatal development of the gas exchange region of rat lungs. Treatment with triiodothyronine (T3, 0.1 microgram . g body wt-1 . day-1) accelerated the increase of the surface-to-volume ratio (S/V) and surface area (Sa) and decrease of the mean chord length (Lm) of the gas exchange structures of pups killed at age 7 days. Propylthiouracil (PTU, 100 micrograms twice daily) from age 1 to 13 days, with death at age 14 days, diminished the rise of S/V and Sa and the fall of Lm compared with diluent-injected pups. Providing drinking water with 0.01% PTU to dams from gestation day 20 (term 22 days) to postnatal day 14 also diminished the rise of S/V and fall of Lm. Treatment of pups nursed by dams drinking 0.01% PTU with thyroxine (0.1 microgram/g body wt) every other day from age 1 to 13 days significantly diminished the effect of PTU on S/V, Sa, and Lm. We conclude thyroid hormones can modulate the postnatal architectural development of the gas exchange region of the rat lung.