277 TRIIODOTHYRONINE NUCLEAR BINDING IN RABBIT LUNG AND CULTURED LUNG CELLS

Abstract

To investigate the possible mechanism of thyroid hormone effects in lung development and function, we examined rabbit lung and two cell lines apparently derived from type II alveolar cells for specific nuclear binding of L-triiodothyronine (T3). Nuclei isolated from lung were incubated at 37 C for 1.5 h with various concentrations of [125I]-T3 in the presence and absence of excess non-labelled T3, and then washed in buffer with 0.2% Triton X-100. In fetal lung, the concentration of T3 binding sites and the dissociation constant (Kd) were constant between 24-30 days gestation with mean±SE values (n=17) of 0.67±0.05 fmol/μg DNA (2400 sites/cell) and 500±52 pM, respectively. Adult lung (n=3) bound 0.31±0.03 fmol T3/μg DNA (1120 sites/cell, p<.01 vs. fetal) and the Kd = 540±144 pM (NS). The L2 and A549 cell lines contained 2280 and 1580 nuclear sites/cell, and had Kd values of 200 and 280 pM, respectively. In fetal lung, the ability of analogs to compete for L-T3 binding (100%) was: 3, 5-diiodo-3′-isopropylthyronine 81%, D-T3 73%, L-T4 6.7%, L-T2 0.19%, 3, 5-dimethyl-3′-isopropylthyronine 0.15%, and reverse T3 0.08%. We conclude that rabbit lung and cultured epithelial lung cells contain nuclear binding sites with a high affinity and specificity for thyroid hormones. This suggests that both fetal and adult lung and their type II cells may be directly influenced by these hormones.