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 I1 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 [125~]-~3 in the presence and absence of excess non-labelled Tj, 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*^^ values (n=17) of 0.67f0.05 fmollug DNA (2400 sites/cell) and 500f52 pM, respectively. Adult lung (n=3) bound 0.31f0.03 fmol T3/ug DNA (1120 siteslcell, p a l vs. fetal) and the Kd = 540f144 pM (NS). The L2 and A549 cell lines contained 2280 and 1580 nuclear siteslcell, and had Kd values of 200 and 280 pM, respectively. In fetal lung, the abil ity 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'-isopropyltbyronine 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 I1 cells may be directly influenced by these hormones. To determine the efficiency of conversion as a function of dose, relative amount of the biologically active metabolite of cortisone (E), hydrocortisone (F), available in systemic circulation was determined following the oral administration of 5 and 50 mg of E containing 1 to 6 uc 14C-E. 26 studies were done: 8 dell subjects; 7 children, adrenogenital syndrome; 5, growth hormo:re deficiency; 2, Crohn's disease. Plasma concentrations of F were determined by liquid scintillation counting following TLC separation using silica ge? HF-254 and a solvent system of methylene chloride-ethanal (90-10). Relative fraction of F which reaches the systemic circulation was estimated by using the area ~nder the plasma concentration time curve normalized for differences in the radioactive dose and surface area of the subject. (AUC'). AUC' values of F for 50 mg E given i.v. is only slightly greater than when 50 mg E was given orally, but the F to E ratio vas much greater by the oral route indicating a greater preponjerance of the E to F conversion pathway during the absorptive ~hase. Mean normalized AUC values (in units of percent radiolctive dose, liter-1, min.) for 5 and 50 mg dose were 283.5 SDt104.7) and 157.8 (SD30.6) respectively, (p-<O.OOl)indicatng almost a 50% difference in conversion efficiencies at two loses. Conclusion: Conversion of E to F is dose-dependent at 5 to 50 mg dosage range apparently due to saturable enzymes in :he gut.and liver and/or saturab1.e transcortin binding during thc bs.orptive 1s neede~h",~e~re~mh6V'tfa%aP%"o\Sb'e"pWrh,"S"cA&YC'se To assess the risks'of dehydration and hGodilutionad;ring potentially normal circumstances in pati...

Thyroxine Metabolism in Cultured Cells Derived from Fetal Rat Lung

“…Using organotypic cultures of fetal rat lung alveolar type I1 cells, we found that T3 had a stimulatory effect on the synthesis of PC (34). The importance of T3 has also been indicated by the demonstration of specific high affinity T3 binding sites in the lung (3,17).The apparent role of T3 in developing lung as well as other organs has been particularly interesting in the face of the normally low serum concentrations of T3 present during the perinatal period (16,38). Additionally, in the rat, serum T3 concentrations remain low through the first week of postnatal life.…”

“…Using organotypic cultures of fetal rat lung alveolar type I1 cells, we found that T3 had a stimulatory effect on the synthesis of PC (34). The importance of T3 has also been indicated by the demonstration of specific high affinity T3 binding sites in the lung (3,17).…”