Regulation of Endothelial Nitric Oxide Synthase Expression in Small Pulmonary Arteries and Airways of Chronically Ventilated Preterm Lambs. † 1700

Nitric oxide is an important signaling molecule involved in the regulation of smooth muscle tone, cell-cell interactions, and cell proliferation. In previous studies we demonstrated that endothelial cells and epithelial cells in culture express endothelial nitric oxide synthase (eNOS), one form of the enzyme responsible for synthesis of nitric oxide, and that eNOS is regulated differently in these two cell types (Am. J. Physiol. 1996;270:L643-L649). In studies designed to investigate the biology of nitric oxide in chronic lung disease, we demonstrated by immunohistochemistry that eNOS is present in two important regions of the developing lung in sheep: distal branches of the pulmonary artery and small airways (Pediatr. Res. 39:339A, 1996). To determine if eNOS is regulated differently in endothelium and epithelium in vivo, we delivered premature lambs at 125 d gestation (term 147 d) and mechanically ventilated them for 3-4 weeks with sufficient supplemental oxygen to keep PaO₂ 50 - 90 mmHg. At the conclusion of the study, we harvested the lungs and dissected distal pulmonary arteries and small airways from the left caudal lobe of each lamb and homogenized the tissue for immunoblot analysis. In small pulmonary arteries, eNOS protein content was 58% less in lambs with chronic lung disease (n=8) compared to control term lambs (n=6) that were matched for the same post conceptual age (control: 204 ± 97 vs. chronic ventilation: 86 ± 52 arbitrary densitometric units, mean± SD, p<0.05). In contrast, eNOS protein expression in small pulmonary airways was similar in chronically ventilated lambs (n=4) and term newborn controls (n=4) (control: 223 ± 99 vs. chronic ventilation: 210±79 arbitrary densitometric units). These results show differential expression of eNOS protein in pulmonary endothelium and epithelium in vivo in lambs with chronic lung disease compared to lambs of similar post conceptual age. Further studies to evaluate the mechanisms by which eNOS is regulated in lung endothelial and epithelial cells may provide important information regarding the regulation of vascular and airway tone, as well as other cellular processes in which nitric oxide impacts lung development.