Expression of C-type natriuretic peptide during development of rat lung

C-type natriuretic peptide (CNP), recently found to be secreted from vascul ar endothelial cells, is now viewed as a novel endothelium-derived relaxing peptide. However, the distribution and expression of CNP during cardiopulm onary development is unclear. To follow changes in the expression of CNP du ring lung development, we examined rat embryos and neonates using Northern blot analysis and in situ hybridization for CNP mRNA and radioimmunoassay a nd immunohistochemistry for CNP protein. A substantial expression of CNP mR NA was first detected on postnatal day 2, and it thereafter remained fairly steady. The level of CNP protein also increased rapidly after postnatal da y 1, reaching a settled level on postnatal day 4. CNP protein and mRNA were detected in the endothelium and smooth muscle cells of blood vessels and i n bronchial airway and alveolar epithelia. Immunoreactivity for CNP protein in the endothelium of blood vessels increased to an intense level after th e saccular stage. These results suggest that the changes in CNP levels may be related to the occurrence of pulmonary vasodilation after birth.