Ultrastructural localization of nitric oxide synthase and endothelin in coronary and pulmonary arteries of newborn rats

This is the first report on the ultrastructural distribution of nitric oxide synthase and endothelin immunoreactivities in the coronary and pulmonary arteries of newborn Wistar rats. The distribution of nitric oxide synthase and endothelin was investigated using pre-embedding peroxidase-antiperoxidase immunocytochemistry. In both arteries examined, positive labelling for nitric oxide synthase was localized both in the endothelium and smooth muscle, whereas positive labelling for endothelin was localized in the endothelium exclusively. In the coronary artery, approximately 80% and 55% of the endothelial cells examined were positive for nitric oxide synthase and endothelin, respectively, whereas in the pulmonary artery, 77% and 60% of the endothelial cells were positive for nitric oxide synthase and endothelin, respectively. These findings indicate that nitric oxide synthase and endothelin are colocalized in some of the endothelial cells of the newborn rat. In the endothelium, nitric oxide synthase and endothelin immunoreactivities were distributed throughout the cell cytoplasm and in association with the membranes of intracellular organelles. In smooth muscle, a relationship of nitric oxide synthase immunoreactivity to endoplasmic reticulum was observed in the pulmonary artery. In summary, in the newborn rat, endothelial cells of the coronary and pulmonary artery are rich in nitric oxide synthase (neuronal isoform) and endothelin, and it is suggested therefore that they may be substantially involved in vasomotor control of the cardiac and pulmonary circulation during early stages of postnatal development.