Reciprocal changes in endothelial and inducible nitric oxide synthase expression following carotid angioplasty in the pig

Objective. Nitric oxide produced by nitric oxide synthase appears to have a n important role in the regulation of arterial tone, platelet adhesion and smooth muscle cell proliferation. Our aim was to investigate the effects of balloon angioplasty on expression of endothelial NO synthase (cNOS) and in ducible NO/synthase (iNOS) in the pig carotid artery and to relate any chan ges in expression to the processes of reendothelialisation and vascular rep air. Methods. Pigs were sacrificed at various time points to follow NOS exp ression in the neointima, media and regenerated endothelium. Immunocytochem ical staining was used to localize cNOS and iNOS expression in the vessel w all. Relative amounts of cNOS were measured using quantitative in vitro aut oradiography. cNOS mRNA and iNOS mRNA was quantified by competitive PCR bas ed on the sequenced cDNA of porcine cNOS and iNOS. Results. Uninjured carot id arteries exhibited dense uniform luminal endothelial staining for cNOS. Balloon angioplasty caused denudation of cNOS immunoreactive cells and a ma rked reduction of cNOS gene expression but a complete recovery was noted by day 35. In normal uninjured carotid arteries no evidence of iNOS immunorea ctivity was demonstrable but 24 h after injury, marked homogeneous iNOS imm unoreactivity was detected in medial vascular smooth muscle cells. By 5 day s, staining was evident in cells within the forming neointimal layer with n o evidence of NOS immunoreactivity in the media. iNOS immunoreactivity pers isted in cells at the luminal surface at 7 days and iNOS gene expression ap peared to be sustained in some animals with ruptured internal elastic lamin a at 21 days. Conclusion. Balloon injury is associated with de-endotheliali sation and a marked reduction in cNOS gene expression and activity. iNOS is induced throughout the arterial media within VSMC soon after balloon injur y and persists for up to 21 days. These observations imply an important reg ulatory role for locally generated NO in the pathophysiological response to balloon injury. (C) 1999 Elsevier Science ireland Ltd. All rights reserved .