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 an 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 inducible NO/synthase (iNOS) in the pig carotid artery and to relate any changes in expression to the processes of reendothelialisation and vascular repair. Methods. Pigs were sacrificed at various time points to follow NOS expression in the neointima, media and regenerated endothelium. Immunocytochemical staining was used to localize cNOS and iNOS expression in the vessel wall. Relative amounts of cNOS were measured using quantitative in vitro autoradiography. cNOS mRNA and iNOS mRNA was quantified by competitive PCR based on the sequenced cDNA of porcine cNOS and iNOS. Results. Uninjured carotid arteries exhibited dense uniform luminal endothelial staining for cNOS. Balloon angioplasty caused denudation of cNOS immunoreactive cells and a marked reduction of cNOS gene expression but a complete recovery was noted by day 35. In normal uninjured carotid arteries no evidence of iNOS immunoreactivity was demonstrable but 24 h after injury, marked homogeneous iNOS immunoreactivity was detected in medial vascular smooth muscle cells. By 5 days, staining was evident in cells within the forming neointimal layer with no evidence of NOS immunoreactivity in the media. iNOS immunoreactivity persisted in cells at the luminal surface at 7 days and iNOS gene expression appeared to be sustained in some animals with ruptured internal elastic lamina at 21 days. Conclusion. Balloon injury is associated with de-endothelialisation and a marked reduction in cNOS gene expression and activity. iNOS is induced throughout the arterial media within VSMC soon after balloon injury and persists for up to 21 days. These observations imply an important regulatory role for locally generated NO in the pathophysiological response to balloon injury. (C) 1999 Elsevier Science ireland Ltd. All rights reserved.