TIME COURSE OF SMOOTH-MUSCLE CELL-PROLIFERATION IN THE INTIMA AND MEDIA OF ARTERIES FOLLOWING EXPERIMENTAL ANGIOPLASTY

Smooth muscle cell (SMC) proliferation is known to be an important factor for the development of restenosis after percutaneous transluminal coronary angioplasty. To determine the time course of intimal and medial SMC proliferation and morphological changes after experimental angioplasty, an intimal atheroma was produced with repeated weak electrical stimulations in the right carotid artery of 45 male New Zealand White rabbits. Angioplasty was subsequently performed in 35 rabbits, and the proliferative responses were analyzed with histomorphological and immunohistological criteria at 3, 7, 14, 21, 28, and 42 days after intervention. A hemodynamic relevant stenosis after angioplasty was found in eight (23%) of 35 dilated arteries. In five rabbits the stenosis was due to a mural thrombus, and in three animals restenosis was caused by intimal SMC proliferation. In all dilated arteries the intimal wall thickness increased from 13 ± 5 intimal cell layers (after electrical stimulation) to 33 ± 14 cell layers during 28 days after angioplasty (p < 0.05). Later than 4 weeks after angioplasty, no additional increase of intimal thickening occurred. Application of bromodeoxyuridine 18 and 12 hours before excision of the vessels allowed determination of the percent of cells undergoing DNA synthesis in the intima and media using monoclonal antibody against bromodeoxyuridine. SMCs were identified by α-actin staining. Immunohistological quantification of intimal SMC proliferation showed a maximum of cells undergoing DNA synthesis within the first 7 days after angioplasty (p < 0.01). In contrast, medial proliferation of SMCs was delayed and showed a small but significant increase 21 days after dilatation (p < 0.05). Twenty-eight days after angioplasty, SMC proliferation in the media as well as in the intima was normalized and comparable to the control group without angioplasty.