Phenotypic modification of arterial smooth muscle cells in response to medial dissection.

Abstract

In the treatment of peripheral arteries, percutaneous transluminal angioplasty is commonly associated with intimal tears and dissections. To investigate the influence of medial dissection on the remodelling of the vessel wall after balloon injury. Aortae were obtained from 14 Fauve de Bourgogne rabbits that had been fed a normal diet. Seven days after the initial pull-back injury, the aortae were examined using morphometric and immunocytochemical methods. Eight rabbits (57%) had a tear that extended into the media. Morphometric measurements showed that the intima was significantly thinner when there was a medial dissection [(18.3 +/- 6.9) x 10(-3) versus (39.1 +/- 3.5) x 10(-3) mm without dissection, P < 0.001]. In the media of injured vessels, medial dissection was associated with a greater accumulation of extracellular matrix proteins (50.5 +/- 9.7 versus 12.4 +/- 2.2% of the surface area), a marked reduction in alpha-smooth muscle actin content (36.6 +/- 5.4 versus 47.4 +/- 7.5% of the surface area), a higher expression of a smooth muscle activation antigen (21.2 +/- 5.7 versus 8.9 +/- 1.5% of the 2P1A2-immunostained surface area) and an increase in the number of medial proliferating cell nuclear antigen-positive nuclei (8.2 versus 1.2% of labelled nuclei). These observations indicated that mechanical injury of the arterial wall induces a phenotypic activation of medial smooth muscle cells. In the case of acute distension, the response of the smooth muscle cells in the media was mainly responsible for wound healing in the presence of medial dissection; moreover, acute distension induced a significant higher state of activation and a medial repairing that could prevent migration towards the intimal space.