Extracellular matrix accumulation on the thickened neointima in a rat double-balloon injury model

We developed a rat double-balloon injury model and studied the thickened ne ointima using immunohistochemical and RT-PCR methods. Fourteen days after t he first balloon injury of the rat left common carotid artery, a second bal loon injury was inflicted in the same place. Histochemical sections taken 1 4 days after the single- and double-balloon injuries were used for calculat ing intimal/medial (I/M) area ratios, as an indicator of neointimal formati on, and were subjected to immunohistochemical staining. Total RNA was also purified from some arteries and mRNA expression of some extracellular matri ces (ECM) and cytokine receptors related to ECM metabolism was estimated us ing the RT-PCR method. The I/M ratio in the rat double-balloon injury model (II) (1.84 +/- 0.62 (mean +/- SE, n = 5)) was significantly (p < 0.05) hig her than that in the single-balloon injury model (I) (1.30 +/- 0.19, n = 10 ). The cell number per neointimal area was less in II than in I. As for the phenotype of smooth muscle cells, alpha-actin staining showed that the neo intima of II consisted of more contractile form than synthetic, whereas tha t of I consisted of more synthetic form than contractile. The neointima of II was strongly stained with laminin and fibronectin, but that of I was sta ined only weakly. Consistent with these data, laminin and fibronectin mRNAs were markedly expressed in the neointima of II. Neointimas of both I and I I were also stained positively with PDGF (alpha and beta) and TGF-beta (typ es I and II) receptors to the same extent. These results show: that ECM acc umulation, particularly of laminin and fibronectin, characterizes the doubl e-balloon injury model; that the marked accumulation of ECM in this model i s due to a mechanism other than the PDGF or TGF-beta signalling pathway; an d that this model resembles the lesion of post-PTCA re-stenosis, and theref ore provides the key for its investigation.