The role of growth factors and proto-oncogene in pulmonary vascular structural remodelling is not well known.The present study examined gene expression of platelet-derived growth factor（PDGF）-A and -B chain and proto-oncogene

c-myc

in lung tissue and pulmonary artery of rats exposed to hypoxia and compared to those levels of gene expression in normal rats.Normal lungs and pulmonary artery expressed PDGF-A chain transcript of 1.7 kb and PDGF-B chain transcript of 3.5 Kb.The c-myc transcript of 2.2 kb was expressed as well. After hypoxic exposure for 7 and 14 days mRNA levels of PDGF-B chain and cmyc were elevated significantly compared with those of control rats.PDGF-A chain mRNA increased after hypoxia for 7 days

and then declined.These results suggest that activation of autocrine and/or paracrine is important in proliferation mechanism of pulmonary artery smooth muscle cells in hypoxic pulmonary hypertensive rats.