Objective:To study the expression of proto-oncogene c-fos、c-jun in arterial wall during the early period after balloon injury. Methods: The balloon catheter injury was performed on left common carotid of rat by imitating the process of angioplasty. Total RNA was isolated from the arterial wall at different time after injury. Expression of c-fos、c-jun mRNA was demonstrated and levels of two mRNA were estimated by the reverse transcriptase-polymerase chain reaction (RT-PCR). Meanwhile

presence of c-fos protein in vascular smooth muscle cells (VSMCs) was detected with immunohistochemistry. Results: The expression of c-jun reached its maximum 30 min after injury and remained elevated at 1 and 2 hour. c-fos level was maximal at 0.5 h and maintained for 1 hour. Afterwards it gradually declined and returned to basal levels after 5 h. Immunostain of c-fos protein was mostly positive in the remaining VSMCs at 45 min ( 86% ). Conclusion: Balloon injury induces high expression of c-fos and c-jun in the very early period. Using RT-PCR to detect proto-oncogene expression provides a sensitive method for studying the principle of VSMCs activition and proliferation during the early period after injury.