In this experiment

expression of tissue-type plasminogen activator （t-PA） in smooth muscle cells （SMCs） was measured at different intervals after the arterial injury. In the normal iliac arteries

only low levels of t-PA activity were estimated. t-PA activity in extracts of the iliac arteries increased significantlyat the 4th day after the injury

equivalent to the process that SMCs migrated from the media to the intima

and the t-PA activity was then decreased approximately to the normal level at the 7th day. Coexistent to the above data

results from in situ hybridization showed that the expression of t-PA mRNA in the intima as well as media increased also significantly at the 4th day after the arterial injury

and at the 7th day

tPA mRNA was detected only in those SMCs locating closely adjacent to the internal elastic lamina. These results suggest that t-PA might play an important role in SMC migration following endothelial injury

andantagonism of t-PA expression and/or activity within the vessel wall might be helpful in intervening the de velopment of restenosis following angioplasty.