Plaque rupture and subsequent embolism as well as thrombosis are major causes of acute myocardial infarction and stroke secondary to atherosclerosis. Pai-1, t-PA, TF and ET-1 are thrombosis- and thrombolysis-related factors which play important roles in thrombosis formation and plaque rupture. Since acute myocardial infarction and stroke are more likely to occur between 6 a.m. and 12 p.m. than at another time of the day, we studied the relationship between circadian rhythm and Pai-1, t-PA, TF and ET-1 in normal and atherosclerotic mice. Atherosclerosis was developed in apoE−/− mice fed a normal diet or a high cholesterol diet. The expression of Pai-1, t-PA, TF and ET-1 in the hearts of control C57BL/6J mice and atherosclerotic mice was measured by real-time RT-PCR at different Zeitgeber times (ZT) including ZT0, ZT4, ZT8, ZT10, ZT12, ZT14, ZT16 and ZT20. The expression of Pai-1, t-PA, TF and ET-1 peaked between ZT14 and ZT16 and bottomed at ZT10 in C57BL/6J mice. Their expression in apoE−/− mice fed a normal diet lost circadian rhythm. Their expression in apoE−/− mice fed a high cholesterol diet peaked at ZT4, indicating a reverse circadian rhythm. Our result indicates that circadian changes in the expression of Pai-1, t-PA, TF and ET-1 may be involved in the onset of myocardial infarction and stroke.

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