EFFECT OF A CHANGE IN THE SLEEP WAKE CYCLE ON THE DIURNAL-VARIATION OF FIBRINOLYTIC PARAMETERS/

The mechanism underlying the circadian rhythm of fibrinolysis is not w ell understood. To evaluate the influences of wakefulness and of the i ntrinsic circadian rhythm on fibrinolytic activity, we examined diurna l changes (8:00 am vs. 8:00 pm) in plasminogen activator inhibitor-1 ( PAI-1) activity, tissue plasminogen activator (t-PA) antigen levels, a nd t-PA activity, as well as in plasma serum cortisol levels, in 10 he althy males (21 +/- 2 years) for two consecutive days. On the first da y, subjects remained awake all day and night. They slept during the da ytime (8:30 am to 5:30 pm) on the following day. PAI-1 activity and co rtisol levels were significantly decreased, and t-PA activity tended t o increase during the daytime on the first day. On the morning followi ng overnight wakefulness, PAI-1 activity and cortisol levels did not r eturn to the levels of the previous morning. On the second day, the af ternoon decrease in PAI-1 activity, but not cortisol levels, was still observed, although its magnitude was substantially attenuated. No sig nificant diurnal changes were observed in the levels of t-PA antigen t hroughout the study period. These findings suggest that the diurnal va riation of fibrinolytic activity may be governed by an intrinsic circa dian rhythm of PAI-1, which can be modified by a change in the time of wakefulness.