Diurnal variation of the fibrinolytic system.

To elucidate which component(s) of the fibrinolytic system is (are) responsible for the diurnal variation of fibrinolytic activity we have studied several parameters of this system in 8 healthy male volunteers during a period of 24 h. Blood was collected at 8 a.m., 10 a.m., 12 a.m., 4 p.m., 8 p.m. and 8 a.m. next morning. The following tests were performed: euglobulin clot lysis time (ECLT), fibrinolytic activity of euglobulins on fibrin plates in the presence and absence of blocking antibodies to tissue-type plasminogen activator (t-PA) and/or urokinase (u-PA), overall plasminogen activator inhibitor (PAI) activity, antigen levels of t-PA, u-PA and PAI-1 and zymography of the euglobulin fraction after SDS-PAGE. From 8-10 a.m. to 4-8 p.m., total fibrinolytic activity increased by 113% (p less than 0.01) or 71% (p less than 0.01) when measured by ECLT or by fibrin plate assay, respectively. The immunoquenching experiments showed that this increase was entirely due to t-PA related activity whereas u-PA activity and t-PA/u-PA independent activity remained constant during the day. Average antigen levels of u-PA and t-PA in the afternoon were 6% and 25% lower than those measured in the morning. During this period, overall PAI activity and PAI-1 antigen decreased by 31% (p less than 0.01) and 52% (p less than 0.01) respectively. Electrophoretic-zymographic analysis of the euglobulins revealed that throughout the day the majority of t-PA was present in the form of the 110 kDa t-PA/PAI-1 complex. The intensity of this complex was lowest in the afternoon.(ABSTRACT TRUNCATED AT 250 WORDS)