SHIFT WORK AND CIRCADIAN-RHYTHM OF BLOOD FIBRINOLYTIC PARAMETERS

The influence of shift work on circadian fluctuation of fibrinolytic parameters was studied in ten men working on alternating 7-day and 7-night shifts. Ten age-matched men working during the day only served as controls. Venous blood was collected on the last day of each shift at 8 a.m., noon, 4 p.m., 8 p.m., midnight and 4 a.m. The well-known diurnal fluctuations were observed in the control subjects t-PA antigen, PAI-1 antigen and PAI-1 activity decreased during the day. A steeper and earlier decrease of PAI-activity explained continuous increase in t-PA activity from the morning hours till late afternoon. In shift workers during both day and night shift t-PA antigen showed much lower fluctuations and an earlier occurrence of the lowest values. This phase advanced shift of several hours was even more evident for PAI-1 activity, which did not lose its amplitude. These results suggest that circadian fluctuation of fibrinolytic activity shows characteristics of disturbed biorhythm: reduction of amplitude and shift of the phase. © 1990.