Circadian interrelationships among levels of plasma fibrinogen, blood platelets, and serum interleukin-6

Circadian (24 h) rhythms of fibrinogen, interleukin-6 (IL-6), and platelet levels were studied in 11 males ages 46 to 72 years. Since there is a known circadian rhythm for fibrinogen and IL-6, we postulated that the peak leve l (acrophase) of fibrinogen would follow the acrophase of IL-6, based on th e fact that IL-6 is the stimulus for fibrinogen production in the liver. Pl atelet levels were measured to show whether there was any correlation with the IL-6 acrophase because it has been reported that IL-6 affects megakaryo cytes and platelets in dogs. We found that the acrophase for IL-6 occurred at 02:03 h and the acrophase for fibrinogen occurred at 09:16 h. Platelet c ounts peaked at 16:56 h. Thus, there was a positive correlation between IL- 6 and fibrinogen acrophases and a negative correlation of each with the acr ophase for platelets. The positive linkage of IL-6 with fibrinogen in this study suggests that suppression of IL-6 production would lower those peak f ibrinogen levels that occur in the morning in association with arterial isc hemic events. This could result in fewer arterial ischemic events, especial ly in the morning.