Circadian Interrelationships Among Levels of Plasma Fibrinogen, Blood Platelets, and Serum Interleukin-6

Circadian (24 h) rhythms of fibrinogen, interleu kin-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 level (acro phase) of fibrinogen would follow the acrophase of IL-6, based on the fact that IL-6 is the stimulus for fibrinogen production in the liver. Platelet levels were measured to show whether there was any correlation with the IL-6 acrophase because it has been reported that IL-6 affects megakaryocytes 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 counts peaked at 16:56 h. Thus, there was a positive correlation between IL-6 and fibrinogen acrophases and a negative corre lation of each with the acrophase for platelets. The positive linkage of IL-6 with fibrinogen in this study suggests that sup pression of IL-6 production would lower those peak fibrinogen levels that occur in the morning in association with arterial ischemic events. This could result in fewer arterial ischemic events, especially in the morning. Key Words: Circadian— Fibrinogen—Interleukin—6 (IL-6)—Platelets—Arterial ischemia.