Flow cytometric analysis of circadian changes in platelet activation usinganti-GMP-140 monoclonal antibody

The hemostatic activity of blood shows a circadian variation with a higher frequency of acute coronary events in the morning. The thrombotic tendency of blood is influenced by many factors, including platelets. Diurnal change s of in vivo platelet activation were investigated by whole blood flow cyto metry in 10 young healthy male volunteers using anti-GMP-140 (anti-alpha-gr anule membrane protein 140 kD) monoclonal antibody at 3h intervals from 06: 00 to 24:00. We also studied circulating platelet aggregates to investigate whether there exists a similarity between the results of these methods. Re sults of flow cytometric analysis indicate that there is an increase in pla telet activation during the period from 06:00 to 09:00. Platelet activation then decreases gradually during the period from noon to midnight. These ch anges are accompanied by a similar trend in circulating platelet aggregates . This suggests that GMP-140 expression on platelets is synchronized with o r followed by platelet aggregate formation in vivo, and increased platelet activation may predispose individuals to thrombosis at this time.