Circadian variation of platelet function measured with the PFA-100

Area of Science:

• Physiology
• Pathophysiology
• Chronobiology

Background:

• Circadian rhythms significantly influence human physiology and disease processes.
• Previous studies indicated circadian variations in platelet function, but were limited by methodology (optical aggregometry, low shear stress).

Purpose of the Study:

• To investigate the impact of circadian rhythms on platelet function in whole blood under high shear rates.
• To evaluate the suitability of the Platelet Function Analyzer-100 (PFA-100) for assessing circadian alterations in platelet activity.

Main Methods:

• Healthy volunteers' platelet function was assessed using the PFA-100 with collagen/epinephrine and collagen/ADP cartridges.
• Measurements were taken at various intervals throughout a 24-hour period.
• Concentrations of fibrinogen and factor VIII activity were also determined.

Main Results:

• Platelet function, indicated by closure time on the PFA-100, exhibited a circadian rhythm, peaking at 2:00 AM.
• Collagen/epinephrine cartridge closure time was significantly longer at 2:00 AM compared to 8:00 AM (p=0.004).
• Fibrinogen levels and factor VIII activity were lowest during nighttime hours (10:00 PM - 4:00 AM).

Conclusions:

• A distinct circadian rhythm exists in human platelet function, measurable with the PFA-100 under high shear conditions.
• The PFA-100 is a practical and effective tool for studying circadian variations in platelet function.
• These findings highlight the importance of considering diurnal variations in platelet activity in physiological and pathological contexts.