The endogenous circadian system caused significant rhythms in platelet surface activated GPIIb-IIIa, GPIb, and P-selectin with 6-17% peak-to-trough amplitudes peaking during the biological morning.
Does the human endogenous circadian system influence platelet activation independent of behavioral stressors?
The endogenous circadian system drives a morning peak in platelet activation independent of behaviors, providing a physiological mechanism for the known morning peak in adverse cardiovascular events.
Effect estimate: 17% peak-to-trough amplitude
p-value: p=0.012
BACKGROUND: Platelets are involved in the thromboses that are central to myocardial infarctions and ischemic strokes. Such adverse cardiovascular events have day/night patterns with peaks in the morning (~9 AM), potentially related to endogenous circadian clock control of platelet activation. The objective was to test if the human endogenous circadian system influences (1) platelet function and (2) platelet response to standardized behavioral stressors. We also aimed to compare the magnitude of any effects on platelet function caused by the circadian system with that caused by varied standardized behavioral stressors, including mental arithmetic, passive postural tilt and mild cycling exercise. METHODOLOGY/PRINCIPAL FINDINGS: We studied 12 healthy adults (6 female) who lived in individual laboratory suites in dim light for 240 h, with all behaviors scheduled on a 20-h recurring cycle to permit assessment of endogenous circadian function independent from environmental and behavioral effects including the sleep/wake cycle. Circadian phase was assessed from core body temperature. There were highly significant endogenous circadian rhythms in platelet surface activated glycoprotein (GP) IIb-IIIa, GPIb and P-selectin (6-17% peak-trough amplitudes; p ≤ 0.01). These circadian peaks occurred at a circadian phase corresponding to 8-9 AM. Platelet count, ATP release, aggregability, and plasma epinephrine also had significant circadian rhythms but with later peaks (corresponding to 3-8 PM). The circadian effects on the platelet activation markers were always larger than that of any of the three behavioral stressors. CONCLUSIONS/SIGNIFICANCE: These data demonstrate robust effects of the endogenous circadian system on platelet activation in humans--independent of the sleep/wake cycle, other behavioral influences and the environment. The 9 AM timing of the circadian peaks of the three platelet surface markers, including platelet surface activated GPIIb-IIIa, the final common pathway of platelet aggregation, suggests that endogenous circadian influences on platelet function could contribute to the morning peak in adverse cardiovascular events as seen in many epidemiological studies.
Scheer et al. (2011) studied Healthy adults (n=12). Forced desynchrony protocol vs. Within-subject across circadian phases was evaluated on Endogenous circadian rhythm in platelet surface activated GPIIb-IIIa (17% peak-to-trough amplitude, p=0.012). The endogenous circadian system caused significant rhythms in platelet surface activated GPIIb-IIIa, GPIb, and P-selectin with 6-17% peak-to-trough amplitudes peaking during the biological morning.