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Mechanisms underlying the morning increase in platelet aggregation: a flow cytometry study
N P Andrews1, H R Gralnick, P Merryman
1Cardiology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA.
Journal of the American College of Cardiology
|December 1, 1996
Summary
The morning increase in platelet aggregation upon standing is not due to platelet activation markers. Instead, higher catecholamine levels, platelet count, and hemoconcentration likely drive this phenomenon.
Area of Science:
- Cardiovascular Physiology
- Hemostasis and Thrombosis
- Biomedical Research
Background:
- The morning surge in platelet aggregability contributes to increased thrombotic cardiovascular events.
- Mechanisms behind the morning increase in platelet aggregation are not well understood.
Purpose of the Study:
- To investigate the mechanisms behind the morning increase in platelet aggregation after arising and assuming the upright posture.
- To examine platelet surface activation markers, whole-blood platelet aggregation, and relevant hematologic factors.
Main Methods:
- Measured platelet surface antigen expression, whole-blood platelet aggregation, platelet count, and hematocrit in 17 healthy volunteers before and after standing.
- Assessed fibrinolytic variables (tissue-type plasminogen activator, plasminogen activator inhibitor 1) and catecholamine levels.
Main Results:
- Platelet aggregation increased significantly upon standing, but without changes in activation-dependent surface markers.
- Platelet count and hematocrit increased, as did norepinephrine and epinephrine levels.
- Hemoconcentration and increased platelet count in vitro mimicked the observed increase in platelet aggregation.
Conclusions:
- The morning increase in platelet aggregation is not associated with the expression of activation-dependent platelet surface receptors.
- Elevated catecholamine levels, increased platelet count, and hemoconcentration are suggested as primary drivers of enhanced whole-blood aggregation upon standing.