1. The effects of mental stress induced by a colour word conflict test (CWT; n = 9) or 3 h infusions of placebo or adrenaline (0.4 nmol min−1 kg−1; n = 9) on platelet function in vivo were studied in 16 healthy male volunteers.

2. Platelet function was assessed by a filtragometry technique, which reflects aggregability in vivo, and by measurements of the plasma levels of β-thromboglobulin (β-TG) and platelet factor 4 (PF4).

3. Adrenaline and CWT induced marked cardiovascular responses as expected. Venous plasma adrenaline increased from 0.1–0.2 nmol/l at rest to 4.87 ± 0.42 nmol/l during adrenaline infusion and to 0.46 ± 0.10 nmol/l during CWT.

4. Filtragometry measurements were reproducible within individuals with coefficients of variation of 7.9% during placebo infusion and 5.4% for resting measurements between days.

5. Platelet aggregability, as measured by filtragometry, was similarly increased during both adrenaline infusion (P < 0.05) and CWT (P < 0.01).

6. The coefficients of variation for β-TG and PF4 levels were 17.3% for log β-TG and 27.9% for log PF4 between days, but could not be calculated for within-day variability. Both β-TG (P < 0.05) and PF4 (P < 0.01) levels decreased time-dependently during placebo infusion, indicating that long resting periods (hours) are needed to attain basal levels. Artefactual results could not be identified by evaluating βTG/PF4 ratios.

7. β-TG and PF4 levels did not decrease time-dependently during adrenaline infusion. There were no significant changes of β-TG or PF4 during CWT.

8. Our results suggest that platelet aggregability in vivo is enhanced by mental stress and high physiological levels of circulating adrenaline. The more pronounced effect of adrenaline and CWT on filtragometry readings than β-TG and PF4 levels in plasma suggests that platelet aggregability in vivo is not necessarily paralleled by increased platelet release.

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