[Low concentrations of epinephrine can augment shear stress-induced platelet aggregation]

Platelet aggregation induced by shear stress is distinct from that induced by an agonist such as ADP or collagen. The physiological significance of shear-induced platelet aggregation was investigated by measuring the effects of the presence of physiological concentrations of epinephrine. Blood samples were taken from 10 normal volunteers who had received no drugs known to interfere with platelet functions for 1 month preceding the study. Blood was mixed with 1/10 volume of 3.1% sodium citrate solution. Platelet-rich plasma and platelet-poor plasma were prepared by centrifugation at 100 g for 15 min and 2,000 g for 15 min, respectively. The platelet count of platelet-rich plasma was adjusted to 3 x 10(5)/microliters. Shear-induced platelet aggregation in platelet-rich plasma was determined using a modified cone and plate viscometer controlled by a personal computer system. The intensity of light transmission was continuously recorded. The percent platelet aggregation was calculated according to the Lambert-Beer equation. Platelet aggregation occurred under both low (12 dyn/cm2) and high (108 dyn/cm2) shear stress. More significant aggregation was observed under high shear stress. The maximum percent platelet aggregation was 44.7 +/- 13.4%, which increased to 53.3 +/- 10.0% in the presence of 10 pg/ml epinephrine. With 100 pg/ml of epinephrine, shear-induced platelet aggregation induced by 12 dyn/cm2 shear significantly increased, but the effects on shear-induced platelet aggregation of 108 dyn/cm2 shear were not uniform. Shear-induced platelet aggregation is enhanced by physiological concentrations of epinephrine, which may be a cause of arterial thrombotic occlusion in sympathomimetic states.