Summary
Platelet thrombi have been observed at bifurcations, constrictions and stenoses in
the arterial tree where flow separation with accompanying vortex formation can occur.
Hence, studies of the flow behavior of human blood cells in models of à vessel obstruction
and a sudden expansion of a vessel lumen were carried out. These showed that the particles
were subjected to first high, and then much lower shear stresses as they entered the
vortices where the environment appeared favorable for the formation of aggregates.
The effects of high and variable shear stress on the release reaction and aggregation
of platelets were therefore studied using cells labeled with C14-Serotonin suspended in Tyrodes-albumin undergoing oscillatory tube flow for 20 min
at 37° C. There was no significant release of serotonin due to flow alone, but the
thrombin-induced release of C14-activity was appreciably greater in suspensions subjected to shear rates > 2000 sec-1 than in control suspensions which had been incubated at rest. The synergistic effects
of the shear flow were also noted in the presence of adrenaline, which increased the
release reaction, and when [Ca++] was raised above the physiological level or acetyl salicylic acid added, which inhibited
the release of serotonin.
