Red blood cell effect on platelet adhesion and aggregation in low-stress shear flow. Myth or fact?

: Evidence has been accumulating which suggests that red blood cells affect platelet adhesion on nonbiological surfaces and platelet aggregation in the bulk; this in vitro study investigated these red blood cell effects. For samples of either whole blood or suspensions of either ghosts or red blood cells in platelet rich plasma undergoing low-stress simple shear flow, data on hemoglobin and adenosine diphosphate (ADP) released from red blood cells, single platelet reduction (which is a measure of platelet adhesion to nonbiological surfaces and platelet aggregation in the bulk) and percent of surface covered with platelets and platelet aggregates were obtained in a cone-and-plate viscometer for shear rates up to 5680 s-1. The results obtained suggest that red blood cells release a significant fraction of their ADP (2% at 5680 s-1), which is enough to induce platelet aggregation, and contribute about 65% to the total ADP release for a sheared blood sample; ADP released from red blood cells contributes about 60% to single platelet reduction and about 28% to platelet adhesion, whereas ADP from platelets contributes about 8% and 14%, respectively; and the physical effect of red blood cells, which is coupled to the chemical effect, acts to catalyze (enhance) the chemical effects. Based on the results obtained a mechanism was developed to describe both the chemical and physical nature of the red blood cell effect.