Physical and chemical effects of red cells in the shear-induced aggregation of human platelets

Abstract

Both chemical and physical effects of red cells have been implicated in the spontaneous aggregation of platelets in sheared whole blood (WB). To determine whether the chemical effect is due to ADP leaking from the red cells, a previously described technique for measuring the concentration and size of single platelets and aggregates was used to study the shear-induced aggregation of platelets in WB flowing through 1.19-mm-diameter polyethylene tubing in the presence and absence of the ADP scavenger enzyme system phosphocreatine-creatine phosphokinase (CP-CPK). Significant spontaneous aggregation was observed at mean tube shear rates, (G) = 41.9 and 335 s-1 (42% and 13% decrease in single platelets after a mean transit time (t) = 43 s, compared to 89 and 95% decrease with 0.2 microM ADP). The addition of CP-CPK, either at the time of, or 30 min before each run, completely abolished aggregation. In the presence of 0.2 microM ADP, CP-CPK caused a reversal of aggregation at (t) = 17 s after 30% of single cells had aggregated. To determine whether red cells exert a physical effect by increasing the time of interaction of two colliding platelets (thereby increasing the proportion of collisions resulting in the formation of aggregates), an optically transparent suspension of 40% reconstituted red cell ghosts in serum containing 2.5-micron-diameter latex spheres (3 x 10(5)/microliters) flowing through 100-microns-diameter tubes was used as a model of platelets in blood, and the results were compared with those obtained in a control suspension of latex spheres in serum alone. Two-body collisions between microspheres in the interior of the flowing ghost cell or serum suspensions at shear rates from 5 to 90 s-1 were recorded on cine film. The films were subsequently analyzed, and the measured doublet lifetime, tau meas, was compared with that predicted by theory in the absence of interactions with other particles, tau theor. The mean (tau meas/tau theor) for doublets in ghost cell suspensions was 1.614 +/- 1.795 (SD; n = 320), compared to a value of 1.001 +/- 0.312 (n = 90) for doublets in serum. Whereas 11% of doublets in ghost cell suspensions had lifetimes from 2.5 to 5 times greater than predicted, in serum, no doublets had lifetimes greater than 1.91 times that predicted. There was no statistically significant correlation between tau meas/tau theor and shear rate, but the values of tau meas/tau theor for low-angle collisions in ghost cell suspensions were significantly greater than for high-angle collisions.

Cell-Free and Erythrocytic S -Nitrosohemoglobin Inhibits Human Platelet Aggregation

“…22 RBCs are also rich sources of ADP, the spontaneous and/or evoked release of which has powerful platelet-activating effects in vitro. 23,24 Likewise, RBCs contain hemoglobin, which readily scavenges EDRF and NO. Thus, not surprisingly, RBCs have been shown to reverse EDRF-and NO-induced inhibition of intravascular platelet aggregation.…”

Are there sufficient standards for the in vitro hemocompatibility testing of biomaterials?

“…Static test systems simulate low flow or even no flow areas in the vasculature and provide a rapid and sensitive setup to determine the thrombogenicity of a biomaterial, in particular platelet adhesion. Dynamic systems are more appropriate to simulate the conditions in flowing whole blood in vivo or of extracorporeal devices and allow an adaptation of the test conditions to the (patho-) physiological situation of specific medical devices [93,94]. Different setups are currently used including: agitators, centrifugation systems, flow chambers, chandler systems and closed loop circulation models.…”

Small aggregates of platelets can be detected sensitively by a flow cytometer equipped with an imaging device: Mechanisms of epinephrine‐induced aggregation and antiplatelet effects of beraprost

“…These findings suggest that some factor(s) that enhance platelet aggregation are released from erythrocytes but not from leukocytes. Because ADP was the most probable candidate in view of the previous findings (9,18,19), the effect of ADP scavenger CP/CPK was examined. Epinephrine-induced and erythrocyte-enhanced platelet aggregation in PRP was inhibited strongly by CP/ CPK (Fig.…”

“…The possible contribution of erythrocytes to thrombosis and hemostasis has been attributed mainly to released ADP from erythrocytes (9). In fact, experiments with combined platelet-erythrocyte suspensions stimulated with a platelet agonist demonstrated that intact erythrocytes markedly enhance platelet activation (18,19). It is also clear now that the platelet-neutrophil interaction occurs at least in part through P-selection mediation and that neutrophils promote platelet reactivity (30,31).…”