Maximum fluid concentrations of materials released from platelets at a surface.

We examine the estimation of local concentrations of materials that are released from the dense and alpha-granules of platelets during accumulation of platelets upon collagen-coated glass. Platelet/red blood cell suspensions were perfused through a 1.3-mm-ID tube. Empirical data were used in a calculation procedure, based on diffusion and convection, designed to yield an upper bound on the interfacial fluid concentration (IFC) for each substance considered. The necessary empirical data are the rate of platelet accumulation and the maximum amount of material in the platelet capable of secretion. It was found that the IFC is dependent on the shear rate at the surface (G) and is proportional to G0.27. This means that an eightfold increase in flow rate would increase the IFCs approximately twofold. Serotonin, pyrophosphate, adenosine 5'-monophosphate (AMP), and adenosine 5'-triphosphate (ATP) were found not to be present in sufficient quantities to produce IFCs that could influence platelet aggregation if used alone at the IFC. A second set of materials, fibrinogen, fibronectin von Willebrand factor, and calcium, had IFCs less than their concentrations normally found in plasma. A third category, containing adenosine 5'-diphosphate (ADP) alone, had an IFC close to those known to affect platelet aggregation. The role of metabolites of arachidonic acid, which may promote or inhibit platelet aggregation, awaits further description.