Maximum fluid concentrations of materials released from platelets at a surface

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Abstract
The estimation of local concentrations of materials that are released from the dense and .alpha.-granules of [human] platelets during accumulation of platelets on collagen-coated glass was examined. Platelet/red blood cell suspensions were perfused through a 1.3-mm-ID [inside diameter] 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. The IFC is dependent on the shear rate at the surface (G) and is proportional to G0.27. This means that an 8-fold increase in flow rate would increase the IFC .apprx. 2-fold. Serotonin, pyrophosphate, AMP and ATP were not present in sufficient quantities to produce IFC that could influence platelet aggregatin if used alone at the IFC. A 2nd set of materials, fibrinogen, fibronectin von Willebrand factor and Ca, had IFC less than their concentrations normally found in plasma. A 3rd category, containing 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.