Comparison of platelet aggregation and adenosine triphosphate secretion in whole blood and platelet-rich plasma from normal dogs

Platelet aggregation and adenosine triphosphate (ATP) secretion were measured in whole blood and platelet-rich plasma (PRP) from normal dogs using electrical impedance and turbidimetric techniques. General appearance of the aggregation curves, ATP secretion, and aggregation rate were similar in PRP in response to adenosine diphosphate (ADP) or collagen using both techniques. In response to ADP, aggregation was detected sooner while the maximum aggregation response decreased at a relatively greater rate with decreasing agonist concentrations using the turbidimetric technique. Shape change was consistently detected using the turbidimetric, but not the impedance, technique. Using electrical impedance, there were differences between whole blood and PRP in aggregation and ATP secretion responses which depended on the agonise used to activate the platelets. In response to ADP, aggregation responses were lower in whole blood relative to PRP. In response to platelet-activating factor (PAF), maximum aggregation was greater in whole blood while aggregation rate and ATP secretion were greater in PRP. In response to collagen, aggregation response and ATP secretion were lower in PRP. Dilution of PRP with buffer instead of platelet-poor plasma (PPP) lessened many of the differences between whole blood and PRP samples. These findings suggest that plasma constituents and blood cells other than platelets affect aggregation and secretion in an agonist-dependent manner.