Thermal analysis of platelet aggregation assessed by differential scanning calorimetry

Calorimetry is an analytical method that measures heat flow between a heat source and sample. The sample gains or losses heat based on physical or chemical composition. Differential scanning calorimetry (DSC) compares the results of heating a sample to those for heating a reference material. DSC then measures internal energy or a sample's calorific capacity. The aim of this study was to examine the thermal characteristics of platelet activation. Blood was obtained from human volunteers by venipuncture and collected in 5 ml siliconised and citronated vacutainer tubes. Platelet counts were measured using a hemocytometer. Platelet-rich (PRP) or platelet-poor plasma (PPP) was obtained by centrifugation. Ten microliters of PRP or PPP were placed into aluminum pans for DSC with or without activation by epinephrine (5.0 microM) or CaCl2 (50 microM). To avoid a spontaneous activation of platelets samples were kept frozen, after a 5 min period of stabilization, 5 microl of aggregation-inducing agent was added. Scans were initiated at a -12 degrees C after stabilization, with an increase of a 5 degrees C/min to a maximum of 60 degrees C. The experiments were performed on a TA Differential Scanning Calorimeter (New Castle, DE, USA). The difference in heat evolved between the PRP and PPP during the process of platelet activation was 253 J/g. The difference of heat flow in the activation of PRP versus PPP may correspond to an exothermic process involved in platelet aggregation.