Pre-Aggregation changes in plate let volume

Previous research on whether platelet volume increases durinq the morphological changes precedinq aqqregation is controversial; resistive-countinq techniques reveal an increase, centrifugal methods do noL. A computerized, resistive-particle counter has therefore been used to size platelets before and after incubation with ADP. The effects of EDIA and centrifugation were also evaluated. ADP (2 mH) significantly increased mean platelet volume from 4.81 to 5.47(p<.001). CDIA (2 mM) inhibited this increase by 50%, and both centrifugation and EDIA also caused platelet swelling.

Platelet shape was experimentally manipulated with colchicine, chlorpromazine and temperature cycling, to test the hypothesis that changes in resistive-volume stem from artifacts of particle shape. Scanning-electron microscopy confirmed that these treatments caused extensive sphering of disc-shaped platelets. However, subsequent exposure to ADP resulted in major increases in resistive volume, and in the case of chlorpromazine, no pseudopodia were extruded. It is concludedthat platelet volume can increase durinq pre-aqqreqation reactions, and that earlier research based on centri-Tuqation in the presence of EDIA failed tn reveal the increase because of inhibitory and swelling effects. This work mas supported, in part, by PHS Grants AM-20727, HL-1S289, and HL-7D759.