Characterization of adhesive and aggregating functions of pig platelets: comparative studies with human platelets and differential effects of calcium chelation

Abstract

We have characterized functional responses of pig platelets in citrate-anticoagulated blood and compared results with those of human platelets. Platelet aggregation was induced with known activating agents using citrated platelet-rich plasma. Adhesive and cohesive functions of platelets were evaluated using a perfusion flow system with whole anticoagulated blood (10 min, 800/s). To test the differential sensitivity to free calcium levels, two citrate concentrations (19 mM {standard} vs 13 mM) were used as anticoagulants. The ability of platelets to produce thromboxane A2 was also quantified, using radioimmunoassay. In the presence of 19 mM citrate concentration, pig platelets responded poorly to ADP and collagen, and did not respond to arachidonic acid and U46619. Pig platelets adhered well onto subendothelium, but failed to form aggregates on previously spreaded platelets. At 13 mM citrate concentration, the aggregating responses of pig platelets improved, but some of the aggregation patterns were still reversible. The lower citrate concentration had a dramatic impact on perfusion studies, where the formation of platelet aggregates was restored up to levels found in humans. Thromboxane levels in pig serum were only 20 to 30% of that found in humans. So, pig platelets possess functional properties that clearly differ from human platelets: they are more sensitive to the calcium chelating effects of citrate. Arachidonic acid metabolism and thromboxane amplification of platelet responses seem less preponderant in the pig species.