Effects of prostacyclin and albumin on platelet loss during in vitro simulation of extracorporeal circulation.

Albumin decreases polymer surface affinity for platelets, and prostaglandin (PG) E1 prevents surface-induced platelet activation. PGI2, like PGE1, inhibits platelet function but is unstable in vitro. We evaluated the ability of surface-adsorbed albumin and circulating PGI2 to prevent platelet alterations during simulated extracorporeal circulation. Fresh heparinized human blood (500 ml) was recirculated at 37’C through a silicone rubber circuit containing an 0.8sq m membrane oxygenator. When circuits were filled (primed) directly with blood, platelet counts decreased maximally to 18 % of initial levels, plasma levels of lowaffinity platelet-specific protein factor 4 (LA-PF4) rose from less than 0.5 g/ml to 15 tg / ml (indicating extensive release of granule contents), and platelets quickly became unresponsive to adenosine diphosphate (ADP) and epinephrine. In contrast. when circuits were primed with albumin (2.5 %) prior to recirculation, the circulating platelet counts remained stable at 95 % of initial levels, release of granule contents was prevented, platelet reactivity was preserved, and platelet subcellular architecture was maintained even after 6 hr of recirculation. Addition of PGI2 (3.5 nM) immediately prior to recirculation duplicated the effects of exposure of the circuit to albumin. The preservative actions of PGI2 persisted despite loss of detectable PGI2-induced inhibition in recirculated platelets. Temporary inhibition of platelet function and alteration of the proteins initially adsorbed to the biopolymer are equally effective means of preventing adverse platelet alterations during extracorporeal circulation. Furthermore, the efficacy of prostacyclin (PGI2) further demonstrates that prevention of initial platelet-surface interactions permits the subsequent appearance of polymer biocompatibility.