Thiopental enhances human platelet aggregation by increasing arachidonic acid release

Conflicting results have been reported regarding the effect of thiopental o n aggregation and cytosolic calcium levels in platelets. The present study attempted to clarify these phenomena. Using platelet-rich plasma or washed suspensions, platelet aggregation, thromboxane (TX) B-2 formation, arachido nic acid (AA) release, and cytosolic free calcium concentrations ([Ca2+](i) ) were measured in the presence or absence of thiopental (30-300 muM). Plat elet activation was induced by adenosine diphosphate (ADP, 0.5-15 muM), epi nephrine (0.1-20 muM) arachidonic acid (0.5-1.5 mM), or (+)-9,11-epithia-11 ,12-methano-TXA(2) (STA(2), 30-500 nM). Measurements of primary aggregation were performed in the presence of indomethacin (10 muM). Low concentration s of ADP and epinephrine, which did not induce secondary aggregation in a c ontrol study, induced strong secondary aggregation in the presence of thiop ental (greater than or equal to 100 muM). Thiopental (greater than or equal to 100 muM) also increased the TXB2 formation induced by ADP and epinephri ne. Thiopental (300 muM) increased ADP- and epinephrine-induced H-3-AA rele ase. Thiopental (300 muM) also augmented the ADP- and epinephrine-induced i ncreases in [Ca2+](i) in the presence of indomethacin. Thiopental appears t o enhance ADP- and epinephrine-induced secondary platelet aggregation by in creasing AA release during primary aggregation, possibly by the activation of phospholipase A(2).