Arachidonic acid causes lysis of human platelets in an artificial medium: protection by plasma

Addition of 1 or 2 mM of arachidonic acid (AA) to a washed platelet suspension (WPS) resulted in an instantaneous rise of light transmission (LT) in the platelet aggreagameter. The LT curves showed no evidence ofshape change patterns and the recording pen showed no fluctuations. This rise of LT was not affected by the absence of CaCl2, or the presence of PGI2 or ASA. However, LT curves, showing shape change patterns and with pen fluctuations, were obtained when plasma, serum or albumin was included in the test system. These latter form of LT curves were also obtained in WPS samples exposed to lower concentrations of AA. Electron microscopic examination of these samples revealed varying degrees of lysis of every platelet in WPS exposed to 1 mM of AA. Numerous lyzed platelets were also found in samples either exposed to 0.5 mM of AA in the absence of added plasma, serum or albumin, or exposed to 1 mM of AA in the presence of 5% of added plasma or 2.5 mg/ml albumin. The LT curves of these samples showed shape change patterns and pen fluctuations. These results indicate a pitfall of relying on platelet aggregometry alone in the study of certain AA-induced responses of washed platelets.