Representative platelet aggregation tracings induced by ADP (1 μmol/L) in normal human platelet-rich plasma with the addition of buffer or GSA (500 μmol/L, 30 seconds of preincubation; A). GSA inhibited the second wave of platelet aggregation induced by 1 μmol/L ADP. Nω-nitro-L-arginine (1 to 2 mmol/L, 1 minute of preincubation) overcame GSA effect and restored ADP-induced irreversible platelet aggregation (B). As a positive control, L-arginine (30 seconds of preincubation) inhibited platelet aggregation when added at a concentration ≥1 mmol/L (C). (Macconi et al, abstract submitted to the Congress of the American Society of Nephrology, 1999).