Effects of S-nitroso-glutathione in the human forearm circulation: evidence for selective inhibition of platelet activation.

Nitric oxide (NO) is a vasodilator and inhibitor of platelet function. The clinical use of NO donors as inhibitors of platelet activation is limited by their concomitant hypotensive effect. S-nitroso-glutathione (GSNO) has a significant antiplatelet effect at doses that cause only a small decrease in blood pressure in rats. The aim of this study was to examine the antiplatelet and vasodilator properties of this nitrosothiol in the human forearm. Forearm blood flow was measured by forearm occlusion plethysmography in five healthy males. Ex vivo platelet aggregation to ADP was performed in a platelet ionised calcium lumi-aggregometer. Intra-arterial infusion of GSNO (0.2, 1, and 5 nmol.min-1) resulted in inhibition of ADP (1-10 microM) induced platelet aggregation. This inhibition was submaximal for 0.2 and maximal for 1 and 5 nmol.min-1. However, the antiaggregatory effect observed at the lowest dose of GSNO was accompanied only by a threshold increase in forearm blood flow. These results show that GSNO is more effective as an inhibitor of platelet activation than as a vasodilator, suggesting that it is possible to achieve selective antiplatelet and potentially antithrombotic effects with NO donors.