Inhibition of platelet aggregation by transdermal glyceryl trinitrate.

OBJECTIVE: To determine the optimum conditions for the demonstration of an antiplatelet effect of nitric oxide and to use these conditions to elucidate the effects of a transdermal glyceryl trinitrate patch on platelet aggregation in normal volunteers. METHODS: An open prospective crossover study. The effects of nitric oxide on platelet aggregation in whole blood and platelet rich plasma as stimulated by adenosine diphosphate and U46619 was assessed in the presence and absence of iloprost and MB22948. Optimum conditions for the demonstration of an antiplatelet effect of nitric oxide were then applied to whole blood from normal volunteers in the presence and absence of a transdermal glyceryl trinitrate patch. SETTING: University hospital. SUBJECTS: Eight normal volunteers. MAIN OUTCOME MEASURES: Platelet aggregation in the presence and absence of transdermal glyceryl trinitrate. RESULTS: The optimum conditions for the demonstration of an antiplatelet effect of nitric oxide in whole blood were collecting blood into a tube containing MB22948 and citrate and stimulating platelet aggregation with adenosine diphosphate in the presence or absence of iloprost. Using this method a significant effect of transdermal glyceryl trinitrate on platelet aggregation was shown (P < 0.03) in the presence and absence of iloprost. CONCLUSIONS: These results are consistent with an inhibitory effect on platelet aggregation of nitric oxide liberated by transdermal glyceryl trinitrate. Optimum test conditions are needed to show this effect. The clinical significance of the antiplatelet effect of transdermal glyceryl trinitrate is unknown.