Inhibition of platelet aggregation by nitric oxide donors improves with rest

Effects of selective cyclooxygenase isoform inhibition on systemic prostacyclin synthesis and on platelet function at rest and after exercise in healthy volunteers

To test the hypothesis that selective inhibition of cyclooxygenase (COX)-2 would result in exercise-induced platelet activation by causing a shift in the endogenous thromboxane (TX)/prostacyclin balance, a double blind, randomized study comparing aspirin (300 mg/d) with rofecoxib (25 mg/d) (cross-over design, 14 days washout between treatments) in n = 10 trained healthy volunteers was carried out. Physical exercise resulted only in a minor platelet activation, as reflected by the expression of basal or ADP-stimulated platelet activation markers or basal plasma concentrations of TXB(2). Aspirin significantly reduced TXB(2) in plasma while rofecoxib significantly increased TXB(2) in urine. Although no increase in systemic prostacyclin concentration was observed, there was a significant exercise-related increase in both platelet cAMP and cGMP without any drug-related effects. It is concluded that, in trained healthy volunteers, selective inhibition of COX-1 (aspirin) or COX-2 (rofecoxib) does not affect systemic prostacyclin synthesis after physical exercise. However, our data do not exclude the possibility that in subjects at risk for atherothrombotic complications (e.g. patients with advanced atherosclerotic disease) COX-2 inhibitors may result in platelet activation by inhibiting endothelial prostacyclin formation.

A new nitrate derivative of piperazine: its influence on platelet activity

Nitric oxide (NO) is a potent vasodilator and inhibitor of platelet activation. Its donors, organic nitrates, are still a main group of drugs administered in ischaemic heart disease. The aim of this study was to investigate the effect of a new NO-donor analogue, 1-(3-piperidinepropionyl)-4-(2-nitrooxy-3-piperidinepropyl) piperazine trihydrochloride (NO-P), on platelet activity. Its influence on the main mechanisms of human platelet activation (adhesion, shape change, secretion and aggregation) was evaluated with the use of a pharmacological model produced on the basis of known platelet activation measuring methods and our computer program. Our experiments revealed that the new NO derivative of piperazine favourably influences platelet activity, and decreases adhesion (spontaneous and induced by ADP) and aggregation. NO-P shows the same direction of action as nitroglycerin (used as a model compound), and is even stronger in the case of ADP-induced and collagen-induced aggregation. These findings broaden the possibility of using NO-P in cardiovascular diseases. Furthermore, our computer program, used to evaluate kinetic parameters of platelet aggregation, shape change, and the adhesion measuring method, provides a simple and accessible experimental model. This model can be useful in in-vitro screening studies, estimating the influence of new compounds (potential drugs) on platelet activity.