ANTIAGGREGATING AND VASODILATORY EFFECTS OF A NEW NITRODERIVATIVE OF ACETYLSALICYLIC-ACID

We studied in vitro the effects on platelet aggregation and vascular tone of a new nitrocompound (nitroxy-butyl-acetylsalicylate: NO-ASA). In order to elucidate any possible activity due to the release of nitric oxide or the inhibition of platelet cyclooxygenase we compared NO-ASA to acetylsalicylic acid. NO-ASA 1 mM inhibited arachidonic acid-induced platelet aggregation (basal 75.4 +/- 2.35%; NO-ASA 22 +/- 3.46%; M +/- SEM; P<0.001; n=6), but proved less active than acetylsalicylic acid (complete inhibition at 2 x 10(-5) M). NO-ASA also significantly reduced thrombin-induced (0.04-0.08 U/ml) platelet aggregation in acetylsalicylic acid-treated platelets (basal 70.5 +/- 1.7%; NO-ASA 35.4 +/- 2.2%; P<0.001; n=10; IC50 7 x 10(-5) M). Methylene blue reduced the effects of NO-ASA on thrombin-induced (NO-ASA 46.7 +/- 5.25%; NO-ASA + MB 59.1 +/- 4.3%; P<0.01; n=8), but not arachidonic acid-induced platelet aggregation, The inhibitory effects of NO-ASA on platelet aggregation were partially removed by oxyhaemoglobin. Platelet thromboxane A(2) production (TXB(2) concentration in the supernatant of the aggregate 35.38 +/- 7.81 ng/ml; n=8), was totally abolished by acetylsalicylic acid (0.17 +/- 0.04 ng/ml; P<0.001; n=8) and reduced by NO-ASA (8.3 +/- 4.05 ng/ml; P<0.01; n=8). In vitro studies on isolated rat aortic rings showed NO-ASA 10(-3) M, but not ASA up to 10(-3) M, induce a dose dependent vasorelaxation (100% of epinephrine-induced contraction) both in intact and endothelium denuded arteries (IC50 5 X 10(-5) M). Addition of methylene blue reversed this relaxation. In conclusion these data demonstrate that NO-ASA acts through a double mechanism: a) by inhibiting cyclo-oxygenase and b) by releasing NO active on guanylyn cyclase both in platelets and in vascular smooth muscle cells.