Bleeding time in laboratory animals. IV. Effects of prostacyclin, pyrimido-pyrimidine compounds and aspirin in rats

Modulation of haemostatic function and prevention of experimental thrombosis by red wine in rats: a role for increased nitric oxide production

1. The effects of ethyl alcohol and wine (red and white) on haemostatic parameters and experimental thrombosis were studied in rats; NO was evaluated as a possible mediator of these effects. 2. We found that red wine (12% alcohol) supplementation (8.4 +/- 0.4 ml d-1 in drinking water, for 10 days) induced a marked prolongation of 'template' bleeding time (BT) (258 +/- 13 vs 132 +/- 13 s in controls; P < 0.001), a decrease in platelet adhesion to fibrillar collagen (11.6 +/- 1.0 vs 32.2 +/- 1.3%; P < 0.01) and a reduction in thrombus weight (1.45 +/- 0.33 vs 3.27 +/- 0.39 mg; P < 0.01). 3. Alcohol-free red wine showed an effect similar to red wine. In contrast, neither ethyl alcohol (12%) nor white wine (12% alcohol) affected these systems. 4. All these effects were also observed after red wine i.v. injection (1 ml kg-1 of 1:4 dilution) 15 min before the experiments. 5. The effects of red wine were prevented by the NO inhibitor, N omega nitro-L-arginine-methyl ester (L-NAME). L-arginine, not D-arginine, reversed the effect of L-NAME on red wine infusion. 6. Red wine injection induced a 3 fold increase in total radical-trapping antioxidant parameter values of rat plasma with respect to controls, while white wine and alcohol did not show any effect. 7. Our study provides evidence that red wine modulates primary haemostasis and prevents experimental thrombosis in rats, independently of its alcohol content, by a NO-mediated mechanism.

Dipyridamole and vascular prostacyclin production

The action of dipyridamole on the vascular production of prostacyclin (PGI2) has been investigated. Dipyridamole (1-100 microM) did not induce a significant stimulation of PGI2 release in any of the following experimental models: rings of rabbit aorta, cultured endothelial cells from bovine aorta or human umbilical vein, cultured explants of bovine aortic smooth muscle. The activity of known stimuli of PGI2 release (ADP, suloctidil, serotonin) and the capacity of dipyridamole to inhibit adenosine uptake into endothelial cells were carefully checked. Pretreatment of the rabbit aorta with dipyridamole (10-100 microM) prolonged the transient stimulation of PGI2 release induced by mechanical deendothelialization: this effect was probably due to a partial protection of the cyclooxygenase against oxidative self-inactivation. Our largely negative results are consistent with the current theory that the antiplatelet action of dipyridamole is mediated by adenosine and not by PGI2.

Different sensitivities of prostaglandin-cyclooxygenases in blood platelets and coronary arteries against non-steroidal antiinflammatory drugs

The action of the non-steroidal antiinflammatory drugs indomethacin, tiaprofenic acid, diclofenac and meclofenamate on vascular and platelet-cyclooxygenases was studied by measuring the arachidonic acid-induced thromboxane A2 (TXA2)-formation of washed human platelets and prostacyclin (PGI2)-formation of bovine coronary artery rings. TXA2 was bioassayed as RCS on rabbit aorta strips, PGI2 in terms of its antiaggregatory activity on ADP-induced aggregation of human platelet-rich plasma. All of the substances studied produced concentration-dependent inhibition of PGI2- and RCS-release. The IC50 [micrometer] in inhibition of RCS-formation was 0.019 for indomethacin, 0.070 for tiaprofenic acid but 44.9 for meclofenamate and 63.2 for diclofenac. The IC50 [micrometer] in inhibition of PGI2-release was 0.42 for diclofenac, 0.63 for indomethacin and 0.99 for tiaprofenic acid. The data suggest (1) high sensitivity of human platelet-cyclooxygenase against indomethacin and tiaprofenic acid, (2) different sequence of the substances studied in inhibiting arachidonic acid-induced TXA2- and PGI2-formation. The possible therapeutic value of selective inhibition of platelets and vascular cyclooxygenases is discussed.