Comparative Arterial Antithrombotic Activity of Clopidogrel and Acetyl Salicylic Acid in the Pig

Summary

We investigated the comparative antithrombotic properties of clopidogrel, an analogue of ticlopidine, and aspirin, using the Folts' model on femoral arteries in 22 pigs. On each animal, clopidogrel or aspirin were used to treat the thrombotic process on the left femoral artery and to prevent this process on the right femoral artery. Sequentially: an injury and stenosis were carried out on the left femoral artery; the thrombotic process was monitored with a Doppler during a 30-min observation period for cyclic flow reductions or permanent cessation of flow; after the first cyclic flow reduction occurred, clopidogrel (5 mg kg-¹) or aspirin (2.5, 5, 100 mg kg^-1) were injected intravenously; if cyclic flow reductions were abolished, epinephrine (0.4 µg kg^-1 min^-1) was injected to try to restore cyclic flow reductions and/or permanent cessation of flow; then injury and stenosis were applied on the right femoral artery. Before and after injection of clopidogrel or aspirin, ear immersion bleeding times and ex-vivo platelet aggregation were performed. Clopidogrel (n = 7) abolished cyclic flow reductions in all animals and epinephrine did not restore any cyclic flow reduction. On the right femoral artery, cyclic flow reductions were efficiently prevented, even for two injuries. Basal bleeding time (5 min 28) was lengthened (>15 min, 30 min after clopidogrel and remained prolonged even after 24 h). ADP-induced platelet aggregation was inhibited (more than 78%). Comparatively, aspirin had a moderate and no dose-dependent effect. Aspirin 2.5 mg kg^-1 (n = 6) abolished cyclic flow reductions in 2 animals, CFR reoccurred spontaneously in one animal and epinephrine restored it in a second animal. Aspirin 5 mg kg^-1 (n = 6) abolished cyclic flow reductions in only 3 animals and epinephrine always restored it. Aspirin 100 mg kg^-1 (n = 3) was unable to abolish cyclic flow reductions. On the right femoral artery, aspirin did not significantly prevent cyclic flow reductions which occurred in all animals after one (n = 14) or two injuries (n = 1), except for one animal. Basal bleeding time was lengthened but it shortened rapidly, reaching its basal value after 24 h. ADP-induced aggregation was not significantly inhibited, whereas arachidonic acid induced aggregation was always inhibited. Clopidogrel appears as a more potent antithrombotic drug than aspirin in this model, in treating and preventing spontaneous or epinephrine-induced cyclic flow reductions and lengthening bleeding time.

• REFERENCES

• 1 Panak E, Maffrand JP, Picard-Fraire C, Vallee E, Blanchard J, Roncucci R. Ticlopidine: a promise for the prevention and the treatment of thrombosis and its complications. Haemostasis 1983; 31: 01-54
• 2 Mc Tavish D, Faulds D, Goa KL. Ticlopidine. An updated review of its pharmacology and therapeutic use in platelet-dependent disorders. Drugs 1990; 40: 238-259
• 3 Janzon L, Bergqvist D, Boberg J, Boberg M, Eriksson I, Lindgärde F, Persson G. Prevention of myocardial infarction and stroke in patients with intermittent claudication; effect of ticlopidine. Results from STIMS, the Swedish Ticlopidine Multicentre Study. J Intern Med 1990; 227: 301-308
• 4 Gent M, Easton JD, Hachinski VC, Panak E, Sicurella J, Blakely JA, Ellis DJ, Harbison JW, Roberts RS. Turpie AGG and the CATS group The Canadian American Ticlopidine Study (CATS) in thromboembolic stroke. Lancet 1989; I: 1215-1220
• 5 Hass WK, Easton JD, Adams HP, Pryse-Phillips W, Molony BA, Anderson S. Kamm B for the Ticlopidine Aspirin Stroke Study Group A randomized trial comparing Ticlopidine hydrochloride with aspirin for the prevention of stroke in high-risk patients. N Engl J Med 1989; 321: 501-507
• 6 Defreyn G, Gachet C, Savi P, Driot F, Cazenave JP, Maffrand JP. Ticlopidine and clopidogrel (SR 25990C) selectively neutralize ADP inhibition of PGEl-activated platelet adenylate cyclase in rats and rabbits. Thromb Haemostas 1991; 65: 186-190
• 7 Gachet C, Cazenave JP, Ohlmann P, Bouloux C, Defreyn G, Driot F, Maffrand JP. The thienopyridine ticlopidine selectively prevents the inhibitory effects of ADP but not of adrenaline on cAMP levels raised by stimulation of the adenylate cyclase of human platelets by PGE1. Biochem Pharmacol 1990; 40: 2683-2687
• 8 Savi P, Pflieger AM, Combalbert J, Herbert JM, Defreyn G, Maffrand JP. Clopidogrel is actively metabolized in the liver. (Submitted.)
• 9 Folts JD, Crowell EB, Rowe GG. Platelet aggregation in partially obstructed vessels and its elimination with aspirin. Circulation 1976; 54: 365-370
• 10 Folts JD, Rowe GG. Epinephrine potentiation of in vivo stimuli reverses aspirin inhibition of platelet thrombus formation in stenosed canine coronary arteries. Thromb Res 1988; 50: 507-516
• 11 Folts JD, Gering SA, Laibly SW, Bertha BG, Bonebrake FC, Keller JW. Effects of cigarette smoke and nicotine on platelets and experimental coronary artery thrombosis. In: Tobacco Smoking and Atherosclerosis. Diana JN. (ed) New York: 1990. pp 339-358
• 12 Nichols TC, Bellinger DA, Johnson TA, Lamb MA, Griggs TR. Von Willebrand's disease prevents occlusive thrombosis in stenosed and injured porcine coronary arteries. Circ Res 1986; 59: 15-26
• 13 Mertz ET. The anomaly of a normal Duke's and very prolonged bleeding time in swine suffering from an inherited bleeding disease. Am J Physiol 1942; 136: 360-362
• 14 Folts JD, Gallagher K, Rowe GG. Blood flow reductions in stenosed canine coronary arteries: vasospasm or platelet aggregation? Circulation. 1982; 65: 248-255
• 15 Coller BS, Folts JD, Smith SR, Scudder LE, Jordan R. Abolition of in vivo platelet thrombus formation in primates with monoclonal antibodies to the platelet GPIIb/IIIa receptor. Correlation with bleeding time, platelet aggregation, and blockade of GPIIb/IIIa receptors. Circulation 1989; 80: 1766-1774
• 16 Just M, Martorana PA. Effect of molsidomine on thrombus formation in stenosed coronary arteries of dogs and pigs. J Cardiovasc Pharmacol 1989; 14: S129-S136
• 17 Samama ChM, Bonneau M, Bailliart O, Pignaud G, Scrobohaci ML, Caen JP, Viars P, Drouet O. Absence of side effects of Hydroxyethyl-starch 200 in a porcine model of experimental arterial thrombosis. Thromb Res 1991; 65: 691-698
• 18 Di Minno G, Lerbone AM, Mattioli PL, Turco S, Iovine C, Mancini M. Functionally thrombasthenic state in normal platelets following administration of ticlopidine. J Clin Invest 1985; 75: 328-338
• 19 Hardisty RM, Powling MJ, Nokes TJC. The action of ticlopidine on human platelets. Studies on aggregation, secretion, calcium mobilization and membrane glycoproteins. Thromb Haemostas 1990; 64: 150-155
• 20 Maffrand JP, Bernat A, Delebassée D, Defreyn G, Cazenave JP, Gordon JL. ADP plays a key role in thrombogenesis in rats. Thromb Haemostas 1988; 59: 225-230
• 21 Bochner F, Siebert DM, Rodgers SE, McIntosh GH, James MJ, Lloyd JV. Measurement of aspirin concentrations in portal and systemic blood in pigs: effect on platelet aggregation, thromboxane and prostacyclin production. Thromb Haemostas 1989; 61: 211-216
• 22 Pedersen AK, Fitzgerald GA. Dose-related kinetics of aspirin. Presystemic acetylation of platelet cyclooxygenase. N Engl J Med 1984; 311: 1206-1211