Experimental Carotid Stenosis and Endothelial Injury in the Rabbit: An In Vivo Model to Study Intravascular Platelet Aggregation

Summary

Previous studies have shown that experimental canine coronary artery stenosis associated with endothelial injury results in a typical pattern of coronary flow characterized by gradual decreases in coronary flow to almost zero values followed by restorations of flow to normal values. This pattern of flow, called cyclic flow reductions (CFRs), is the consequence of recurrent platelet aggregation at the site of the stenosis and endothelial injury and subsequent dislodgement of the thrombus. In the present study, platelet activation and aggregation in vivo was induced by placing an external constrictor around carotid arteries with endothelial injury in anesthetized rabbits. Carotid blood flow velocity was measured continuously with a Doppler flow probe positioned proximally to the constrictor. After placement of the constrictor, CFRs developed in 14 of 14 rabbits with a mean frequency of 16.5 ± 2.3 cycles/h. CFRs were observed for 30 min, and the animals were treated with either an i.v. bolus of aspirin (10 mg/kg) or R 68070 (20 mg/kg), a drug with simultaneous TxA₂ synthase and TxA₂/PGH₂ receptor blocking properties. Aspirin completely inhibited CFRs in 4 of 7 rabbits, whereas R 68070 eliminated CFRs in 7 of 7 animals. In the 3 animals that did not respond to aspirin, administration of ketanserin (0.25 mg/ kg i.v.), a selective serotonin S₂ receptor antagonist, completely abolished CFRs. Both aspirin and R 68070 resulted in a marked reduction in serum TxB₂ formation and in a complete inhibition of ex vivo platelet aggregation in response to arachidonic acid, whereas aggregation in response to U46619, a TxA₂ mimetic, was inhibited only in R 68070-treated rabbits. We conclude that 1) CFRs develop in rabbit carotid arteries at sites of experimental stenosis and endothelial injury; 2) this model can be usefully employed to study platelet aggregation and platelet-vessel wall interaction in vivo and to test the efficacy of antiplatelet interventions.

• References

• 1 Willerson JT, Golino P, Eidt J, Campbell WB, Buja LM. Specific platelet mediators and unstable coronary artery lesions. Experimental evidence and clinical implications. Circulation 1989; 80: 198-205
• 2 Hirsh PD, Hillis LD, Campbell WB, Firth BG, Willerson JT. Release of prostaglandins and thromboxane into the coronary circulation in patients with ischemic heart disease. N Engl J Med 1981; 304: 685-690
• 3 Van den Berg EK, Schmitz JM, Benedict CR, Malloy CR, Willerson JT, Dehemer GJ. Transcardiac serotonin concentration is increased in selected patients with limiting angina and complex coronary lesion morphology. Circulation 1989; 79: 116-124
• 4 Folts JD, Crowell Jr EB, Rowe CG. Platelet aggregation in partially obstructed vessels and its elimination by aspirin. Circulation 1976; 69: 365-370
• 5 Bush LR, Campbell WB, Buja LM, Tilton GD, Willerson JT. Effects of the selective thromboxane synthase inhibitor dazoxiben on variations in cyclic blood flow in stenosed canine coronary arteries. Circulation 1984; 69: 1161-1170
• 6 Golino P, Buja LM, Ashton JH, Kulkami P, Taylor AL, Willerson JT. Effect of thromboxane and serotonin receptor antagonists on intracoronary platelet deposition in dogs with experimentally stenosed coronary arteries. Circulation 1988; 78: 701-711
• 7 Golino P, Ashton JH, Buja LM, Taylor AL, Rosolowsky M, McNatt J, Campbell WB, Willerson JT. Local platelet activation causes vasoconstriction of large epicardial canine coronary arteries in vivo: thromboxane A₂ and serotonin are possible mediators. Circulation 1989; 79: 154-166
• 8 De Clerck F, Beetens J, De Chaffoy de Courcelles D, Freyne F, Janssen PAJ. R 68070: Thromboxane A₂ synthase inhibition and thromboxane A₂/prostaglandin endoperoxide receptor blockade combined in one molecule - I Biochemical profile in vitro. Thromb Haemostas 1989; 61: 35-42
• 9 De Clerck F, Beetens J, Van de Water A, Vercammen E, Janssen PAJ. R 68070: Thromboxane A₂ synthase inhibition and thromboxane A₂/prostaglandin endoperoxide receptor blockade combined in one molecule - II. Pharmacological effects in vivo and ex vivo. Thromb Haemostas 1989; 61: 43-49
• 10 Yao SK, Rosolowsky M, Anderson V, Golino P, McNatt J, De Clerck F, Buja LM, Willerson JT. Combined thromboxane A₂ synthetase inhibition and receptor blockade are effective in preventing spontaneous and epinephrine-induced canine coronary cyclic flow variations. J Am Coll Cardiol 1990; 16: 705-713
• 11 Van Neuten JM, Janssen PAJ, Van Beek J, Xhonneux R, Verbeuren TJ, Vanhoutte PM. Vascular effects of ketanserin (R 41468), a novel antagonist of 5-HT₂ serotonergic receptors. J Pharmacol Exp Ther 1981; 218: 217-230
• 12 Ashton JH, Benedict CR, Fitzgerald C, Rahaja S, Taylor AL, Campbell WB, Buja LM, Willerson JT. Serotonin as a mediator of cyclic flow variations in stenosed canine coronary arteries. Circulation 1986; 73: 572-578
• 13 Bult H, Beetens J, Herman A. Blood levels of 6-oxo-prostaglandin Fi_a during endotoxin-induced hypotension in rabbits. Eur J Pharmacol 1980; 63: 47-56
• 14 Ashton JH, Ogletree ML, Michel IM, Golino P, McNatt J, Taylor AL, Rahaja S, Schmitz J, Buja LM, Campbell WB, Willerson JT. Serotonin and thromboxane A₂/prostaglandin H₂ receptor activation cooperatively mediates cyclic flow variations in dogs with severe coronary artery stenoses. Circulation 1987; 76: 952-959
• 15 Moncada S, Bunting S, Mullane KM, Thorogood P, Vane JR, Raz A, Needleman P. Imidazole: A selective inhibitor of thromboxane synthetase. Prostaglandins 1977; 13: 611-618
• 16 Defreyn G, Deckmyn H, Vermylen J. A thromboxane synthetase inhibitor reorients endoperoxide methabolism in whole blood towards prostacyclin and prostaglandin E₂ . Thromb Res 1982; 26: 389-400
• 17 Mullane KM, Fomabaio D. Thromboxane synthetase inhibitors reduce infarct size by a platelet-dependent, aspirin-sensitive mechanism. Circ Res 1988; 62: 668-678
• 18 Grimm LJ, Knapp DR, Senator D, Halushka PV. Inhibition of platelet thromboxane synthesis by 7-(l-imidazolyl) heptaenoic acid: dissociation from inhibition of aggregation. Thromb Res 1981; 24: 304-317