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South African Medical Journal

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The sensitivity of tests to detect in vivo platelet activation induced by the removal of arterial endothelium of the baboon (Papio ursinus)

H. F. Kotze, A du P. Heyns, V van Wyk, J.G. Steyn, L. J. Duyvene De Wit, P.N. Badenhorst

Abstract


The relative sensitivities for the various in vivo and in vitro tests for platelet activation are unknown. This was studied in a baboon model where limited and more substantial injury to the vascular endothelum was inflicted. The endothelium of a segment of the right carotid artery was removed with a balloon catheter on day 0(limited de-endothelialisation), and that of the left carotid artery, abdominal aorta and left femoral artery on day 7 (substantial de-endothelialisation). Eight baboons (Papio ursinus) were used. Baseline tests for platelet activation (platelet volume, platelet density, platelet aggregate ratio, and platelet and plasma levels of platelet factor 4 [PF4] and β-thromboglobuln [β-TG]) were performed 7 days before de-endothelialisation and repeated on days 1, 9 and 16. The kinetics of indium-111-labelled platelets were measured after substantial de-endothelalisatiori. Sham operations were done on 3 animals eXactly as in the test, except that the balloon injuries were not inflicted. No influence on the results of the platelet function tests was found. Tile only test capable of detecting limited injury to the endothelium was the measurement of plasma PF4: The mean platelet life-span (MPLS) shortened, mean platelet density decreased, the circulating platelet aggregate ratio decreased, and plasma levels of PF4 and β-TG increased (P < 0,05 in all instances) after the substantial endothelal injury. The mean platelet volume, intraplatelet PF4 and β-TG, and the in vivo distribution and sites of sequestration of labelled platelets were poor tests for in vivo platelet activation. Nine days after the substantial deendothelialisation, the only remaining evidence of platelet activation was an increase in the number of circulating platelet aggregates. It is concluded that the most sensitive tests for in vivo platelet activation are the measurement of the circulating platelet aggregate ratio (sensitivity 0,63) and plasma β-TG (sensitivity 0,63), and the estimate of the MPLS (sensitivity 0,50).




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