DIFFERENTIAL EFFECT OF A LOW-MOLECULAR-WEIGHT HEPARIN (DALTEPARIN) AND UNFRACTIONATED HEPARIN ON PLATELET INTERACTION WITH THE SUBENDOTHELIUM UNDER FLOW CONDITIONS

Abstract

Effects of heparins on platelet function are controversial, but perfusion studies, that simulate physiological conditions, might help to explain their clinical behaviour. We used a perfusion system to test the effect unfractionated heparin and a low-molecular-weight heparin (dalteparin, Fragmin R) on platelet adhesion promoted by a damaged vascular surface. Normal blood samples containing increasing concentrations of unfractionated heparin and dalteparin were perfused through annular chambers containing enzymatically denuded rabbit aorta segments (5 min at 800 sec −1). Segments were evaluated morphometrically measuring the total surface covered by platelets and by large aggregates (thrombi). Unfractionated heparin inhibited platelet interaction with subendothelium in a lesser extent than dalteparin in both covered surface and thrombi (p<0.01). At heparin doses that caused maximal inhibition covered surface was 10.0%±3.1% with dalteparin and 18.3%±4.2% with unfractionated heparin, and thrombi were 5.6%±3.2% and 12.3% ±3.0%, respectively. These results may collaborate to explain some differences observed in the clinical results obtained with unfractionated heparin and with dalteparin. © 1997 Elsevier Science Ltd