Effect of heparin on platelet aggregation

Abstract

The effect of heparin on platelet aggregation was systematically examined on platelets in plasma (PRP), as well as on gel-filtered, washed, and formaldehyde-fixed platelets. Results indicate that, although heparin causes a mild potentiation of platelet aggregation in the PRP systems, a significant inhibitory activity is observed when heparin is added to isolated platelets. This inhibitory activity appears to be specific and not related to the impurities in the heparin preparations, as heparinase, as well as protamine, effectively neutralizes the heparin-mediated inhibitory activity on platelet aggregation. Although heparin-mediated inhibitory activity can be demonstrated in the presence of a number of different agonists (ADP, arachidonic acid, thrombin, Ionophore A23187, epinephrine, and ristocetin), the most pronounced inhibition is seen in the presence of ristocetin. Further studies show that heparin enhances thromboxane generation in isolated platelets. Platelets pretreated with heparin, however, fail to respond to preformed thromboxane. These findings suggest that, in addition to the potentiation of thromboxane production in platelets, heparin may also attribute some change(s) to the platelet(s)/platelet membrane, which interferes with their ability to respond to the agonists of platelet aggregation. This antiaggregatory activity of heparin was found to be inhibited by a factor(s) present in plasma but not in serum.

The Mechanism of Cold-Induced Platelet Aggregation in the Presence of Heparin.

“…On the other hand, the aggregation did not occur in heparinized PRP that was incubated at room temperature. These results indicate that the increase of CIPA in heparinized PRP results from the proaggregatory effect of heparin (Thomson et al 1973;Chen and Sylven 1992) and not from platelet aggregation induced by heparin itself (Eika 1972;Saba et al 1984;Brace and Fareed 1985). Chilled platelets spontaneously aggregated only when they were stirred and the spontaneous aggregation diminished when the chilled PRP was allowed to warm at 37°C.…”

Heparin-induced Thrombocytopenia

“…This interaction is not influenced by whether the individual from whom the plate lets were collected has ever received heparin. However, the platelet reactivity to heparin varies among individuals [1][2][3][4][5][6]. More impor tant factors influencing platelet aggregation arc the characteristics of the heparin prepara tion.…”

Interaction Between Glycosaminoglycans, Platelets, and Leukocytes

“…However, it has been questioned whether anticoagulation is fully re sponsible for the antithrombotic activity of heparin. [1][2][3] Heparin has been reported to influence platelet function, either by reducing [4][5][6] or enhancing platelet aggrega tion, [7][8][9][10][11][12] and to increase the number of fibrinogen recep tors on the platelet surface. 13 About 5% of patients re ceiving heparin develop thrombocytopenia.…”