5HT2-RECEPTORS AND SEROTONIN RELEASE - THEIR ROLE IN HUMAN PLATELET-AGGREGATION

Involvement of 5HT2 receptors in human platelet aggregation was assess ed by studying the effect of ADP, epinephrine and thrombin on H-3-5HT release from platelets. The release experiments were made with a perfu sion method to preserve any compound, released or formed by platelet, from interacting with platelet itself. In these conditions, aggregatio n does not occur, as confirmed by Scanning Electron Microscopy. These release experiments showed that the platelet activation by such agents is coupled with 5-HT release. The aggregation experiments, made on di fferent aliquots of the same platelet-rich plasma (PRP), showed that t he released 5-HT, interacting with its own receptors on platelet activ ated surface, determines aggregation. In fact, although it is known th at 5-HT added to PRP was only able to induce a moderate platelet aggre gation, the 5-HT2 antagonist ketanserin counteracted the aggregation i nduced by ADP, epinephrine and thrombin. These results suggest that a 5HT2 antagonist could be therapeutically important in those pathologic al states in which serotonin, released by activated platelets, may inc rease aggregation.