Enhancement by cyclosporine A and tacrolimus of serotonin-induced formation of small platelet aggregation.

Abstract

Cyclosporine A (CsA) may increase the incidence of thrombotic events, but whether tacrolimus (Tc) has such effects is still unclear. The serotonergic system has been linked to the thrombotic effects of CsA, but a direct effect of CsA on serotonin-induced platelet aggregation has not been demonstrated because of methodological difficulties. We measured the effects of CsA and Tc on serotonin-induced platelet aggregate formation by particle counting using light scattering. CsA and Tc both enhanced serotonin-induced formation of small platelet aggregates, however, neither CsA nor Tc affected aggregation induced by high or low concentrations of ADP, with or without addition of a serotonin receptor antagonist. Both CsA and Tc enhance platelet aggregation induced via the serotonin pathway.