Modulation of in vitro platelet 5-HT release by species of Erythrina and Cymbopogon

Extracts of Australian plants were screened to detect constituents affectin g adenosine di-phosphate (ADP) induced platelet aggregation and [C-14]5-hyd roxytryptamine (5-HT) release. Extracts of four tested plants including, Er emophila gilesii, Erythrina vespertilio, Cymbopogon ambiguus, and Santalum acuminatum, were found to cause significant inhibition of platelet 5-HT rel ease. Inhibition levels ranged from 56 - 98 %, and was not due to the non-s pecific effects of protein binding tannins. These extracts, and those we ha ve previously identified as being active, were examined further to determin e if they affect epinephrine (EPN), arachidonic acid (A.A) or collagen stim ulated platelet aggregation and 5-HT release. Among those extracts investig ated, we found that both the methanolic extract of E. vespertilio and the d ichloromethane (DCM) extract of C. ambiguus were most potent and caused sig nificant inhibition of platelet activation induced by EPN, A.A and to a les ser extent by collagen. Inhibition of ADP induced platelet 5-HT release by both of these extracts, was dose-dependent, with IC50 values for E. vespert ilio and C. ambiguus estimated to be 20.4 mul (1.855 mg/ml) and 8.34 mul (0 .758 mg/ml), respectively. Overall, C. ambiguus exhibited most activity and also caused dose-dependent inhibition of A.A induced platelet activation. These results indicate that inhibition may occur specifically at a site wit hin the A.A pathway, and suggest the presence of a cyclo-oxygenase inhibito r. Both E. vespertilio and C. ambiguus are reported to be traditional heada che treatments, with the present study providing evidence that they affect 5-HT release. (C) 2001 Elsevier Science Inc. All rights reserved.