[Effects of ketotifen on rabbit platelet aggregation and platelet activating factor formation from rat neutrophils]

The effects of ketotifen (Ket) on rabbit platelet aggregation induced by platelet activating factor (PAF), ADP and arachidonic acid (AA) and PAF formation from A-23187-stimulated rat neutrophils in vitro were studied. PAF (15-100 pmol/L) induced rabbit platelet aggregations, with an EC50 of 33 pmol/L. Ket shifted the PAF dose-dependent platelet aggregation curve to the right in a parallel fashion with no depression of the maximal response and reversed the secondary aggregation phase, suggesting that Ket had competitive antagonistic activity against PAF-induced platelet aggregation. It also showed inhibitory effects on platelet aggregations induced by ADP 10 mumol/L and AA 50 mumol/L, the IC50 were 94.5 and 143.5 mumol/L respectively. However, it failed to influence PAF formation from rat neutrophils stimulated by A-23187 2.5 mumol/L in vitro. The inhibitory effects of Ket on platelet activation, particularly PAF-induced platelet aggregation, may contribute to its anti-asthmatic properties.