Effect of Nigella sativa L. and thymoquinone on rat platelet aggregation

ABSTRACT

The aim of the present study was to evaluate platelet responsiveness in rats following Nigella sativa L. [NS] and thymoquinone [TQ] administration. Additionally, the in vitro rat platelet aggregation response to TQ was investigated. Four doses of NS; 90, 180, 360 and 540 mg / Kg were fed daily to rats for 1, 2 and 4 weeks before running the aggregation study. TQ was administered as a single i. p. injection [4, 8, 12, 16 and; 20 mg /kg] 2-3 hours before testing the platelet response. Platelet rich plasma [PRP] was prepared from the treated rats, and platelet aggregation in response to collagen [10 micro,g / ml] and adenosine 5' - diphosphate [ADP; 20, 5 and 2.5 micro.M] was tested. Samples of 0.45 ml PRP from normal rats were also incubated with TQ [5, 10, 20, 50 micro.g] for 1 minute. Thereafter platelet aggregation response to collagen [10 micro g / ml] and ADP [20 micro.M] was performed by adding 0.05 ml of agonist [giving final concentrations of TQ 10, 20, 40, 100 micro,g / ml]. Platelet aggregation in response to collagen and ADP was not different in NS fed rats when compared with that in controls. Also tolerable doses of TQ [4 and 8 mg / Kg] and low concentration of TQ in vitro [10 micro.g / ml] neither affected collagen nor ADP induced platelet aggregation response. A dose of 12 mg TQ / Kg induced significant inhibition [p < 0.05] of platelet aggregation only when 2.5 micro.M of ADP was used for aggregation. Increasing TQ doses either in vivo or in vitro resulted in progressive inhibition of platelet aggregation. At a dose of 16 mg TQ / Kg there was significant inhibition by 25.1, 33.3, 74.7 and 75.7% with collagen and 20, 5 and 2.5 micro M ADP, respectively. The inhibition became more than 90% when 20 mg TQ / kg was administered. In vitro concentrations of TQ [20, 40 and 100 micro g / ml] caused significant inhibition of collagen and ADP [20 micro M]- induced aggregation by 37.8, 61.8,. 72% and 38.6, 83.1, 88.7%, respectively. These results suggest that regular consumption of NS would not influence platelet aggregation in humans. In the meantime, the findings show that TQ, NS major component, induces an inhibitory effect only when large doses are administered