Effect of raw versus boiled aqueous extract of garlic and onion on platelet aggregation

The effects of aqueous extracts of raw and boiled garlic and onions were st udied in vitro on the collagen-induced platelet aggregation using rabbit an d human platelet-rich plasma. A dose dependant inhibition of rabbit platele t aggregation was observed with garlic. Onion also showed dose-dependent in hibitory effects on the collagen-induced platelet aggregation but this inhi bition was of a lesser magnitude compared to garlic when related to dose. T he concentration required for 50% inhibition of the platelet aggregation fo r garlic was calculated to be approximately 6.6 mg ml(-1) plasma, whereas t he concentration for onion was 90 mg ml(-1) plasma. Boiled garlic and onion extracts showed a reduced inhibitory effect on platelet aggregation. Garli c but not onion significantly inhibits human platelet aggregation in a dose -dependent fashion. The potency of garlic in inhibiting the collagen-induce d platelet aggregation is approximately similar to that of rabbit platelets (8.8 mg ml(-1) produced 50% inhibition of platelet aggregation). The resul ts of this study show that garlic is about 13 times more potent than onion in inhibiting platelet aggregation and suggest that garlic and onion could be more potent inhibitors of blood platelet aggregation if consumed in raw than in cooked or boiled form.