Grape juice but not orange or grapefruit juice inhibits platelet activity in dogs and monkeys.

Platelet aggregation (PA) contributes to both the development of atherosclerosis and acute platelet thrombus formation (APTF) followed by embolization producing cyclic flow reductions (CFR) in stenosed and damaged dog and human coronary arteries. In seven anesthetized dogs with coronary stenosis and medial damage, CFR occurred at 7 +/- 3/30 min and were abolished 127 +/- 18 min after gastric administration of 10 mL of purple grape juice/kg. Collagen-induced ex vivo whole blood PA decreased by 49 +/- 9% after the abolishment of CFR with grape juice. Ten mL of orange juice/kg (n = 5) and 10 mL of grapefruit juice/kg (n = 5) had no significant effect on the frequency of the CFR or on ex vivo PA. In vitro studies have suggested that flavonoids bind to platelet cell membranes and thus may have an accumulative or tissue-loading effect over time. To test this we fed 5 mL of grape juice/kg to 5 cynomologous monkeys for 7 d. Collagen-induced ex vivo PA decreased by 41 +/- 17% compared to control (pre-reatment) after 7 d of feeding. In the same 5 monkeys, neither 5 mL of orange juice/kg nor 5 mL of grapefruit juice/kg given orally for 7 d produced any significant change in PA. Grape juice contains the flavonoids quercetin, kaempferol and myricetin, which are known inhibitors of PA in vitro. Orange juice and grapefruit juice, while containing less quercetin than grape juice, primarily contain the flavonoids naringin, luteolin and apigenin glucoside. The flavonoids in grapes were shown in vitro to be good inhibitors of PA, whereas the flavonoids in oranges and grapefruit to be poor inhibitors of PA. The consumption of grape juice, containing these inhibitors of PA, may have some of the protection offered by red wine against the development of coronary artery disease (CAD) and acute occlusive thrombosis, whereas orange juice or grapefruit juice may be ineffective. Thus, grape juice may be a useful alternative dietary supplement to red wine without the concomitant alcohol intake.