Dietary soy isoflavones inhibit in-vivo constrictor responses of coronary arteries to collagen-induced platelet activation

Background Soy isoflavones (particularly genistein) improve impaired acetyl choline-induced dilator responses of atherosclerotic coronary arteries. Gen istein reduces platelet accumulation of serotonin, whose constrictor proper ties are augmented by dyslipoproteinemia and atherosclerosis. Studies were therefore designed to examine the effects of soy protein (with and without the isoflavones) on platelet-induced constrictor responses of coronary arte ries of primates. Methods Twelve adult female rhesus monkeys were fed for 6 months an atherog enic diet identical in composition, except that isoflavones were either ext racted with alcohol [n = 6, Soy(-)] or left intact (n = 6, Soy(+)]. Vasomot or responses were assessed in vivo using quantitative coronary angiography and intravascular Doppler measurements of blood flow velocity. Results As shown previously, soy isoflavones improve impaired dilator respo nses to acetylcholine, Furthermore, in response to activation of platelets by intracoronary infusion of collagen, reductions in blood flow through the left circumflex coronary artery, but not large artery constriction, were l ess in the Soy(+) (10 +/- 5%) than in the Soy(-) monkeys (35 +/- 6%, P = 0. 02). In-vitro platelet aggregation to thrombin and serotonin were less in t he Soy(+) than in the Soy(-) monkeys (P < 0.05). However, soy diets did not affect vascular reactivity properties of large artery or resistance size a rteries to adenosine diphosphate (ADP), nitroglycerin, or serotonin (P > 0. 05). Conclusions We conclude that components of the soy protein removed by alcoh ol extraction (probably the isoflavones) promoted endothelium-modulated dil ation and inhibited constrictor responses to collagen infusion by inhibitin g platelet aggregation or platelet release of vasoconstrictors, or both. Co ronary Artery Dis 9:759-764 (C) 1998 Lippincott Williams & Wilkins.