J K Williams1, T B Clarkson. 1. Department of Comparative Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1040, USA. kwilliams@cpm.bgsm.edu
Abstract
BACKGROUND: Soy isoflavones (particularly genistein) improve impaired acetylcholine-induced dilator responses of atherosclerotic coronary arteries. Genistein reduces platelet accumulation of serotonin, whose constrictor properties 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 arteries of primates. METHODS: Twelve adult female rhesus monkeys were fed for 6 months an atherogenic diet identical in composition, except that isoflavones were either extracted with alcohol [n = 6, Soy(-)] or left intact (n = 6, Soy(+)]. Vasomotor 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 responses 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 less 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 the Soy(+) than in the Soy(-) monkeys (P < 0.05). However, soy diets did not affect vascular reactivity properties of large artery or resistance size arteries to adenosine diphosphate (ADP), nitroglycerin, or serotonin (P > 0.05). CONCLUSIONS: We conclude that components of the soy protein removed by alcohol extraction (probably the isoflavones) promoted endothelium-modulated dilation and inhibited constrictor responses to collagen infusion by inhibiting platelet aggregation or platelet release of vasoconstrictors, or both.
BACKGROUND: Soy isoflavones (particularly genistein) improve impaired acetylcholine-induced dilator responses of atherosclerotic coronary arteries. Genistein reduces platelet accumulation of serotonin, whose constrictor properties 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 arteries of primates. METHODS: Twelve adult female rhesus monkeys were fed for 6 months an atherogenic diet identical in composition, except that isoflavones were either extracted with alcohol [n = 6, Soy(-)] or left intact (n = 6, Soy(+)]. Vasomotor 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 responses 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 less 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 the Soy(+) than in the Soy(-) monkeys (P < 0.05). However, soy diets did not affect vascular reactivity properties of large artery or resistance size arteries to adenosine diphosphate (ADP), nitroglycerin, or serotonin (P > 0.05). CONCLUSIONS: We conclude that components of the soy protein removed by alcohol extraction (probably the isoflavones) promoted endothelium-modulated dilation and inhibited constrictor responses to collagen infusion by inhibiting platelet aggregation or platelet release of vasoconstrictors, or both.