Soy isoflavones enhance coronary vascular reactivity in atherosclerotic female macaques

Objective: To examine the effects of soy phytoestrogens on coronary vascular reactivity in atherosclerotic male and female rhesus monkeys. Design: A prospective, randomized, blinded, controlled study. Setting: Comparative Medicine Clinical Research Center of an academic medical center. Patient(s): Twenty-two young adult rhesus monkeys with pre-existing diet-induced atherosclerosis. Intervention(s): Monkeys were fed soy-based diets for 6 months identical in composition, except that the isoflavones were extracted from one (low-isoflavone) and intact in the other (high-isoflavone). Quantitative coronary angiography was performed at the end of the study, period. Females in the low-isoflavone group underwent a second angiography after an acute IV dose of genistein. Main Outcome Measure(s): Percent change in diameter of the proximal left circumflex coronary artery in response to intracoronary acetylcholine and nitroglycerin, compared with control diameter. Result(s): Arteries from males constricted in response to acetylcholine. Arteries from females in the low-isoflavone group constricted (-6.2% +/- 2.8%, mean +/- SEM), whereas arteries from females in the high-isoflavone group dilated (6.4 +/- 1.2%, mean +/- SEM). Intravenous administration of genistein caused dilation in the previously constricting low-isoflavone females (3.3 +/- +/- 2.8%). Conclusion(s): Like mammalian estrogens, dietary soy isoflavones enhance the dilator response to acetylcholine of atherosclerotic arteries in female monkeys.