Soy isoflavones enhance coronary vascular reactivity in atherosclerotic female macaques

To examine the effects of soy phytoestrogens on coronary vascular reactivity in atherosclerotic male and female rhesus monkeys. A prospective, randomized, blinded, controlled study. Comparative Medicine Clinical Research Center of an academic medical center. Twenty-two young adult rhesus monkeys with pre-existing diet-induced atherosclerosis. 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. Percent change in diameter of the proximal left circumflex coronary artery in response to intracoronary acetylcholine and nitroglycerin, compared with control diameter. 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%). Like mammalian estrogens, dietary soy isoflavones enhance the dilator response to acetylcholine of atherosclerotic arteries in female monkeys.