Interactive effects of soy protein and estradiol on coronary artery reactivity in atherosclerotic, ovariectomized monkeys

Objective: Results of recent clinical trials indicate that mammalian estrog ens may be less effective in reducing coronary heart disease risk than once thought. This study was designed to determine whether mammalian estrogen's coronary artery dilator benefits could be enhanced by adding soy with phyt oestrogens. Design: Forty-five atherosclerotic, ovariectomized monkeys were fed one of four diets: (1) atherogenic diet with casein/lactalbumin as source of prote in (Casein, n = 12); (2) casein diet with micronized estradiol equivalent t o a woman's dose of 1 mg/day (Casein + E-2, n = 12); (3) atherogenic diet w ith soy protein with phytoestrogens (129 mg woman/day equivalent) (Soy, n = 11); and (4) the soy diet plus estradiol (Soy + E-2, n = 10). Methods: Quantitative angiography and intravascular Doppler were done after 6 months of experimental diet to measure changes in diameter and coronary flow reserve in the circumflex coronary artery in response to intracoronary acetylcholine and nitroglycerin. Results: Arteries from the E-2 and Soy + E-2 groups dilated in response to acetylcholine 5 +/- 3% and 12 +/- 5% respectively (p < 0.05 vs. Casein). Th ere was an interactive effect of soy and E2 on dilator response to acetylch oline (p < 0.05). Flow reserve was greatest in animals fed casein + E-2 and soy + E-2 (2.3 <plus/minus> 0.3 and 2.6 +/- 0.5, respectively; p < 0.05 vs . Casein). Soy protein alone had no effect on coronary artery reactivity (p <greater than> 0.05). Conclusion: Soy protein itself does not affect coronary artery dilator resp onses but interacts with estradiol to promote dilator responses to acetylch oline.