Dietary soy exerts an antihypertensive effect in spontaneously hypertensive female rats

This study tested the hypothesis that dietary soy would attenuate the devel opment of hypertension in female spontaneously hypertensive rats (SHR). Fem ale SHR and control Wistar-Kyoto rats were obtained at 4 wk of age, randoml y assigned to either an ovariectomized (OVX) group or a sham-operated group , and placed on a soy diet or control casein diet. After a minimum of 8 wk on their respective diets, mean arterial pressure (MAP) and heart rate (HR) were recorded before and after inhibition of nitric oxide synthase, air-je t stress, or ganglionic blockade. The major finding of this study is that M AP was reduced in the OVX SHR consuming soy diet compared with the casein-f ed controls (150 +/-4 vs. 164 +/-3 mmHg). Plasma genistein concentrations w ere increased in the soy-fed OVX SHR (1.23 +/-0.31 muM) compared with the c asein-fed OVX SHR (nondetectable). However, there was no difference in plas ma genistein concentrations between sham-operated and OVX SHR (1.37 +/-0.42 vs. 1.23 +/-0.31 mM). Inhibition of nitric oxide synthase increased MAP an d decreased HR in all groups; diet did not affect this response. Air-jet st ress increased MAP and HR in all groups. However, these responses were exag gerated in the soy-fed SHR. Finally, ganglionic blockade abolished the anti hypertensive effect of soy diet in the OVX SHR. These findings indicate tha t dietary soy exerts an antihypertensive effect in OVX SHR. This effect doe s not involve the nitric oxide system but may be related to an as yet undef ined interaction with the autonomic nervous system.