Pepsin-digested soy protein hydrolysate has been reported to be responsible for many of the physiological benefits associated with soy protein consumption. In the present study, we investigated the effects of soy protein hydrolysate with angiotensin-converting enzyme (ACE) inhibitory potential on the blood pressure and cardiovascular remodeling in rats with Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME)-induced hypertension. Rats were fed a diet containing l-NAME (50 mg/kg body weight) with or without soy protein hydrolysate (1%, 3% or 5%) for 6 weeks. We found that ingestion of soy protein hydrolysate retarded the development of hypertension during the 6-week experimental period without affecting the amount of food intake. Although there was no difference in plasma ACE activity or tissue nitric oxide levels, ACE activity in the heart of rats consuming soy protein hydrolysate was significantly lower than that of the control group. Moreover, cardiac malonaldehyde and tumor necrosis factor-α concentrations were also lower in the soy protein hydrolysate group. No difference in plasminogen activator inhibitor-1 level was found in plasma or cardiovascular tissue. In the histopathological analysis, we also found that soy protein hydrolysate ameliorated inflammation and left ventricle hypertrophy in the heart. These findings suggest that soy protein hydrolysate might not only improve the balance between circulating nitric oxide and renin-angiotensin system but also show beneficial effects on cardiovascular tissue through its ACE inhibitory activity.
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