Hypotensive and physiological effect of angiotensin converting enzyme inhibitory peptides derived from soy protein on spontaneously hypertensive rats

Angiotensin converting enzyme (ACE) inhibitory peptides prepared from soy protein by the action of alcalase enzyme was tested for its hypotensive effect on spontaneously hypertensive rats (SHR). Captopril, an ACE inhibitor used widely for hypertension treatment, was also applied in comparison. A significant (p < 0.05) decrease in systolic blood pressure of SHR was observed when soy ACE inhibitory peptides were orally administrated at three different dose levels (100, 500, and 1000 mg/kg of body weight/day), whereas little change occurred in the blood pressure of normotensive rats even at the highest dose. After a month-long feeding, blood pressure readings of SHR fell by 38 mmHg from the original level at the lowest dose; a steadily and progressively hypotensive effect existed for these soy ACE inhibitory peptides administration groups. An obvious fluctuation was observed at the third week, although Captopril had a stronger hypotensive effect. The ACE activity of serum, aorta and lung, and lipid content of serum of SHR upon administration of soy ACE inhibitory peptides did not show a significant difference from that of the control group, whereas the serum ACE activity increased and the aorta ACE activity decreased significantly (p < 0.05) for the Captopril group. Serum Na+ concentration decreased significantly in both the peptides-treated groups and the Captopril-treated group in comparison with the control group, whereas no lowering effect was observed for serum K+ and serum Ca2+ concentrations. These results suggested that the hypotensive effect of ACE inhibitory peptides derived from soy protein could be at least partly attributed to the action on salt/water balance.