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 p rotein by the action of alcalase enzyme was tested for its hypotensive effe ct on spontaneously hypertensive rats (SHR). Captopril, an ACE inhibitor us ed widely for hypertension treatment, was also applied in comparison. A sig nificant (p < 0.05) decrease in systolic blood pressure of SHR was observed when soy ACE inhibitory peptides were orally administrated at three differ ent dose levels (100, 500, and 1000 mg/kg of body weight/day), whereas litt le change occurred in the blood pressure of normotensive rats even at the h ighest dose. After a month-long feeding, blood pressure readings of SHR fel l by <similar to>38 mmHg from the original level at the lowest dose; a stea dily and progressively hypotensive effect existed for these soy ACE inhibit ory peptides administration groups. An obvious fluctuation was observed at the third week, although Captopril had a stronger hypotensive effect. The A CE activity of serum, aorta and lung, and lipid content of serum of SHR upo n administration of soy ACE inhibitory peptides did not show a significant difference from that of the control group, whereas the serum ACE activity i ncreased and the aorta ACE activity decreased significantly (p < 0.05) for the Captopril group. Serum Na+ concentration decreased significantly in bot h 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 hypotens ive effect of ACE inhibitory peptides derived from soy protein could be at least partly attributed to the action on salt/water balance.