Kinetics of in vitro enzyme inhibition and blood pressure-lowering effects of salmon (Salmo salar) protein hydrolysates in spontaneously hypertensive rats

A salmon protein hydrolysate (SPH) was produced from consecutive enzymatic hydrolysis of salmon muscle proteins with pepsin followed by trypsin + chymotrypsin. The SPH was separated into four (SF1-SF4) reverse-phase HPLC peptide fractions. The SF3 peptide fraction was the most active against both angiotensin I-converting enzyme (ACE) and renin activities during in vitro tests. SPH and SF3 inhibited ACE activity uncompetitively but renin inhibition was non-competitive. SPH and SF3 were orally administered (200 and 30 mg/kg body weight, respectively) to spontaneously hypertensive rats, followed by systolic blood pressure (SBP) measurements. The SF3 significantly (p < 0.05) reduced SBP by a maximum value of -42.1 ± 3.4 mmHg when compared to -21.1 ± 4.5 mmHg for SPH 2 h after oral administration. Mass spectrometry analysis showed some differences in the peptide ion composition, which may have contributed to the observed differences in SBP-reducing effects of SPH and SF3.