In this study, the antihypertensive activity in spontaneously hypertensive rats of two peptides isolated from β-lactoglobulin hydrolysates with thermolysin was evaluated. These peptides, with sequences LLF [β-lg f(103–105)] and LQKW [β-lg f(58–61)], showed potent in vitro ACE-inhibitory activity. Two hours after administration, both sequences caused a clear and significant decrease in the blood pressure of these rats. The impact of a simulated gastrointestinal digestion on ACE-inhibitory and antihypertensive activities of these peptides was also studied. The results showed that both fragments were susceptible to proteolytic degradation after incubation with pepsin and Corolase PP®. In addition, their in vitro ACE-inhibitory activity decreased after the simulated digestion. It is likely that fragment LQK was the active end product of the gastrointestinal digestion of peptide LQKW. The fragment LL, observed after digestion of peptide LLF, probably exert its antihypertensive effect through a mechanism of action different than ACE-inhibition.

We describe a clinical trial to study the efficacy of a casein hydrolysate, prepared using an Aspergillus oryzae protease, containing the major angiotensin-I-converting enzyme inhibitory peptides Val-Pro-Pro (VPP) and Ile-Pro-Pro (IPP) in a single-blind, placebo-controlled study. A total of 131 volunteers with high-normal blood pressure and mild hypertension were randomly divided into four groups (n 32 or 33 in each group). Each volunteer was given two tablets containing four different dosages of VPP and IPP (VPP+IPP: 0, 1·8, 2·5 and 3·6 mg), daily for 6 weeks. A significant decrease in systolic blood pressure was observed at 6 weeks in the active group receiving 1·8 mg (P<0·01) VPP and IPP; in the active groups receiving either 2·5 mg or 3·6 mg, systolic blood pressure was decreased at both 3 weeks (P<0·05 and P<0·05) and 6 weeks (P<0·001 and P<0·0001) compared with systolic blood pressure measured before treatment. Changes in the systolic blood pressure after 6 weeks of treatment in the four groups were −1·7, −6·3, −6·7 and −10·1 mmHg, and these effects were dose dependent. In addition, a significant difference in systolic blood pressure between the placebo group and the VPP and IPP group receiving 3·6 mg was observed (P<0·001) by two-way ANOVA. The antihypertensive effect was greater in mildly hypertensive subjects (n 20 or 21 in each group) than in any of the other subjects. No significant change of diastolic blood pressure was observed for all the test groups, and no differences in diastolic blood pressure in the test sample groups compared with the placebo group were observed during the test period.