Acute effect of whey peptides upon blood pressure of hypertensive rats, and relationship with their angiotensin-converting enzyme inhibitory activity

Scope: The aim of this study was to investigate the antihypertensive effect of a peptide fraction (PepC) obtained from a whey protein concentrate following hydrolysis by Cynara cardunculus, as well as of its fraction with MW below 3 kDa (PepCF). Both these concentrates encompassed peptides that exhibited potent in vitro inhibition of angiotensin-converting enzyme (ACE): two were released from alpha-lactalbumin - KGYGGVSLPEW and DKVGINYW, and one from beta-lactoglobulin - DAQSAPLRVY. Methods and results: Upon oral administration, by gastric intubation, of 400 mg/kg body weight (bw) of those peptide concentrates, or 5 mg/kg bw of the corresponding synthetic peptides, to 12 wk-old spontaneously hypertensive rats (SHR), the systolic and diastolic blood pressures were monitored by the tail-cuff method - before, and 2, 4, 6, 8 and 24 h afterwards. Water and zofenopril (5 mg/kg bw) - a known ACE-inhibitor, were used as negative and positive controls, respectively. Acute administration of PepC, PepCF, KGYGGVSLPEW, DKVGINYW and DAQSAPLRVY caused antihypertensive effects in SHR; the maximum effect occurred by 4 h and 6 h after administration of the peptide concentrates and the synthetic peptides, respectively. PepC and KGYGGVSLPEW also showed ACE-inhibitory activity in vivo: the pressor effect of angiotensin I was significantly lower, and the response to bradykinin increased when the rats were pre-treated with either product. Conclusion: Our results strongly suggest that PepC will be effective as nutraceutical ingredient for the formulation of functional foods aimed at hypertension control.