In vitro ACE-inhibitory peptide KGYGGVSLPEW facilitates noradrenaline release from sympathetic nerve terminals: relationship with the lack of antihypertensive effect on spontaneous hypertensive rats

This study aimed to validate the antihypertensive activity of the angiotensin-converting enzyme (ACE)-inhibitor whey protein hydrolysate (WPH) obtained through the action of proteolytic enzymes from Cynara Cardunculus. The antihypertensive activity of WPH fractions containing peptides with molecular weight below 3 kDa (Whey < 3 kDa) and 1 kDa (Whey < 1 kDa) along with the antihypertensive activity of three potent ACE-inhibitory peptide sequences (DKVGINYW, DAQSAPLRVY and KGYGGVSLPEW), previously identified in WPH, were also investigated. In parallel, the influence of KGYGGVSLPEW (the most potent ACE-inhibitory peptide sequence) on AT1 receptors (a common pharmacological target of antihypertensive therapies beyond ACE), was evaluated. The effect of WPH and fractions (300 mg/kg) and peptide sequences (5 mg/kg) on systolic, diastolic and mean blood pressure was evaluated by telemetry on spontaneously hypertensive rats (SHR), after single oral administration. Despite their ACE-inhibitory effect in vitro, neither WPH, Whey <3 kDa, Whey <1 kDa or peptide sequences exhibited antihypertensive activity. In addition, KGYGGVSLPEW was not only devoid of AT1 receptor antagonism but, on the contrary, had a similar effect to that of Ang II by facilitating the noradrenaline release from sympathetic nerve terminals. In vitro ACE blockade does not always correlate with antihypertensive activity and food-derived peptides cannot be classified as antihypertensive agents based exclusively on in vitro assays. The absence of an antihypertensive effect may also be a result of the interaction of these compounds with other components of the systems involved in the blood pressure control.