Release of angiotensin-(1-7) from the rat hindlimb - Influence of angiotensin-converting enzyme inhibition

The results of recent, studies have demonstrated that angiotensin (Ang)-(1- 7) contributes to the antihypertensive actions of either combined ACE/Ang I I type 1 receptor blockade or ACE inhibition alone. The vasculature is a ke y site of action for either drug regimen, and evidence favors a local Ang s ystem within these tissues. Because ACE may degrade Ang-(1-7), we determine d whether ACE inhibition alters Ang-(1-7) release from the rat hindlimb per fused with Krebs-Ringer buffer containing Ficoll. Ang-(1-7) release average d 36+/-13 fmol (period 1, 15-minute collection) and 44+/-11 fmol (period 2) in the control buffer. The addition of the ACE inhibitor lisinopril to the perfusion buffer augmented levels of Ang-(1-7) in periods 3 (144+/-39 fmol ) and 4 (163+/-35 fmol; P<0.05 versus 1 or 2, n=8). HPLC and radioimmunoass ay of effluent from control or lisinopril treatment demonstrated a single i mmunoreactive peak with a retention time identical to that of Ang-(1-7). Th e addition of the neprilysin inhibitor SCH 39370 reduced Ang-(1-7) release in the lisinopril buffer from 177+/-32 (period 1) and 173+/-39 (period 2) f mol to 112+/-24 (period 3) and 87+/-23 fmol (period 4; P<0.05 versus 1 or 2 , n=6). Ang I metabolism in the collected perfusate revealed the formation of Ang-(1-7) that was sensitive only to thimet oligopeptidase inhibition; A ng II generation was not detected. The present study demonstrates the recov ery of endogenous Ang-(1-7) from the perfused hindlimb. The release of Ang- (1-7) is significantly influenced by inhibition of ACE, which may reflect b oth increased substrate (Ang I) levels and reduced metabolism of the peptid e. Neprilysin inhibition reduced but did not abolish Ang-(1-7) release, whi ch suggests that other endopeptidases may contribute to the release of the peptide.