Ile-Pro-Pro attenuates sympathetic activity and hypertension

Isoleucine-proline-proline (Ile-Pro-Pro, IPP) is a natural food source tripeptide that inhibits angiotensin-converting enzyme (ACE) activity. The aim of this study was to determine the central and peripheral roles of IPP in attenuating sympathetic activity, oxidative stress and hypertension. Male Sprague-Dawley rats were subjected to sham-operated surgery (Sham) or two-kidney one-clip (2K1C) surgery to induce renovascular hypertension. Renal sympathetic nerve activity and blood pressure were recorded. Bilateral microinjections of IPP to hypothalamic paraventricular nucleus (PVN) attenuated sympathetic activity (-16.1 ± 2.5%, P < 0.001) and hypertension (-8.7 ± 1.5 mmHg, P < 0.01) in 2K1C rats by inhibiting ACE activity and subsequent angiotensin II and superoxide production in the PVN. Intravenous injections of IPP also attenuated sympathetic activity (-15.1 ± 2.1%, P < 0.001) and hypertension (-16.8 ± 2.3 mmHg, P < 0.001) via inhibiting ACE activity and oxidative stress in both PVN and arteries of 2K1C rats. The duration of the effects of the intravenous IPP was longer than those of the PVN microinjection, but the sympatho-inhibitory effect of intravenous injections occurred later than that of the PVN microinjection. Intraperitoneal injection of IPP (400 pmol/day for 20 days) attenuated hypertension and vascular remodeling via inhibiting ACE activity and oxidative stress in both PVN and arteries of 2K1C rats. These results indicate that IPP attenuates hypertension and sympathetic activity by inhibiting ACE activity and oxidative stress. The sympathoinhibitory effect of peripheral IPP is mainly caused by the ACE inhibition in PVN, and the antihypertensive effect is related to the sympathoinhibition and the arterial ACE inhibition. Long-term intraperitoneal IPP therapy attenuates hypertension, oxidative stress and vascular remodeling.