Handle Region Peptide Counteracts the Beneficial Effects of the Renin Inhibitor Aliskiren in Spontaneously Hypertensive Rats

To investigate whether the putative (pro) renin receptor blocker, the handle region peptide (HRP), exerts effects on top of the blood pressure-lowering and cardioprotective effects of the renin inhibitor aliskiren, spontaneously hypertensive rats were implanted with telemetry transmitters to monitor heart rate and mean arterial pressure (MAP). After a 2-week recovery period, vehicle, aliskiren, HRP (100 and 1 mg/kg per day, respectively), and HRP+aliskiren were infused for 3 weeks using osmotic minipumps. Subsequently, the heart was removed to study coronary function according to Langendorff. Baseline MAP and heart rate in vehicle-treated rats were 146 +/- 3 mm Hg and 326 +/- 4 bpm. HRP did not affect MAP, whereas aliskiren and HRP+aliskiren lowered MAP (by maximally 29 +/- 2 and 20 +/- 1 mm Hg, respectively) without affecting heart rate. Aliskiren significantly reduced MAP throughout the 3-week infusion period, whereas the blood pressure-lowering effect of HRP+aliskiren returned to baseline within 2 weeks of treatment. In comparison with vehicle, aliskiren increased the endothelium-dependent response to bradykinin and decreased the response to angiotensin II in the coronary circulation, whereas these responses were not altered after treatment with HRP or HRP+aliskiren. HRP did not alter plasma renin activity, plasma angiotensin levels, or the renal angiotensin content, either alone or on top of aliskiren, nor did it alter the aliskiren-induced decrease in renal Ang II type 1 receptor expression. Yet, it did reverse the aliskiren-induced reduction in cardiomyocyte area, without affecting this area when given alone. In conclusion, HRP counteracts the beneficial effects of aliskiren on blood pressure, coronary function, and cardiac hypertrophy in an angiotensin-independent manner. (Hypertension. 2011;57:852-858.)