Treatment with the arginase inhibitor Nω-hydroxy-nor-L-arginine improves vascular function and lowers blood pressure in adult spontaneously hypertensive rat

Objective High vascular arginase activity and subsequent reduction in vascular nitric oxide production were recently reported in animal models of hypertension. The present study investigated the effects of in-vivo arginase inhibition on blood pressure and vascular function in adult spontaneously hypertensive rats. Methods Ten-week-old spontaneously hypertensive rats and normotensive age-matched Wistar-Kyoto rats were treated with or without the selective arginase inhibitor N-omega-hydroxy-nor-L-arginine for 3 weeks (10 or 40 mg/kg per day, intraperitoneally). Systolic blood pressure and cardiac rate were measured before and during treatment. Flow and pressure-dependent reactivity as well as remodeling of mesenteric arteries, acetylcholine-dependent vasodilation of aortic rings, cardiac hypertrophy, arginase activity and nitric oxide production were investigated in 13-week-old spontaneously hypertensive rats. Results In spontaneously hypertensive rats, N-omega-hydroxy-nor-L-arginine treatment decreased arginase activity (30-40%), reduced blood pressure (similar to 35mmHg) and improved the reactivity of mesenteric vessels. However, vascular and cardiac remodeling was not different between treated and untreated spontaneously hypertensive rats. In Wistar-Kyoto rats, N-omega-hydroxy-nor-L-arginine did not affect blood pressure. Finally, arginase inhibition was associated with increased nitric oxide production. Consistent with this, the response of aortic rings to acetylcholine was fully restored by N-omega-hydroxy-nor-L-arginine, and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the effect of N-omega-hydroxy-nor-L-arginine on flow-dependent vasodilation. Conclusion Pharmacological inhibition of arginase in adult spontaneously hypertensive rats decreases blood pressure and improves the reactivity of resistance vessels. These data represent in-vivo argument in favor of selective arginase inhibition as a new therapeutic strategy against hypertension.