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 ω-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 ω-hydroxy-nor-L-arginine treatment decreased arginase activity (30–40%), reduced blood pressure (∼ 35 mmHg) 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 ω-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 ω-hydroxy-nor-L-arginine, and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the effect of N ω-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.