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(Hypertension. 2007;49:893.)
© 2007 American Heart Association, Inc.

Original Articles

Novel Nitric Oxide Synthase–Dependent Mechanism of Vasorelaxation in Small Arteries From Hypertensive Rats

From the Vascular Biology Center, Medical College of Georgia, Augusta.

Correspondence to Jennifer S. Pollock, Vascular Biology Center, CB 3213, Medical College of Georgia, Augusta, GA 30912. E-mail jpollock{at}mcg.edu

To determine the mechanism(s) involved in vasorelaxation of small arteries from hypertensive rats, normotensive (NORM), angiotensin II-infused (ANG), high-salt (HS), ANG high-salt (ANG/HS), placebo, and deoxycorticosterone acetate-salt rats were studied. Third-order mesenteric arteries from ANG or ANG/HS displayed decreased sensitivity to acetylcholine (ACh)-induced vasorelaxation compared with NORM or HS, respectively. Maximal relaxations were comparable between groups. Blockade of Ca²⁺-activated K⁺ channels had no effect on ANG versus blunting relaxation in NORM (log EC₅₀: –6.8±0.1 versus –7.2±0.1 mol/L). NO synthase (NOS) inhibition abolished ACh-mediated relaxation in small arteries from ANG, ANG/HS, and deoxycorticosterone acetate-salt versus blunting relaxation in NORM, HS, and placebo (% maximal relaxation: ANG: 2.7±1.8; ANG/HS: 7.2±3.2; NORM: 91±3.1; HS: 82.1±13.3; deoxycorticosterone acetate-salt: 35.2±17.7; placebo: 79.3±10.3), indicating that NOS is the primary vasorelaxation pathway in these arteries from hypertensive rats. We hypothesized that NO/cGMP signaling and NOS-dependent H₂O₂ maintains vasorelaxation in small arteries from ANG. ACh increased NOS-dependent cGMP production, indicating that NO/cGMP signaling is present in small arteries from ANG (55.7±6.9 versus 30.5±5.1 pmol/mg), and ACh stimulated NOS-dependent H₂O₂ production (ACh: 2.8±0.2 µmol/mg; N-nitro-L-arginine methyl ester hydrochloride+ACh: 1.8±0.1 µmol/mg) in small arteries from ANG. H₂O₂ induced vasorelaxation and catalase blunted ACh-mediated vasorelaxation. In conclusion, Ca²⁺-activated K⁺ channel–mediated relaxation is dysfunctional in small mesenteric arteries from hypertensive rats, and the NOS pathway compensates to maintain vasorelaxation in these arteries through NOS-mediated cGMP and H₂O₂ production.

Key Words: NO • hydrogen peroxide • hypertension • endothelium-dependent vasorelaxation • mesenteric arteries • aorta

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