NG-Nitro-L-Arginine Contracts Vascular Smooth Muscle by an Endothelium-Independent Mechanism

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Abstract
We characterized the contractile effect of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) in endothelium-denuded rat aortic rings. Incubation with L-NNA (4 x 10(-6)-6.4 x 10(-5) M) for 5 h dose-dependently contracted endothelium-denuded aortic rings. In contrast, incubation with NG-nitro-D-arginine (D-NNA 6 x 10(-6)-4 x 10(-4) M), diphenyleneiodonium (DPI, NO synthase inhibitor, 3.2 x 10(-6) M) or dexamethasone (10(-7) M, inhibitor of expression of inducible NO synthase) did not contract the denuded rings. The L-NNA-induced contraction was not significantly altered by the presence of the endothelium or by pretreatment with L-arginine (L-Arg 2 x 10(-3) M) or lipopolysaccharide (100 ng/ml). These results suggest that L-NNA causes slow contraction of endothelium-denuded vascular smooth muscle (VSM) by a mechanism independent of the inhibition of constitutive or inducible NO biosynthesis.

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