Altered vascular reactivity in mice made hypertensive by nitric oxide synthase inhibition

This study tested the hypothesis that nitric oxide (NO) synthase inhibition in mice would result in hypertension characterized by increased agonist-induced vasoconstrictor responsiveness and attenuated endothelium-dependent vasodilation. Administration of N-nitro-L-arginine (L-NNA), an NO synthase inhibitor (1 g/L, 4 weeks), via drinking water to mice resulted in significant elevations in blood pressure. Phenylephrine-induced contraction was significantly increased in aortic rings from L-NNA-treated mice compared with rings from control mice. Aortic rings from control mice showed a concentration-dependent relaxation to acetylcholine whereas those obtained from L-NNA-treated mice showed a biphasic response, contracting at lower concentrations while relaxing at higher concentrations. Aortic rings from L-NNA-treated mice had decreased relaxation to acetylcholine and increased sensitivity to sodium nitroprusside compared with control rings. The relaxation induced by an NO-independent soluble guanylyl cyclase activator was not different between groups. In aortic rings from control and L-NNA-treated mice pre-contracted with phenylephrine, the administration of L-NNA to the organ bath caused additional and sustained contraction. When compared with the contraction induced by phenylephrine, L-NNA-induced contraction in aorta from control mice was significantly higher than that in aorta from L-NNA-treated mice. We conclude that mice treated with L-NNA develop hypertension and that a reduction in NO availability is responsible for the changes observed in vascular reactivity.