Neuronal Nitric Oxide Synthase Regulates Basal Microvascular Tone in Humans In Vivo

Nitric oxide (NO) has a pivotal role in the regulation of vascular tone and blood flow, with dysfunctional release contributing to disease pathophysiology. These effects have been attributed to NO production by the endothelial NO synthase (eNOS); however, recent evidence suggests that a neuronal NO synthase (nNOS) may also be expressed in arterial vessels. We undertook a first-in-humans investigation of the role of nNOS in the local regulation of vascular blood flow in healthy subjects. Brachial artery infusion of the nNOS-specific inhibitor S-methyl-L-thiocitrulline (SMTC, 0.025 micromol/min to 0.2 micromol/min) caused a dose-dependent reduction in basal flow, with a 30.1+/-3.8% decrease at the highest dose (n=10; mean+/-SE; P