NOS3 and obstructive sleep apnea syndrome: Yamauchi et al. studied 32 OSA and 15 control patients, in which they quantified endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (the active form of the enzyme responsible for producing NO in the vasculature), inflammation (cyclooxygenase-2 and inducible NOS), and oxidative stress (nitrotyrosine).