FIGURE 4.

Serum levels of analytes involved in the arginine/nitric oxide pathway. a) Ratio of acetyl-ornithine to ornithine; (b) ratio of total arginine to the inferred activity of the nitric oxide synthase (NOS) enzyme expressed as arginine/(ornithine+citrulline); (c) ratio of endogenous NOS inhibitors (sum of asymmetric and symmetric dimethylarginine (ADMA + SDMA)) with arginine; and (d) concentration of the endogenous NOS inhibitor ADMA. Significance was calculated using the nonparametric Mann–Whitney test. Subjects are divided into smokers with normal lung function and smokers with chronic obstructive pulmonary disease (COPD). Data are from the targeted metabolomics method (Biocrates).