NPY and type 2 diabetes mellitus: DPP‐4 reportedly cleaves not only GLP‐1 but also other peptides, such as SDF‐1a, neuropeptide Y, peptide YY, substance P, GLP‐2, and neuropeptide pituitary adenylate cyclase‐activating polypeptide 38, all of which are known to have vascular effects.33–36 Although there was no significant correlation between the changes in FMD and those in DPP‐4 activity (Table 6), it is conceivable that known or unknown substrates of DPP‐4 might be involved in DPP4‐I‐induced attenuation of FMD in T2DM patients.