Notes: Normetanephrine is an active metabolite of norepinephrine.{32483,66603,66604} It is formed from norepinephrine by catechol-O-methyltransferase (COMT).{32483} Normetanephrine induces contractions in isolated rabbit aortic strips in a concentration-dependent manner.{66603} It inhibits norepinephrine uptake in isolated rat heart (IC50 = 200 µM).{66604} Plasma levels of normetanephrine are increased in patients with von Hippel-Lindau disease and pheochromocytomas compared with patients with von Hippel-Lindau disease without pheochromocytomas.{66605} It has been used as a marker of authentic human urine specimens.{62138}