Test Background Metanephrines are the inactive metabolites of the catecholamines epinephrine (adrenaline) and norepinephrine. Catecholamines are a group of similar hormones produced in the nervous system and in the medulla of the adrenal glands. The primary catecholamines are dopamine, epinephrine (adrenaline) and norepinephrine. These hormones are released into the bloodstream in response to physical or emotional stress; they help transmit nerve impulses in the brain, increase glucose and fatty acid release for energy, dilate small air passages in the lungs called bronchioles, and dilate the pupils. Norepinephrine also constricts blood vessels, which increases blood pressure while epinephrine increases heart rate and metabolism. After completing their actions, the catecholamines are metabolised to form inactive compounds. Dopamine becomes homovanillic acid (HVA), norepinephrine breaks down into normetanephrine and vanillylmandelic acid (VMA) and epinephrine becomes metanephrine and VMA. Both the hormones and their metabolites are excreted in the urine. The catecholamines that a pheochromocytoma produces can cause persistent hypertension and/or bouts or episodes of severe hypertension.