Final answer:
Increased levels of Vanillylmandelic acid (VMA) and metanephrines in plasma and urine are indicators of Pheochromocytoma, a tumor causing overproduction of epinephrine and norepinephrine from the adrenal medulla.
Step-by-step explanation:
The two catecholamine metabolites that, when found in increased levels in plasma and urine, are diagnostic of Pheochromocytoma are Vanillylmandelic acid (VMA) and metanephrines. These metabolites are produced when epinephrine and norepinephrine, hormones secreted by the adrenal medulla, are broken down by enzymes such as Catechol-O-Methyl-Transferase (COMT) and Mono-Amine Oxidase (MAO). Pheochromocytoma is a tumor of the adrenal medulla that causes excessive production of catecholamines, leading to symptoms such as hypertension.