Catecholamine metabolites Catecholamine metabolites VMA HVA metanephrines Significance

Catecholamine metabolites

• Catecholamine metabolites • VMA, HVA, metanephrines • Significance • Urinary catecholamines, VMA, HVA as indicators for • Pheochromocytoma & neuroblastoma. VMA, Vanillylmandelic acid; HVA, homovanillic acid.

Pheochromocytoma • Tumors of the adrenal medulla • Hypertension syndrome • Norepinephrine / epinephrine is often increased

Metabolism of catecholamines • Catecholamines • Loose association with albumin • Extremely short biologic half-life (10— 30 seconds). • Catechol-O-methyltransferase • O-Methoxylated derivatives • Homovanillic acid • Normetanephrine • Metanephrine • Conjugation with glucuronic or sulfuric acid • Monoamine oxidase • deamination

Metabolism of catecholamines • Metanephrines • Methoxy derivatives of epinephrine and norepinephrine • Vanillylmandelic acid (VMA) • O-methylated deaminated • Production occurs mainly in the liver

Pathways of metabolism of catecholamines

• HVA is formed in multiple tissues • about 30% of circulating and urinary HVA arising from mesenteric organs • Up to 20% from the brain.

Pathways of metabolism of catecholamines (VMA)

• HVA and conjugates of HVA are the main metabolic end products of dopamine metabolism. • In humans, VMA and the sulfates and glucuronide conjugates of MHPG represent the main end products of norepinephrine and epinephrine metabolism AD, & ADH AD, aldehyde dehydrogenase; ADH, alcohol dehydrogenase MHPG; 3 -methoxy-4 -hydroxyphenylglycol

• Values from either the 24 -h urine collection or plasma catecholamines that are two to three times the upper limit of normal are usually diagnostic of pheochromocytoma.