Metanephrine

Metanephrine is a metabolite of the neurotransmitter epinephrine (adrenaline). It is produced in the adrenal medulla and the adrenal glands as part of the body's response to stress. Metanephrine is broken down into vanillylmandelic acid (VMA) and excreted in the urine.

Production and Function

Metanephrine is produced by the action of the enzyme catechol-O-methyltransferase (COMT) on epinephrine. This reaction occurs primarily in the adrenal medulla, a part of the adrenal glands. The adrenal glands are small, triangular glands located on top of the kidneys. They produce hormones that regulate the body's response to stress, including epinephrine.

The production of metanephrine is part of the body's fight-or-flight response. When the body is under stress, the adrenal glands produce more epinephrine. This hormone increases heart rate, blood pressure, and blood glucose levels, preparing the body for a sudden burst of activity. Some of the epinephrine is converted into metanephrine, which can be measured in the blood or urine as a marker of adrenal activity.

Clinical Significance

Measurement of metanephrine levels in the blood or urine can be used to diagnose pheochromocytoma, a rare tumor of the adrenal glands that produces excess amounts of epinephrine and norepinephrine. High levels of metanephrine can indicate the presence of a pheochromocytoma.

In addition, metanephrine levels can be elevated in certain other conditions, including severe stress, heart failure, and certain types of cancer. Therefore, measurement of metanephrine levels is not specific for pheochromocytoma and must be interpreted in the context of the patient's overall clinical picture.

See Also

• Epinephrine
• Norepinephrine
• Pheochromocytoma
• Adrenal gland
• Catechol-O-methyltransferase