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76

 Functional Assessment of Urinary Neuro-biogenic Amines—A COMPREHENSIVE GUIDE

ed plasma epinephrine while at rest.

Experimental administration of epi-

nephrine to men decreased thyroid

hormone metabolism and free T4 lev-

els, and increased thyroid hormone

binding globulin levels. Experimental

administration of epinephrine to male

Type II diabetics altered the metabo-

lism of glycerol, non-esterified fatty ac-

ids and triacylglycerols in adipose tis-

sues. Mild, asymptomatic hypoglycemia

may increase epinephrine compared

to norepinephrine levels. Elevated epi-

nephrine concentrations may decrease

the serum potassium concentrations.

Epinephrine:norepinphrine ratios may

increase after surgical sympathectomy.

Symptoms of elevated epinephrine may

include:

Headaches (severe)

High blood pressure

Excess sweating (generalized)

Racing heart (tachycardia)

Anxiety or nervousness

Tremors

Epigastric pain (lower chest or

upper abdomen)

Nausea or vomiting

Weight loss

Heat intolerance

Epinephrine is usually present in the

urine in small fluctuating amounts and

may be increased during and shortly

after stress exposures. Monoamine ox-

idase inhibitors (MAOIs) may elevate

epinephrine and metanephrine levels.

Drugs that stimulate nicotinic, angioten-

sin II, or glucagon receptors may also in-

crease plasma epinephrine levels.

Synthesis and Metabolism:

NMet-SO

4

MHPG-SO

4

VMA

Met-SO

4

MHPG-SO

4

VMA

Normetanephrine

Metanephrine

DPHG

Norepinephrine

Epinephrine

SULT1A3

SULT1A3

MAO-A+AR

COMT

SULT1A3

ADH

COMT

COMT

PNMT

D H

MAO-A

MAO-A

AR

AR

Enephrine is primarily synthesized in

the chromaffin cells of the adrenalmedul-

la; small amounts are synthesized in the

Central Nervous System (CNS) and the

vagus nerve. Epinephrine is derived from

norepinephrine. Phenylethanolamine

N-methyltransferase (PNMT) meth-

ylates norepinephrine to form epi-

nephrine, using S-adenosyl methionine

(SAM) as a cofactor. High concentra-

tions of PNMT are found in the adre-

nal medulla, and PNMT is found in cer-

tain areas of the brain and vagus nerve.

Individual production and response to

epinephrine levels may be influenced in

part by genetic polymorphisms (SNPs)

in the PNMT enzyme. Animal studies

indicate that PNMT activity may be up-

regulated by excercies, high cortisol lev-

els (such corticosteroid medications) or

stress. Epinephrine is stored in vesicles

until it is released into the circulation.

Adrenomedullary chromaffin cells

possess monoamine oxidaseA (MAO-A)

and catechol-O-methyl transferase

(COMT). Approximately 90% of epi-

nephrine is metabolized before the

neurotransmitter is released. COMT