Flashcards in Adrenal Catecholamines Deck (37):
What stain turns chromaffin cells yellow?
What are chromaffin cells thought of in terms of pre or post ganglionic nerves?
Think of them as post-ganglionic sympathetic neurons considering their contents
What do chromaffin granules contain?
Chromogranin A (tumor marker)
Chromogranin B (tumor marker)
How are catecholamines concentrated?
By 4:1 binding with an ATP molecule (proton pumps them in)
What is the vesicular proton pump needed for?
Catecholamine concentration in chromaffin granules
What is Adrenomedullin?
It is a marker for catecholamine release; increased would mean pheochromocytoma
What is the pathway for formation of the catecholamines?
Phenylalanine-> Tyrosine-> Dopa-> Dopamine-> Norepinephrine-> Epinephrine
What step does the catecholamine synthesis usually begin?
Rate limiting step in normal catecholamine synthesis?
Tyrosine to Dopa Tyrosine hydroxylase
What enzyme is needed for phenylalanine to tyrosine formation?
What enzyme is needed for tyrosine to dopa formation?
What enzyme is needed for dopa to dopamine formation?
L-Aromatic amino acid decarboxylase
What enzyme is needed for dopamine to norepinephrine formation?
What enzyme is needed for norepinephrine to epinephrine formation?
What is the rate limiting step in pheochromocytoma patients?
Norepinephrine to epinephrine formation (PNMT)
What controls the action of PNMT?
Normal persons epinephrine to norepinephrine ratio?
Pheochromocytoma patient epinephrine to norepinephrine?
Where is the only place that epinephrine is synthesized?
What inhibits tyrosine hydroxylase?
What inhibits vesicular monoamine transport?
Selective norepinephrine reuptake inhibitors
What effect do monoamine oxidase inhibitors have?
Inhibit the breakdown of catecholamines
What effect do COMT inhibitors have?
Inhibit breakdown of catecholamines
What two enzymes are needed for breakdown of catecholamines?
What do you use alpha-methyl tyrosine to treat?
Pheochromocytoma inoperable one
What are the side effects of alpha-methyl tyrosine?
Cystalluria (renal damage)
Parkinson's syndrome (decreased dopamine)
What are the two breakdown pathways of norepinephrine?
Norepinephrine to Normetanephrine via COMT Normetanephrine to Vanillylmandelic acid via MAO
Norepinephrine to Dihydroxymandelic acid via MAO Dihydroxymandelic acid to Vanillylmandelic acid via COMT
What are the two breakdown pathways of epinephrine?
Epinephrine to Metanephrine via COMT Metanephrine to Vanillylmandelic acid via MAO
Epinephrine to Dihydroxymandelic acid via MAO Dihydroxymandelic acid to Vanillylmandelic acid via COMT
What test has high specificity for Pheochromocytoma?
Plasma Metanephrine levels
Why are metanephrine levels tested and not Normetanephrine for pheochromocytoma?
Because only the adrenal medulla forms epinephrine and a pheochromocytoma acts as that; the periphery can increase norepinephrine levels
What test has the greatest sensitivity to pheochromocytoma?
24 hour urine measurements of epinephrine, norepinephrine and VMA
What is given in imaging studies to locate the pheochromocytoma tumor?
How is meta-iodobenzylguanidine uptaken?
Via neuronal uptake
What has a higher sensitivity and specificity but is often only used in PET scanners?
Where is meta-iodobenzylguanidine uptaken?
Moderate in liver, salivary glands, urine
What is the treatment of symptomatic pheochromocytoma?
Alpha-1-antagonist Prazosin + Beta blocker in preparation for surgery