Question:medium
Which of these is most often secreted by a pheochromocytoma?
Which of these is most often secreted by a pheochromocytoma?
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Pheochromocytoma cells often skip the last conversion step, so this catecholamine builds up and dominates.
Updated On: Jul 8, 2026
- Epinephrine
- Norepinephrine
- Dopamine
- Serotonin
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Start from the normal pathway.
Catecholamine synthesis runs tyrosine to dopa to dopamine to norepinephrine to epinephrine. The last step, turning norepinephrine into epinephrine, needs the enzyme PNMT, found mainly in normal adrenal medulla cells.
Step 2: See what changes inside the tumor.
A pheochromocytoma is a chromaffin cell tumor, but its cells frequently have reduced PNMT activity compared with normal tissue. This means the pathway often stalls one step earlier, so norepinephrine piles up instead of being fully converted.
Step 3: Connect this to the overall secretion pattern.
Across the whole group of pheochromocytoma patients, norepinephrine ends up being the catecholamine found in the largest amount, and it drives the sustained high blood pressure that is typical of this tumor.
Step 4: Place the other options.
Epinephrine is still secreted and gives the sudden attack symptoms, but it is not the dominant hormone overall. Dopamine only rises when the tumor is malignant or sits outside the adrenal gland. Serotonin belongs to a totally different tumor, the carcinoid, and has nothing to do with pheochromocytoma.
\[ \boxed{\text{Norepinephrine}} \]
Catecholamine synthesis runs tyrosine to dopa to dopamine to norepinephrine to epinephrine. The last step, turning norepinephrine into epinephrine, needs the enzyme PNMT, found mainly in normal adrenal medulla cells.
Step 2: See what changes inside the tumor.
A pheochromocytoma is a chromaffin cell tumor, but its cells frequently have reduced PNMT activity compared with normal tissue. This means the pathway often stalls one step earlier, so norepinephrine piles up instead of being fully converted.
Step 3: Connect this to the overall secretion pattern.
Across the whole group of pheochromocytoma patients, norepinephrine ends up being the catecholamine found in the largest amount, and it drives the sustained high blood pressure that is typical of this tumor.
Step 4: Place the other options.
Epinephrine is still secreted and gives the sudden attack symptoms, but it is not the dominant hormone overall. Dopamine only rises when the tumor is malignant or sits outside the adrenal gland. Serotonin belongs to a totally different tumor, the carcinoid, and has nothing to do with pheochromocytoma.
\[ \boxed{\text{Norepinephrine}} \]
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