Question about carcinoid heart syndrome & bronchospams

[mybluedog]

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I don’t know anything about serotonin but had a question that popped up in my head:
When the carcinoid tumor metastasizes into the liver via the portal vein from the small bowel, it bypasses the liver MAO enzymes, so serotonin doesn’t get converted into 5-HIAA to go into urine.

In carcinoid syndrome, serotonin released from the liver carcinoid tumor can go to the lungs and cause bronchospasm via the hepatic vein→ thoracic duct→ systemic blood supply, which is one of the symptoms of carcinoid syndrome.

In carcinoid heart syndrome, only the R side of the heart is affected because there are MAOs in the lung to convert serotonin to 5-HIAA, this spares fibrosis of the L heart.

If there are MAOs to begin with in the lung, how come carcinoid syndrome presents with bronchospasm/affects the lungs? Again, I don’t know anything about serotonin, so that probably doesn’t directly cause the bronchospasm?

 

[MaxPlancker]

I could be wrong but carcinoid syndrome is not exclusive to serotonin release, it is a mixture of vasoactive compounds including histamine which is more likely to cause bronchospasm.

 

[jdh71]

I don’t know anything about serotonin but had a question that popped up in my head:
When the carcinoid tumor metastasizes into the liver via the portal vein from the small bowel, it bypasses the liver MAO enzymes, so serotonin doesn’t get converted into 5-HIAA to go into urine.

In carcinoid syndrome, serotonin released from the liver carcinoid tumor can go to the lungs and cause bronchospasm via the hepatic vein→ thoracic duct→ systemic blood supply, which is one of the symptoms of carcinoid syndrome.

In carcinoid heart syndrome, only the R side of the heart is affected because there are MAOs in the lung to convert serotonin to 5-HIAA, this spares fibrosis of the L heart.

If there are MAOs to begin with in the lung, how come carcinoid syndrome presents with bronchospasm/affects the lungs? Again, I don’t know anything about serotonin, so that probably doesn’t directly cause the bronchospasm?

Depending on their site of origin, carcinoid tumors can have the ability to secrete vasoactive peptides. Serotonin (5-hydroxytryptamine [5-HT]) production is the most prominent, especially in midgut tumors. However, 5-hydroxytryptophan (5-HTP), bradykinins, tachykinins, histamine, substance P, adrenocorticotropic hormone, and several other peptides are also reported to be produced by carcinoids.

Bottom line: It’s likely not the serotonin causing the bronchospasm. If there even is any bronchospasm. When they teach this they make it seem like this “either/or” clinical scenario and it simply is not. Expression of the pathophysiology is often minimal or incomplete. But that’s the way they write questions. Real patients are complicated and tricky. Also if you see ONE in your career you’ll be lucky. But every year Med students will learn about them. I know I did.

 

[mybluedog]

Depending on their site of origin, carcinoid tumors can have the ability to secrete vasoactive peptides. Serotonin (5-hydroxytryptamine [5-HT]) production is the most prominent, especially in midgut tumors. However, 5-hydroxytryptophan (5-HTP), bradykinins, tachykinins, histamine, substance P, adrenocorticotropic hormone, and several other peptides are also reported to be produced by carcinoids.

Bottom line: It’s likely not the serotonin causing the bronchospasm. If there even is any bronchospasm. When they teach this they make it seem like this “either/or” clinical scenario and it simply is not. Expression of the pathophysiology is often minimal or incomplete. But that’s the way they write questions. Real patients are complicated and tricky. Also if you see ONE in your career you’ll be lucky. But every year Med students will learn about them. I know I did.

Thank you, the explanation was super clear & thanks for the insight into real clinical pearls 🙂