5-HT in carcinoid syndrome - question

[CaptainZero]

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a quick question that has been annoying the hell out of me:
5-HT is predominately a vasoconstrictor...thus it is assoc. with increased PVR, vasospasm in migrains etc...However 2 of the major symptoms of Carcinoid Syndrome are rapid drops in BP and facial flushing (which I usually assume to be due to cutaneous vasodilation). This is a bit counterintuative to me...of course the reason may be perfectly obvious and I'm missing it because I'm on hour twelve of studying for the day...but I can't seem to find a conclusive answer in any books or online...so if anyone could explain this, I'd appreciate the help...

 

[JayZee]

serotonin syndrome too...also get fever, flushing...except you have HTN, tachy...curious...Captain I never thought about it before...I'm not a big 'why' person.
probably not a good thing.

 

[exmike]

a quick question that has been annoying the hell out of me:
5-HT is predominately a vasoconstrictor...thus it is assoc. with increased PVR, vasospasm in migrains etc...However 2 of the major symptoms of Carcinoid Syndrome are rapid drops in BP and facial flushing (which I usually assume to be due to cutaneous vasodilation). This is a bit counterintuative to me...of course the reason may be perfectly obvious and I'm missing it because I'm on hour twelve of studying for the day...but I can't seem to find a conclusive answer in any books or online...so if anyone could explain this, I'd appreciate the help...

Remember that 5HT has very different actions depending on site and receptor. In an inflammatory response, 5HT plays a role similar to histamine which is why you'll get flushing and other symptoms associated with a Type I hypersensitivity. 5HT is released from platelets in the clotting cascade which is intricately tied to inflammatory responses.

Also remember that carcinoids release other things besides 5HT that could cause symptoms.

Lets see. 5HT in the GI would cause nausea, vomiting, as would stimulation of the CTZ in the brainstem. 5HT in the blood would cause vasodilation wherease centrally acting 5HT could cause vasodilation resulting in flashes of flushing.. (reaching on that one)

 

[surgwannabe]

serotonin syndrome too...also get fever, flushing...except you have HTN, tachy...curious...Captain I never thought about it before...I'm not a big 'why' person.
probably not a good thing.

5HT acts on several different receptors. These receptors have a variety of tissue distributions and functions. Here is a list of what I know:

5HT1 receptor: vasoconstriction (drug: triptan family)
5HT2 receptor: vasodilation (drug: nefazodone)
5HT3 receptor: vomiting (drug: ondansetron)
5HT4 receptor: decrease GI motility

Hope this helps.