Serotonin

Question 1

What releases serotonin?

Answer 1

GI enterochromaffin cells: mechanical stimulation, hypertonicity, NE, vagal
platelets: aggregation, degranulation
neurons: NT
carcinoid tumors

Question 2

serotonin receptors types

Answer 2

G protein coupled receptor

ligand gated ion channel (5HT3)

Question 3

5HT1 receptors

Answer 3

Gi/o protein coupled, typically decreases adenosine cyclase; 5HT1A increases ad cyc in heart only; 5HT1C increases phospholipase C, increases NO, Gq coupled
*indirect vasodilation (inhibit NE release on sympathetic neurons, release NO & prostaglandins o endothelial cells)

Question 4

5HT2 receptors

Answer 4

increase phospholipase C; increases Ca for contractions & plt aggregation; Gq coupled
*direct vasoconstriction of VSM, normal thrombosis

Question 5

5HT3 receptors

Answer 5

ligand gated cation channels

Question 6

Bezold-Jarisch reflex

Answer 6

5HT3 mediated reflex bradycardia d/t stimulation of sensory nerve endings; inhibition of SNS; increased activity of vagus nerve

Question 7

mechanism of action of triptans

Answer 7

activation of prejunctional 5HT1B,D receptors on sensory nerves resulting in blockade of trigenimovascular system; inhibited release of inflammatory peptides; vasoconstriction secondarily in cranial blood vessels