2016 Lower GI Pharmacology

Serotonin

5-HT is a key mediator of sensory and motor function in the GI tract, and >95% of 5-HT in the body is contained within the enteric nervous system.

Here is a simplified explanation for the effects of 5HT3 antagonists and 5HT4 agonists.

Serotonin & peristaltic reflexOne of the major roles for serotonin in the gut is thought to be regulation of the peristaltic reflex, which consists of both PROXIMAL CONTRACTION and DISTAL RELAXATION.  In both cases, 5HT primarily acts on vagal afferents, which subsequently invoke a complicated reflex loop (which I simplified considerably by having the 5HT “neuron” act directly on the ACh and NANC neurons).  It’s also important to consider that the phrases “smooth muscle contraction” and “GI motility” (i.e., co-ordinated muscle contractions) are not necessarily synonymous.

First, the easier to understand stuff.

Now for the tough stuff.

ABSOLUTE BOTTOM LINE:

5HT4 agonists increase GI motility (decrease transit time)

5HT3 antagonists increase contractility but decrease co-ordination (increase transit time)

Email: Dr. Janet Fitzakerley | ©2016 University of Minnesota Medical School Duluth | Last modified: 25-jan-16 12:25 PM