AJP - Gastrointestinal and Liver Physiology, Vol 244, Issue 4 426-G434, Copyright © 1983 by American Physiological Society
Multiple 5-hydroxytryptamine receptors on feline ileum and ileocecal sphincter
A. Ouyang and S. Cohen
The effects of 5-hydroxytryptamine (5-HT) on the feline ileum and ileocecal
sphincter (ICS) were studied in vivo using simultaneous myoelectric and
pressure recordings. Both inhibitory and excitatory responses were seen in
the ileum and ICS, with the inhibitory response being seen with lower doses
of 5-HT (EDmax for inhibition was 5.0 micrograms/kg and EDmax for
contractile response was 80.0 micrograms/kg). The inhibitory and excitatory
responses were antagonized separately by different 5-HT antagonists.
Methysergide inhibited the ICS relaxation response only, whereas cinanserin
inhibited the ICS contractile response. Neither effect was inhibited by
tetrodotoxin, suggesting that 5-HT acts directly on the smooth muscle at at
least two separate receptors. In addition, methysergide alone resulted in a
usually tonic increase (8.6 +/- 0.6 mmHg) in basal ICS pressure (P less
than 0.05) without an ileal effect, and tetrodotoxin alone induced phasic
ileal and ICS contractions (delta ICS = 7.3 +/- 1.5 mmHg). These data
suggest the action of at least two inhibitory neurons tonically at the ICS.
