Abstract
Objective: To determine with the mechanism of action involved in the therapeutic potential of
serotonin and its blocker on gastrointestinal motility.
Method: The standard method was used for obtaining the longitudinal and circular muscles strip
of rabbit ileum for in vitro studies. Each muscle strip was exposed to serotonin and its blocker
and the result obtained was recorded on polygraph apparatus. The effects were recorded in vice
versa fashion i.e. agonist v/s antagonist and antagonist v/s agonist on longitudinal and circular
muscle strip separately.
Results: Serotonin had depressant effect on the force of contraction. On addition of antagonist in
the presence of agonist, the effects were increased. Longitudinal muscle showed more
pronounced effect i.e. 52.7% with methysergide in comparison to circular muscle, which was
15.6%. Circular muscle showed reduction in the force of contraction with serotonin, which was
increased on addition of antagonist, but still below the level of base line contraction.
Conclusion: Serotonin when given from external source in vitro, decreased the force, however,
there was minimal increase in the rate of contraction. Hence, serotonin decreases the intestinal
motility giving an impression of having antispasmodic effect. The results of this study can be
utilized in the development of new drug related to G.I. motility mediated through 5HT receptors.
(Rawal Med J 2006;31:2-5)

Key words: Serotonin, 5HTreceptors, Irritable bowel syndrome