ABSTRACT
Serotonin receptors are widely distributed throughout the body and there are at least seven different types as well as 14 serotonin receptor subtypes. They are present exclusively on peripheral and central neurons. The 5-HT3 receptor is a ligand-gated cation channel belonging to the nicotine/GABA receptor superfamily (11). 5-HT3 receptors are mainly found in the substantia gelatinosa of the spinal cord, in multiple nucleoli of the brainstem, in the area postrema, and in the enteric nervous system. They are linked to several serotonin-mediated processes including vasomotor reflexes, pain, cardiovascular regulation, behavior and limbic--eortical functioning, and the enteric nervous system (12). 5-HT3 receptor antagonists (serotonin type 3 receptor antagonists) were developed for relief of cherootherapy-induced nausea and vomiting. Further established indications are radiotherapy-induced and postoperative emesis (11). There are several 5-HT3 receptor antagonists such as ondansetron, tropisetron, granisetron, dolasetroh, azasetron, and ramosetron. In vitro studies demonstrated differences in receptor binding: tropisetron has a high affinity for the 5-HT3 receptor and a weak affinity for the 5-HT4 receptor. Ondansetron has low affinity for the 5-HT Ib, 5-HT 1c, adrenergic, and opioid receptors. Thus, pharmacokinetic differences among these drugs are unlikely to contribute significantly to clinical differences in activity (13,14).
