Given an abstract from a research paper, your task is to identify and label relationships between chemical compounds and genes mentioned in the abstract.

The relationship type must be one of ['DOWNREGULATOR', 'SUBSTRATE', 'INDIRECT-REGULATOR', 'PART-OF', 'MODULATOR-ACTIVATOR', 'REGULATOR', 'INHIBITOR', 'COFACTOR', 'UPREGULATOR', 'ACTIVATOR', 'ANTAGONIST', 'NOT', 'INDIRECT-DOWNREGULATOR', 'SUBSTRATE_PRODUCT-OF', 'INDIRECT-UPREGULATOR', 'AGONIST', 'PRODUCT-OF', 'MODULATOR', 'DIRECT-REGULATOR', 'UNDEFINED', 'AGONIST-INHIBITOR', 'AGONIST-ACTIVATOR', 'MODULATOR-INHIBITOR'].

Please format your output as a JSON array. Each entry in the array should express a single relation, formatted as ["<Entity_A>", "<RELATION_A_B>", "<Entity_B>"]. If no relations can be found, please output an empty JSON array [].

Abstract:

Review article: 5-hydroxytryptamine agonists and antagonists in the modulation of gastrointestinal motility and sensation: clinical implications. Serotonin (5-hydroxytryptamine; 5-HT) is found in the enteric nervous system where it has been implicated in controlling gastrointestinal motor function. A number of receptor or recognition sites have been identified in the gut, but recently most attention has focused on the 5-HT3 and 5-HT4 receptors. The functional role of the 5-HT3 receptor remains incompletely understood, but it is probably involved in the modulation of colonic motility and visceral pain in the gut. A number of selective 5-HT3 antagonists have been developed including ondansetron, granisetron, tropisetron renzapride and zacopride. While the substituted benzamide prokinetics (for example, metoclopramide, cisapride) also block 5-HT3 receptors in high concentrations, their prokinetic action is believed to be on the basis of their agonist effects on the putative 5-HT4 receptor. Some 5-HT3 antagonists have 5-HT4 agonist activity (for example, renzapride, zacopride) and others do not (for example, ondansetron, granisetron), while tropisetron in high concentrations is a 5-HT4 antagonist. Based on the pharmacological data, it has been suggested that specific 5-HT antagonists and agonists may prove to be beneficial in a number of gastrointestinal disorders including the irritable bowel syndrome, functional dyspepsia, non-cardiac chest pain, gastrooesophageal reflux and refractory nausea. In this review, the rationale for the use of these compounds is discussed, and the available experimental evidence is summarized.
[["granisetron", "NOT", "5-HT4"], ["metoclopramide", "INHIBITOR", "5-HT3"], ["metoclopramide", "AGONIST", "5-HT4"], ["benzamide", "INHIBITOR", "5-HT3"], ["ondansetron", "NOT", "5-HT4"], ["ondansetron", "ANTAGONIST", "5-HT3"], ["renzapride", "ANTAGONIST", "5-HT3"], ["ondansetron", "NOT", "5-HT3"], ["zacopride", "AGONIST", "5-HT4"], ["tropisetron", "ANTAGONIST", "5-HT3"], ["cisapride", "INHIBITOR", "5-HT3"], ["zacopride", "ANTAGONIST", "5-HT3"], ["cisapride", "AGONIST", "5-HT4"], ["granisetron", "NOT", "5-HT3"], ["renzapride", "AGONIST", "5-HT4"], ["benzamide", "AGONIST", "5-HT4"], ["granisetron", "ANTAGONIST", "5-HT3"], ["tropisetron", "ANTAGONIST", "5-HT4"]]