Three chemical classes of serotonin 5-HT4 receptor agonists have been identified so far: 5-substituted indoles (e.g. 5-HT), benzamides (e.g. renzapride) and benzimidazolones (e.g. BIMU 8). In a search for 5-HT4 receptor antagonists, we have discovered that the benzimidazolone derivative DAU 6285 (for structure see text), is 3-5 times more potent than tropisetron in blocking 5-HT, renzapride and BIMU 8 induced stimulation of adenylate cyclase activity in mouse embryo colliculi neurons. Schild plot analysis yielded Ki values of 220, 181 and 255 nmol/l, respectively. In addition, DAU 6285 showed poor activity as a 5-HT3 receptor ligand with respect to tropisetron, as demonstrated by in vitro binding studies (Ki, 322 vs 2.8 nmol/l) and by its antagonistic activity in the Bezold-Jarisch reflex test (ID50, 231 vs 0.5 micrograms/kg, i.v.). No significant binding (Ki greater than 10 mumol/l) of DAU 6285 to serotonergic 5-HT1A, 5-HT1B, 5-HT1C, 5-HT1D, and 5-HT2 receptors as well as to adrenergic alpha 1, alpha 2, dopaminergic D1, D2 or muscarinic M1-M3 receptor subtypes was found. The data indicate that DAU 6285 has a somewhat higher affinity than tropisetron for 5-HT4 receptors, a property confirmed in functional tests, and much lower affinity than tropisetron for 5-HT3 receptors. The compound represents a new interesting tool for investigating the pharmacological and physiological properties of 5-HT4 receptors.

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In several animal models orally administered morniflumate, the beta-morpholinoethyl ester of niflumic acid, proved almost equal to the parent compound in anti-inflammatory, analgesic and antipyretic activity with the advantage of complete freedom from the ulcerogenic effects of the acidic parent compound. Further, it was 5 times less active in intestinal perforation experiments and 10 times less toxic in acute toxicity experiments than niflumic acid. Bioavailability and pharmacokinetics tests after oral and intravenous administration suggest that morniflumate is absorbed as such from the gastrointestinal tract and then undergoes rapid hydrolysis in the plasma, releasing the free acidic form, the molecule responsible for the pharmacological effects. In addition to being free from ulcerogenic effects, the ester actually displayed a gastroprotective effect against the ulcerogenic effects of niflumic acid; this finding is discussed in the light of the concept of 'cytoprotection' recently reported for a series of mild gastric irritants.

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