Gastric Antisecretory and Antigastrolesive Pharmacology of Rioprostil

Abstract

Rioprostil, a primary alcohol prostaglandin E1 analogue, inhibits gastric acid secretion, both in vivo and in vitro, and prevents the formation of experimentally-induced gastric lesions in rats and dogs. In vitro experimental evidence suggests that the mechanism of the gastric antisecretory activity of rioprostil involves inhibition of the membrane bound histamine-stimulated adenylate cyclase. In vivo, rioprostil inhibits gastric acid secretion in 4-h pylorus-ligated rats, in gastric fistula dogs stimulated by betazole, tetragastrin, bethanechol, or 2-deoxy-D-glucose, and in Heidenhain pouch dogs stimulated by food. Rioprostil can completely prevent macroscopically visible gastric lesions induced by a variety of noxious agents in rats, including 50% ethanol, aspirin, indomethacin, strong acid, strong base and hypertonic saline. In dogs, rioprostil, but not the H2-blockers cimetidine or ranitidine, totally prevents endoscopically visible gastric lesions induced by aspirin tablets or 60% ethanol, and accelerates the healing of established aspirin-induced gastric lesions from 20 days (vehicle control) to 6 days (33 micrograms/kg p.o., t.i.d.) or 11 days (3 micrograms/kg p.o., t.i.d.). The precise mechanism for the antigastrolesive activity of rioprostil is not known, but may involve increased mucus and bicarbonate secretion, maintaining or increasing gastric mucosal blood flow, increasing the rate of cellular restitution, or possibly antigastrin activity that has been demonstrated in dogs. In rats, rioprostil also prevents duodenal lesions induced by cysteamine, small intestinal lesions induced by indomethacin, and colonic lesions induced by ethanol. The antisecretory and antigastrolesive potency of rioprostil given transdermally to rats is similar to its potency when given systemically, although its diarrhoeagenic potential is lower when given topically compared to oral administration. When used in combination with several non-steroidal anti-inflammatory drugs (NSAIDs) in a model of arthritis in rats, rioprostil inhibits gastric lesion formation without interfering with the anti-inflammatory or analgesic potency of the NSAIDs. In addition, concomitant use of either antacid or cimetidine with rioprostil does not inhibit either the antisecretory or antigastrolesive potency of rioprostil, with the effect of the combination being additive. The doses required to inhibit formation of experimentally-induced gastric lesions in both rat and dog are lower than those required to inhibit gastric acid secretion. This separation of antigastrolesive from antisecretory activity distinguishes rioprostil from other non-prostanoid antisecretory agents, such as histamine H2- receptor antagonists, and establishes rioprostil as a 'selective antigastrolesive agent' (SAGA).(ABSTRACT TRUNCATED AT 400 WORDS)