N-phenyl-2-pyridinecarbothioamides as gastric mucosal protectants.

A series of substituted 2-pyridinecarbothioamides was synthesized and evaluated for gastric mucosal protectant activity in the rat. Out of this investigation N-(3,5-difluorophenyl)-2- pyridinecarbothioamide (23, AY-31,574) was identified. This compound was much more potent than sucralfate and ranitidine against ethanol-induced lesions. Compound 23 was equipotent with ranitidine against gastric injury caused by stress. Unlike ranitidine, 23 was found to be devoid of antisecretory activity in the pylorus-ligated rat model, making it a selective mucosal protectant. Such a potent selective mucosal protectant may provide a novel clinical approach in treating ulcers.

Alpha-2 receptors in the gastrointestinal system: a new therapeutic approach.

Alpha-2 receptor activation mediates the inhibition of a number of gastrointestinal functions including gastric and intestinal secretions. Alpha-2 receptors are located in the brain and presynaptically on cholinergic nerve terminals; activation of either inhibits vagus nerve activity. Intestinal secretions are inhibited by postsynaptic alpha-2 receptors located on intestinal epithelial cells. Agents which selectively activate alpha-2 receptors in the gut may therefore be beneficial in treating gastric ulcers and diarrheal states. Two such agents which activate alpha-2 receptors in the gut are WHR-1370A [1-n-butoxy-3-(2,6-dimethylphenylcarbamoyl) guanidine hydrochloride] and lidamidine. WHR-1370A is a potent gastric antisecretory and antiulcer agent which inhibits the release of acetylcholine from the vagus nerve. WHR-1370A's activity is blocked by yohimbine. Lidamidine is a clinically effective antidiarrheal agent. Lidamidine's response is partially inhibited by yohimbine in animal diarrheal models. Alpha-2 agonists represent a new class of drugs which have a promising future in the treatment of gastrointestinal disorders.

Spasmolytic effect of lidamidine on uterine smooth muscle.

1-(2,6-Dimethylphenyl)-3-methylamidinourea hydrochloride (lidamidine hydrochloride) has previously been reported to inhibit intestinal smooth muscle contractile activity in vivo and in vitro. This study showed lidamidine also inhibited contractile activity in the isolated gravid rat uterus preparation and antagonized, the spasmogenic effects of acetylcholine, serotonin, oxytocin, and PGF2 alpha and BaCl2. Increasing Ca2+ concentrations in the bathing medium from 0.9 mmol/l to 7.2 mmol/l effectively antagonized the lidamidine inhibition of responses to BaCl2 and acetylcholine in the gravid rat uterus preparation. These results suggest that the spasmolytic effect of lidamidine may be due to its interference with the availability of Ca2+ necessary for excitation-contraction coupling in smooth muscle.

Hyperglycemic effect of lidamidine in the rat.

Lidamidine, a new antidiarrheal agent, produced a dose-dependent increase in plasma glucose levels in fed rats. The hyperglycemic response was evident 10 min after oral administration of lidamidine and lasted for 4 hr. Lidamidine's effect was absent in alloxanized rats. Insulin administration prevented the hyperglycemia. Pretreatment with the alpha 2-adrenoceptor antagonists yohimbine or RX781094A blocked the hyperglycemic response, while prazosin, propranolol, and hexamethonium pretreatment had no effect. These results indicate that the hyperglycemic effect of lidamidine is primarily due to the activation of peripherally located alpha 2-adrenoceptors that inhibit the release of insulin from pancreatic beta-cells.

A semichronic diarrheal model.

A method of producing semichronic diarrhea is presented. It has been shown that, when fed a combination diet of 50% lactose and 50% commercially available feed, rats are subjected to continuous diarrhea, which lasts for 96 hr or more. The relative lack of the enzyme lactase in the rat results in the accumulation of lactose in the gut and probably by an osmotic effect, sets up conditions for the passage of a watery diarrhea. Various combinations of lactose and commercially available feed were tried and it was observed that rats function without any ill effects (e.g., body-weight loss) and produce consistent watery diarrhea with the above-mentioned combination.

Gastric antisecretory and antiulcer effects of WHR1582A, a compound exerting alpha-2 adrenoceptor agonist activity.

The gastric antisecretory and antiulcer effects of a novel compound, [1-(2,-dimethylphenyl)-3-isobutoxyamidinourea]hydrochloride (WHR1582A), are described. WHR1582A was active in preclinical ulcer models induced by 18-hr pylorus ligation, aspirin, indomethacin, reserpine, stress or cysteamine. WHR1582A inhibited acid secretion in the pylorus-ligated rat and in the anesthetized, lumen-perfused rat. The antisecretory effects of WHR1582A were antagonized by yohimbine, RX781094A and phentolamine. Propranolol, prazosin, corynanthine, methysergide, sulpiride and pimozide were unable to block its activity. WHR1582A blocked acid secretion stimulated by 2-deoxy-D-glucose but was inactive against the direct parietal cell stimulants carbachol and dimaprit. WHR1582A also inhibited electrically stimulated contractions that were mediated via the vagus in the isolated rat stomach preparation. The antisecretory activity of WHR1582A was not due to a reduction in gastric mucosal blood flow. These results demonstrate that WHR1582A is an effective antiulcer-antisecretory agent that exerts its gastric effects through the activation of alpha-2 adrenoceptors located presynapitcally on the vagus.

Cytoprotective and antiulcer activities of the antacid magaldrate in the rat.

The cytoprotective and antiulcer activities of the antacid magaldrate (ES Riopan) as well as its effects on gastric mucosal blood flow and mucus secretions, were determined in the rat. Magaldrate afforded protection against gastric necrotic lesions induced by absolute ethanol (ED50, as magaldrate, 419 mg/kg); gastric ulcers induced by acidified acetylsalicylic acid (ED50 540 mg/kg), stress (cold restraint, ED50 388 mg/kg), indometacin (ED50 281 mg/kg), and pylorus ligation; and intestinal ulcers induced by cysteamine (ED50 243 mg/kg) and indometacin (ED50 184 mg/kg). At a dose of 8 ml/kg (1728 mg/kg magaldrate), the cytoprotective effect of magaldrate against ethanol was evident 1 min after oral administration and lasted more than 8 h. The cytoprotection induced by magaldrate was decreased by pretreatments with the depletor of endogenous thiols, n-ethylmaleimide, or with the cyclooxygenase inhibitor, indometacin. Magaldrate did not affect gastric mucosal blood flow, but it increased gastric mucus secretion. This later effect may be a factor responsible for the cytoprotective activity of the agent. The efficacy of magaldrate may be due not only to its antacid, bile sequestering, and antipeptic activities, but also to its cytoprotective activity. The present results suggest that magaldrate could be effective in preventing gastric damage caused by alcohol and antiinflammatory drugs.

Activated aluminum complex derived from solubilized antacids exhibits enhanced cytoprotective activity in the rat.

Removing the buffering capacity of aluminum-containing antacids by acidification greatly increased their cytoprotective activity over the parent antacid. Commercially available antacids were acidified with 6 N HCl. Peak mucosal protective activity occurred at pH 2.5, and declined at lower pH. At pH 2.5, the antacid suspensions became solubilized and no acid-neutralizing capacity remained. This solution was named activated aluminum complex. Based on aluminum ion content, each aluminum-containing antacid suspension tested demonstrated a comparable increase in potency on acidification against ethanol-induced lesions. HCl (pH 2.5) was inactive against ethanol-induced lesions. At cytoprotective doses, activated aluminum complex did not cause gastric lesions when orally administered by itself, demonstrating that it is not acting as a local mucosal irritant. The data suggest that solubilization of aluminum-containing antacids in acidic medium enhances their mucosal protective activity, probably by releasing an activated species of aluminum ion reported to be a hexaaquoaluminum cation.

Antisecretory and antiulcer activities of a potent new histamine H2-receptor antagonist with an intermediate duration of action.

The antisecretory activities of 4-(dimethylamino)- N-[2-[3-[3-(1-piperidinyl)methyl]phenoxy]propyl]amino]- 1,2,5-thiadiazol-4-yl]amino]ethyl]-butanamide, S-oxide (AY-29,315) and ranitidine were determined in the rat, dog and monkey. In conscious, chronically cannulated rats, AY-29,315 was 10 and 208 times more potent than ranitidine as an inhibitor of spontaneous gastric acid secretion by the p.o. and i.v. routes, respectively. Tolerance did not develop in the conscious rat with either compound when administered for 8 consecutive days at doses equivalent to 4 times their antisecretory ED50. In lumen-perfused, anesthetized rats, AY-29,315 i.v. was 44 times more potent than ranitidine as an inhibitor of dimaprit-induced acid secretion. In the gastric fistula dog, AY-29,315 was 7.5 times more potent than ranitidine as an inhibitor of dimaprit-induced secretion by the i.v. route but 3 times less potent by the oral route. In the monkey, against dimaprit, AY-29,315 was 3 and 12 times more potent than ranitidine by the oral and i.v. routes, respectively. p.o./i.v. ratios indicate that, relative to ranitidine, the bioavailability of AY-29,315 by the oral route was low, particularly in the dog. In the dog, at 4 times the oral ED50 dose, the antisecretory effect of ranitidine lasted 190 +/- 3 min, while that of AY-29,315 lasted more than 9 h. AY-29,315 was 8 times more potent than ranitidine as an inhibitor of acetylsalicylic acid-induced ulcers in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity studies on lidamidine hydrochloride (WHR-1142A), a novel antidiarrheal agent.

The acute oral LD50 of 1-(2,6-dimethylphenyl)-3-amidinourea hydrochloride (WHR-1142A, lidamidine hyrochloride) was 260 (208, 328) mg/kg in male mice, 267 (212, 336) mg/kg in male rats and 160 (130, 197) mg/kg in female rats. A daily oral dose of 10 mg/kg for 30 days was well tolerated in the rat and monkey. Histologic changes were reversible and for the most part could be explained on the basis of one or more of the several pharmacologic effects of WHR-1142A. A short-lived hyperglycemic effect was a prominent effect in mice and rats. This effect was seen occasionally in high doses in the monkey, suggesting a species difference.

Mucosal protective activity of activated aluminum complex.

The antacid ES Riopan was acidified ex vivo to pH 2.5 to completely eliminate its buffering capacity and was then tested as a mucosal protective agent. The pH 2.5 acidified antacid solution was named activated aluminum complex. Activated aluminum complex was 8.2 times more potent than its parent antacid in protecting against acidified aspirin-induced gastric lesions in the rat. Activated aluminum complex had a duration of action greater than 10 h in the ethanol-induced gastric lesion model, while ES Riopan was active for 6 h. Activated aluminum complex was able to inhibit both acid- and nonacid-mediated ulcers in the stomach and intestine. Its mucosal protective activity was not blocked by pretreatment with indomethacin. These results demonstrate that the nonbuffering antacid activated aluminum complex exerted a more potent and longer-lasting mucosal protective activity than its parent antacid. The activity was probably due to the presence of a hexaaquoaluminum cation and supports the argument that antacids possess mucosal protective effects independent of their acid-neutralizing capacity.