Aspirin-induced gastric mucosal damage in dogs: protection by the prostanoid Ro 22-1327.

Aspirin and other non-steroidal anti-inflammatory drugs are associated with gastritis and mucosal injury. The present study examined the efficacy of the synthetic prostanoid, Ro 22-1327, as a mucosal protectant against aspirin. Dogs were orally administered either vehicle followed by 650 mg of aspirin, or Ro 22-1327 followed one hour later by 650 mg of aspirin. Two hours later the dogs were endoscoped and lesions were scored. In separate dogs, with gastric pouches, acid secretion stimulated by food was monitored in the absence and presence of Ro 22-1327 for four hours. There were no gastric lesions in the dogs treated with the vehicle (polyethylene glycol 400; PEG) for Ro 22-1327 followed by vehicle (carboxymethylcellulose) for aspirin. Dogs dosed with PEG followed by aspirin had gastric lesions: mean (+/- S.E.) scores were 2.16 +/- 0.24 and 2.75 +/- 0.18 for the antrum and body, respectively. Ro 22-1327 provided protection from aspirin-induced injury. Significant (P less than 0.01) protection occurred at 1.0 mcg/kg of Ro 22-1327 in the antrum (0.60 +/- 0.40) and body (1.60 +/- 0.40). An oral dose of 10 mcg/kg did not inhibit peak or total food-stimulated gastric acid output. Ro 22-1327 is a potent mucosal protectant against aspirin-induced mucosal injury and this activity is not dependent upon inhibition of gastric acid secretion.

Effect of dextromethorphan and levomethorphan on gastric emptying and intestinal transit in the rat.

Dextromethorphan and levomethorphan were evaluated using 51Cr as a marker for their effects on gastric emptying and intestinal transit in the rat. Levomethorphan at 10 mg/kg i.p. and 10 and 50 mg/kg p.o. significantly (P less than or equal to .05) inhibited gastric emptying; dextromethorphan did not inhibit gastric emptying at p.o. doses up to 100 mg/kg or i.p. doses up to 10 mg/kg. Naloxone (1 mg/kg i.p.) significantly antagonized the effect of p.o. levomethorphan (50 mg/kg). Levomethorphan (10 and 50 mg/kg p.o. and 1 and 10 mg/kg i.p.) significantly inhibited intestinal transit. Dextromethorphan significantly inhibited intestinal transit after p.o. (10, 50, 100, 200 mg/kg) and i.p. (50 mg/kg) administration. As in the case of gastric emptying, naloxone inhibited the effect of levomethorphan but did not alter the effect of dextromethorphan. Naloxone itself (1 mg/kg i.p.) did not affect gastric emptying or intestinal transit. The results suggest that levomethorphan exerts inhibitory effects on intestinal transit and gastric emptying that are probably mediated partly through an opiate mechanism whereas the effects of dextromethorphan may be mediated through a nonopiate mechanism of action.

Influence of antacids on the gastric antisecretory activity of the synthetic prostanoid (8R,11R,12S,15R,5Z,13E)-15-(acetyloxy)- 11,16,16-trimethyl-9-oxoprosta-5,13-dien-1-oic acid in dogs.

Liquid antacids that contain aluminum-magnesium hydroxides reduce the absorption of various therapeutic agents. To assess the potential for such an interaction with the synthetic anti-ulcer prostanoid (8R,11R,12S,15R,5Z,13E)-15-(acetyloxy)-11, 16,16-trimethyl-9-oxoprosta-5,13-dien-1-oic acid (1; Ro 22-6923), we studied the effect of Mylanta and DiGel liquid on the gastric antisecretory activity of this drug in dogs. Dogs were prepared with a modified Pavlov (innervated) pouch. Compound 1 was administered alone or with liquid antacid into the main stomach while acid secretion into the pouch was measured. Mylanta (30 mL) and DiGel (35 mL) failed to significantly reduce the ability of 1 (0.5 mg/kg, orally) to inhibit histamine (25 micrograms/kg/h)-stimulated secretion. Neither the onset nor the duration of action of 1 was affected by either antacid. The total acid output over the 4 h after administration of 1 was not significantly affected by the antacids. The results suggest that Mylanta and DiGel, or antacids of a composition similar to that of these products are not likely to interfere with the antisecretory activity of 1 in humans.

Inhibition of canine gastric secretion by the prostanoid Ro 22-6923.

The synthetic prostanoid, Ro 22-6923, was studied for its effects on canine gastric secretion. Histamine-stimulated acid secretion was inhibited for up to 8 hr after an orally administered dose of 0.25 mg/kg Ro 22-6923. In the Amdrup (modified Pavlov) pouch model, Ro 22-6923 significantly inhibited food-stimulated acid secretion at an oral dose of 0.5 mg/kg. The effect lasted for 4 hr and was of greater intensity than that observed with 5 mg/kg cimetidine. The ED50 for Ro 22-6923 in this model was 0.25 mg/kg and 0.09 mg/kg for oral and intrapouch administration, respectively. Natural prostaglandin E2 was inactive up to 1 mg/kg orally, but had an ED50 of 0.08 mg/kg when administered directly into the pouch. The results indicate that Ro 22-6923 is a potent, long-acting antisecretory drug that may be useful in the therapy of peptic ulcer disease in man.

Effect of the synthetic prostanoid Ro 22-6923 on gastric secretion and blood flow in Heidenhain pouch dogs.

The synthetic trimethyl prostanoid Ro 22-6923 was studied for its effects on histamine-stimulated gastric acid secretion in Heidenhain pouch dogs. The prostanoid (at a p.o. dose as low as 0.05 mg/kg) produced significant inhibition of gastric acid secretion induced by 12 micrograms/kg/h of histamine for 5 h. A dose of 0.5 mg/kg p.o. produced a significant antisecretory effect within 45 min that lasted for 8.5 h. Cimetidine (5 mg/kg p.o.) produced an inhibitory effect on acid output equivalent to the 0.5-mg/kg dose of Ro 22-6923, but the duration of the cimetidine effect was less than 6 h. Administration of Ro 22-6923 i.v. (0.25 mg/kg) inhibited acid output for longer than 8 h. Against a 25-micrograms/kg/h histamine challenge, Ro 22-6923 (0.5 and 1.0 mg/kg) inhibited acid output to an equal degree but for a longer duration than cimetidine (5 mg/kg). Pepsin output was totally inhibited by 0.5 mg/kg of Ro 22-6923, whereas 5 mg/kg of cimetidine inhibited pepsin output by approximately 60%. Pepsin activity in the gastric juice was reduced by Ro 22-6923 and was increased by cimetidine. Blood flow, as estimated by the aminopyrine clearance technique, was reduced slightly by Ro 22-6923 and cimetidine. However, the ratio of clearance to acid secretory rate increased with both compounds, suggesting a direct effect of Ro 22-6923 and cimetidine on acid secretion at the parietal cell level. The results suggest that Ro 22-6923 may be a useful therapeutic agent for peptic ulcer disease in humans.

Quantification of pepsin A activity in canine and rat gastric juice with the chromogenic substrate azocoll.

The activity concentration of pepsin may be quantified by using azocoll as a chromogenic substrate. The measured enzyme activity is constant between pH 1.2 and 3.4 and is proportional (r = 0.61) to the activity measured with hemoglobin as substrate. The activity of purified porcine pepsin is inhibited by pepstatin A with an apparent Ki of 115 nmol/L. The azocoll method is useful for measuring changes in pepsin secretion in response to pharmacological agents. For example, pepsin activity of canine gastric juice is decreased by 80% after in vivo administration of 0.5 mg of the synthetic trimethyl prostanoid Ro 22-6923 per kilogram of body weight. The method is sufficiently sensitive to measure the pepsin activity in 0.2 microL of canine gastric juice with a CV of approximately 10%, is simpler than the hemoglobin-substrate methods, and the substrate is commercially available.