Prevention by prostaglandins of caerulein-induced pancreatitis in rats.

Acute edematous pancreatitis was produced in rats by subcutaneous administration of caerulein. Pancreas weight, pancreas histology and plasma amylase were used as endpoints to quantitate the severity of the syndrome. A caerulein dose of 10 micrograms/kg.hour produced the most severe pancreatitis, whereas at 5 micrograms/kg.hour the values were half-maximal. The pancreatic lesions were characterized by edema, formation of cytoplasmic vacuoles, leukocytic infiltration, necrosis, and with time (12-hour caerulein infusion) dilated acini. Cholecystokinin octapeptide also produced pancreatitis when given at ten times the dose required for caerulein (50 micrograms/kg.hour instead of 5 micrograms/kg.hour). Carbachol did not induce pancreatitis. Two prostaglandins, 16,16-dimethyl prostaglandin E2 injected subcutaneously and prostaglandin E2 infused subcutaneously, dose dependently prevented caerulein-induced pancreatitis (pancreatic edema, leukocytic infiltration, and necrosis) and reduced the number and size of intracellular vacuoles. The ED50 were 15 to 25 micrograms/kg for 16,16-dimethyl prostaglandin E2 and 90 micrograms/kg.hour for prostaglandin E2. Neither prostaglandin, given at doses inhibiting the development of pancreatitis, prevented the retardation of gastric emptying caused by caerulein, a finding suggesting that the prostaglandins may act specifically on the effect of caerulein on the pancreas but not on caerulein receptors in gastric smooth muscle. Indomethacin, an inhibitor of prostaglandin synthesis, and methscopolamine bromide, an anticholinergic agent, had no effect on caerulein-induced pancreatitis. We concluded that prostaglandins of the E type prevent the development of caerulein-induced pancreatitis. The mechanism by which prostaglandins protect the pancreas may involve stabilization of lysosomes within the acinar cells and inhibition of intracellular activation of pancreatic digestive enzymes.

Ulcer formation and cytoprotection by acetazolamide.

Acetazolamide, a carbonic anhydrase inhibitor, was administered orally and subcutaneously to rats. Acetazolamide increased the gastric ulcerogenicity of indomethacin, but inhibited gastric ulcers produced by acidified aspirin. When administered alone to fasted rats, it did not produce gastric ulcers. Acetazolamide was also cytoprotective for the stomach (it reduced dose dependently the number of gastric necrotic lesions caused by absolute ethanol given orally) and for the small intestine (it prevented dose dependently intestinal lesions produced by administration of a high dose of indomethacin). Acetazolamide did not prevent the antiulcer effect of PGE2 (against aspirin-induced ulcers) nor the cytoprotective effect of 16,16-dimethyl PGE2 (against ethanol-induced gastric lesions). The degree of gastric cytoprotection increased with time after a single administration of acetazolamide; the optimal effect occurred 60 and 90 min after oral and subcutaneous administration, respectively. Pretreatment with indomethacin completely prevented the cytoprotective effect of acetazolamide; this suggests that the cytoprotective effect may be mediated by endogenous release of prostaglandins by the stomach. All the effects of acetazolamide reported here were observed after either oral or subcutaneous administration. The mechanism by which acetazolamide influences ulcer formation and is cytoprotective is unknown.

Prevention of cecitis in hamsters by certain prostaglandins.

Acute inflammation of the colon (cecitis) was produced in hamsters by daily subcutaneous administration of an antibiotic for 3 days. The following prostaglandins completely prevented the cecitis: 16,16-dimethyl-PGE2, 15(R)-15-methyl-PGE2, and 2-acetyl-2-decarboxy-15(S)-15-methyl-PGF2 alpha. PGF2 beta was less active. The synthesis of 2-acetyl-2-decarboxy-15(S)-methyl-PGF2 alpha is described. Castor oil also prevented the cecitis and peanut oil exerted partial protection. Since these oils contain linoleic acid, a precursor of PGE1, protection may have been due to endogenous formation of that prostaglandin. A partial block of the protective effect of castor oil by treatment with indomethacin supports such mechanism. The tissue level of endogenous prostaglandins seems to exert protection since administration of cyclooxygenase inhibitors, indomethacin and aspirin, markedly increased the incidence of cecitis. Magnesium sulfate given orally and sodium salicylate given subcutaneously reduced the incidence of cecitis only partially. The following agents were inactive: loperamide, an antidiarrheic agent; carbachol, a cholinergic and diarrheogenic agent, atropine, an anticholinergic agent; and acetazolamide, a carbonic anhydrase inhibitor. These results, show that certain prostaglandins, which have been shown earlier to be cytoprotective for the stomach and the small intestine, are cytoprotective for the large intestine as well.

Timoprazole is a unique cytoprotective agent in the rat.

Timoprazole, a substituted benzimidazole, is an antisecretory agent that inhibits gastric acid secretion by interference with (H+-K+)-ATPase. In the studies reported herein, timoprazole given orally was found to be cytoprotective for the stomach when given 30 min prior to a challenge to boiling water, ethanol, or 0.6 N HCl. Timoprazole also prevented necrosis of the mucosa and acute ulcerations induced by alcohol in the rat fundus, as evaluated by histopathology. The ED50 for cytoprotection was between 1 and 3 mg/kg of timoprazole depending on the challenge, whereas the antisecretory ED50 was approximately 12 mg/kg. Timoprazole was an active antisecretory agent when given subcutaneously (ED50 10 mg/kg), but was not cytoprotective when given by this route. Indomethacin pretreatment (5 mg/kg orally) blocked the cytoprotective activity of oral timoprazole at doses of 1 or 3 mg/kg given 30 min later. However, at higher doses of timoprazole (5 mg/kg), indomethacin did not inhibit the cytoprotective activity. The ability of high doses of timoprazole to overcome the indomethacin blocks is different than the cytoprotective activity of mild irritants, which is always blocked by indomethacin. However, when tested in vitro, timoprazole exhibited only mild inhibitory activity on both prostaglandin cyclooxygenase and 15-hydroxyl-dehydrogenase and only at high doses, suggestive of nonspecific activity.

Distinction between antiulcer effect and cytoprotection.

Gastric ulcerations were produced in rats by oral administration of aspirin (ASA) suspended in a vehicle consisting of either water or increasing concentrations of HCl (0.005 M to 0.35 M). The lesions were prevented by antisecretory doses of a histamine H2 blocker (cimetidine) and by an anticholinergic agent (pro-banthine), but only when the acidity of the vehicle was low (0.05 M to 0.15 M), not at higher (0.35 M). On the other hand, 16,16-dimethyl PGE2 prevented ulcer formation even when ASA was suspended in all HCl concentrations, including 0.35 M HCl. In other studies, gastric mucosal necrosis was produced by oral administration of absolute ethanol. These lesions were not affected by cimetidine or two anticholinergic agents, pro-banthine and methscopolamine bromide, nor by alkalinization of the gastric lumen with NaHCO3 or pH 7 buffer; however, these ethanol-induced lesions were completely prevented by 16,16-dimethyl PGE2. We conclude that antisecretory agents, by blocking endogenous formation of acid, are antiulcer as long as no acid or only small amounts of acid (1 ml of 0.15 M or less) are given together with ASA. When higher concentrations are used (e.g. 0.35 M HCl), the antisecretory effect of the inhibitors is overcome by the exogenous acid, and ulcers still form. Under these conditions, only "true" cytoprotective agents, such as 16,16-dimethyl PGE2, prevent ASA-induced ulcers, even in the presence of high acidity. Although cimetidine and pro-banthine were shown earlier to reduce ASA-induced ulcers at nonantisecretory doses, these agents may still decrease acid formation within the gastric glands.(ABSTRACT TRUNCATED AT 250 WORDS)

Mild irritants prevent gastric necrosis through "adaptive cytoprotection" mediated by prostaglandins.

Several prostaglandins (PG) were found earlier to be cytoprotective for the stomach and the intestine. We now report that mild irritants, given intragastrically, are also cytoprotective by stimulating the release of PG by the stomach. Several "mild irritants," 10-20% ethanol, 0.2-0.35 M HCl, 0.05-0.075 M NaOH, 2-4% NaCl, and water at 70 degrees C, were given orally to fasted rats. Fifteen minutes later, one of the following necrotizing agents was administered orally: 100% ethanol, 0.6 M HCl, 0.2 M NaOH, 25% NaCl solution, and boiling water. One hour later, the stomachs were removed and necrotic lesions graded. The mild irritants inhibited the necrotic lesions dose dependently. After a single treatment, protection lasted 1 h; repeated administrations maintained cytoprotection for as long as the mild irritants were being given. Indomethacin, an inhibitor of PG synthesis, abolished cytoprotection by mild irritants. After oral administration of NaOH at cytoprotective concentrations (0.01-0.1 M), the amounts of PGE2, PGF2 alpha, and thromboxane B2 formed by the gastric mucosa increased steadily up to threefold. The protection elicited by mild irritants is called "adaptive cytoprotection." The increased synthesis of PG may represent a physiological, natural defense mechanism that may be necessary to maintain cellular integrity of the gastrointestinal mucosa, in spite of the hostile environment caused by luminal contents.

Comparison of prostacyclin and prostaglandin E2 on gastric secretion, gastrin release, and mucosal blood flow in dogs.

In dogs with gastric fistulae (GF) and Heidenhain pouches (HP), intravenous graded doses of prostacyclin (PGI2) (dose range: 2.5-20 micrograms/kg/hr), and prostaglandin E2 (PGE2) (dose range: 10-80 micrograms/kg/hr) produced a dose-dependent inhibition of acid and pepsin secretion stimulated by pentagastrin (3 micrograms/kg/hr). The ID50 (dose inhibiting acid output by 50% were 6 micrograms/kg/hr for PGI2 and 26 micrograms/kg/hr for PGE2 for the GF, and 7 micrograms/kg/hr for PGI2 and 22 micrograms/kg/hr for PGE2 for the HP. Acid secretion from the GF stimulated by histamine (20 micrograms/kg/hr) was also inhibited by both prostaglandins: the ID50 were 16 micrograms/kg/hr for PGI2 and 22 micrograms/kg/hr for PGE2. For the HP, the ID50 were about 20 and 40 micrograms/kg/hr for PGI2 and PGE2, respectively. Meal-induced acid secretion from the GF reached a level similar to that observed in tests with pentagastrin and was inhibited by both prostaglandins. The ID50 were 5 and 20 micrograms/kg/hr for PGI2 and PGE2, respectively. PGI2 significantly increased serum gastrin above that obtained with meal alone whereas PGE2 did not affect postprandial serum gastrin. The inhibition of pentagastrin and meal-induced acid secretion was accompanied by a marked reduction in gastric mucosal blood flow (MBF) measured by the [14C]aminopyrine method, without significant change in the ratio of gastric blood flow to gastric secretion. The MBF in the resting HP mucosa was significantly increased by PGI2 but reduced by PGE2. This study shows that PGI2 is about 3-4 times more potent than PGE2 in inhibiting pentagastrin and meal-induced gastric secretion and MBF; PGI2 unlike PGE2, increases the postprandial serum gastrin and raises the MBF of the resting mucosa. Therefore, both PGI2 and PGE2 are antisecretory, but their effects on gastrin release and resting MBF are qualitatively different.

Cytoprotection by prostaglandins in rats. Prevention of gastric necrosis produced by alcohol, HCl, NaOH, hypertonic NaCl, and thermal injury.

Oral administration to fasted rats of either absolute ethanol, 0.6 N hydrochloric acid, 0.2 N sodium hydroxide, 25% sodium chloride, or boiling water produced extensive necrosis of the gastric mucosa. Pretreatment with several prostaglandins of the A, E, or F type, either orally or subcutaneously, prevented such necrosis, and the effect was dose-dependent. This property of prostaglandins is called "cytoprotection." The protective effect against oral administration of absolute ethanol was already maximal 1 min after PGE2 given orally, and 15-30 min after PGE2 given subcutaneously. Cytoprotection by prostaglandins is unrelated to the inhibition of gastric acid secretion since, (a) it is maximal at doses that have no effect on gastric secretion, and (b) anti-secretory compounds (cimetidine, methscopolamine bromide) and antacids are not cytoprotective. Although the mechanism of gastric cytoprotection is unknown, prostaglandins appear to increase the resistance of gastric mucosal cells to the necrotizing effect of strong irritants. These results suggest that certain prostaglandins, by a mechanism other than the inhibition of gastric acid secretion, maintain the cellular integrity of the gastric mucosa, and might be beneficial in the treatment of a variety of diseases in which gastric mucosal injury is present.

Enteropooling assay: a test for diarrhea produced by prostaglandins.

An assay (enteropooling assay) to test the diarrheogenic property of prostaglandins is described. Fasted rats are given a prostaglandins either orally or subcutaneously, and are killed 30 min later. The entire small intestine is removed and its contents collected into a test tube. The greater the volume of this intestinal fluid, the more diarrheogenic is the prostaglandin. The assay is simple, rapid, quantitative, and predictive of diarrhea. It can be used to grade the relative diarrhoegenic activity of prostaglandins as well as to test agents that may block this effect. The accumulation of fluid into the small intestine is called "enteropooling". It is the sum of (a) the fluid being excreted from the blood into the lumen, and (b) to a lesser extent, the portion of fluid already into the lumen but whose absorption is inhibited by the prostaglandin. The degree of enteropooling depends also on how much fluid flows from the small to the large intestine. Our results support the hypothesis that the diarrhea observed after administration of high doses of prostaglandins is due to accumulation of abundant fluid into the small intestine, and not intestinal hypermotility. This fluid is then carried into the large intestine and eventually expelled as diarrhea. Agents other than prostaglandins were tested for enteropooling activity. Laxatives such as castor oil, hypertonic solutions and bile salts caused enteropooling.

Gastric antisecretory and antiulcer properties of PGE2, 15-methyl PGE2, and 16, 16-dimethyl PGE2. Intravenous, oral and intrajejunal administration.

15-Methyl PGE2 and 16,16-dimethyl PGE2 were found (1) to be 40 and 100 times, respectively, more potent than PGE2 after intravenous administration in inhibiting histamine-stimulated gastric secretion in dogs with a denervated (Heidenhain) gastric pouch, (2) to be active orally and intrajejunally, whereas PGE2 was inactive, and (3) to exert antisecretory activity for longer duration than PGE2. 16,16-Dimethyl PGE2 was about 2.5 times more potent than 15-methyl PGE2. Volume, acid concentration, and output, and pepsin output (but not concentration) were reduced in a dose-dependent manner. In the rat, 16,16-dimethyl PGE2 also inhibited gastric secretion and prevented the formation of ulcers produced by various methods: gastric ulcers (Shay, and steroid induced) and duodenal ulcers (secretogogue induced). In this species, 1l816-dimethyl PGE2 was 2 to 50 times more potent than PGE2, depending on the endpoint, and was active orally. These prostaglandins appear to inhibit gastric acid secretion by acting directly on the parietal cells, and making these unresponsive to most stimulants. Vomiting was a side effect of the prostaglandin analogues in the dog, but almost exclusively when these were given orally. After intravenous or intrajejunal administration at doses inhibiting gastric secretion by 80%, vomiting was seen only once. These results suggest that 15-methyl PGE2 and 16,16-dimethyl PGE2 may be of value in the treatment of peptic ulcer.

Inhibition by prostaglandin E 1 of gastric secretion in the dog.

1. The effect of prostaglandin E(1) (PGE(1)) on gastric secretion was studied in dogs equipped with gastric fundic pouches, either innervated (Pavlov) or denervated (Heidenhain).2. PGE(1) inhibited gastric secretion (volume, acid concentration, acid output, pepsin output) when given either by constant intravenous infusion or by single intravenous injection. The degree of inhibition was dose dependent.3. The antisecretory effect of PGE(1) was demonstrated against gastric stimulants which operate through different mechanisms. Thus, PGE(1) counteracted the secretogogue effect of:(a) histamine dihydrochloride; the ED(50) was 0.5-1.0 mug/kg. min for a submaximal dose, and 1.0-1.5 mug/kg. min for a maximal dose;(b) pentagastrin; the ED(50) was around 0.25 mug/kg. min;(c) food; the ED(50) was 0.5 to 0.75 mug/kg. min;(d) 2-deoxyglucose; the ED(50) was less than 0.1 mug/kg. min.4. Although in some experiments, nausea and vomiting were observed during administration of PGE(1), the antisecretory property of the substance is not related to a vomiting reflex, since(a) an antiemetic, such as atropine, prevented vomiting without interfering with the effect of PGE(1), and(b) profuse vomiting elicited by apomorphine did not reduce gastric secretion stimulated by either histamine or pentagastrin.5. The mechanism by which PGE(1) inhibits gastric secretion is unknown. Studies by others have shown that the compound reduces gastric mucosal blood flow, inhibits acid formation from gastric mucosa when applied in vitro and may change the rate of formation of gastric cyclic AMP. It is likely that PGE(1) interferes with biochemical processes, within parietal and chief cells, which lead to elaboration of gastric juice.6. Unlike most gastric inhibitors, PGE(1) appears to act as a protective shield against most, if not all, gastric stimulants. Since prostaglandins of the E series are naturally occurring substances and are normally present in the stomach, they may play a role in the regulation of gastric secretion.