Epinephrine potentiation of in vivo stimuli reverses aspirin inhibition of platelet thrombus formation in stenosed canine coronary arteries

In 18 anesthetized dogs with a 70% mechanically produced coronary artery stenosis, blood flow measured with an electromagnetic flowmeter showed cyclical reductions in flow due to periodic acute platelet thrombus formation. These were abolished in eight of nine dogs with 2.5 mg/kg of aspirin given intravenously and in nine of nine dogs with 5 mg/kg of aspirin. However in 14 of 18 dogs the cyclical flow reductions were temporarily renewed with the infusion of epinephrine 0.4 microgram/kg/min. Human platelets inhibited with aspirin can be reactivated with physiologic amounts of epinephrine. We postulate that in patients with atherosclerotic stenotic lesions the use of aspirin to inhibit arterial thrombus formation may be less effective when they have elevated catecholamines.

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)

Damage and protection of the human gastric mucosa. A multiparameter assessment

Studies in animals and humans have indicated that endogenous prostaglandins as well as synthetic prostaglandin analogues can prevent gastric mucosal damage induced by various agents. Methods were developed to assess induced damage and the effects of potentially protective agents (synthetic prostaglandin analogues and the histamine [H2]-receptor antagonist cimetidine) on the human gastric mucosa by measuring ion fluxes and transmucosal potential difference, as well as by observations with gastrointestinal endoscopy. Commonly ingested agents, such as aspirin, 1,300 mg, and 20 percent ethanol increased hydrogen ion and sodium ion fluxes, decreased potential difference, and caused gross mucosal damage, as observed by endoscopy. Conversely, acetaminophen, 2,600 mg, and 10 percent ethanol did not have any significant effects. Hyperosmolar solutions (1,800 and 3,600 mOsm/kg) also produced acute damage. Sodium taurocholate (10 mmol/liter) when instilled into the stomach, either at pH 1.1 or 7.0, produced both functional and structural damage. When given as a single dose, neither 15(R)15-methyl PGE2 nor the synthetic PGE1 analogue, misoprostol, prevented mucosal damage induced by aspirin and taurocholate (pH 1.1), respectively. Cimetidine, 400 mg orally, however, did reduce aspirin-induced mucosal damage, and this effect was independent of gastric acid inhibition.

Role of H2-receptor blockers in the prevention of gastric injury resulting from nonsteroidal anti-inflammatory agents

Nonsteroidal anti-inflammatory drugs (NSAIDs) can produce injury to the gastric and duodenal mucosa. The histamine (H2)-receptor blocker cimetidine was studied to determine whether protection of the gastric mucosa of normal volunteers could be provided against a single dose of aspirin, 1,300 mg. Gastric mucosal injury was assessed with gastroscopy performed two hours after aspirin intake. Three liquid cimetidine doses were administered over 24 hours prior to the aspirin dose, the last dose one hour before the aspirin. The 200-mg and 400-mg doses of cimetidine protected a sufficient number of subjects to warrant further study. In the second study, these two doses were further examined to determine whether three doses were necessary and whether the final dose could be coadministered with the aspirin instead of one hour before. Concomitant administration of a single dose of cimetidine with aspirin was found to protect the gastric mucosa from aspirin damage as effectively as the other cimetidine regimens employed. A final, double-blind comparison of cimetidine, 200 mg, with placebo administered with the aspirin, 1,300 mg, confirmed that cimetidine protected the gastric mucosa from the hemorrhagic effects of aspirin.

The antiemetic drug trimethobenzamide prevents hypophagia due to acetyl salicylate, but not to 5-HT1B or 5-HT1C agonists

Pretreatment with the antiemetic agent trimethobenzamide (TMB) prevented the hypophagic response of rats to acetyl salicylate (a known emetic in man and dogs). However, it did not affect the hypophagic responses to the 5-HT1B agonist RU24969, or to the 5-HT1C/5-HT1B agonists mCPP and TFMPP. The results therefore suggest that the hypophagic effects of the 5-HT agonists do not involve a malaise-dependent mechanism similar to that mediating the effect of acetyl salicylate.

Misoprostol attenuates aspirin-induced changes in potential difference and associated damage in canine gastric mucosa

Aspirin induces ulceration, cellular exfoliation, and blood loss associated with decreases in gastric mucosal potential difference (PD). Certain prostaglandins prevent the development of experimental gastric and duodenal ulcers and modify indices related to ulceration. Misoprostol, a synthetic PGE1 derivative with gastric antisecretory and mucosal protective activities, was examined at gastric antisecretory doses in dogs with Heidenhain pouches, to determine its effect on aspirin-associated changes in PD, K+ efflux, blood loss, and cell shedding, as measured by DNA release. These parameters were examined before, during, and up to 4 hours after exposure of the pouches to aspirin. Disruption of the gastric mucosal barrier (GMB) by aspirin was associated with a fall in PD and losses of K+, DNA, and blood into the pouches. Misoprostol inhibited the fall in PD and prevented blood loss over the entire period examined. Cell loss was inhibited only during the recovery period immediately following aspirin. The effect of misoprostol on GMB is consistent with studies in which prostaglandins preserve the GMB and prevent necrotic ulcerations while allowing superficial cell damage.

Lack of cytoprotection by acetaminophen against ethanol-, HCl.ethanol- and HCl.aspirin-induced gastric mucosal lesions in rats

Effects of acetaminophen against gastric mucosal lesions induced by three different necrotizing agents were studied. Acetaminophen (30, 100 mg/kg), given p.o. 0.5 hr before absolute ethanol, HCl . ethanol, or HCl . aspirin administration, afforded no cytoprotection against gastric mucosal lesions induced by the above agents in 24 hr fasted rats. However, 16,16-dimethyl prostaglandin E2 (3 micrograms/kg), given p.o. 0.5 hr before these necrotizing agents, completely prevented development of these lesions.

[Effects of troxipide on acute gastric lesions in rats]

Effects of troxipide on several acute gastric lesions in rats were investigated in comparison with those of cetraxate. Troxipide (100, 200, 300 mg/kg) and cetraxate (100, 300, 1,000 mg/kg), given orally, dose-dependently protected the gastric mucosa from damage due to ethanol. Aspirin- and 0.6 N HCl-induced gastric lesions were dose-dependently inhibited by troxipide (200, 300 mg/kg), but only significantly inhibited by cetraxate at high dose (1,000 mg/kg). Troxipide (100, 200, 300 mg/kg) dose-dependently prevented the formation of gastric lesions induced by water-immersion stress, whereas cetraxate (600, 1,000 mg/kg) also significantly prevented gastric lesions. That is, protective effects of troxipide were much more potent than those of cetraxate against aspirin-, 0.6 N HCl- and water-immersion stress-induced gastric lesions, whereas both were almost equal against ethanol-induced gastric lesions. In addition, cytoprotective effects of troxipide against ethanol-induced lesions were most remarkable at 10, 30, 60 min after administration (100, 300 mg/kg) and lasted for up to 240 min. These results suggested that troxipide might be useful for the treatment of acute gastric lesions in humans.

Protective effect of exogenous phospholipid on aspirin-induced gastric mucosal injury

The protective effects of exogenous phospholipid on aspirin-induced gastric mucosal injury were examined in a canine chamber model which provided two separate segments of mucosa supplied by a single vascular pedicle. In each dog, one segment was treated with a suspension of surface-active phospholipid, similar in composition to that normally present in the gastric mucosa, whereas the other segment served as the control. Pretreatment of the test segments significantly prevented aspirin-induced disruption of the mucosal barrier as evidenced by an increase in potential difference and a decrease in acid back-diffusion and sodium ion and potassium ion flux. These findings were associated with a marked reduction in the degree of mucosal injury. Our results support the recent hypothesis that surface-active phospholipid plays an important role in gastric mucosal defense against the damaging effects to luminal acid.

Effect of sofalcone on acute gastric mucosal lesions induced by aspirin and ethanol in reference to the biosynthesis of gastric mucosal glycoprotein

Sofalcone prevented the formation of lesions by 50% ethanol and aspirin dose dependently, prevented the decrease in the gastric mucosal macromolecular glycoprotein content caused by these treatments, and prevented the decrease in the incorporation of 3H-glucosamine caused by ethanol and aspirin into the macromolecular glycoprotein. 35S-Sulfate incorporation, which was slightly decreased, by the administration of ethanol and aspirin, was significantly increased, and the specific activity of sulfated macromolecular glycoprotein synthesis which was not changed by ethanol or aspirin was increased by the administration of sofalcone prior to these treatments. These results suggest that the maintenance of the mucosal macromolecular glycoprotein content is involved in the protective effects of sofalcone against the formation of acute gastric lesions induced by ethanol and aspirin.

Effect of esaprazole on gastric mucosal potential difference after oral administration of aspirin (ASA)

The potential protective properties of esaprazole on the gastric mucosa following administration of aspirin were evaluated by measurement of the potential difference across the gastric mucosa. Twelve patients with non-ulcer dyspepsia were admitted to the study and were divided into two groups of six patients each. In association with a randomized double-blind scheme the two groups of patients underwent two tests, with placebo and esaprazole 600 or 900 mg. After 30 min of basal recording of the potential difference, patients received either esaprazole or placebo i.v. and recording was continued for a further 30 min. Afterwards, 600 mg of unbuffered aspirin was instilled into the stomach through a naso-gastric tube and the potential difference was measured for 60 min. Esaprazole 600 mg did not prevent the fall in the potential difference across the gastric mucosa caused by aspirin. A higher dose of esaprazole, however, did significantly (p less than 0.05) reduce the fall. These results suggest that esaprazole exerts a dose-dependent cytoprotective effect on the gastric mucosa in man.

Epinephrine reverses the inhibitory influence of aspirin on platelet-vessel wall interactions

The effect of in vitro aspirin treatment and alpha adrenergic receptor stimulation on the interaction of platelets with the subendothelium was studied using citrated human blood obtained from normal control donors. Reconstituted blood following drug treatment was circulated through a chamber which housed everted segments of deendothelialized rabbit aorta. The wall shear rate was 800 sec-1. Surface coverage of platelets were morphometrically evaluated. Aspirin treatment significantly reduced platelet thrombi on exposed subendothelium. However, platelet spreading was increased. There was no significant difference in the total percent coverage of platelets in the vascular surface between the aspirin treated group and normal controls. Epinephrine exposure of aspirin treated platelets completely reversed the effect of alterations induced in platelet behavior by aspirin. Epinephrine exposed aspirin treated platelets had as many platelet thrombi on exposed subendothelium as normal control platelets. In addition, epinephrine treatment decreased the spreading of aspirin treated platelets on the vascular surface. Results of the present study and our earlier findings suggest that the epinephrine induced membrane modulation may be a major mechanism for protecting the hemostatic role of platelets after their function is compromised in vivo and in vitro. The failure of aspirin to offer significant protection in many clinical trials may be due to the presence of a salvage pathway in platelets provided by the mechanism of membrane modulation.

Prevention of the acetylsalicylic acid-induced changes of the gastric potential difference by the new synthetic prostaglandin E1 analogue rioprostil

The protective effect of 50 and 100 micrograms of the synthetic prostaglandin E1 analogue rioprostil (2-decarboxy-2-hydroxymethyl-15-deoxy-16RS-hydroxy-16-methyl PGE1) against the 0.5 and 1 g acetylsalicylic acid (ASA)-induced changes of gastric potential difference (PD) was compared to that of placebo in a double-blind cross-over study in 8 volunteers. Rioprostil 50 and 100 micrograms reduced significantly (p = 0.45) the intensity (area under baseline) of the 0.5 g ASA-induced PD changes. Both doses reduced highly significantly (p = 0.003) the time taken for PD to return to baseline value (15.1 min with 50 micrograms and 17.2 min with 100 micrograms rioprostil vs 43.5 min with placebo). Both doses of rioprostil also reduced significantly (p = 0.04) the PD maximal drop induced by 1 g ASA and reduced highly significantly (p = 0.006) the time taken for PD to return to baseline value (18.9 min with 50 micrograms and 16.8 min with 100 micrograms rioprostil vs 64.6 min with placebo). This study shows that rioprostil protects the stomach against the ASA-induced alterations of the gastric mucosa even when it is given at the same time as ASA and in doses which have only a small antisecretory effect.

[Effects of gastric proton pump inhibitors on gastric secretion and peptic ulcers]

This is a review article on newly developed antisecretory drugs which are now called proton pump inhibitors. Gastric H+ is secreted from the secretory membrane of parietal cells into the lumen of the stomach, using energy obtained by destructing ATP with H+, K+-ATPase (proton pump). Various substituted benzimidazoles such as timoprazole, picoprazole, omeprazole, or NC-1300 potently inhibits this proton pump at pH 6.0, thereby resulting in a strong inhibition of gastric H+ secretion. This inhibition of H+ secretion lasts for a long period, ie, 1-3 days after a single oral or intraduodenal administration, both in experimental animals and humans. This long lasting activity of these compounds appears to be due to their accumulation in the parietal cells because of their low pKa values (about 4.0). Proton pump inhibitors dose-dependently inhibit the development of various experimental ulcers and accelerate healing of chronic gastric ulcers in animals. Since these compounds also potently inhibit the development of HCl X ethanol or HCl X aspirin-induced gastric ulcers in animals, they are considered to have a cytoprotective activity. Some of the compounds (e.g., omeprazole) afforded a complete healing of peptic ulcers in man when it was given once daily for 2 to 4 weeks, without any adverse effects. Therefore, these proton pump inhibitors appear to be promising drugs for the treatment of peptic ulcer diseases.

Salicylate antagonism of acetylsalicylic acid inhibition of platelet aggregation in male and female subjects: influence of citrate concentration

Platelets from volunteers were exposed for 1 min to sodium salicylate (SA) before and after the addition of acetylsalicylic acid (ASA) to produce greater than or equal to 50% inhibition of aggregation induced by arachidonic acid (AA) or collagen. SA:ASA concentrations = 20:1. SA protection against ASA inhibition was always observed even if ASA exposure time was 15 min, whereas reversal could not be demonstrated once exposure of platelets to ASA exceeded a minimum of 3-10 min with AA as the stimulus. Reversal was even less effective when collagen was the stimulus. An apparent, increased sensitivity to SA reversal of ASA inhibition in females disappeared when citrate concentration was adjusted to compensate for lower packed cell volume. The proposed male dependency for protection in ASA treatment of thromboembolic disorders cannot be explained on the basis of differences in the SA-ASA competition at platelet cyclooxygenase and, if collagen is an important in vivo stimulus of platelet interaction with damaged vessel wall, the antagonism of ASA by SA may not be important.

Gastrointestinal cytoprotective effects of misoprostol. Clinical efficacy overview

The cytoprotective effects of misoprostol, a synthetic analog of prostaglandin E1, were investigated in healthy human subjects using randomized and placebo-controlled studies. Misoprostol significantly inhibited established aspirin (975 mg q.i.d.)-induced gastric microbleeding at 50 micrograms q.i.d., and to some extent, but not significantly, at 25 micrograms q.i.d. Misoprostol also reduced acid and chloride secretion significantly at 50 micrograms q.i.d., but not at 25 micrograms q.i.d. When administered concurrently with aspirin 650 mg q.i.d., misoprostol 25 micrograms q.i.d. significantly inhibited aspirin-induced fecal blood loss without affecting plasma salicylate concentration. The fact that misoprostol was tested at a sub-therapeutic gastric antisecretory dose (25 micrograms) indicates that the inhibition of fecal blood loss was not due to its gastric antisecretory property. Misoprostol tended to reduce antral erosion and DNA content of gastric fluid, but increased mucus concentrations in subjects with ethanol-induced damage. However, the dose of ethanol used produced gastric damage in only six of the 10 subjects and did not provide a satisfactory baseline. Misoprostol attenuated the drop in transmucosal potential difference induced by sodium taurocholate. It is concluded that misoprostol has cytoprotective activity in man. These effects may be of great importance in the treatment of acid peptic disease of the gastrointestinal tract.

Reduction of aspirin-induced fecal blood loss with low-dose misoprostol tablets in man

Misoprostol (SC-29333), a synthetic prostaglandin E1 methyl ester analog, was given simultaneously with acetylsalicylic acid in a double-blind, placebo-controlled randomized prospective study of 32 healthy human male subjects. Fecal blood loss was measured for eight days using the 51Cr-labeled red blood cell technique. Aspirin (650 mg qid) and misoprostol (25 micrograms qid) or placebo were given during days 3, 4, and 5. There was a significant (P less than 0.05) increase in median blood loss (modified Friedman test) from 0.81 to 6.05 ml/day in the aspirin with placebo group (N = 16). Median blood loss was increased (from 0.75 to 3.75 ml/day) in the aspirin with misoprostol group (N = 16), but this was significantly less (Mann-Whitney U test, P less than 0.01) than the placebo group. Mean serum salicylate concentrations in the placebo and misoprostol groups were similar (7.8 and 6.8 micrograms/ml, respectively). There were no significant changes in laboratory values in any of the subjects studied, nor were any major side-effects encountered. This study demonstrates that oral misoprostol reduces aspirin-induced gastrointestinal bleeding even when administered simultaneously and at a dose level below its threshold for significant acid inhibition. This indicates a potential role for misoprostol in the prevention of gastric mucosal damage in selected patients.

Attenuation of aspirin analgesia by calcium loading in healthy subjects

To clarify the mechanism of aspirin analgesia, the relationship among analgesic and hypocalcemic effects and pharmacokinetics of aspirin was investigated in 20 healthy subjects at 20-23 years old. Four experimental groups were made, that is, (1) aspirin 1.0 g, (2) aspirin 1.0 g + calcium gluconate 1.5 g X 2, (3) calcium gluconate 1.5 g X 2, (4) control (placebo). Calcium gluconate was administered orally twice, that is, 30 and 90 min after oral administration of aspirin. The experiments were carried out under a double blind method. As an analgesic test, the ultrasonic method was used. Aspirin (1.0 g) caused a significant analgesia, the effect reaching the maximum at 90 min and prolonging for about 3 h. Simultaneously, plasma calcium level significantly decreased and kept going down, at least, until 180 min after administration of aspirin. However, when calcium gluconate was loaded at 30 and 90 min after administration of aspirin, both the analgesic and hypocalcemic effects of aspirin were significantly inhibited. The plasma aspirin concentration reached a maximum 30-60 min after administration of aspirin in both groups: aspirin alone and aspirin with calcium gluconate. On the other hand, plasma salicylic acid concentration kept increasing up to 180 min after administration of aspirin in either group. The plasma aspirin and salicylic acid levels in both groups were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between sodium salicylate and acetyl salicylic acid evaluated using ADP induced platelet aggregation and bleeding time

1 g acetyl salicylic acid orally significantly enhanced the initial rate of platelet aggregation induced by 1 mumol/l and 2.5 mumol/l ADP. Sodium salicylate was without effects on the platelet aggregation and specifically it did not prevent acetylsalicylic acid from inhibiting the secondary aggregation. Sodium salicylate was without effect on the bleeding time and did not inhibit the prolongation induced by acetyl salicylic acid. Our study does not lend support to the concept of an important interaction in vivo between acetyl salicylic acid and its first metabolite salicylate in man.

[Effects of gefarnate on acute gastric lesions in rats]

The effects of gefarnate on several acute gastric lesions were studied in rats. Gefarnate, given at either 100 approximately 1000 mg/kg orally or intraduodenally, dose-dependently inhibited the formation of gastric lesions induced by HCl-ethanol, HCl-taurocholate and aspirin. Cimetidine, given at 30 approximately 100 mg/kg as a reference drug, also significantly inhibited both HCl-ethanol and aspirin-induced lesions. The present study suggests that gefarnate, as well as cimetidine, is useful for the treatment of acute gastric lesions in man.

Protection against aspirin-induced antral and duodenal damage with enprostil. A double-blind endoscopic study

Prostaglandins protect against aspirin-induced damage to the gastrointestinal tract. This study tested the ability of enprostil, a synthetic analog of prostaglandin E2, given concurrently to prevent gastroduodenal injury. Twenty-four healthy subjects were randomly assigned to one of three groups. All received aspirin 650 mg q.i.d. for 5 days. One group received placebo and the other groups were given either 7 or 70 micrograms of enprostil b.i.d. for 5 days. Upper endoscopy was performed at entry and 2 h after the final dose of aspirin. Enprostil 70 micrograms b.i.d. afforded significant protection of both the antral and duodenal mucosa. The 7-micrograms dose protected only the antral mucosa. Side effects were not observed with the lower dose of enprostil. Serum salicylate levels did not differ significantly between the groups.

Effects of 16,16-dimethyl prostaglandin E2 on ethanol-induced and aspirin-induced gastric damage in the rat. Scanning electron microscopic study

Ethanol and aspirin were administered orally to fasted rats and the effects of 16,16-dimethyl prostaglandin E2 (given orally as a pretreatment) were studied using scanning electron microscopy. Gastric secretory studies (pylorus ligation for 2 h) showed that 3 and 30 micrograms/kg of 16,16-dimethyl prostaglandin E2 were nonantisecretory doses and that 100 micrograms/kg was an antisecretory dose. 16,16-Dimethyl prostaglandin E2, given orally at 3-100 micrograms/Kg, induced no appreciable changes in the gastric surface epithelial cells. Oral administration of 1 ml of 50% ethanol invariably induced, within 10 min, extensive exfoliation of surface epithelial cells throughout the corpus and antrum and exposed the lamina propria. 16,16-Dimethyl prostaglandin E2, given orally at 3, 30, and 100 micrograms/kg 30 min before ethanol treatment, had no protective effect. Aspirin, given orally at 30 or 100 mg/kg, also damaged the surface epithelium of both the corpus and the antrum within 10 min. This damage ranged from apical cellular erosions to widespread exposure of the lamina propria. 16,16-Dimethyl prostaglandin E2, given orally at 3 or 30 micrograms/kg 30 min before aspirin treatment, significantly inhibited the gastric damage induced by both 30 and 100 mg/kg of aspirin. The inhibition of damage index was about 50%-60% at either 30 or 100 micrograms/kg of 16,16-dimethyl prostaglandin E2. The mechanism of the protection seen with 16,16-dimethyl prostaglandin E2 remains to be determined.