Acid instillation increases gastric luminal prostaglandin E2 output in man

Gastric Antiulcer Activity of Syngonanthus arthrotrichus SILVEIRA

Syngonanthus arthrotrichus SILVEIRA, popularly known as "sempre-vivas mini-saia," is found in mountains of the Espinhaço range in the Brazilian states of Bahia and Minas Gerais. Extracts of this species contain several constituents, including flavonoids which may have antiulcerogenic activity. An ethanolic extract (EEOH), and flavonoid-rich (FRF) and flavonoid-deficient (FDF) fractions obtained from the scapes of S. arthrotrichus were investigated for their ability to prevent ulceration of the gastric mucosa in mice and rats. In the ethanol/HCl-induced ulcer model, lansoprazole (30 mg/kg), EEOH (50, 100, 250 mg/kg) given orally protected the gastric mucosal against injury in mice by 79%, 78%, 73%, and 64% respectively. In the ethanol-induced gastric ulcer model in rats, the lansoprazole (30 mg/kg), FRF and FDF (100 mg/kg) significantly protected the gastric mucosal of rats by 65%, 38% and 25% respectively when compared with the negative control group. In indomethacin/bethanechol-induced gastric ulcers, cimetidine (100 mg/kg) and the EEOH (100, 250 mg/kg) inhibited gastric ulcer formation by 73%, 55% and 32% respectively. In this exactly model other treatments as cimetidine, FRF and FDF (100 mg/kg) each caused 54%, 36% and 45% inhibition, respectively. In the stress-induced gastric ulcer model, cimetidine (100 mg/kg) and the EEOH (50, 100, 250 mg/kg), inhibited gastric ulcer formation by 63%, 73%, 68% and 69% respectively. In the same model, cimetidine, FRF and FDF (100 mg/kg) significantly protected the gastric mucosal of the mice by 60%, 51% and 47% when compared to the control group. In pylorus-ligated mice, cimetidine (positive control) and FRF significantly decreased gastric acid secretion, increased gastric pH and reduced the acid output when compared to the negative control. FDF had no significant effect on these parameters. The protection provided by FRF probably involved an antisecretory mechanism mediated by flavonoids which were absent in FDF. The amount of adherent mucous in the stomach contents was also evaluated with the treatments carbenoxolone (200 mg/kg), FRF and FDF (100 mg/kg) treatment. Each treatments significantly increased the amount of adherent mucous in the gastric juice (8.67+/-1.73, 3.35+/-1.59, 2.1+/-0.41 mg/g of wet tissue, respectively) compared to the control group, indicating a cytoprotective action on the gastric mucosa. Treatment with FRF plus indomethacin and FDF plus indomethacin reduced the prostaglandin biosyntesis (13.6+/-6.5, 27+/-5.5 pg/well) by the mucosa, indicating that the cytoprotective action on the gastric mucosa was not related to the level of prostaglandins. Only FDF (38+/-17 pg/well) maintained the level of prostaglandins and guaranteed the integrity of the mucosa. The results indicate that the EEOH, FRF and FDF have antisecretory and cytoprotective actions, that may be related to the presence of luteoline in the extract and active fractions.

Gastroprotective effects of honey and glucose-fructose-sucrose-maltose mixture against ethanol-, indomethacin-, and acidified aspirin-induced lesions in the rat

The gastric cytoprotective properties of natural honey (monofloral and polyfloral specimens) and of a glucose-fructose-sucrose-maltose mixture (GFSM) was evaluated in the rat using absolute ethanol, indomethacin and acidified acetylsalicylic acid (ASA-HCl) as necrotising agents. Prior gastric administration of honey (2.5 g/kg) to animals induced a net reduction of hemorrhagic lesions length of the mucosa. Protection of the stomach elicited by both types of honey and GFSM was almost total against ethanol-induced lesions. Similar results were also observed when using ASA-HCl except that the percent protection was 87%. The percent reduction of indomethacin-induced gastric lesions was variable according to the nature of the test solution: GFSM mixture (41.1%) < polyfloral honey (55.2%) < monofloral honey (64.0%). Perfusion of the stomach with isotonic honey resulted in (1) a 70% reduction of the area of the lesions caused by ethanol, (2) the failure to prevent the transmural potential difference fall induced by ethanol, (3) an increase of basal and histamine-stimulated acid secretion. These results suggest that sugar rich solutions (GFSM and honey) may prevent gastric damage by a mechanism involving the release of some protective agents.

Gastric mucosal integrity: gastric mucosal blood flow and microcirculation. An overview

The stomach is in a state of continuous exposure to potentially hazardous agents. Hydrochloric acid together with pepsin constitutes a major and serious threat to the gastric mucosa. Reflux of alkaline duodenal contents containing bile and pancreatic enzymes are additional important injurious factors of endogenous origin. Alcohol, cigarette smoking, drugs and particularly aspirin and aspirin-like drugs, and steroids are among exogenous mucosal irritants that can inflict mucosal injury. The ability of the stomach to defend itself against these noxious agents has been ascribed to a number of factors constituting the gastric mucosal defense. These include mucus and bicarbonate secreted by surface epithelial cells, prostaglandins, sulfhydryl compounds and gastric mucosal blood flow. The latter is considered by several researchers to be of paramount importance in maintaining gastric mucosal integrity. The aim of this paper is to review the experimental and clinical data dealing with the role of mucosal blood flow and in particular the microcirculation in both damage and protection of the gastric mucosa.

HCl-stimulated duodenal HCO3- secretion in conscious rat. Interactions among VIP, nicotinic receptor mechanisms, and prostaglandins

Using an isolated loop of the proximal duodenum of conscious rats, the role of vasoactive intestinal peptide (VIP) in the duodenal HCO3- response to HCl was examined, especially interactions with participating cholinoceptor mechanisms and prostaglandins. A 5-min perfusion with 150 mmol/liter HCl increased luminal VIP during 3 hr, with a peak output during and immediately after the acid challenge. The HCl-stimulated output was unaffected by atropine and hexamethonium, but was augmented by indomethacin from 13.6 (9.5-17.8) to 39 (20-85) fmol/cm/min. The HCO3- secretion in response to graded doses of intravenous VIP (0.00625-6 nmol/kg/30 min) was dose-dependent to maximally 33.5 +/- 10.5 mumol/cm/hr. The HCO3- secretion during a single intravenous infusion of VIP (12 nmol/kg/hr), 13.9 +/- 4.2 mumol/cm/hr, was unchanged by atropine, reduced to 10.0 +/- 3.5 mumol/cm/hr by hexamethonium, and augmented to 18.9 +/- 4.7 mumol/cm/hr by indomethacin. Exogenous VIP did not change the basal luminal output of PGE2; neither did exogenous PGE2 nor indomethacin affect the basal luminal output of VIP. HCl-induced increases in luminal outputs of VIP, substance P, and neurokinin A (the two latter with unknown roles) were differentially affected by atropine, hexamethonium, and indomethacin, indicating that the acid challenge released the peptides through controlled mechanisms. In conclusion, in the duodenal HCO3- response to luminal HCl, VIP may have a stimulatory role, which partially depends on nicotinic, but not on muscarinic cholinoceptor mechanisms, and which is negatively modulated by prostaglandins.

Impaired increase of prostaglandin E2 in gastric juice during steroid therapy in children

To investigate the aetiology of steroid-induced peptic ulcers in children, prostaglandin E2 (PGE2) release and acid secretion into gastric juice was evaluated in 10 children receiving a corticosteroid before and after injection of pentagastrin. The concentration of luminal PGE2 was measured by radio-immunoassay. The basal levels of PGE2 concentration and acid secretion in gastric juice did not differ significantly between the steroid therapy group and control group. After stimulation with pentagastrin, acid secretion increased significantly (P < 0.01) in both groups and PGE2 concentration increased significantly (P < 0.01) only in the control group. Prostaglandin E2 concentration was significantly lower in the steroid therapy group than in the control group 20-40 and 40-60 min after pentagastrin stimulation (P < 0.01 and P < 0.05, respectively). Since PGE2 has a cytoprotective effect on the gastric mucosa, the results of impaired increase of PGE2 in response to increased acid secretion during steroid therapy may indicate causality with the development of steroid-induced peptic ulcers.

Cholinergic mechanisms involved in release and effect of prostaglandin E2 in HCl-stimulated duodenal HCO-3 secretion in the conscious rat

Using a proximal duodenal loop in conscious rats, we investigated interactions between prostaglandin E2 and nicotinic and muscarinic receptor mechanisms previously found to be involved in the duodenal HCO3- response to HCl. In previous studies using the same model, a 5-min perfusion of the duodenal loop with 150 mmol l-1 HCl produced a marked and sustained HCO3- response. In the present study, the identical challenge produced a rapid 20-fold increase in the luminal output of prostaglandin E2 during acid exposure, followed by a sustained more than twofold elevation above the basal level during the 45 min monitored. The prostaglandin synthesis inhibitor indomethacin (4 mg kg-1 i.p.) suppressed the output of prostaglandin E2 during the HCl challenge from 131 +/- 84 to 15.4 +/- 10.0 pmol cm-1 h-1, and in the post-stimulatory period from 17.3 +/- 9.1 to 4.4 +/- 2.2 pmol cm-1 h-1. The nicotinic receptor antagonist hexamethonium (20 mg kg-1 i.v.) had no effect on the output of prostaglandin E2. The muscarinic receptor antagonist atropine (0.5 mg kg-1 s.c.) had no effect on the output of prostaglandin E2 during HCl challenge, but reduced the post-stimulatory output to 7.7 +/- 4.1 pmol cm-1 h-1. Perfusion of the duodenal loop with 0.1 mmol l-1 prostaglandin E2 produced a HCO3- response that was abolished by hexamethonium (20 mg kg-1 i.v.), but not affected by atropine (0.5 mg kg-1 s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin E2 formation by rat gastroduodenal tissue following intragastric acid perfusion

Rat gastroduodenal mucosa forms prostaglandin (PG) E2. However, little is known about regional differences in PGE2 formation or the effect of gastric hydrochloric acid (HC1) perfusion on regional PGE2 formation. In this study, the rats were divided into 3 groups. Group 1 received intravenous (i.v.), 1 Ml/h, and intragastric (i.g.), 8 ml/h, perfusions of saline simultaneously for 3 h. Group 2 received saline i.v. and 0.15 N HC1 i.g., 8 ml/h. Group 3 was injected with a bolus of asprin (ASA), 60 mg/kg, followed by ASA, 40 mg/kg/h i.v., and 0.15 N HC1 i.g.. The gastric aspirates were analyzed for volume and pH. Segments of gastroduodenal tissue from the fundus, corpus, antrum, and duodenum were minced and then incubated in 1 ml of 5 mM Tris buffer, pH 8.4, for 30 sec with mixing; the incubate was assayed for PGE2 by radioimmunoassay. Intragastric HC1 decreased the pH of aspirate without producing gastric mucosal lesions. However, when combined with i.v. ASA, ulcer formation was present in all animals (p less than 0.05). PGE2 was formed by isolated tissue from four different gastroduodenal regions. The duodenum formed significantly greater amounts than the fundus, antrum, or corpus, which were similar. Intragastric HC1 produced a trend toward increased PGE2 formation (pmol PGE2/mg tissue) in the fundus, 143 +/- 36 to 237 +/- 57; corpus, 87 +/- 13 to 200 +/- 57; antrum, 157 +/- 28 to 224 +/- 65; and duodenum, 235 +/- 56 to 338 +/- 51. However, statistical significance was not reached.

A second antibody solid-phase enzyme immunoassay of prostaglandin E2 in human gastric juice

A second antibody solid-phase enzyme immunoassay for the determination of prostaglandin E2 in human gastric juice was developed using acetylcholine esterase as label, covalently coupled to the eicosanoid. The assay was performed on 96-well microtiter plates coated with the second antibody (swine antirabbit IgG antibody). The enzyme-labeled and unlabeled prostaglandin E2 were allowed to react in a competitive manner with the immobilized specific antibody (rabbit anti-prostaglandin E2 serum). After addition of the enzyme substrate, the specifically bound acetylcholine esterase was determined at 414 nm by means of a colorimetric assay and the enzyme activity was correlated with the amount of unlabeled prostaglandin E2. According to the calibration curve, prostaglandin E2 was determined in the range of 0.5-250 pg/ml. The minimal detectable concentration of prostaglandin E2 was 1.9 +/- 0.2 pg/ml. The intraassay coefficient of variation was less than 10%. Most prostaglandins and their metabolites tested showed a cross-reactivity of less than 1%.

Gastric prostaglandin E2 release induced by aluminium hydroxide and aluminium hydroxide-containing antacids in rats. Effect of low doses and citric acid

Suspensions of aluminium hydroxide or a commercial antacid containing aluminium hydroxide (Trigastril) was instilled intragastrically in rats in doses comparable to high and low human therapeutic doses (aluminium hydroxide, 125 mg and 12.5 mg/kg, respectively). Corresponding experiments were carried out with 0.6% citric acid added to the antacid suspensions. Prostaglandin E2 (PGE2) in the gastric content was analysed by radioimmunoassay 6 h after drug administration. Both high and low doses of aluminium hydroxide and Trigastril increased the concentration of PGE2 significantly. Citric acid did not significantly affect the antacid-induced PGE2 release except in combination with a low dose of aluminium hydroxide, with which a significant increase was seen. Release of PGE2 by low doses of antacids implies the possibility that enhanced cytoprotection may be involved in the mechanism by which antacids promote the healing of peptic ulcers.

Prostaglandin synthesis in the human gastrointestinal mucosa

Prostaglandins derive from polyunsaturated fatty acids, of which arachidonic acid is the most abundant. Arachidonic acid occurs in all cell membranes, where it is bound to phospholipids and can, once liberated by phospholipases, be metabolized by cyclooxygenase into prostaglandins and thromboxanes and by lipoxygenases into hydroxyacids, leukotrienes and lipoxins. In most studies on prostaglandin formation in the human gastrointestinal mucosa PGE2 and PGF2 alpha seem to be the regularly occurring products. Quantification of mucosal prostaglandin synthesis in vivo is problematic. Mechanical handling of tissues immediately activates arachidonic acid metabolism, and the determination of "tissue levels" of prostaglandins or prostaglandin biosynthesis in biopsy specimens ex vivo thus becomes unreliable as a measure of in vivo formation. A more reliable approach may be to measure prostaglandins in gastrointestinal luminal contents, which can be obtained atraumatically. Most measurements are made by radioimmunological methods, but the specificity of most assays has not been satisfactorily examined. More specific methods such as gas chromatography-mass spectrometry should be used to validate of a radioimmunoassays. Prostaglandin E2, which can be measured by gas chromatography-mass spectrometry, is regularly found in human gastroduodenal luminal contents. Exposure of the mucosa to hydrochloric acid increases the output of PGE2 to the lumen, indicating increased mucosal PGE2 formation during physiological activation of mucosal defense mechanisms.