The effects of a prostaglandin endoperoxide analogue on canine gastric acid and mucus secretion

Responses of glucose absorption and fructose absorption to prostaglandin E2 in intestinal loops of sheep

This study was designed to clarify whether the anti-absorptive action of prostaglandin E2 (PGE2) on glucose absorption was specific or non-specific to the glucose absorptive process, by investigating its effect on fructose absorption which has a different mechanism from that of glucose absorption. The effect of PGE2 on mucus secretion was also evaluated as one of the non-specific inhibiting factors. PGE2 significantly stimulated the secretion of water and mucus, and the absorptions of glucose and fructose were inhibited 49.3 per cent and 31.1 per cent respectively at the highest dose. However, fructose absorption was not inhibited by lower doses of PGE2, although the secretion of fluid and mucus was stimulated significantly and glucose absorption was inhibited significantly at the lower doses.

Inhibition of acid formation in rabbit parietal cells by prostaglandins is mediated by the prostaglandin E2 receptor

The affinities of seven natural and synthetic prostaglandins [PGE2; 16,16-dimethyl PGE2; iloprost (stable prostacyclin analogue); PGF2 alpha; PGD2; BW245c (stable PGD2 analogue); and U46619 (stable thromboxane analogue)] to the PGE2 binding site of rabbit gastric mucosa were determined by measuring [3H]PGE2 displacement from its high-affinity plasma membrane binding sites. In parallel, the potency of each prostaglandin in inhibiting acid generation in vitro was determined by measuring the inhibition of histamine-stimulated [14C]aminopyrine accumulation in rabbit parietal cells prepared by enzymatic dispersion and enriched by counterflow elutriation. All seven prostaglandins displaced [3H]PGE2 and inhibited histamine-stimulated [14C]aminopyrine accumulation in a concentration-dependent manner. For all tested prostaglandins, the IC50 values were in excellent agreement for both variables measured. It is concluded that (a) a PGE2 receptor is localized on the parietal cell and mediates inhibition of acid formation by all prostaglandins and (b) the different in vitro antisecretory potencies of prostaglandins can be attributed to their different affinities to this PGE2 receptor.

U46619 and carbocyclic thromboxane A2-induced increases in tracheal mucous gel layer thickness

U46619 or carbocyclic thromboxane A2 (CTA2) administered intravenously (IV) to rats produced dose-related increases of tracheal mucous gel layer thickness. Significant gel thickening was observed at doses ranging from 3.5 pg to 35 ng and from 500 pg to 50 ng for U46619 and CTA2, respectively. Intravenous treatment with pinane thromboxane A2 (PTA2), a thromboxane antagonist, prior to injection of U46619 or CTA2 attenuated the mucous gel layer response. The effect of PTA2 on U46619 and CTA2 was dose-dependent over the dosage range of PTA2 tested (1.0-31.6 micrograms/kg). PTA2 was equiactive against U46619 and CTA2 stimulated increases in gel thickness (ED50's 6.64 and 6.43 micrograms/kg respectively) suggesting a similar site of action for U46619 and CTA2. Slow reacting substance (SRS) injected IV into rats stimulated mucous gel layer thickening that was also inhibited by pretreatment with PTA2. These findings lend further support for the role of thromboxane in pathophysiologic conditions in which bronchorrhea contributes to the symptomatology.

Close-arterial administration of the thromboxane mimetic U-46619 induces damage to the rat gastric mucosa

The pro-ulcerogenic actions of the thromboxane mimetic, U-46619 on the rat gastric mucosa have been investigated, utilizing a novel technique which allows administration directly into the left gastric artery. Local intra-arterial infusion of U-46619 (100-500 ng/kg/min for 10 min) induced dose-dependent macroscopic damage in both the corpus and antral regions, characterized as vasocongestion, disruption and haemorrhage, with deep penetrating ulcers in the antral mucosa. Vascular congestion, epithelial cell and glandular disruption was observed histologically in both corpus and antral regions. Local intra-arterial infusion of lower doses of U-46619 (25-100 ng/kg/min) significantly disrupted the mucosa in the presence of 10% ethanol in a concentration which itself did not induce macroscopic damage. The damaging actions of U-46619 were substantially reduced by pretreatment with the thromboxane-receptor antagonist, BM 13,177 (5mg/kg i.v.) or 16,16-dimethyl PGE2 (5 micrograms/kg s.c.). These findings support the role of endogenous thromboxane A2 as a local mediator of gastric injury.

Thromboxane receptors can modulate gastric acid secretion in the rat

The effects of PGE2 and the thromboxane A2 mimetic, U-46619, have been investigated on gastric secretion in the rat isolated gastric mucosa. Both compounds produced concentration-related inhibitions of histamine-induced secretion whereas only U-46619 inhibited methacholine-stimulated and basal secretion, and neither compound had any effect on the secretory response to dbcAMP. Indomethacin had no effect on the antisecretory activity of PGE2 but markedly reduced the potency of U-46619 suggesting that endogenous prostaglandins play a role in the U-46619 responses. However, direct inhibitory effects of U-46619 were seen at high concentrations. The thromboxane receptor antagonist AH23848, at concentrations selective for thromboxane receptors, had no effect on responses to PGE2 but markedly inhibited the effects of U-46619. We conclude that the antisecretory profile of U-46619 differs from that of PGE2. U-46619 has both direct and indirect antisecretory effects and these are mediated via thromboxane receptors in the rat gastric mucosa.

Effects of prostaglandin E2, 16,16-dimethyl prostaglandin E2 and a prostaglandin endoperoxide analogue (U-46619) on gastric secretory volume, [H+] and mucus synthesis and secretion in the rat

The effects of orally administered prostaglandin E2, 16,16-dimethyl prostaglandin E2 and U-46619, an analogue of the prostaglandin endoperoxide PGH2, on gastric secretory volume, acid and mucus were studied in the rat. All of the compounds significantly increased the volume of gastric secretion, mucus secretion, measured as N-acetylneuraminic acid and mucus synthesis measured as the incorporation of [3H]-glucosamine into mucosal glycoprotein; however, only PGE2 and 16,16-dimethyl PGE2 inhibited acid secretion. U-46619, 1.5 mg/kg provided significant protection against ethanol-induced gastric ulcers, an effect that has been previously shown for the other two compounds. These studies provide additional evidence that prostaglandin induced mucosal protection may be related to an effect on mucus and on stimulation of nonparietal cell gastric secretion. Further study of these parameters may be important in the development of antiulcer drugs for long term clinical use.

A new PGE1 analogue (CL115,574) III. Effects on gastric acid and mucus secretion in man

CL115,574, an analogue of PGE1, is a potent inhibitor of gastric acid secretion in animals. The effects of this compound on gastric acid and mucus secretion were studied in 8 male volunteers. The compound was well tolerated, and its maximally effective antisecretory dose (750 micrograms) inhibited pentagastrin stimulated acid secretion by approximately 40% over a 2-hour period, with stimulation beginning one hour after the drug was orally administered. CL115,574 proved to have a significant and sustained effect upon the stimulation of mucus secretion into gastric juice. Considering the possible role that mucus may play in mucosal cytoprotection, CL115,574 because of its antisecretory and mucogenic actions may prove to be an important clinical anti-ulcer compound.

A new prostaglandin E1 analogue (CL115,574). I. antisecretory and cytoprotective effects in the rat

The effects of a new analogue of PGE1 (CL115,574) on gastric acid secretion, mucus secretion and protection against stress and indomethacin-induced ulcers were studied in the rat. CL115,574 was more potent than PGE1 and cimetidine in inhibiting acid secretion. CL115,574 protected against the development of stress and indomethacin-induced ulcers and prevented the indomethacin-induced decrease in hematocrit at an ED50 (3 micrograms/kg) far below the antisecretory ED50 (1 microgram/kg). While inhibiting acid secretion, CL115,574 increased the volume of gastric secretion indicating a stimulation of nonparietal cell secretion by the rat stomach. In addition the compound stimulated the secretion of mucus into the gastric juice. On the basis of its potency as an inhibitor of acid secretion and these additional effects which are indicative of cytoprotective activity, CL115,574 should be further studied as a possible anti-ulcer agent in man.

Prevention of aspirin-induced faecal blood loss by prostaglandin E2

Prostaglandins have been shown in animal laboratory studies to be capable of protecting the gastrointestinal tract against injury by exogenous agents. This study was conducted to determine if prostaglandin E2 (PGE2), which is native to the human gastric mucosa, could influence the increase in faecal blood loss associated with the ingestion of aspirin (ASA). A randomised double-blind study was performed on 27 healthy men. Faecal blood loss was measured by the 51Cr labelled red cell technique. ASA (600 mg four times daily) caused a significant increase in faecal blood loss. PGE2 (1 mg four times daily) had no effect on faecal blood loss when administered alone. When given in addition to ASA it resulted in a faecal blood loss not significantly different from control. No significant alteration in intestinal transit occurred. It is concluded that PGE2 protects man from the gastrointestinal injury associated with ASA.