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 by 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.     

Mucus and pepsin role in gastric damage prevention by H2-receptor antagonists and antiulcer drugs

The effects of cimetidine and ranitidine, alone or combined with sulglycotide or carbenoxolone, and those of 16,16-dimethyl prostaglandin E2 were investigated on mucosal lesions induced in pylorus-ligated rats. The drugs were administered orally after pylorus ligation; 3 hr later the animals were killed, the stomachs removed and examined for the presence of mucosal lesions. Volume, pH, total acidity, pepsin, free and barrier mucus were determined. H2-antagonists both at nonantisecretory and antisecretory doses failed to prevent gastric mucosal lesions or to affect significantly mucus and pepsin. Sulglycotide and carbenoxolone inhibited pepsin secretion, the latter enhanced barrier mucus and both reduced lesion severity. A nearly complete prevention of mucosal damage was observed after anti-secretory doses of cimetidine plus sulglycotide or carbenoxolone. Data obtained compared with those of 16,16-dimethyl prostaglandin E2 suggest that mucus and pepsin might have a partial role in ulcer prevention.     

Effects of 16, 16-dimethyl prostaglandin E2 on bile-induced histamine release and permeability alterations in canine oxyntic mucosa.

Damage to the stomach results in excessive movement of hydrogen ion (H+) out of the lumen, and increased movement of sodium (Na+) and potassium (K+) into the lumen. Histamine liberation during damage probably adds to the destruction by increased capillary permeability and formation of edema. Previous reports have shown that the synthetic prostaglandin analogue 16,16-dimethyl prostaglandin E2 (Dm PGE2) protects dog gastric mucosa from aspirin- and ethanol-induced gastric mucosa damage. The effects of dm PGE2 on bile salt (sodium taurocholate) induced injury has not been investigated. Using the canine Heidenhain pouch, the present study examined the action of dm PGE2 on gastric mucosal damage induced by 5 mM sodium taurocholate in 100 mM HCl. Bile salt damaged the pouch mucosa as evidenced by an increased loss of H+, and increased net fluxes of both Na+ and K+. There was also an increase in the histamine content of the fluid irrigating the Heidenhain pouch. Intravenous injection of dm PGE2 in the doses 0.1 and 1.0 microgram/kg 1/2 h before administration of the sodium taurocholate in HCl significantly reduced the net loss of H+ and the gain of Na+, K+, and histamine. It is concluded the dm PGE2 effectively protects the canine gastric mucosa from the damaging effects of bile salt and that the mechanism of dm PGE2 protection of canine oxyntic mucosa may be mediated in part via inhibition of the gastric mucosal release of histamine.     

Partial characterization of the gastrointestinal weight changes produced in the female rat by 16,16-dimethylprostaglandin E2

Oral and subcutaneous administration of 16,16-dimethylprostaglandin E2 (16,16-dimethyl PGE2) resulted in an increase in the dry weight of the stomach and small intestine of the female rat. This weight response was rapid, controlled rather than continuously progressing, dose dependent and reversible. The dry weight of the colon also increased but this was not studied in detail. Two-day treatment with 16,16-dimethyl PGE2 caused an increase in the incorporation of 3H-thymidine into the duodenum, jejunum and colon suggesting an increase in cell number. Incorporation into the stomach and ileum was not changed. The number of goblet cells per crypt was increased by prostaglandin treatment in all parts of the small intestine. Since these are mucus producing cells, the small intestine may have increased in cell number and mucus production. Both anti-secretory and cytoprotective doses of 16,16-dimethyl PGE2 caused weight increases in the stomach and small intestine. However, the weight gain by itself was not sufficient to protect the stomach or small intestine from necrotic agents after the prostaglandin was discontinued.     

Structure and function of gastric corpus mucosa in suckling rats after treatment with 16,16-dimethyl prostaglandin E2

Suckling rats were treated every 8 h by intragastric instillation of 16,16-dimethyl prostaglandin E2 (PG) from postnatal day 7 to 11. As compared to saline control treatment, PG increased the thickness of antral and corpus mucosa, the volume density of parietal cells, the mean individual parietal cell volume and pentagastrin-stimulated acid secretion at the end of the treatment. Plasma gastrin and corticosterone levels were depressed by PG while plasma thyroxine levels were unchanged. These structural and functional changes suggest PG-induced accelerated maturation of gastric mucosa.     

Effects of 16,16-dimethyl prostaglandin E2 and indomethacin on leukotriene B4 and inflammation in rabbit colitis

The role of increased prostaglandin production and the effects of exogenous prostaglandins on inflammation of colitis are not established. We administered intramuscular 16,16-dimethyl prostaglandin E2 (DiM-PGE2) and indomethacin to rabbits with formalin immune-complex colitis and measured leukotriene B4 (LTB4), prostaglandin E2 (PGE2) and severity of inflammation. DiM-PGE2 (100 micrograms/kg/BID) reduced LTB4 production (from 401 +/- 108 to 216 +/- 58 pg/ml) and infiltration of neutrophils, mucosal necrosis, inflammatory exudate and edema (all P less than 0.05). Other studies determined that parenteral DiM-PGE2 did not reduce the initial chemical damage induced by formalin, suggesting that cytoprotection of chemical insult was not the mechanism of suppressed inflammation in the immune colitis model. Indomethacin (10 mg/kg/d) reduced endogenous PGE2 by 80%, but did not reduce leukotriene production or inflammation. Exogenous prostaglandins cause a dose-dependent suppression of inflammation in experimental colitis, by a mechanism other than cytoprotection of chemical-induced mucosal injury.     

Effects of 16,16-dimethyl prostaglandin E2 and indomethacin on leukotriene B4 and inflammation in rabbit colitis

The role of increased prostaglandin production and the effects of exogenous prostaglandins on inflammation of colitis are not established. We administered intramuscular 16,16-dimethyl prostaglandin E2 (DiM-PGE2) and indomethacin to rabbits with formalin immune-complex colitis and measured leukotriene B₄ (LTB4), prostaglandin E2 (PGE2) and severity of inflammation. DiM-PGE2 (100 ug/kg/BID) reduced LTB4 production (from 401±108 to 216±58 pg/ml) and infiltration of neutrophils, mucosal necrosis, inflammatory exudate and edema (all P<0.05). Other studies determined that parenteral DiM-PGE2 did not reduce the initial chemical damage induced by formalin, suggesting that cytoprotection of chemical insult was not the mechanism of suppressed inflamation in the immune colitis model. Indomethacin (10 mg/kg/d) reduced endogenous PGE2 by 80%, but did not reduce leukotriene production or inflammation. Exogenous prostaglandins cause a dose-dependent suppression of inflammation in experimental colitis, by a mechanism other than cytoprotection of chemical-induced mucosal injury.     

Failure of prostaglandins E1 and E2 to alter canine gastric mucosal cyclic nucleotides.

The action of prostaglandins and indomethacin on gastric mucosal cyclic nucleotide concentrations was evaluated in 18 anesthetized mongrel dogs. Prostaglandins E1 (PGE1) and E2 (PGE2) (25 microgram/kg bolus, then 2 micrograms/kg/min) were administered both intravenously (4 experiments; femoral vein) and directly into the gastric mucosal circulation (10 experiments; superior mesenteric artery). The possible synergistic effect of pre-treatment and continuous arterial infusion of indomethacin (5 mg/kg bolus for 5 min, then 5 mg/min), a prostaglandin synthetase inhibitor, with PGE2 was studied in 4 experiments. Antral and fundic mucosa were biopsied and measured by radioimmunoassay for cyclic nucleotides. Doses of PGE1 and PGE2 which inhibited histamine-stimulated canine gastric acid secretion did not significantly alter antral or fundic mucosal cyclic nucleotide concentrations. Concomitant infusion of PGE2 with indomethacin did not potentiate the mucosal nucleotide response compared to PGE2 alone. These studies fail to implicate cyclic nucleotides as mediators of the inhibitory acid response response induced by PGE1 or PGE2 in intact dog stomach.     

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.     

Pertussis toxin blocks an inhibition of hormone-stimulated glycogenolysis by prostaglandin E2 and its analogue in cultured hepatocytes

Prostaglandin E2 (PGE2) and 16,16-dimethyl PGE2 were found to inhibit a hepatic glycogenolysis stimulated by epinephrine in the presence of propranolol (alpha 1-adrenergic response), isoproterenol (beta-adrenergic response) and glucagon in primary cultures of rat hepatocytes. The inhibitory effects to these stimulations were maximally increased (60-100%) in the cultures on day 2 or 3. Pretreatment of the cultured hepatocytes with pertussis toxin (islet-activating protein) resulted in a complete blockage of the prostaglandin-induced inhibition of glycogenolysis in a dose-dependent manner. Pertussis toxin had no significant effect on the glycogenolysis stimulated by these compounds in the absence of prostaglandin. The data suggest that the hepatic glycogenolysis stimulated by alpha 1- and beta-adrenergic responses and glucagon are modulated by the E series of prostaglandins via pertussis toxin-sensitive guanine nucleotide regulatory protein.     

Interaction of dimethyl prostaglandin E2 and ethanol on the pancreatic secretion of the rat

We have studied the action of 16,16-dimethyl prostaglandin E2 methyl ester (DiMePGE2) on pancreatic secretion in the unanesthetized rat with pancreatic and duodenal fistulae. DiMePGE2 inhibited volume, protein secretion and bicarbonate output. The inhibition of protein concentration is dose related (ED50 = 5.35 microgram/rat). DiMePGE2 was effective by the intraduodenal, intravenous, and intraperitoneal routes. Intraduodenal infusion of ethanol alone (2 mL 16% (v/v) in 1 h) strongly increased protein secretion (concentration, +30%; output, +69%) When 4 microgram DiMePGE2 was injected intraperitoneally just before the ethanol infusion, the secretory effect of ethanol disappeared and the inhibition was similar to that observed with DiMePGE2 alone.     

Influence of the thromboxane-mimetic U-46619 and the prostacyclin metabolite 6-keto prostaglandin E1 on vasoconstriction induced by noradrenaline and 5-HT in rat mesenteric vasculature

The aim of this study was to investigate the effects of U-46619, a thromboxane A2-mimetic, and 6-keto prostaglandin E1 (6-keto PGE1) a biologically active metabolite of prostacyclin, on vasoconstrictor responses to noradrenaline and 5-hydroxytryptamine (5-HT). In vitro, U-46619 (3-100 nmol/l) amplified responses to both noradrenaline and 5-HT in a concentration-dependent manner. This effect was not caused by an increase in the affinity of the alpha-adrenoceptor for noradrenaline because U-46619 (100 nmol/l) did not alter the pA2 of phentolamine. In vivo, U-46619 (100 nmol/l) induced vasoconstriction and consequently significantly shifted the log-concentration-effect curves to noradrenaline and 5-HT upward in an additive manner. 6-Keto PGE1 (1 mumol/l) did not affect either perfusion pressure or vasoconstriction in response to noradrenaline in vivo. The study highlights some differences in responses between in vitro- and in vivo-perfused mesentery.     

Roles of endogenous prostaglandins and nitric oxide in gastroduodenal ulcerogenic responses induced in rats by hypothermic stress.

We examined the roles of endogenous prostaglandins (PGs) and nitric oxide (NO) in the gastroduodenal ulcerogenic responses to hypothermic stress (28 approximately 30 degrees C) in anesthetized rats. Lowering body temperature provoked damage in the gastroduodenal mucosa, with an increase of gastric acid secretion and motility. These responses were completely abolished by bilateral vagotomy or atropine, while 16,16-dimethyl PGE2 decreased the mucosal ulcerogenic response with no effect on acid secretion. The non-selective COX inhibitors, indomethacin or aspirin, worsened these lesions with enhancement of gastric motility and no effect on acid secretion, while the selective COX-2 inhibitor NS-398 did not affect any of these responses. On the other hand, the non-selective NOS inhibitor L-NAME but not aminoguanidine (a relatively selective inhibitor of iNOS), significantly potentiated the acid secretory and mucosal ulcerogenic responses in the stomach but reduced the duodenal damage in response to hypothermia, the effects being antagonized by co-administration of L-arginine. Hypothermia itself decreased duodenal HCO3- secretion under both basal and mucosal acidification-stimulated conditions. Both indomethacin and aspirin further decreased the HCO3- response to the mucosal acidification, while L-NAME significantly increased the HCO3- secretion even under hypothermic conditions, similar to 16,16-dimethyl PGE2. These results suggest that 1) hypothermic stress caused an increase of acid secretion and motility as well as a decrease of duodenal HCO3-secretion, resulting in damage in both the stomach and duodenum, 2) the COX-1 but not COX-2 inhibition worsened these lesions by enhancing gastric motility and further decreasing duodenal HCO3- response, 3) the cNOS but not iNOS inhibition worsened gastric lesions by increasing acid secretion but decreased duodenal damage by increasing HCO3- secretion. Thus, it is assumed that the gastroduodenal ulcerogenic and functional responses to hypothermic stress are modified by cNOS/NO as well as COX-1/PGs.     

Structure and function of gastric corpus mucosa in suckling rats after treatment with 16,16-dimethyl prostaglandin E2

Suckling rats were treated every 8 h by intragastric instillation of 16,16-dimethyl prostaglandin E₂ (PG) from postnatal day 7 to 11. As compared to saline control treatment, PG increased the thickness of antral and corpus mucosa, the volume density of parietal cells, the mean individual parietal cell volume and pentagastrin-stimulated acid secretion at the end of the treatment. Plasma gastrin and corticosterone levels were depressed by PG while plasma thyroxine levels were unchanged. These structural and functional changes suggest PG-induced accelerated maturation of gastric mucosa.     

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.     

Characterization of gastric mucosal prostaglandin E2 receptor

1. The binding characteristics of gastric mucosal prostaglandin (PG) E2 (PGE2) receptor were investigated using mucosal cell membranes from rat stomach. The binding was found to be dependent upon PGE2 and membrane protein concentration, the time of incubation and the pH of the mixture, being highest at pH 3.0. 2. Scatchard analysis of the binding data revealed a curvilinear plot with high affinity binding (Kd = 2 nM; Bmax = 0.106 pmol/mg protein) and low affinity binding (Kd = 319 nM; Bmax = 2.262 pmol/mg protein) sites. 3. Competitive displacement study indicated that the receptor was specific for PGs of the E series, as PGF2 alpha and 6-keto-PGF1 alpha failed to displace the PGE2. 4. The study is the first report to provide biochemical parameters of specific PGE receptors in rat gastric mucosa.     

Up-regulation of prostaglandin E2 binding and of prostanoid release in rabbits producing antibodies against prostaglandin E2

German Giant rabbits successfully immunized against prostaglandin (PG) E2 as shown by a rise in antibody titers developed gastric mucosal lesions. Enzymatically dispersed gastric mucosal cells of these animals had a significantly enhanced production of PG E2 and PG I2 as measured by specific radioimmunoassays. This may be explained by an increased supply with endogenous arachidonic acid (as indicated by an enhanced phospholipase A2/LAT ratio) and by a higher activity of the subsequent PG forming enzymes (as indicated by a more effective stimulation of PG production by exogenous arachidonic acid). Gastric mucosal plasma membranes of immunized rabbits had significantly higher PG E2 binding capacity (108 +/- 9 fmol/mg protein) than those of nonimmunized rabbits (72 +/- 5 fmol/mg protein). The ligand affinity was not affected by immunization. Neither histamine-stimulated 14C-amino-pyrine uptake of isolated parietal cells as a marker for acid production nor its inhibition by PG E2 were influenced by receptor up-regulation. The increased eicosanoid release can be regarded as an endogenous defense mechanism against increased mucosal vulnerability caused by PG E2 scavenging. The potential role of PG E2 receptor up-regulation in support of this process remains to be established.     

Interleukin-1 is cytoprotective, antisecretory, stimulates PGE2 synthesis by the stomach, and retards gastric emptying

Human recombinant interleukin 1 beta (IL-1) administered intraperitoneally to rats produced the following gastric effects: 1. It was cytoprotective, preventing gastric mucosal necrosis produced by oral administration of one ml of absolute ethanol to fasted animals. The ED50 was 1200 units/kg (110 ng per animal). IL-1 was 125 times more potent than prostaglandin E2 (on a weight basis), and 6,000 times more potent (on a molar basis). 2. The cytoprotective effect of IL-1 was blocked by indomethacin (inhibitor of prostaglandin synthesis) and by IRAP (a specific interleukin-1 receptor antagonist protein). IRAP did not inhibit cytoprotection induced by PGE2. 3. IL-1 prevented the formation of gastric erosions induced by aspirin. 4. IL-1 inhibited gastric secretion (volume, acid concentration and output), in the pylorus-ligated rat, with an ED50 of 300 units/kg (3.2 ng per animal). 5. Indomethacin and IRAP blocked the antisecretory effect of IL-1. 6. IL-1 retarded gastric emptying, an effect blocked by IRAP, but not by indomethacin. 7. IL-1 increased synthesis of prostaglandin E2 by the gastric mucosa by 111%. IL-1 is the most potent of known agents that are gastric cytoprotective, antiulcer, antisecretory, and delay gastric emptying. It appears to act mostly by stimulating the synthesis of prostaglandins by the stomach. These studies suggest that the stomach possesses IL-1 receptors. These are probably located on parietal cells (that produce acid), on prostaglandin-producing cells, on smooth muscle cells (responsible for gastric emptying), and on as yet unidentified cells involved in gastric cytoprotection. Both IL-1 and IRAP, being natural substances, may play a physiological role in the maintenance of gastric mucosal integrity, and in the regulation of acid secretion and gastric motility.     

Rupture of the uterus following treatment with 16-16-dimethyl E 2 prostaglandin vagitories

Rupture of the uterine body was found after induction of therapeutic abortion with vaginal suppositories containing 16,16-dimethyl prostaglandin E 2 in a 20-year-old primigravida. A short discussion is given on the cervical complications that can occur after prostaglandin induction of abortion, stating that rupture of the uterine body also can be seen. So far, no prostaglandin compound seems to avoid such complications.