Effects of ethanol alone or after pretreatment with 20% ethanol on phospholipid metabolism in rat gastric mucosa.

Changes in phospholipid metabolism in gastric mucosa caused by instillation of absolute ethanol (a cell-damaging agent) into the stomach of rats and the effects of pretreatment with 20% ethanol (a mild irritant) were investigated by using radioisotope-labeled fatty acids and glycerol. The labeled precursors were incorporated mainly into phosphatidylcholine and triacylglycerol, and also to lesser extents into phosphatidylethanolamine and phosphatidylinositol + phosphatidylserine. The instillation of absolute ethanol reduced the incorporation of fatty acids and glycerol into phospholipids within 15 min, indicating the inhibition by ethanol of de novo synthesis of phospholipids. Pretreatment with 20% ethanol caused the incorporation of fatty acids into phospholipids to be maintained after absolute ethanol instillation. These results suggest that the pretreatment with 20% ethanol may protect the cellular synthetic activity of phospholipids against damage by absolute ethanol. The incorporation of fatty acids into the free fatty acid fraction, monoacylglycerol and diacylglycerol was increased by absolute ethanol instillation, suggesting damage to the blood vessels of the gastric mucosa, and these changes were inhibited to some extent by the pretreatment with 20% ethanol.

Effects of 15(S)-15-methyl prostaglandin E2 methyl ester on phospholipid metabolism in rat gastric mucosa.

The effects of 15(S)-15-methyl prostaglandin E2 (PGE2) methyl ester on gastric mucosal metabolism of phospholipids in intact rats and rats injured by intragastric instillation of acidified taurocholic acid were examined by using radioisotope-labeled precursors. The incorporation of palmitic, oleic and arachidonic acids into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was reduced by treatment with 15(S)-15-methyl PGE2 methyl ester in the intact rats, but the incorporation of glycerol was unaffected or affected only slightly. Instillation of acidified taurocholic acid resulted in decreased incorporation of palmitic acid and glycerol into PC and PE, whereas pretreatment with 15(S)-15-methyl PGE2 methyl ester caused the incorporations of these precursors to be maintained after acidified taurocholic acid treatment. These results suggest that 15(S)-15-methyl PGE2 methyl ester may reduce the incorporation of fatty acids into PC and PE by inhibition of the deacylation-reacylation cycle either directly or indirectly, whereas acidified taurocholic acid decreases de novo synthesis of PC and PE, and probably also the reacylation of fatty acid into phospholipids. Pretreatment with 15(S)-15-methyl PGE2 methyl ester protected the PC- and PE-synthesizing activity against the injury induced by acidified taurocholic acid, and this effect may be involved in the prevention of mucosal damage.

Enhancement of the lipid content and physical properties of gastric mucus by geranylgeranylacetone.

The effects of intragastric administration of geranylgeranylacetone (GGA) on the content, composition and physical properties of the mucus component of the gastric mucosal barrier were investigated. One group of rats received twice daily for 3 consecutive days a dose of 100 mg/kg body weight of GGA, while the control group was subjected to daily doses of the vehicle. Sixteen hours following the last dose, the animals were killed, and their stomach was cut open and subjected to measurements of the adherent mucus gel content, analysis of its lipids and molecular forms of elaborated mucin, and evaluation of the viscosity and H+ retardation capacity. The results revealed that GGA elicited a 62% increase in the adherent mucus gel and caused a marked decrease in the proportion of the lower molecular weight mucin. Furthermore, the mucus of the GGA group exhibited a 67% higher content of covalently bound fatty acids and contained 46% more total lipids which were greatly (143%) enriched in phospholipids. The physical measurements demonstrated that mucus elaborated in the presence of GGA also exhibited 2.3 times higher viscosity and had a 32% greater ability to retard the diffusion of H+ than the mucus of the control group. The results suggest that GGA exerts a profound effect on the lipid content and the properties of gastric mucus associated with the maintenance of the mucosal integrity.

Effects of taurocholic acid/HCl alone or after pretreatment with geranylgeranylacetone on phospholipid metabolism in rat gastric mucosa.

Changes in phospholipid metabolism in gastric mucosa caused by instillation of taurocholic acid (TCA)/HCl (80 mM/300 mM) into the stomach of rats and the effects of pretreatment with an antiulcer agent, geranylgeranylacetone (GGA), were studied after intravenous injection of radioisotope-labeled precursors. The instillation of TCA/HCl rapidly reduced the incorporation of labeled fatty acids and glycerol into phosphatidylcholine and phosphatidylethanolamine, indicating the inhibition of de novo synthesis of phospholipids. These changes were restored by 120-150 min after the TCA/HCl treatment. Pretreatment with GGA enhanced the incorporation of precursors into phosphatidylcholine immediately after the instillation of TCA/HCl. Experiments in which the mucosal lipids were labeled with fatty acids prior to the instillation of TCA/HCl showed that the degradation of cellular lipids and release of the products into the gastric lumen were induced by TCA/HCl and that these changes were not prevented by GGA. Since GGA almost completely inhibited the gastric lesions induced by TCA/HCl, the enhancement of synthesis of mucosal phosphatidylcholine induced by GGA may be involved in the prevention of gastric damage. The incorporation of labeled fatty acids into free fatty acid fraction and diacylglycerol was increased quickly by the TCA/HCl treatment, suggesting early damage to the blood vessels of the gastric mucosa; these changes were inhibited significantly by GGA.

Centrally administered NPY stimulated gastric acid and pepsin secretion by a vagally mediated mechanism.

We investigated the possible roles of centrally administered neuropeptide Y (NPY) on gastric secretion, serum gastrin levels and gastric mucosal blood flow in anesthetized rats. Centrally administered NPY dose-dependently stimulated gastric acid and pepsin secretion. The stimulatory effect of intracerebroventricular administration of NPY was more potent than that of intracisternal administration. Centrally administered NPY also increased gastric secretion in the central noradrenaline depleted rats. In contrast, intravenously administered NPY had no influence on gastric secretion. These stimulatory effects were abolished by vagotomy or atropine pretreatment. The serum gastrin levels did not change after central NPY injection. Although intravenously administered NPY slightly increased gastric mucosal blood flow, centrally administered NPY slightly diminished gastric mucosal blood flow. These results indicate that centrally administered NPY markedly influences gastric functions in the rat.

[Effects of centrally administered NPY on stress induced gastric ulcers in the rat].

We investigated the central effects of neuropeptide Y (NPY) on stress-induced gastric ulcers in water immersion rats. Intracisternally administered NPY dose-dependently aggravated, but intravenously administered NPY did not affect stress ulcers in rats. Intraperitoneal pre-treatment of atropine completely blocked the central effect of NPY, but neither pyrilamine nor cimetidine affected. Intracisternal administration of NPY aggravated stress ulcers not through histamine mediated mechanism but by parasympathetic pathway. It is suggested that centrally administered NPY acted by the inhibition on gastric motility and by the suppression on gastric mucosal blood flow rather than by the stimulation on gastric secretion in rats.

Studies on the pepsinogens of human gastric mucosal extracts.

1. Electrophoretic separation of proteases from human gastric mucosal extracts of five patients with gastric ulcer, one with duodenal ulcer and three with gastric cancer were investigated by agar-gel electrophoresis at pH 8.3 and pH 5.0. 2. In the fundic mucosal study, there were seven faster moving proteases in all nine cases, but the slowest moving protease showed a slightly different picture in each case. In the antral mucosal study, two of eight cases showed mainly group II pepsinogens, seven of nine cases, however, showed the same results as in the fundic mucosal study. 3. In the cases of the nine mucosal extracts activated at pH 1.5 or pH 4.0, they all showed the same electrophoretic separation at each pH level. At these two pH levels, however, quite different electrophoretic patterns were observed. The presence of pepsin 3 appeared to diminish at the higher levels of pH, although that of pepsin 5 and pepsin 7 appeared to increase at pH 4.0 and above. Pepsin 6 appeared for the first time at pH 4.0 and existed at higher pH levels. 4. We thus conclude that electrophoretic patterns of pepsins in the gastric mucosal extracts are changeable depending on the pH level of the incubating medium, and further that diversity of pepsins in gastric juices may also depend on the pH level of gastric juices.

Effect of topical application of amino acids on gastric pepsin secretion in the rat. Part II: effect of pH changes and glycine in separate perfusion preparation.

Gastric acid and pepsin were measured in antrum and fundus separately by perfusing each region of the stomach in anaesthetized rats. Perfusion of the antral region with alkaline and acid solutions did not affect gastric acid and pepsin secretions in the fundic gland region. Gastric secretions in the antrum and acid secretions in the fundus remained unchanged when each region of the stomach was instillated with glycine. Pepsin stimulation was observed in the fundic region only when perfused with glycine. We confirmed our previous observation that topical amino acid in the oxyntic gland stimulated pepsin secretion directly. The pepsin stimulatory effect of amino acid was found to be independent of antral regulation.

Effect of topical application of amino acids on gastric pepsin secretion in the rat.

The effect of amino acids and other chemicals of intragastric perfusion on pepsin secretion was studied in anaesthetized rats. Irrigation of the stomach with glycine caused concentration-dependent increase in pepsin output, but not in acid output. Pepsin stimulatory effect was decreased by an increase of the carbon chain between the amino group and carboxyl group of glycine and by transposing the amino group from alpha- to gamma-position in amino-n-butyric acid. Acidification of perfusate, a local irrigation of lidocaine and an intravenous infusion of atropine reduced but did not abolish the pepsin response to chemical stimulation. Since serum gastrin level was not changed from basal levels during pepsin secretion induced by amino acids, the mechanism of chemical stimulation appears to be gastrin-independent. The comparison of the secretagogue activity of amino acids shows that glycine exhibited the strongest stimulation of pepsin output, reaching 208% of the response to tetragastrin at the dose of 8 microgram/kg/hour. All other amino acids tested were found to stimulate pepsin secretion, whereas bovine serum albumin and hydrochloric acid were inert in this respect. The result indicates that the chemical stimulation of the stomach by amino acids is capable of inducing pepsin secretion by a local, gastrin-independent mechanism sensitive to pH and related to the molecular configuration of amino acids.

Central effects of pituitary adenylate cyclase activating polypeptide (PACAP) on gastric motility and emptying in rats.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a new member of the secretin-glucagon-vasoactive intestinal peptide (VIP) peptide family. PACAP is widely distributed not only in the mammalian brain but also in the gastrointestinal tract. Here, we investigated the effects of central and peripheral administrations of PACAP on gastric motility and gastric emptying in rats. We found that the intracerebroventricular or intracisternal injection of PACAP increased gastric motility in a dose-dependent manner. The intracisternal injection of PACAP delayed gastric emptying. These central effects of PACAP on gastric motility and emptying were blocked by bilateral vagotomy. In contrast, intravenous administration of PACAP decreased gastric motility and delayed gastric emptying. The peripheral inhibitory effect was unaffected by bilateral vagotomy, adrenalectomy, phentolamine, and propranolol. We investigated the effect of PACAP38 on blood glucose levels (BGL) at the same doses as those used in the gastric motility and emptying studies in urethane-anesthetized rats. The intravenous but not intracerebroventricular injection of PACAP38 (1-8 nmol/rat) produced a significant increase in the BGL. We conclude that PACAP has opposite central and peripheral effects on gastric motility, ie, central PACAP activates the vagal pathway in the central nervous system to increase gastric motility, whereas peripheral PACAP inhibits gastric motility via an unknown pathway. The delay in gastric emptying after the central administration of PACAP might be due to the lack of coordinated gastropyloroduodenal contraction, whereas that after the peripheral administration might be due to the inhibition of gastric contraction, and this effect may be related to the hyperglycemic action of PACAP.

Effects of anti-GRP gamma-globulin on gastrin release and gastric secretion in the rat: evidence for the physiologic role of endogenous GRP in the regulation of gastric function.

To assess the effects of endogenous GRP on vagal gastrin release and acid secretion, anti-GRP gamma-globulin was infused in anesthetized rats to bind endogenously released GRP. Anti-GRP gamma-globulin blocked the gastrin-releasing effects caused by 4 micrograms/kg/hr of exogenous GRP infusion and suppressed gastrin release by electrical vagal stimulation. In spite of this suppression, anti-GRP gamma-globulin did not alter basal or vagal-stimulated acid secretion.

New device for the measurement of hydrogen clearance rate from the gastric mucosa.

The hydrogen clearance rate of the nucosa of the glandular stomach of the anesthetized rat was obtained with the platinum electrode in contact with the surface of the gastric mucosa (Contact Electrode Method). By using two indicator electrodes, the gastric blood flow was measured simultaneously with one electrode in contact with the mucosal surface (Contact Electrode Method), and with the other electrode inserted into the gastric wall (Inserted Electrode Method). Pentagastrin produced increase in blood flow by both contact and inserted electrode methods. Isoproterenol stimulated blood flow as determined by the contact electrode method, but when the flow was determined by the inserted electrode method it reduced the blood flow. The combination of these two methods is useful in the determination of the blood flow in the different layers of the stomach.

The role of gastric mucosal hexosamine in aspirin-induced ulcers.

In order to elucidate the role of gastric tissue hexosamine, used as an index of mucopolysaccharide content, in the development and healing process of peptic ulcers, the distribution of hexosamine and the changes of gastric hexosamine content in the development and healing of aspirin-induced ulcers in rats were studied. In addition, the effects of proglumide and L-glutamine on gastric hexosamine were also studied. The hexosamine content was found to be the highest in the antrum, followed by the corpus and then the forestomach. The mucosa contained significantly higher hexosamine than the smooth muscle layer in both the antrum and the corpus. Prior treatment with proglumide significantly increased the mucosal hexosamine to the extent of 10.3--18.1% in the glandular stomach. Administration of aspirin decreased the gastric mucosal hexosamine and induced the onset of ulcer, while administration of proglumide suppressed the gastric lesions in proportion to dosage and correspondingly prevented a decrease of the hexosamine. In contrast, L-glutamine showed an anti-ulcerogenic effect without suppressing a decrease of the hexosamine. In the process of curing gastric lesions, proglumide accelerated the healing of the ulcers and simultaneously returned the total hexosamine content to its original level. These results suggest that the gastric mucosal hexosamine is closely related to the onset and healing of aspirin-induced ulcer in rats, and that proglumide contributes to both the prevention and healing of ulcers by increasing gastric mucosal hexosamine.

Effect of topical application of amino acids on gastric pepsin secretion in the rat. Part III: effect of L- and D-isomers of amino acids on gastric secretion in reperfusion system.

This study was undertaken to compare the potency of each L- and D-isomers of 5 amino acids in stimulating gastric acid and pepsin secretion by the intragastric reperfusion preparation in rats. Gastric basal and glycine-stimulated secretions in this preparation were lower than those Ghosh-Lai preparation, but not to a statistically significant extent. All D- and L-isomers of amino acids tested were found to markedly stimulate pepsin secretion, but to only slightly stimulate acid secretion. Pepsin stimulatory response to each D and L-isomer of amino acid was similar. The stimulatory effects of amino acids thus seem to be unrelated to the optical stereoisomeric configuration.