On the biochemical background of cimetidine's anti-ulcerogenic effect in the rat.

It was published earlier that during gastric ulceration an elevation in the antral and fundic mucosal cAMP/cGMP ratios can be encountered in rats. This phenomenon was interpreted as a probable sign of the reparative, antiulcerogenic processes. This assumption received further evidence when the experimental animals were treated with prostacyclin. According to the present investigations the H2-receptor blocker cimetidine, in such small dose which does not interfere with the gastric acid secretion, evoked the same cAMP/cGMP ratio elevating effect. On the basis of the performed investigations the questions raised, namely: Does the cytoprotective (anti-ulcerogenic) effect of different drugs have a common molecular basis in the (rat) gastric mucosa? If so, what is the possible role of the mucosal cyclic nucleotides in this process? Further studies are being needed in this field to clarify all details.     

The effect of different prostaglandins on gastric mucosal intracellular second messenger system in the rat.

After an oral administration of 100 micrograms/kg dose, the investigated prostaglandins: PGF2 alpha, PGE2 and a synthetic PGE2 derivative: FCE-20700, exerted a significant effect on cAMP and cGMP content of both parts (antral and fundic) of gastric mucosa, resulting in an elevated cAMP/cGMP ratio, while 6-keto-PGF1 alpha, the stable break-down product of prostacyclin, was inactive. Since the above-mentioned phenomenon seems to be proportionate to the cytoprotective (anti-ulcerogenic) property of the investigated prostaglandins, this cAMP/cGMP ratio "shift" is interpreted as a probable (molecular) sign of the reparative, (anti-ulcerogenic) processes.     

Gastric anti-ulcerogenic drug effect. A possible mechanism of its molecular basis.

During experimental gastric ulceration in rats an elevation in the mucosal cAMP/cGMP ratio can be encountered. The cause of this significant elevation is mainly (but not entirely) the dramatic fall of the cGMP level. Similar observations were obtained with prostacyclin application (100 micrograms/kg, p.o.), too. This prostaglandin derivative is well known, among others, because of its pronounced anti-ulcerogenic (cytoprotective) effect, too. Other substances of different molecular structure and properties may also exert such effect. The exact mechanism of action of this above-mentioned cytoprotection is still not completely understood. H2-receptor blocker drug cimetidine, given in such small dose (5 mg/kg, p.o.) which does not interfere with gastric acid secretion, also exerts very significant cytoprotective effect in stress (restraint)- and drug (indomethacin)-induced gastric ulcer models. Under cimetidine effect--together with a noticeable endogenous prostacyclin mobilization--the gastric mucosal cAMP/cGMP ratio was also strongly elevated. We conclude that this elevation in the mucosal cAMP/cGMP ratio might be a possible molecular basis of the gastric cytoprotective (anti-ulcerogenic) drugs but it needs further investigations whether all substances exerting cytoprotective effect, e.g. atropine, somatostatin, sulfhydryl drugs, etc., have the same "shifting" property or not? Moreover the phenomenon of the so-called "adaptive cytoprotection" can not be ruled out completely either, therefore this problem needs attention, too.     

Effects of radioprotectors on the cAMP and cGMP systems

Summary The sulphur-containing radioprotectors mercaptoethylamine (MEA), aminoethylisothiourea (AET), 2-aminothiazoline, 4-oxo-2-aminothiazoline, and S-S-3-oxapentane-1,5-diisothiourea, and the radioprotective biogenic amines serotonin, histamine, and dopamine, caused the elevation of cAMP content and intensified the rate of cAMP-dependent protein phosphorylation in tissues of animals following intraperitoneal injection at radioprotective doses. Biogenic amines stimulated the adenylate cyclase activity in membrane preparations from liver, spleen, and small-intestine mucosa; sulphur-containing radioprotectors caused no such effects. None of the radioprotectors affected cAMP and cGMP phosphodiesterases in vitro. AET and MEA inhibited guanylate cyclase in vitro, whereas serotonin and dopamine stimulated the enzyme. A biphasic change in the level of cGMP was observed in tissues after the administration of MEA and AET (more than 2-fold fall by 1–3 min after the administration of drug and 1.4-fold rise after 15–20 min); serotonin and dopamine caused a slow rise in the cGMP level; the cAMP/cGMP ratio in liver showed biphasic changes in level during the 20 min following injection of serotonin.The data obtained support the conclusion that the action of radioprotectors on cellular metabolism in animals may be mediated by the cAMP system. The reciprocal regulation of radioresistance by cAMP and cGMP is unlikely to exist.     

Effect of agents for the chemical prevention of radiation sickness on the cyclic nucleotide content in the bone marrow of mice

The effect of different chemical compounds on the cAMP/cGMP ratio in the bone marrow of mice and radioresistance of animals has been studied. It has been shown that all compounds possessing radioprotective properties give rise to the cAMP/cGMP ratio in the bone marrow of mice. No changes in cAMP and cGMP level were noted after the administration of nonradioprotective substances. The maximal radioprotective effect coincide in time with the largest increase of the cAMP/cGMP ratio. The injection of radioprotectors at different doses demonstrate clearly that only at radioprotective doses the increase in the cAMP/cGMP ratio takes place. The administration of some substances 2, 15 and 60 min after the irradiation of mice shows that the radioprotective effect, though modest, was evident only in one case of elevated cAMP/cGMP ratio (the injection of 2-Mercaptoethylamine 2 min after the irradiation). Evident radioprotective effect occurs at the cAMP/cGMP ratio of about 170-200%; the ratio of about 130-140% corresponds to small radioprotection.     

Changes of gastric mucosal biochemistry in ethanol-treated rats with and without acute surgical vagotomy

The biochemical background of ethanol-(ETOH) induced gastric mucosal damage was studied in rats with intact vagus and after acute surgical vagotomy. Observations were carried out on Sprague-Dawley (CFY) strain rats of both sexes. Gastric mucosal lesions were produced by intragastric administration of 1 ml 96% ethanol. Bilateral truncal surgical vagotomy was carried out 30 min before ETOH administration. The number and severity of gastric mucosal lesions was noted 1 h after ETOH administration. Biochemical measurements (gastric mucosal level of ATP, ADP, AMP, cAMP and lactate) were carried out from the total homogenized gastric mucosa. The adenylate pool (ATP + ADP + AMP), energy charge ((ATP + 0.5 ADP)/(ATP + ADP + AMP)) and ratio of ATP/ADP were calculated. It was found that: 1) ATP transformation into ADP increased, while ATP transformation in cAMP decreased in ethanol-treated animals with intact vagus nerve, while these transformations were quite the opposite in vagotomized animals; 2) no significant changes were found in the tissue level of lactate: and 3) the extent of biochemical changes was significantly less after surgical vagotomy. It is concluded that an intact vagus is basically necessary for the metabolic adaptation of gastric mucosa.     

Decrease in cAMP levels and increase in cGMP levels in the small intestine mucosa after treatment with fluoride

Sodium fluoride was studied for its effect on the cAMP and cGMP amount in the small intestine mucosa of rats under conditions of acute and chronic experiments. A significant decrease in the cAMP level and an increase in the cGMP level were revealed in both cases. Changes in the content of cyclic nucleotides were followed by marked changes in their physiologically important ratios.     

The role of the adenylate cyclase system in the inhibition of gastric secretion by products of limited hydrolysis of kappa-casein

The influence of the peptide inhibiting gastric acid secretion and derived from kappa-casein on the levels of cAMP, cGMP and adenylate cyclase activity of rat gastric mucosa was studied. Intravenous peptide preparation administration failed to alter cyclic nucleotide levels. The revealed decrease of adenylate cyclase activity was due to the presence of calcium in the investigated peptide preparation. It was assumed that cyclase system of the rat gastric mucosa cells were not involved in the inhibition of gastric acid secretion by the peptide preparations under study.     

Local changes in fractional saturation of cGMP- and cAMP-receptors in intestinal microvilli in response to cholera toxin and heat-stable Escherichia coli toxin

Cyclic nucleotide modulation of electrolyte transport across intestinal brushborder membranes is initiated by binding of cGMP and cAMP to high-affinity receptors at the interior of the microvilli. Previously these receptors have been identified by photoaffinity-labelling techniques as regulatory domains of cGMP- and cAMP-dependent protein kinases. In the present study, the receptor concentration in isolated brushborder membrane vesicles and their fractional saturation in absorptive and secretory states of the tissue were estimated. In microvillous membrane vesicles isolated from rat small intestine in the absorptive state, about 10% of the total number of cGMP receptors (25.5 pmol/mg protein) and 40% of all cAMP receptors (28.7 pmol/mg protein) were occupied by endogenous cyclic nucleotides. Luminal exposure of the intestinal segments in vivo to heat-stable Escherichia coli toxin for 3-5 min increased the occupancy of cGMP receptors by about 5-fold without affecting receptor-bound cAMP levels. In contrast, incubation with cholera toxin for 2 h increased the fractional saturation solely of cAMP receptors by 2-fold. Addition of heat-stable E. coli toxin to cholera toxin-pretreated segments, again raising the cGMP levels by 5-fold, did not reduce the amount of receptor-bound cAMP. This finding argues against the concept that increased levels of cAMP during cholera would mimick cGMP effects on ion transport by low-affinity binding to microvillar cGMP receptors. This analysis of local changes in cyclic nucleotide levels at the microvillous level might help to explore the mechanism of action of other secretagogues or antidiarrhoeal agents and to delineate a possible compartmentation of cGMP and cAMP pools within the intestinal mucosa responding differently to external signals.     

Prostacyclin-induced activation of 3'-5'-cyclic adenosine monophosphate-dependent protein kinase in rat antral and fundic gastric mucosa.

The present investigations showed that after oral prostacyclin administration (100 micrograms/kg) as soon as the intracellular level of cAMP is elevated the activation of cAMP-dependent protein kinase follows in both parts (antrum and fundus) of rat gastric mucosa. The enzyme activation seems to be more significant in the fundic region which is in a complete agreement with the previously published results, i.e. the fundic mucosa reacts with de novo protein synthesis toward noxious agents (resulting finally in new cell formation), while the antral mucosa is more durable against damaging noxae. Taking into consideration all available data in the literature it seems that the intracellular effect of the exogenously administered prostacyclin in the gastric mucosa is a polyphasic effect, which contains the following consecutive steps: 1. Binding to the cell surface; 2. Effect on the intracellular second messenger system, (cAMP, cGMP); 3. Activation of the calmodulin system; 4. cAMP-dependent protein kinase activation; 5. DNA, RNA changes; 6. Influence on protein synthesis, and finally; 7. New cell formation.     

氨甲酰胆碱(Carbamylcholine)对大鼠缺血心室致颤阈值的影响及其与cAMP、cGMP的关系

本实验以心室颤动阈(VFT)作为心室易颤性的指标,观察胆碱类物质氨甲酰胆碱对大鼠缺血心室 VFT 的影响及其与心肌 cAMP 和 cGMP 水平的关系。实验结果表明,氨甲酰胆碱可提高正常心脏和急性局部缺血心脏的 VFT,提高缺血和未缺血心肌的 cGMP 水平,但明显降低缺血心肌 cAMP 水平,使缺血和未缺血心肌的 cAMP/cGMP 比值显著降低,其作用与肾上腺素正好相反。实验结果还表明,急性局部缺血心脏的 VFT 与缺血心肌 cAMP/cGMP 比值之间有密切的负相关关系,相关系数 r=-0.905(n=22,P<0.001)。上述结果提示缺血心肌 cAMP/cGMP 比值的提高可能是急性心肌梗塞早期发生心室纤维性颤动的重要因素。     

Cyclic nucleotide metabolism in mouse epididymal spermatozoa during capacitation in vitro

The role of cyclic nucleotides in sperm capacitation is equivocal. Using conditions known to support mouse sperm capacitation after 120 min incubation in vitro, the cAMP and cGMP contents of epididymal spermatozoa were measured and the cGMP/cAMP ratio determined. The initial high cAMP content detected upon release of spermatozoa decreased within 30 min to a lower plateau, which was then maintained throughout incubation. With the cGMP content remaining approximately constant, the cGMP/cAMP ratio increased over 120 min. In the presence of 2 mM caffeine, an increased cAMP content was noted at 0 and 30 min before a fall to the plateau level. To investigate cyclic nucleotide metabolism, adenylate cyclase and phosphodiesterase activities were compared in two sperm populations, one essentially uncapacitated and the other incubated for 120 min. Adenylate cyclase activity, higher in the presence of 2 mM Mn²⁺ compared to Mg²⁺, showed increased activity at 120 min compared to 30 min incubation, while phosphodiesterase activity decreased during this period. The ability of spermatozoa to form adenosine and inosine from cAMP indicated endogenous 5′-nucleotidase and deaminase, as well as phosphodiesterase, activities. Although the endogenous cAMP content appeared to remain constant during the time that acrosome loss, hyperactivated motility and fertilizing ability can be demonstrated, activities of the enzymes responsible for cAMP metabolism indicate an increased potential for cAMP availability and turnover. The increased cGMP/cAMP ratio may also play a role during capacitation.     

Effect of phosphaden and unithiol on the cyclase system of the small intestine mucosa in rabbits in experimental salmonellosis

The study was made on 59 chinchilla rabbits. S. typhimurium 1847 live culture was introduced into the lumen of an isolated loop of the thin intestine. The activity of adenylate cyclase (AC), guanylate cyclase (GC), the levels of cyclic adenosine 3,5-monophosphate (cAMP), cyclic guanosine 3,5-monophosphate (cGMP), the activity of cAMP- and cGMP-phosphodiesterases were determined in the mucous membrane of the ligated part of the intestine. Considerable fluid accumulation in the loop, activation of AC and cGMP-phosphodiesterase, a rise in the level of cAMP and a drop in the level of cGMP in the mucosa of the ligated part of the intestine were registered. In one group of the animals phosphadene and in the other group unitiol were introduced into the infected intestinal loop; as a result, a decrease in the accumulation of fluid in the loop, on the average, by 40% and a tendency to an increase in the level of cAMP and a drop in the level of cGMP in the mucous membrane of the ligated part of the intestine were observed. Changes in the level of cGMP play, seemingly, a more important role in the development of diarrhea in salmonellosis.     

Cyclic nucleotides and lipids in the realization of the radioprotective effect of ceruloplasmin

Ceruloplasmin administered 60 min before irradiation diminished cAMP and cGMP levels, which were increased by irradiation at LD50 and LD100, and normalized cAMP/cGMP ratio in the rat liver during the first 24 h following irradiation with a dose of 6.24 Gy. The content of phospholipids increased and that of cholesterol decreased under the effect of ceruloplasmin leading to normalization of the molar cholesterol/phospholipid ratio in the rat liver on the 7th day of radiation sickness (LD50, 6.24 Gy).     

Acid hydrolase activity and cyclic nucleotide contents in the rat heart during myocardial ischemia and postischemic reperfusion

The acid phosphatase and cathepsin D activities and cAMP and cGMP levels in isolated perfused rat heart were investigated during various periods of ischaemic myocardial injury and postischaemic reperfusion. The effect of phosphodiesterase inhibitor--caffeine was also studied. Free acid hydrolases activities and cyclic nucleotide content were increased under 40 and 60 min ischemia and 20 min postischaemic reperfusion. Addition of 50 microM caffeine to perfusion solution after 30 min of ischaemia resulted in increase of cAMP level, cAMP/cGMP ratio, lysosomal bound activities of acid hydrolase and decrease of free acid hydrolase activities. The obtained results suggested that defect in cAMP synthesis might be present in lysosomal membranes labilization in cardiomyocytes injured during ischaemic conditions. Addition of such agents, as caffeine, which increased heart cAMP level, may be effective in lysosomal membranes stabilization under reversible heart ischaemia and reperfusion.     

The differentiation of human gastric adenocarcinoma cell line MGc80-3 induced by dibutyryl cAMP in vitro

For providing some experimental basis in establishing malignant phenotypic reversed indexes of gastric carcinoma cells, human gastric adenocarcinoma cell line MGc-80-3 was induced by dBcAMP in vitro to appraise the effect of gastric carcinoma cell differentiation by chemical inducers. Under light microscope, MGc 80-3 cells, after treated with 1 mM dBcAMP, tended to be flat and disperse, and their volume gradually enlarged, with their nucleus relatively smaller and their shape rather regular. Morphological changes, became like normal differentiated epithelial cells, were observed. The cells attached firmly, grew slowly, their growth curve showed inhibitory rate amounted to 52.87%, and cellular division exponent displayed their peak value 1.5 times less than that of MGc 80-3 cells. It was clear that dBcAMP could effectively inhibit the multiplication activity of MGc-80-3 cells. In the cells after dBcAMP treatment, remarkable changes of cell surface charges was indicated by cell electrophoresis, the ratio dropped to 3.043 from 3.988, and their retardant ratio reached up to 31.2%. cAMP content in cells after this treatment, detected by cAMP and cGMP radioimmunoassay, was enhanced by 2.42 times; and cAMP/cGMP ratio, by 1.73 times. Thus, cAMP level within MGc 80-3 cells was raised obviously by dBcAMP. Heterotransplantation experiments showed that tumoriferous rate of MGc 80-3 cells (transplanted subcutaneously to BABL/c mice) amounted to 100%, and that of the cells after this treatment was only 5.6%. Their tumorigenic ability was extremely reduced. These results fully confirmed that dBcAMP was able to change MGc 80-3 cell's malignant phenotypic characteristics and produce a reversed alteration; thus, it has a remarkable inductive effect in differentiating gastric carcinoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of endogenous and exogenous prostacyclin in the gastric mucosa under physiological and pathological circumstances

The intracellular effect of exogenously administered prostacyclin in the gastric mucosa seems to be a polyphasic effect, namely: 1. Effect on the cyclic nucleotide (cAMP, cGMP), turnover; 2. Effect on the calmodulin-content; 3. DNA and RNA changes; 4. Influence on protein synthesis; 5. New cell formation. While the endogenous prostacyclin exerts a natural protection against damaging noxae.     

Cyclic nucleotide content and protein phosphorylation during maturation of Spisula oocytes

Cyclic nucleotide levels in the oocytes of the surf clam Spisula solidissima were measured during germinal vesicle breakdown (GVBD) induced by fertilization. The level of cAMP and cGMP in untreated oocytes was 8.23 ± 0.95 and 4.89 ± 0.39 pmol/10⁶ oocytes. The ratio of cAMP to cGMP ranged from 1.5 to 2.0. The cAMP level in Spisula oocytes fluctuated after fertilization and before GVBD. The cGMP level showed minimal fluctuation, with a tendency to decrease initially followed by a subsequent rise to the basal level in a nonsynchronous manner. These changes were not statistically significant. There was a general increase in protein phosphorylation during the period after fertilization and before GVBD. The greatest increase occurred with proteins of estimated molecular weights of 52, 18, and 12 kD, analyzed by gel electrophoresis and autoradiography.     

Cellular energy systems and reserpine ulcer in rats

Gastric ulcer was elicited in rats by reserpine (5 mg x kg-1 sc.) administration. Ulcer formation (number and severity) was measured 6, 12, 18 and 24 hr after reserpine administration. At the time of killing of the animals, tissue levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), cyclic adenosine monophosphate (cAMP) were measured enzymatically and by radioimmunoassay in the gastric fundal mucosa. The sum of ATP + ADP + AMP (adenylate pool) and the ratio of ATP x ADP-1 were calculated. It was found that (1) the tissue levels of ATP, AMP, cAMP, sum of ATP / ADP + AMP (adenylate pool) and ratio of ATP x ADP-1 increased significantly in the gastric fundal mucosa 6 hr after reserpine administration, thereafter these values decreased gradually and significantly; (2) the tissue level of ADP increased significantly in the gastric fundal mucosa 6 hr after reserpine administration, meanwhile its level increased significantly at 18 and 24 hr; (3) the value of energy charge (ATP + 0.5 ADP x ATP + ADP + AMP-1) remained unchanged; (4) the peaks of biochemical alterations in the gastric fundus mucosa preceded he appearance of ulcers. It was concluded that (1) reserpine ulcer appears after an active metabolic response in the rat gastric fundal mucosa; (2) hypoxaemic damage in the gastric fundal mucosa can be excluded as a possible underlying mechanism of ulcer formation produced by reserpine administration; (3) before the appearance of reserpine ulcer, significant changes in the feedback mechanism, system, i.e. between the ATP--membrane ATPase--ADP and the ATP--adenylate cyclase--cAMP energy systems, can be observed in the rat gastric fundal mucosa.     

Enhancement of gastric mucosal integrity by Lactobacillus rhamnosus GG

The gastric mucosa is frequently exposed to different exogenous and endogenous ulcerative agents. Alcoholism is one of the risk factors for the development of mucosal damage in the stomach. This study aimed to assess if a probiotic strain Lactobacillus rhamnosus GG (LGG) is capable of protecting the gastric mucosa from acute damage induced by intragastric administration of ethanol. Pre-treatment of rats with LGG at 10(9) cfu/ml twice daily for three consecutive days markedly reduced ethanol-induced mucosal lesion area by 45%. LGG pre-treatment also significantly increased the basal mucosal prostaglandin E(2) (PGE(2)) level. In addition, LGG attenuated the suppressive actions of ethanol on mucus-secreting layer and transmucosal resistance and reduced cellular apoptosis in the gastric mucosa. It is suggested that the protective action of LGG on ethanol-induced gastric mucosal lesions is likely attributed to the up-regulation of PGE(2), which could stimulate the mucus secretion and increase the transmucosal resistance in the gastric mucosa. All these would protect mucosal cells from apoptosis in the stomach.