Interaction between prostacyclin and colchicine on the gastric mucosa of rat in different experimental ulcer models

The effect of prostacyclin and colchicine on the fundic gastric mucosa of adult female Wistar rats was investigated in stress (immobilization) and indomethacin induced ulcer models. Under prostacyclin treatment the ulcer index decreased significantly in both ulcer models. This effect was inhibited by colchicine. The nuclear volume of fundic epithelial cells increased significantly after application of either type of ulcerogenic stimulus. Prostacyclin did not influence the nuclear volume changes in stress ulcer, while it prevented this phenomenon in indomethacin-induced ulceration. Following colchicine treatment the nuclear volume decreased in both ulcer models. After combined prostacyclin and colchicine treatment the nuclear shrinkage remained unaltered in stress ulcer, while in indomethacin ulcer the nuclear volume decreasing effect of the separately administered drugs disappeared after combined treatment. The latter phenomenon was interpreted as an antagonistic interaction between prostacyclin and colchicine.     

The effect of graded single oral doses of prostacyclin on the nucleic acid content of rat gastric mucosa.

Graded single oral doses of prostacyclin significantly enhance in dose-dependent manner the DNA and RNA content of rat gastric fundic mucosa, - resulting in a decreased RNA/DNA ratio. This latter phenomenon is convincing sign of new cell formation. In the antral region no significant changes could be encountered but the RNA content showed a tendency-like elevation, evoking an elevated RNA/DNA ratio, which corresponds to de novo protein synthesis. The diversity of the noted changes gives further evidence to the tenet the antral and the fundic gastric mucosa of the rat reacts differently toward external stimuli.     

Effect of diacarb on the carbonic anhydrase activity in the blood and gastric mucosa and pepsinogen concentration in the gastric mucosa of the rat

It was established that the activity of blood and gastric mucosa carboanhydrase increased after the introduction of food irritant (milk) into the stomach, as well as after the subcutaneous injection of histamine. This was accompanied by the increase of pepsinogen content in the gastric mucosa. When introduced into the stomach before the food irritant or histamine, acetazolamide inhibited blood and gastric mucosa carboanhydrase and reduced the content of pepsinogen in the gastric mucosa. Oral administration of acetazolamide for 5 days resulted in a more remarkable inhibition of blood and gastric mucosa carboanhydrase and in a drastically reduced content of pepsinogen in the gastric mucosa. The rate of pepsinogen biosynthesis by the gastric mucosa seems to depend on the activity of carboanhydrase in blood and in the gastric mucosa.     

Effect of ebrotidine on the density of antral G-cells in the gastric mucosa in the rat

Two groups of male rats were treated orally for 60 days with ebrotidine and cimetidine, used as reference standard, respectively. The dose used of both drugs was 500mg/kg. A third group, used as control, received 10 ml/kg of an aqueous agar suspension. After receiving the last dose, the animals were killed by inhalation of CO₂ in a sealed chamber and the stomachs were removed for histological preparation. The purpose of this study was to count antral G-cells throughout the gastric mucosa by light microscope. A PAP system-associated antigastrin immunohistochemical method was used for cell identification. Cell density, with respect to their location in the gastric mucosa and the treatments given, was calculated using image analysis techniques. The results showed that ebrotidine did not cause any significant differences in the density of the population of these cells compared with the control group, while cimetidine induced a significant proliferation of antral G-cells.     

Phosphorylation of membranes from the rat gastric mucosa

Gastric mucosal membranes derived primarily from parietal cells were found to contain endogenous protein kinase systems as well as several phosphate-accepting substrates. One specific membrane protein with a molecular weight of 88 000 was phosphorylated only in the presence of calcium, while the degree of phosphorylation of three other membrane proteins was similarly increased. The activity of the calcium-dependent protein kinase was found to be totally inhibited in the presence of trifluoperazine, a phenothiazine known to specifically inactivate calmodulin. These results suggest that a calmodulin- and calcium-dependent phosphorylation system may be a component of the parietal cell membrane. Phosphorylation of the membrane proteins was not affected by either cyclic AMP or cyclic GMP. The heat-stable inhibitor protein of cyclic AMP-dependent protein kinase did not inhibit the endogenous protein kinase activity suggesting that the membrane enzyme is not similar to the cytosolic protein kinase. However, the catalytic subunit of the soluble enzyme was capable of phosphorylating a number of membrane proteins indicating that after maximal autophosphorylation of the gastric membranes, phosphate-acceptor sites are still available to the cytosolic cyclic AMP-dependent protein kinase.     

Effect of paracetamol on gastric mucosa.

The effect of paracetamol on the gastric mucosa was examined in seven healthy volunteers. The dose used (2 g instilled in 100 ml isotonic saline) was equivalent to about six tablets taken with water. Biopsy specimens were taken before and 10 and 60 minutes after instillation. The mean incidence of damaged surface cells in the control period was 1.7%. Ten minutes after instillation 3.5% of the surface cells were damaged. This increase was not significant. Light microscopy showed focal cell disruption and infiltration of red blood cells. Scanning electronmicroscopy showed minimal loss of normal cell apices. No erosions were seen on microscopy. Biopsy specimens taken 60 minutes after paracetamol showed similar changes. These findings differ appreciably from the extensive cell damage and microscopic erosions caused by therapeutic doses of 600 mg (two tablets) of aspirin. We conclude that large "analgesic" doses of paracetamol cause minimal ultrastructural changes in normal human gastric mucosa. The continued use of paracetamol in place of aspirin appears to be justified when there is a possibility of gastric mucosal injury.     

细胞更新对慢性饮酒大鼠胃黏膜适应性细胞保护的影响

目的: 以低浓度酒精作为弱刺激,通过慢性饮酒的大鼠动物模型,探讨慢性饮酒和大鼠胃粘膜适应性细胞保护作用之间的关系,以及胃粘膜细胞更新的作用.方法: 分别在饮酒不同时程的大鼠胃内灌注2 ml 100%酒精,分析胃粘膜的损伤情况.以流式细胞术、免疫组化和计算机图像处理技术观察大鼠胃粘膜的细胞增殖和凋亡,探讨胃粘膜的细胞更新情况.结果: ①纯酒精可使大鼠的胃体和胃窦出现溃疡和出血,饮用6%(v/v)酒精3～14 d的大鼠这种现象明显减轻,饮用6%(v/v)酒精1 d和28 d的大鼠则无改变.②饮用6%(v/v)酒精3～14 d的大鼠胃粘膜细胞更新加快,而饮酒28 d大鼠胃粘膜细胞凋亡增加,细胞增殖减少.结论: 细胞更新加快是适度低浓度酒精刺激引起的胃粘膜适应性细胞保护作用的重要原因,低浓度酒精刺激超过一定时限可引起胃粘膜萎缩性病变的趋势,使胃粘膜抵抗能力降低.     

Consequences of long-term selenium-deficient diet on the prostacyclin and thromboxane release from rat aorta

It is known that peroxides, which are increased during Se deficiency because of reduced glutathione peroxidase (GSH-Px) activity, can influence the prostacyclin I₂/thromboxane A₂ (PGI₂/TXA₂) ratio. In this study we analyzed the PGI₂ and TXA₂ formation of aortas of long-term Se-deficient rats. Despite low GSH-Px activity in the Se-deficient group, the basal PGI₂ and TXA₂ formation was not different versus control animals (PGI₂: 2295 ± 1134 pg/mg vs 2940 ± 1134 pg/mg; TXA₂: 3.83 ± 1.06 pg/mg vs 5.67 ± 2.99 pg/mg). However, we checked the capacity of the aortas of Se-deficient rats to compensate for a suddenly increased peroxide concentration. After peroxide stimulation, the PGI₂ release was significantly lower in the Se-deficient group compared to the control group (PGI₂: 3507 ± 1829 pg/mg vs 7986 ± 2636 pg/mg). Again, the TXA₂ release did not show any differences. The release ratio of PGI₂/TXA₂ decreased under peroxide stress in Se-deficient animals. Although long-term Se deficiency showed a relatively well-balanced metabolism under resting conditions, sudden stress, accompanied by an excessive radical production, cannot be compensated.     

Transcytosis of gastric leptin through the rat duodenal mucosa

Leptin is secreted into the gastric juice by epithelial Chief cells and reaches the duodenum in a biologically intact active form. We assessed the possibility that this gastric leptin crosses the intestinal mucosa by transcytosis through enterocytes to reach blood circulation. Endogenous gastric leptin secretion was triggered by cholinergic stimulation. In another set of experiments, recombinant leptin was inserted in vivo into the duodenal lumen. Plasma levels of leptin were assessed by enzyme immunoassay and Western blot, and duodenal tissue was processed for immunocytochemistry. We first observed that leptin was found inside duodenal enterocytes from fed rats but not inside those from fasted ones. Stimulation of gastric secretion by a cholinergic agent led to rapid increases in plasma leptin levels (202 +/- 39%) except when the pylorus was clamped. Insertion of recombinant leptin into the duodenal lumen raised plasma leptin concentrations (558 +/- 34%) quite rapidly, whereas carrier solution without leptin had no effect. The use of FITC-tagged leptin reinforced these results. Light and electron microscopy revealed the cellular compartments involved in its transcytosis, namely, the enterocyte microvilli, the endocytotic vesicles, the Golgi complex, and the basolateral interdigitations. Leptin was also present in the lamina propria, in capillary endothelial cell plasmalemmal vesicles, and in capillary lumina. These results demonstrate that gastric exocrine leptin is internalized by duodenal enterocytes and delivered to the lamina propria and blood circulation. It may thus be able to play important paracrine and endocrine functions for the control of gastric emptying and nutrient absorption.     

Muscarinic acetylcholine receptors in rat gastric mucosa

Summary The muscarinic cholinergic innervation of the rat gastric mucosa was investigated by localizing the muscarinic receptors using a tritiated muscarinic antagonist, pirenzepine. Radioautography was performed by freeze drying stomach tissue, which was then embedded in Epon and wet sectioned with ethylene glycol, and dry mounting on emulsion film by the wire-loop method to prevent loss of the labelled substance during fixation and the radioautographic procedure. Light and electron microscopy showed that the specific pirenzepine-binding sites were localized predominantly on parietal cells, chief cells and perivascular plexuses. Analysis of the grain distribution on parietal cells revealed that the silver grains corresponding to the pirenzepine-binding sites were mainly on the basolateral plasma membrane. On the other hand, the surface mucous or mucous neck cells had few pirenzepine-binding sites.     

Luminal amino acid sensing in the rat gastric mucosa

Recent advancements in molecular biology in the field of taste perception in the oral cavity have raised the possibility for ingested nutrients to be "tasted" in the upper gastrointestinal tract. The purpose of this study was to identify the existence of a nutrient-sensing system by the vagus in the rat stomach. Afferent fibers of the gastric branch increased their firing rate solely with the intragastric application of the amino acid glutamate. Other amino acids failed to have the same effect. This response to glutamate was blocked by the depletion of serotonin (5-HT) and inhibition of serotonin receptor(3) (5-HT(3)) or nitric oxide (NO) synthase enzyme. Luminal perfusion with the local anesthesia lidocaine abolished the glutamate-evoked afferent activation. The afferent response was also mimicked by luminal perfusion with a NO donor, sodium nitroprusside. In addition, the NO donor-induced afferent activation was abolished by 5-HT(3) blockade as well. Altogether, these results strongly suggest the existence of a sensing system for glutamate in the rat gastric mucosa. Thus luminal glutamate would enhance the electrophysiological firing rate of afferent fibers from the vagus nerve of the stomach through the production of mucosal bioactive substances such as NO and 5-HT. Assuming there is a universal coexistence of free glutamate with dietary protein, a glutamate-sensing system in the stomach could contribute to the gastric phase of protein digestion.     

Histochemical findings in the rat gastric mucosa during starvation

Summary The influence of starving on the activity of enzymes of the rat gastric mucosa was investigated by selected histochemical methods. Beside the conventional methods of enzymatic histochemistry the technique of semipermeable membranes was used in the proof of lysosomal enzymes. Dehydrogenases were proved in aqueous and also in gel media with PMS.During the starvation in the parietal cells a marked increase took place in the activity of acid phosphatase, E-600 resistant esterase, less in -glucuronidase. High activity of the lysosomal enzymes in macrophages did not change during starvation. Nor did any changes took place in the activity of alkaline phosphatase in the endothelium of the capillaries. The chief cells in the control and starving animals, in contrast to the human gastric mucosa, did not contain any non-specific esterase. Concerning dehydrogenase, parietal cells with a different activity of these enzymes were observed both in starved and control animals.In the rat gastric mucosa starving induced changes in the activity of the enzymes which mark important organelles of the cells. Thus it is possible to consider the observed histochemical changes as a functional manifestation of morphological damage of cellular structures which are affected during starvation.     

Effects of alcohol on laminin in rat gastric mucosa.

Following ethanol exposure, the gastric surface epithelium often exfoliates, leaving a denuded basal lamina. Viable cells from the gland migrate along the basal lamina to repair the defect, a process known as restitution. Laminin, the major non-collagenous glycoprotein of basal laminae, functions in cellular adhesion and migration and, therefore, any alteration of this molecule by ethanol may influence subsequent restitution. After a 5 or 60 minutes treatment with saline, 50% or 100% ethanol, gastric tissues were removed from fasted female Sprague-Dawley rats, fixed in 1% paraformaldehyde and processed in Lowicryl. Once embedded and sectioned, specimens were incubated in anti-laminin followed by protein A-gold. The area of lamina densa from interfoveolar, pit and gland regions was measured and gold particles counted. Absolute ethanol caused diminished immunogold binding in all regions at all time periods, except the gland at 60 minutes. Exposure to 50% ethanol for 5 minutes did not alter laminin binding, although 60 minutes after 50% alcohol, laminin immunolabelling was increased. Alcohol concentration alters laminin immunogold binding, and therefore may influence restitution.