On the synthesis of prostaglandins by human gastric mucosa and its modification by drugs.

1. Specific radioimmunoassays for the prostaglandins E2, A2 and F2alpha were used to study the synthesis of prostaglandins by gastroscopically obtained small biopsy specimens of human gastric corpus mucosa. 2. Both prostaglandin E2 and prostaglandin F2alpha were found to be synthesized from arachidonic acid by themicrosomal fraction of human gastric mucosa. The synthesis of prostaglandin E2 exceeded that of prostagladin F2alpha by a factor of about 10. 3. Synthesis of prostaglandin A2 or prostaglandin B2 was not observed under the same incubation conditions. 4. Indometacin effectively inhibited synthesis of both prostaglandin E2 (ID50 4.2 microng/ml) and prostaglandin F2alpha (ID50 1.8 microng/ml) by human gastric mucosa, while paracetamol even in a concentration of 310 microng/ml did not influence prostaglandin synthesis. The anti-ulcer agent carbenoxolone, which has been shown to inhibit prostaglandin inactivation, at the same concentration only slightly inhibited (about 20%) prostaglandin synthesis. 5. The results support the hypothesis that the gastro-intestinal effects or side effects of several drugs are mediated by an influence on the enzymes of prostaglandin synthesis or inactivation.     

Biosynthesis of proteins by human gastric mucosa in vitro.

Incorporation of L-[U-14C]leucine and of D[U-14C]glucose into proteins of fresh human gastric mucosa in vitro was studied after incubation of homogenized tissue and of intact mucosal pieces. CsCl centrifugation was used to separate high-density mucus glycoproteins from other mucosal proteins, and the macromolecular nature of radioactive mucosal glycoprotein fractions was confirmed by SDS/polyacrylamide-gel electrophoresis and autoradiography of the polyacrylamide gels. In all experiments a substantial proportion of total incorporated radioactivity was associated with gastric-mucosal glycoprotein fractions (CsCl fraction L3), indicating their biosynthesis. Radioactivity of these fractions was shown to co-chromatograph with carbohydrates when fractionated either directly or after reduction and alkylation (1) Sephadex G-200 chromatography in the excluded fractions and (2) by DEAE-cellulose ion-exchange chromatography. On incubation of intact mucosa, the major portion of radioactivity associated with the glycoprotein fractions of both leucine- and glucose-labelled specimens was secreted into the mucosal media during the course of the experiment. It is suggested that biosynthesis of mucus in vivo by gastric mucosa may be associated with rapid secretion of the synthesized macromolecules into the lumen of the stomach and that investigations of the metabolic processes within the mucosa should consider the products of secretion of the tissue. Incorporation of L-[U-14C]leucine implies biosynthesis of the polypeptide components of the macromolecules.     

Interaction between prostaglandins and cyclic amp in the gastric mucosa

Possible mechanisms accounting for the inhibition of acid secretion by prostaglandins were studied using cells dispersed from canine fundic mucosa by enzymes and enriched in the content of parietal cells by elutriation. The accumulation of ¹⁴C-aminopyrine (AP) was used as an index of parietal cell response to stimulation. PGE₂ inhibited histamine-stimulated AP uptake, with 50% inhibition (ID₅₀) found at 10 nM, but did not block the response to carbachol, gastrin, or dibuturyl cyclic AMP. PGE₂ did, however, inhibit aminopyrine uptake stimulated by carbachol and gastrin when the response to these agents was potentiated by histamine. PGE₂, at namomolar concentrations, also inhibited histamine-stimulated cyclic AMP production. When mucosal cells were treated with only PGE₂ at concentrations above 1 μM, stimulation of cyclic AMP production was found. In cell separation studies with the elutriator rotor, PGE₂ appeared to stimulate cyclic AMP production primarily in nonparietal cells.Prostacyclin (PGI₂) and two stable analogues, 6_β-PGI₁ and the 16-phenoxy analogue (5_α)5,9-epoxy-16-phenoxy-PGF₁, also specifically inhibited histamine-stimulated AP accumulation. PGI₂ required relatively high concentrations for this effect (ID₅₀ = 1 μM), whereas the 16 phenoxy derivative was much more potent in its inhibition of histamine-stimualted AP accumulation (ID₅₀ = 10 nM), with this difference probably accounted for by the rapid degradation of PGI₂ compared to the stable 16-phenoxy analogue. All three of these prostanoids also inhibited histamine-stimulated cyclic AMP production. As was found with PGE₂, at high concentrations and in the absence of histamine PGI₂ and PGI₁ also stimulated cyclic AMP production. However, the 16-phenoxy analogue failed to stimulate cyclic AMP production either in the parietal cell enriched fractions or in the nonparietal cell fractions.These data indicate that PGE₂ and prostacyclin analogues are potent, direct and specific inhibitors of histamine-stimulated parietal cell function and that it is the inhibition, rather than the stimulation, of cyclic AMP formation that is linked to the antisecretory actions of the prostanoid compounds.     

A-like cells of the gastric mucosa as a possible source of prostaglandins

AL cells of the oxyntic stomach area were studied in rats using ultrastructurometric technique. High-threshold, short-term direct electrical vagostimulation (5 V, 4 msec, 30 Hz, 10 sec) was performed in experimental group of 12 animals. Animals were killed 1, 10 and 30 min after stimulation. High post-stimulation lipolytic activity of AL cells and intensification of "granule autophagy" phenomenon were noted. Our findings as well as the literature data suggest a hypothesis on possible prostaglandin production by AL cells. Direct evidence in favour of this hypothesis is difficult to obtain due to the lack of sufficiently reliable methods of their morphological detection in cells.     

A neutral collagenase from human gastric mucosa.

Biopsy specimens of human gastric mucosa, maintained in culture for 7 days in the absence of serum, released a collagen-degrading enzyme into the medium. The yield of active enzyme reached a maximum after 2-3 days, and viable tissue, capable of protein synthesis, was essential for its production. 2. At 25 degrees C the enzyme attacked undenatured collagen in solution, resulting in a 55% loss of specific viscosity and producing the two products TCA and TCB characteristic of neutral-collagenase action. 3. Electron microscopy of segment-long-spacing crystallites of these reaction products showed the exact cleavage locus of the collagen molecules to be between bands 43 and 44 (I-43). The larger TCA and smaller TCB products were fragments representing 77 and 23% respectively of the length of the collagen molecule. 4. Optimal enzyme activity was observed over the pH range 7.5-8.5 and a mol.wt. of approx. 38000 was derived from gel-filtration studies. 5. The enzyme was shown to be inhibited by the human serum proteins alpha2-macroglobulin and a smaller component of mol.wt. approx. 40000; alpha1-anti-trypsin was not inhibitory. 6. EDTA, 1, 10-phenanthroline, cysteine and dithiothreitol all inhibited collagenase activity. 7. The gastric enzyme has properties similar to other well characterized collagenases, but differences exist with respect to its molecular size and the site of attack on the collagen molecule.     

Tauroursodeoxycholic acid reduces damaging effects of taurodeoxycholic acid on fundus gastric mucosa

We investigated the effects of tauroursodeoxycholic acid (TUDCA) to assess whether this acid may also have "protective" effects similar to those found with ursodeoxycholic acid (UDCA). We used a well-known amphibian model of gastric mucosa, and studied the effects of taurodeoxycholic acid (TDCA) on electrical transepithelial parameters, acid secretion and histology in absence or in presence of TUDCA. Mucosal exposure to TDCA, after stimulation with histamine, caused a reduction in transepithelial potential difference (V(t)) and transepithelial resistance (R(t)) and a decrease in acid secretion while mucosal exposure to TUDCA did not cause a significant change in the electrical parameters. Moreover, TDCA primarily affected the neck cells, while TUDCA affected only oxyntic cells, causing a similar degree of injury to that observed in controls. Mucosal exposure to TUDCA plus TDCA caused a reduction in short circuit current (I(sc)) and R(t), whereas acid secretion did not change. These results suggest that: (1) TUDCA reduces the damaging effects of TDCA on fundus gastric mucosa; (2) TUDCA may play an important role in the treatment of gastritis associated with bile reflux.     

Endocrine cells of the human gastric mucosa

Summary By light and electron microscopy investigation of the human gastric mucosa five types of ultrastructurally different endocrine cells have been detected: 5-hydroxytryptamine storing enterochromaffin (EC) cells, gastrin storing G cells, and functionally undefined ECL, D and D₁ cells. By direct application of Masson's argentaffin reaction as well as of Sevier-Munger's and Grimelius' argyrophil method to electron microscopy specimens, selective deposition of silver grains upon the endocrine granules of such cells was obtained. In particular, only EC cell granules reacted to the argentaffin method, granules of both EC and ECL cells heavily reacted to Sevier-Munger's technique, granules of EC, ECL, G and D₁ cells reacted to Grimelius' technique, while D cell granules failed to react either to argentaffin or argyrophil methods. By the application of the same silver methods to paraffin sections as well as by other selective staining methods for endocrine granules (5-hydroxytryptamine techniques, lead-haematoxylin, HCl-basic dye method), at least four of the above cell types were also identified under light microscope. This opens the way for extensive studies of such cells in conventional histologie specimens.This investigation was supported in part by grant N.70.01022.04 from the Italian Consiglio Nazionale delle Ricerche.     

Cannabinoid CB1 receptors are expressed by parietal cells of the human gastric mucosa.

Experimental data suggest that the endogenous cannabinoid system is involved in gastric function in different animal species. In most of them, CB(1) receptors have been localized on vagal terminals innervating the external wall of the stomach. We aimed at studying the putative presence and distribution of these receptors in the human gastric mucosa. To this end, we first performed Western blotting, RT-PCR, in situ hybridization, and immunohistochemical analysis of CB(1) protein distribution in biopsy samples of healthy individuals. To determine the precise cell populations expressing CB(1) receptors, we performed double immunofluorescence plus confocal microscopy analysis of the same samples. Our results show that CB(1) receptors are present in the gastric epithelium of the mucosa. Specifically, they are expressed by a subpopulation of mucosal cells, the acid-secreting parietal cells, as shown by double immunohistochemical staining and by their differential abundance in subregions of the gastric mucosa. These results reinforce the notion of a prominent role for the endocannabinoid system in the gastric function in humans and postulate the use of cannabinoid CB(1) receptors in parietal cells as new therapeutic targets for the regulation of gastric acid production.     

Progesterone metabolism in the gastric mucosa microsomes of guinea pig

The microsomes from guinea pig gastric mucosa were found to convert [4-14C]progesterone to two major metabolites in the presence of NADPH. The gastric metabolizing activity was the highest among the gastrointestinal tissues of guinea pig. 5 alpha-Pregnane-3,20-dione and 3 beta-hydroxy-5 alpha-pregnan-20-one were identified as the major metabolites by thin-layer chromatography and crystallization to constant specific activity, suggesting the presence of steroid 5 alpha-reductase and 3 beta-hydroxysteroid dehydrogenase activities in the gastric mucosa microsomes. Furthermore, time course of progesterone metabolism and analysis of 5 alpha-pregnane-3,20-dione metabolites suggest that the gastric progesterone metabolism is initiated by 5 alpha-reductase and followed by 3 beta-hydroxysteroid dehydrogenase. The progesterone-metabolizing activity was strongly inhibited by SKF 525-A and disulfiram. The activity was also inhibited by methyrapone to a somewhat lesser extent than the above inhibitors. From gastric mucosa microsomes, the progesterone-metabolizing activity was successfully solubilized with 2% digitonin using 0.1 M potassium chloride and 1 mM dithiothreitol, 0.4 mM NADPH and 20% glycerol as stabilizers for the solubilized activity. Among these stabilizers, glycerol was found to be most effective for stabilizing the activity of the solubilized microsomes.     

Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla

The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10⁻⁴ mol · l⁻¹) or aspirin (10⁻⁴ mol · l⁻¹) in different experimental conditions. Both the anti-inflammatory drugs produced ulcers, but the effects were more severe in the presence of histamine and in the absence of HCO₃ ⁻ in the incubation bath. The effects of prostaglandin E₂ (PGE₂) on acid secretion rate (J_H) and on alkaline secretion rate (J_OH) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that PGE₂ (10⁻⁸–10⁻⁵ mol · l⁻¹) increased J_H in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10⁻⁴ mol · l⁻¹), PGE₂ stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO₃ ⁻ or Na⁺ and by serosal ouabain (10⁻⁴ mol · l⁻¹). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection seems partially due to a stimulation of exogenous HCO₃ ⁻ transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled to Na⁺ transport. Accepted: 14 April 2000     

Acute effect of prostaglandins and somatostatin on thymidine uptake of gastric mucosa cells

This study compares the in vivo effect of exogenous administration of prostaglandin E2 (30 micrograms/kg) and its precursor, arachidonic acid (30 micrograms/kg), with the effect of indomethacin (5 mg/kg) on the 6-[3H]thymidine uptake of antral mucosa of mice by autoradiographical methods. Likewise, the effect of somatostatin (30 micrograms/kg) on 6-[3H]thymidine uptake is studied. Evaluation of the number of labeled cells, in the histological sections of the gastric mucosa, showed that arachidonic acid, prostaglandin E2, and somatostatin induced an increase in the number of labeled cells (107, 44, and 45%, respectively), while indomethacin induced a decrease of 32% compared to the control group. These results suggest that prostaglandins may mediate stimulatory effects on thymidine uptake of gastric mucosa cells in the first step after drug administration.     

Immunoreactive-FSH in human normal gastric mucosa

Using indirect immuno-peroxidase staining technique, localization of immunoreactive follicle-stimulating hormone (IR-FSH) is demonstrated in the cytoplasm of the epithelial cells of normal human stomach. In view of their triangular shape and central nucleus and their predominance in the intermediate glands of the gastric mucosa, these cells are identified as parietal cells. The stromal tissue is devoid of staining reaction.