Review article: Esomeprazole--enhanced bio-availability, specificity for the proton pump and inhibition of acid secretion.

Esomeprazole, the S-isomer of omeprazole, is the first proton pump inhibitor available for clinical use as a single isomer. It demonstrates pharmacological and clinical benefits beyond those seen with the racemic omeprazole. Esomeprazole has higher and more consistent bio-availability than omeprazole, which results in a greater area under the plasma concentration-time curve. It is the area under the plasma concentration-time curve of omeprazole and esomeprazole that determines how much of each reaches the parietal cell, and thus the control of gastric acid secretion that is achieved. Esomeprazole, like other proton pump inhibitors, has a high specificity for the acidic environment of the parietal cell, where it is accumulated, activated and covalently inhibits the proton pump. Proton pumps elsewhere in the body do not achieve the level of acidity needed for accumulation and activation. Esomeprazole, 40 mg once daily, provides more effective control of gastric acid secretion than omeprazole, 20 or 40 mg once daily, and all other proton pump inhibitors given at their standard doses. This translates into greater clinical effect compared with omeprazole, 20 mg once daily, and lansoprazole, 30 mg once daily, in the management of reflux disease. Esomeprazole therapy is well tolerated, with a low adverse events profile, similar to that seen with omeprazole.

Inhibition of the human sodium/bile acid cotransporters by side-specific methanethiosulfonate sulfhydryl reagents: substrate-controlled accessibility of site of inactivation.

Mammalian sodium/bile acid cotransporters (SBATs) constitute a subgroup of the sodium cotransporter superfamily and function in the enterohepatic circulation of bile acids. They are glycoproteins with an exoplasmic N-terminus, seven or nine transmembrane segments, and a cytoplasmic C-terminus. They exhibit no significant homology with other members of the sodium cotransporter family and there is limited structure/function information available for the SBATs. Membrane-impermeant methanethiosulfonates (MTS) inhibited bile acid transport by alkylation of cysteine 270 (apical SBAT)/266 (basolateral SBAT) that is fully conserved among the sodium/bile acid cotransporters. The accessibility of this residue to MTS reagent is regulated by the natural substrates, sodium and bile acid. In experiments with the apical SBAT, sodium alone increases the reactivity with the thiol reagents as compared to sodium-free medium. In contrast, bile acids protect the SBATs from inactivation, although only in the presence of sodium. The inhibition and protection data suggest that cysteine 270/266 lies in a sodium-sensitive region of the SBATs that is implicated in bile acid transport.

Cytostar-T scintillating microplate assay for measurement of sodium-dependent bile acid uptake in transfected HEK-293 cells.

Real-time measurements of bile acid uptake into HEK-293 cell monolayers expressing the human sodium/bile acid cotransporters have been demonstrated using Cytostar-T microplates with an integral scintillating base. In these 96-well microplates, which permits culturing and observation of adherent cell monolayers, uptake of (14)C-labeled glycocholate and taurocholate into transfected HEK-293 cells was time-dependent, sodium-stimulated, and saturable. The sodium-activated uptake of 30 microM [(14)C]glycocholate (GC) via the ileal (IBAT) and liver (LBAT) transporters was 30-40 times higher than GC uptake in a sodium-free background. In addition, ouabain inhibition of the plasma membrane Na(+), K(+)-ATPase, causing the sodium gradient to collapse, resulted in total loss of glycocholate transport. Induction of gene expression by sodium butyrate showed that the amount of labeled bile acid accumulated in the cell monolayers at steady state was a function of the total amount of transporter expressed. Uptake of labeled bile acids was inhibited both by the specific IBAT inhibitor, 2164U90, and by various bile acids. No major difference was observed between IBAT and LBAT in their specificity for the bile acids tested while the dihydroxy bile acids had the highest affinity for both the transporters studied. The Cytostar-T proximity assay has been demonstrated to be an accurate and reproducible method for monitoring specific bile acid transport in transfected mammalian cells and the results are similar to those obtained by traditional methods. We conclude that the technique is an attractive approach to the cellular study of membrane transport of radiolabeled solutes in general and suggest a role in screening and characterization of novel transport inhibitors.

In vitro antibacterial activity of omeprazole and its selectivity for Helicobacter spp. are dependent on incubation conditions.

Factors affecting the in vitro antibacterial activity of omeprazole were studied. Our data show that 3H-labeled omeprazole covalently bound to Helicobacter pylori and to other gram-negative and gram-positive bacteria. The compound was found to bind to a broad range of proteins in H. pylori, and at pH 5, binding was enhanced 15-fold compared with binding at pH 7. The bactericidal activity correlated to the degree of binding, and at pH 5, a pH at which omeprazole readily converts to the active sulfenamide form, beta-mercaptoethanol, a known scavenger of sulfenamide, and fetal calf serum, to which noncovalent protein binding of omeprazole is known to occur, reduced the level of binding and almost entirely abolished the bactericidal activity. At pH 7 the killing activities of omeprazole and structural analogs (e.g., proton pump inhibitors) were dependent on the time-dependent conversion (half-life) to the corresponding sulfenamide. The bactericidal activity exerted by the sulfenamide form at pH 5 was not specific for the genus Helicobacter. However, in brucella broth at pH 7 with 10% fetal calf serum, only Helicobacter spp. were susceptible to omeprazole, with MBCs in the range of 32 to 64 micrograms/ml, and MBCs for more stable proton pump inhibitors were higher. Wild-type H. pylori and its isogenic urease-deficient mutant were equally susceptible to omeprazole. Thus, the urease is not a lethal target for omeprazole action in H. pylori. In conclusion, the antibacterial activities of omeprazole and analogs are dependent on pH and the composition of the medium used. Thus, at a low pH in buffer, these compounds have a nonselective action, whereas in broth at neutral pH, the mechanism of action is selective for Helicobacter spp.

Structure-activity relationship of omeprazole and analogues as Helicobacter pylori urease inhibitors.

Helicobacter pylori urease belongs to a family of highly conserved urea-hydrolyzing enzymes. A common feature of these enzymes is the presence of two Lewis acid nickel ions and a reactive cysteine residue in the active site. The H+/K(+)-ATPase inhibitor omeprazole is a prodrug of a sulfenamide which covalently modifies cysteine residues on the luminal side of the H+/K(+)-ATPase of gastric parietal cells. Omeprazole and eight analogues were selected based on their chemical, electronic, and kinetic properties, and each was incubated with viable H. pylori in phosphate-buffered saline at pH 7.4 for 30 min, after which 100 mM urea was added and the amount of ammonia formed analyzed after a further 10 min. Inhibition between 0% and 100% at a 0.1 mM concentration was observed for the different analogues and could be expressed as a function of the pKa-value of the pyridine, the pKa-value of the benzimidazole, the overall lipophilicity, and, most importantly, the rate of sulfenamide formation, in a quantitative structure-activity relationship. The inhibition was potentiated by a lower pH (favoring the formation of the sulfenamide) but abolished in the presence of beta-mercaptoethanol (a scavenger of the sulfenamide). Structural analogues incapable of yielding the sulfenamide did not inhibit ammonia production. Treatment of Helicobacter felis-infected mice with 230 mumol/kg flurofamide b.i.d. for 4 weeks, known to potently inhibit urease activity in vivo, as a means of eradicating the infection, was tested and compared with the effect of 125 mumol/kg omeprazole b.i.d. for 4 weeks. Neither treatment proved efficacious.

Partial characterization and effect of omeprazole on ATPase activity in Helicobacter pylori by using permeabilized cells.

ATPase activity in permeabilized cells of Helicobacter pylori as well as those of Helicobacter felis and Campylobacter jejuni was analyzed. The ATPase activities in these cells were most susceptible to sodium azide, fluoroaluminate, and dicyclohexylcarbodiimide, which are typical inhibitors of F ATPases. Optimal values for maximal activity were found to be at approximately pH 6.4, 6.0, and 6.0 for C. jejuni, H. pylori, and H. felis, respectively. The substituted benzimidazole compounds omeprazole, lansoprazole, and Eisai 3810 were found to have no effect on the F ATPase activity of H. pylori at concentrations which are inhibitory for cell growth (MICs). In addition, an extracellular, vanadate-susceptible ATPase activity was detected in H. pylori, which was also relatively insusceptible to the benzimidazole compounds. Thus, the mechanism of killing mediated by omeprazole and related compounds in Helicobacter pylori does not appear to be due to diminished ATPase activity.

Effects of chloride transport inhibitors on intestinal fluid and ion transport in vivo and in vitro.

The hypothesis that intestinal fluid secretion is driven by Cl- has been tested by investigating the effects of NPPB (5-nitro-2-(3-phenyl-propylamino)-benzoate), a blocker of Cl- channels in nephrons, and the loop diuretic bumetanide, an inhibitor of the Na+, K+, 2Cl(-)-co-transporter. Both NPPB (IC50 (inhibitory concentration) approximately 100 microM) and bumetanide (IC50 approximately 2 microM) inhibited stimulated short-circuit current (Isc) in monolayers of a colonic cell line T84. NPPB also inhibited 36Cl- uptake by these cells, indicating that NPPB acts as a Cl- channel blocker in the T84 cells. NPPB (300 microM) and bumetanide (10 microM) abolished both stimulated Isc and Cl- secretion in isolated rat colonic mucosa. As judged by autoradiography, [3H]NPPB was found both in the crypts and at the surface after exposure of either side to the compound. In line with these results, NPPB and bumetanide reduced stimulated fluid secretion in everted colon sacs from the rat. In the anaesthetized rat model, neither bumetanide nor NPPB affected the net fluid transport. After luminal administration of [3H]NPPB to the rat, radioactivity was found mainly in the villus tips, whereas no labelling was found in the crypts. NPPB was bound to plasma protein (99%), and the inhibitory effects of both NPPB and bumetanide on Isc in T84 cells and fluid secretion in the colonic sacs decreased in the presence of albumin, again indicating that the compounds might not reach the in vivo target, or that the mechanism for fluid secretion in vivo may not be explained solely by the secretion of Cl-.

Omeprazole does not cause unscheduled DNA synthesis in rabbit parietal cells in vitro.

Parietal cells from rabbit gastric mucosa, enriched to greater than 90% purity, were used to study the effect of the H+,K(+)-ATPase inhibitor omeprazole on DNA in vitro. In this preparation, omeprazole undergoes acid-catalyzed conversion to its active form, the sulfenamide, which subsequently binds to luminal SH groups of the H+,K(+)-ATPase and thereby inhibits acid secretion. In the parietal cell fraction the S-phase inhibitor hydroxyurea (HU) decreased [3H]thymidine uptake by 40% as measured by liquid scintillation counting (LSC), presumably due to inhibition of scheduled DNA synthesis in contaminating stem cells. In the presence of HU, irradiation with ultraviolet light (UV) or treatment with the gastric carcinogen, 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) increased [3H]thymidine uptake by a factor of 5. Autoradiography of isolated, stimulated parietal cells showed that UV irradiation and MNNG treatment increased the average number of silver grains over the nuclei 18-fold and 4-fold, respectively. In contrast, treatment of histamine-stimulated parietal cells with omeprazole or ranitidine in concentrations 100 times the IC50 value for inhibition of acid secretion in the parietal cells did not increase [3H]thymidine incorporation above the control levels, measured either by LSC or by autoradiography. Extracted DNA from stimulated parietal cells treated with [3H]omeprazole or [3H]MNNG showed no binding of [3H]omeprazole but considerable binding of [3H]MNNG. It is concluded that parietal cells can undergo DNA repair, but there is no indication that omeprazole, or its acid-derived metabolites, should cause any damage to DNA, nor does it bind to DNA in its target cell, where the highest concentrations of omeprazole and its acid-derived products are found.

Partial pronase digestion of rat gastric mucosa isolates cells undergoing replicative DNA synthesis.

A pronase digestion procedure for the isolation of gastric mucosal cells was evaluated for its usefulness in measuring unscheduled DNA synthesis (UDS). The method has been claimed to be suited for assessing the genotoxicity potential of compounds. Compounds were given orally to rats. After 13 h [3H]thymidine was injected and after another hour the animals were killed. The dissected stomachs were treated with pronase for 45 min and the incorporation of radioactivity into DNA was determined. Autoradiography was also performed both on the mucosa and on the isolated cell suspension. The cell suspensions were found to include cells undergoing normal replicative (S phase) DNA synthesis. Of all cells isolated, 4.8 +/- 0.6% consisted of S phase cells. The total amount of DNA recovered (corresponding to the number of cells isolated) was variable and ranged from 20 to 671 micrograms DNA, i.e. approximately 30-fold variation. Neither omeprazole (10, 30 and 80 mg/kg) nor ranitidine (215 mg/kg) had any effect on [3H]thymidine incorporation. The known carcinogen 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) increased incorporation. Refeeding of fasted animals increased incorporation of [3H]thymidine almost 4-fold, showing that animal feeding status influences incorporation. Hydroxyurea, the selective inhibitor of S phase DNA synthesis, inhibited [3H]thymidine incorporation in control and omeprazole-treated animals as well as that induced by MNNG by 92-98%. The results clearly show that the pronase digestion procedure used releases cells undergoing normal, replicative DNA synthesis and can therefore neither be used for measurements of UDS nor for the assessment of the genotoxic potential of drugs.

Coupling of H(+)-K(+)-ATPase activity and glucose oxidation in gastric glands.

The production of 14CO2 from uniformly labeled glucose was shown to account for the entire increase in histamine-stimulated O2 consumption in rabbit gastric glands when no other substrate was added to the medium. The increased production of CO2 was correlated to the increase in O2 consumption and the accumulation of [14C]-aminopyrine (AP) after stimulation with several secretagogues. Inhibitors of H(+)-K(+)-ATPase reduced the secretagogue-induced increase in CO2 production by greater than 90%, showing that the activity of this enzyme was responsible for the greater part of gastric gland metabolism under stimulated conditions. In contrast to AP accumulation, inhibition of CO2 production by omeprazole, an acid-activated inhibitor of the H(+)-K(+)-ATPase, was not reversed by washing. The reversal of AP accumulation after omeprazole treatment and washing was most likely due to a recruitment of residual pumps bordering a nonacidic space, which had not previously been inhibited by omeprazole. These residual pumps slowly generate a pH gradient and hence AP uptake. Adding NH4+ to gastric glands resulted in a concentration-dependent increase of CO2 production up to the maximal stimulated level but without formation of the pH gradient as measured by AP uptake and loss of the omeprazole inhibition of glucose oxidation. As NH4+ can act as a K+ surrogate for H(+)-K(+)-ATPase, and as NH3 is membrane permeant, full stimulation of CO2 production is evidence that the major mechanism of H(+)-K(+)-ATPase activation in situ is an increase in the KCl permeability of the pump membrane.

Tritiated thymidine incorporation into DNA in rat gastric mucosal cells.

The parietal cell acid pump inhibitor, omeprazole, has undergone numerous genotoxicity studies, the conclusions of which have all been negative. A recent report by Burlinson described a method which is claimed to measure unscheduled DNA synthesis (UDS) in gastric mucosa, based on the incorporation of tritiated thymidine (3H-TdR) into DNA. In a subsequent letter it was concluded that omeprazole induces a significant increase in UDS, and it was suggested that 'for omeprazole, a genotoxic action cannot be discounted'. The Burlinson method of measuring UDS relies upon selective separation of non-dividing oxyntic mucosal surface cells from the stem cells located in the proliferative zone. These stem cells undergo normal cell division, subsequently migrate to the top and bottom of the gland, differentiating into the various specialized cells of the gland such as surface, parietal and chief cells. In the oxyntic mucosa the majority of stem cells are located at a level corresponding to one fifth of the mucosal thickness from the surface. The purpose of this study was to evaluate the Burlinson method, which depends upon the selective isolation of non-dividing surface cells by pronase digestion. The fraction used for measurement was investigated in terms of 3H-TdR uptake, the cellular distribution of 3H-TdR by autoradiography, the number of parietal cells and the sensitivity of 3H-TdR uptake for hydroxyurea (an inhibitor of normal, scheduled DNA synthesis). The results show that pronase digestion did not selectively isolate surface epithelial cells and that the digest contained both parietal cells (15 +/- 1.5%) and glandular fragments.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma-interferon-mediated down-regulation of electrolyte secretion by intestinal epithelial cells: a local immune mechanism?

Active chloride (Cl-) secretion by intestinal crypt enterocytes is the central pathophysiological disturbance in most cases of acute diarrhoea. We examined monolayers of the human intestinal cell line T84 mounted in Ussing chambers to see whether the T-cell lymphokine gamma interferon (IFN-gamma) might affect the Cl- secretory properties of these cells, which morphologically and functionally resemble native crypt enterocytes. Pretreatment of T84 cell layers with IFN-gamma for 24 h (but not for 3 h) markedly decreased the Cl- secretory response to vaso-active intestinal polypeptide (VIP) and to cholera toxin and carbachol without appreciably affecting the overall morphology, electrical resistance, or cyclic AMP response of the T84 cell monolayer. The IFN-gamma treatment, however, did induce subtle changes in the T84 cell membrane protein composition which might have affected ion channels regulating Cl- secretion. Our results may indicate a possible novel 'cell-mediated' immune mechanism through which activated gut T cells could modulate the extent of intestinal electrolyte and fluid secretion in, for example, enteric infections.

Specific labelling of gastric H+,K+-ATPase by omeprazole.

Acid secretion is conducted by the parietal cell of the gastric mucosa. The H+,K+-ATPase has been shown to be specifically located to this cell and during recent years been recognized as the gastric proton pump. Omeprazole, a known inhibitor of acid secretion, administered in vivo was found to bind specifically to the H+,K+-ATPase of the rabbit gastric mucosa. A stoichiometry of 2.1 mol radiolabel per mol phosphoenzyme was calculated at total inhibition of the H+,K+-ATPase enzyme activity. In isolated gastric glands prepared from omeprazole-treated animals, the secretagogue-induced increase in oxygen consumption, related to acid secretion, was inhibited to the same level as the H+,K+-ATPase activity. Both the degree of acid secretion inhibition induced by omeprazole and the amount of inhibitor bound to the H+,K+-ATPase were found to be dependent on the stimulation state of the parietal cell. Inhibition of secretion by the H2-receptor blocker ranitidine prior to omeprazole treatment prevented both the inhibition of H+,K+-ATPase and oxygen consumption normally observed with omeprazole and, furthermore, reduced the binding levels of radiolabel to the enzyme. Inhibition of acid secretion by the H+,K+-ATPase inhibitor SCH 28080 totally prevented the binding of radiolabel to the H+,K+-ATPase. The inhibition by omeprazole could be fully reversed in gastric glands and H+,K+-ATPase isolated from omeprazole-treated animals by addition of beta-mercaptoethanol. The major product formed during reactivation was the reduced form of omeprazole, compound H 168/22. Neutralization of the gastric glands in vitro with imidazole totally prevented the inhibitory action of omeprazole. These experiments demonstrate the necessity of acid for the inhibition of gastric acid secretion by omeprazole and the binding of the inhibitor to the H+,K+-ATPase, both in vivo and in vitro, and also the specificity of omeprazole for the H+,K+-ATPase.

Function and structure of parietal cells after H+-K+-ATPase blockade.

Omeprazole was administered to rabbits as a single dose or daily for 1 wk. H+-K+-ATPase and isolated gastric glands were prepared from the oxyntic corpus mucosa and used for functional and quantitative morphological studies. Both 10 and 100 mumol omeprazole/kg increased the pH of the gastric content when measured at death. The stimulated oxygen uptake and the rate of aminopyrine (AP) uptake were both inhibited in the isolated gastric gland preparations. Morphometric studies of biopsy specimens taken from the corpus mucosa and isolated gastric glands showed that omeprazole treatment increased the volume density of the acid compartments. This expansion provides an increased accumulation space for AP. Therefore, an increased AP uptake might be seen in glands isolated from omeprazole-treated animals. Blockade of the H2-receptor by ranitidine transformed the morphology of the cell into a more resting type and, furthermore, reduced the omeprazole-induced increase in the volume density of the acid compartments in the parietal cell. The H+-K+-ATPase activity measured in membrane fractions from the omeprazole-treated animals was decreased dose dependently and inhibited by 95% after 100 mumol omeprazole/kg. However, the concentration of the enzyme in these fractions did not change. These results indicate a specific inhibitory action of omeprazole on the H+-K+-ATPase.

Rat parietal cell function after prolonged inhibition of gastric acid secretion.

Female rats were treated orally for 3 mo with omeprazole (40 and 400 mumol/kg). Both doses caused total inhibition of gastric acid secretion and recovery was parallel to that of H+-K+-ATPase activity (30-50 and 60-80% inhibition 24 h after doses, respectively). The H+-K+-ATPase activity returned to control levels within 1 wk after the last dose. Plasma gastrin levels were dose-dependently increased during treatment but reversed to control levels within 9 days after the last dose. Parallel with a general increase in corpus mucosal mass, both pepsinogen and H+-K+-ATPase total content increased. However, their tissue concentrations did not differ from control values, suggesting that neither parietal nor chief cell density are changed by omeprazole treatment and also that their growth is parallel to the general hyperplasia. In contrast, the oxyntic mucosal histamine concentration was increased, indicating an increase in the enterochromaffin-like (ECL) cell density. Maximal capacity of the mucosa to secrete acid increased in parallel with the increase in mucosal mass and total H+-K+-ATPase content. However, basal acid secretion did not differ between treatment groups. Increased capacity slowly declined toward control levels over the 70-day recovery period after withdrawal of omeprazole. These results suggest that hypergastrinemia, induced in the rat by pharmacological inhibition of gastric acid secretion, causes a hyperplasia of oxyntic mucosal cells, ECL cells growing faster than the others. The hyperplastic mucosa has an increased capacity to produce acid and is functionally normal.

Inhibition of gastric H+,K+-ATPase and acid secretion by SCH 28080, a substituted pyridyl(1,2a)imidazole.

A hydrophobic amine, SCH 28080, 2-methyl-8-(phenylmethoxy)imidazo(1,2a)pyridine-3-acetonitrile, previously shown to inhibit gastric acid secretion in vivo and in vitro, was also shown to inhibit basal and stimulated aminopyrine accumulation in isolated gastric glands when histamine, high K+ concentrations, or dibutyryl cAMP were used as secretagogues. Stimulated, but not basal, oxygen consumption was also inhibited. Neutralization of the acid space of the parietal cell by high concentrations of the weak base, imidazole, reduced the potency of the drug, suggesting that SCH 28080 was active when protonated. Studies on the isolated H+,K+-ATPase showed that the compound inhibited the enzyme competitively with K+, whether ATP or p-nitrophenyl phosphate were used as substrates. In contrast, the inhibition was mixed with respect to p-nitrophenyl phosphate and uncompetitive with respect to ATP. The drug reduced the steady state level of the phosphoenzyme but not the observed rate constant for phosphoenzyme formation in the absence of K+ nor the quantity of phosphoenzyme reacting with K+. The drug quenched the fluorescence of fluorescein isothiocyanate-modified enzyme and also inhibited the ATP-independent K+ exchange reaction of the H+,K+-ATPase. Its action on gastric acid secretion can be explained by inhibition of the H+,K+-ATPase by reversible complexation of the enzyme. This class of compound, therefore, acts as a reversible inhibitor of gastric acid secretion.

Sulfide and sulfoxide derivatives of substituted benzimidazoles inhibit acid formation in isolated gastric glands by different mechanisms.

The sulfoxide and sulfide forms of three pairs of substituted benzimidazoles, including omeprazole, were investigated using isolated gastric glands and microsomal membranes containing H+,K+-adenosine Triphosphatase (ATPase). The sulfoxides inhibited stimulated aminopyrine (AP) uptake giving IC50 values between 0.47 and 1.1 microM, whereas the sulfides were less potent and showed a greater variation in IC50 values, 9.5 to 170 microM. The decrease in stimulated oxygen consumption induced by the sulfoxides was parallel to their inhibition of AP-uptake, with IC50 values of 0.40 to 3.7 microM, whereas the sulfides were virtually without effect, IC50 greater than 100 microM. The permeable buffers imidazole and 2,6-dimethylpyridine mimiced the effect of the sulfides on both AP accumulation and oxygen consumption. When tested on H+, K+-ATPase, an enzyme suggested to be the proton pump of the gastric mucosa, the sulfoxides inhibited the ATPase activity with IC50 values between 0.25 to 2.8 microM, in contrast to the sulfides, which were without inhibitory action. The sulfoxide-induced inhibition of AP-uptake in gastric glands and H+, K+-ATPase activity was prevented by the addition of beta-mercaptoethanol, whereas the mercaptane was without effect on sulfide-induced inhibition of AP-accumulation. When tested on vesicles containing H+, K+-ATPase, both the sulfide and sulfoxide derivatives dissipated the proton gradient generated by the enzyme, but only the sulfoxide-induced inhibition was prevented by the addition of beta-mercaptoethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic stimulation of pepsinogen release from rabbit isolated gastric glands.

Isolated gastric glands from the rabbit were used for studying the effect of catecholamines on the release of pepsinogen. Isoprenaline, adrenaline and noradrenaline stimulated pepsinogen release in a dose-dependent manner with similar maximal effects, but isoprenaline was significantly more potent than the other two agonists. The effect was mediated through beta-adrenoceptors, since the response was inhibited by the beta-adrenoceptor antagonist, propranolol, and since the alpha-adrenoceptor agonist, phenylephrine, was without effect in the concentration range 0.01 - 10 microM. Concentration-response curves for isoprenaline were shifted to the right in parallel by increasing doses of propranolol, and maximal response was not influenced by propranolol per se, which indicates a competitive type of antagonism. A Schild plot showed a pA2-value for propranolol of 7.70 and the slope of the regression line was 1.02. Studies with the beta 1-selective antagonist pafenolol and the beta 2-selective antagonist ICI 118.551 demonstrated that isoprenaline acted through beta 1-adrenoceptors. The results suggest an adrenergic component in the control of the peptic cells in rabbit gastric mucosa.

Effect of omeprazole on gastric secretion in H+,K+-ATPase and in pepsinogen-rich cell fractions from rabbit gastric mucosa.

In order to study the effects of the substituted benzimidazole omeprazole on gastric secretory functions, parietal cells and chief cells from rabbit gastric mucosa were separated and enriched by density gradient centrifugation in Percoll. H+,K+-ATPase activity, as well as a 100,000 dalton protein, was found to copurify with a cell fraction morphologically characterized as mainly parietal cells (purity approximately 65%), while pepsinogen copurified with a cell fraction morphologically characterized as chief cells (purity approximately 90%). A spontaneous pepsinogen release (9.9 micrograms/mg cell dry wt X 2 hr), unaffected by both atropine and omeprazole, was found in the chief cell fraction. The release was approximately doubled by both carbacholine (4 X 10(-5)M) and dibutyryl cAMP (db-cAMP, 10(-3)M). The cholinergic stimulation was selectively blocked by atropine, while omeprazole had no effect on pepsinogen release induced by either of the secretagogues. On the other hand, omeprazole inhibited both db-cAMP- and histamine-stimulated acid secretion quantified as [14C]aminopyrine (AP) accumulation in the parietal cell fraction. Cimetidine counteracted only acid secretion induced by histamine. These findings indicate that omeprazole has a specific effect on acid secretion, and are consonant with the hypothesis that the effect is due to H+,K+-ATPase inhibition.