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The stimulation of oxyntic cell by gastric secretagogues is associated to the activation of oxidative metabolism. The mechanisms of this activation are not exactly known. In the present work, we investigated the possible direct effect of Ca2+ on both oxoglutarate oxidation in rabbit gastric glands and oxoglutarate dehydrogenase activity (OGDH) in isolated gastric mitochondria. Both carbachol and Ca2+ ionophores (A23187 and ionomycin) significantly stimulated oxoglutarate oxidation in a dose-dependent manner. This effect was only observed in the presence of low substrate concentrations. BAPTA-AM, an intracellular calcium chelator, significantly inhibited the rate of oxoglutarate oxidation. OGDH activity was stimulated by physiological concentrations of Ca2+ in a dose-dependent manner. This effect was reduced by ruthenium red, an inhibitor of mitochondrial Ca2+ uptake, and it was additionally increased by spermine, a stimulant of Ca2+ influx to the mitochondria. The results support the hypothesis that Ca2+ plays a direct role in the activation of oxidative metabolism in the oxyntic cell.

The effects of gastric secretagogues, and other agents that modify H+,K(+)-ATPase activity and cell calcium concentration, on the rate of oxoglutarate oxidation were investigated in isolated gastric glands. Oxoglutarate was oxidized in a dose-dependent manner by gastric glands, with an apparent Km for oxoglutarate of 3.9 +/- 0.5 mM. Oxoglutarate progressively inhibited the rate of glucose oxidation. In the presence of 0.5 mM oxoglutarate plus 10 mM glucose, the latter substrate was preferentially oxidized and contributed most to oxygen uptake. With 10 mM oxoglutarate plus 10 mM glucose, the rate of glucose oxidation was greatly inhibited and oxoglutarate oxidation accounted for most of the oxygen consumption. Acid secretion (aminopyrine accumulation) was significantly increased by 0.1 mM histamine in glands oxidizing 10 mM oxoglutarate, although this stimulation was significantly lower than that observed in the presence of 0.5 mM oxoglutarate plus 10 mM glucose. Omeprazole, an inhibitor of the H+,K(+)-ATPase, significantly reduced the oxidation of oxoglutarate, whereas NH4+, an activator of the enzyme, stimulated the oxidation of a submaximal dose of oxoglutarate. Carbachol at 0.1 mM significantly increased the rate of oxidation of non-saturating concentrations of oxoglutarate. The calcium ionophore ionomycin at 10 microM produced a similar effect. Chelation of intracellular calcium by BAPTA AM caused a significant inhibition of oxoglutarate oxidation. The results provide further evidence that changes in the ATP:ADP ratio resulting from activation of the H+,K(+)-ATPase, and calcium ions are involved in the mechanisms of activation of oxidative metabolism in the parietal cell.

The effects of pure ethanol and some alcoholic beverages on acid secretion and metabolism were examined in the isolated toad gastric mucosa. Pure ethanol applied to the luminal side or to the submucosal side at low concentrations (2%-10%) was a potent stimulant of acid secretion, whereas high concentrations (greater than or equal to 20%) were inhibitory. Cimetidine and calcium-free solutions did not abolish the secretory effect of ethanol. Beer and wine, but not rum and whisky, caused a significant stimulation of acid secretion. Respiration was progressively increased by ethanol at concentrations between 2% and 20%. This effect was not affected by cimetidine or by SCH 28080, an inhibitor of the gastric hydrogen-potassium-stimulated adenosine triphosphatase. Ethanol (10%) significantly increased by 46% the tissue lactate-pyruvate ratio. The oxidations of glucose, butyrate, and acetate were progressively reduced by low concentrations of ethanol (5% and 10%). The results indicate that (a) low concentrations of ethanol and alcoholic beverages with low ethanol content are direct stimulants of acid secretion and (b) the secretory and metabolic effects of low concentrations of ethanol seem to be mediated via its oxidation.

Peptic ulcer is an heterogeneous and multifactorial disease. Secretion of acid/pepsin is a critical permissive factor in gastroduodenal peptic ulceration. Therapy of this disease has been based mostly on this principle. The sole presence of the aggressive factor, acid/pepsin, is not enough to explain peptic ulceration. Mucosal defense (resistance) is another critical factor involved in pathogenesis of this disease. Defects in some gastroduodenal defense mechanisms have been found in patients with peptic ulcer disease, such as: synthesis and release of prostaglandins, mucus and bicarbonate secretions, and the luminal hydrophobic layer. Both the dictum "no acid-no ulcer" and the coroliary "normal healing-no ulcer" seems to be valid. Correction of a possible deficiency in mucosal defense/resistance may be a useful and practical principle is management of patients with peptic ulcer disease.

The role of beta-oxidation in the mechanism of stimulation of acid secretion was examined in toad gastric mucosa in vitro. The incubation with 4-pentenoate selectively inhibited in a dose-dependent manner the rate of 14CO2 formation from [1-14C]octanoate. Pretreatment with 20 mM 4-pentenoate sharply reduced the respiratory and secretory responses to theophylline and histamine. Tracer studies showed a major utilization of exogenous octanoate over glucose and pyruvate by the in vitro toad gastric mucosa. Theophylline and histamine stimulated by 69% the rate of octanoate oxidation. Over 60% of the increments in oxygen uptake produced by theophylline and histamine accounted for the increments in octanoate oxidation, whereas glucose and pyruvate together accounted for less than 25%. Octanoate-dependent respiration was shown to correlate with octanoate oxidation under both inhibition with 4-pentenoate and stimulation with theophylline. Theophylline stimulated by 25% the rate of octanoate oxidation in Cl--free glucuronate-nutrient solutions. The present work provides further evidence for the primary role of fatty acid oxidation in the mechanism of acid secretion in amphibian.

Histamine and theophylline, two gastric secretagogues, significantly increased tissue glycerol content by 121 and 66%, respectively, in the isolated toad gastric mucosa. This is new evidence in favor of the hypothesis that gastric secretagogues may act via lipid mobilization.

Pyruvate carboxylation was stimulated by 2 gastric secretagogues, histamine and dibutyryl cyclic AMP, and by butyrate. Thiocyanate, an inhibitor of acid secretion, produced a slight decrease. Avidin significantly reduced acid secretion and this effect was overcome by biotin and oxalacetate. The results suggest that carboxylation of pyruvate is one of the reactions controlling oxidative metabolism and acid secretion in toad gastric mucosa.

1. The effects of cimetidine, a histamine H2-receptor antagonist, on acid secretory and respiratory responses induced by histamine, theophylline and dibutyryl cyclic AMP were investigated in the in vitro toad gastric mucosa. 2. Histamine- and theophylline-stimulated acid secretion was competitively inhibited by cimetidine. A significant but lesser degree of inhibition was observed on oxygen uptake. 3. Cimetidine significantly inhibited acid secretion and oxygen uptake stimulated by dibutyryl cyclic AMP. 4. The results may suggest that cimetidine may have an additional action beyond the point of cyclic AMP in the oxyntic cells.

The effects of bile salts on energy metabolism and acid secretion were investigated in the amphibian gastric mucosa in vitro. Serosal exposure to deoxycholate (0.2-2 mM), cholate (2-8 mM), or taurocholate (4-80 mM), at pH 7.4, decreased acid secretion depending on the concentration and time of exposure. Mucosal application of cholate and taurocholate at pH 5.6 caused a more pronounced reduction in the apparent rate of acid secretion. Oxygen uptake and substrate oxidations were significantly inhibited by bile salts in a dose-dependent manner. At pH 7.4, 1 mM deoxycholate inhibited the respiration by 49% and the rates of oxidation by 51%, 52%, 78%, 74%, and 54% of control values, for glucose, pyruvate, succinate, acetate, and butyrate, respectively. Cholate and taurocholate were found to be less potent than deoxycholate. Tissue adenosine triphosphate concentration was decreased by 13%, 57%, and 67% with 0.5, 1, and 2 mM deoxycholate, respectively. We believe the impairment of energy metabolism could be involved in the mechanism of bile salt injury to the gastric mucosa.

In the present work the isolation and some characteristics of a membrane fraction from toad gastric mucosa are described. By combining differential centrifugation in a discontinuous gradient of sucrose it was possible to obtain a band at the interphase of 22% sucrose 37%, whose enzymatic and electron microscopic analysis indicated to be a fraction enriched of luminal plasma membranes from oxyntic cells, with very poor contamination by other subcellular organelles. This is a suitable membrane preparation that can be used to perform studied on the mechanisms of acid secretion in toads.

The effect of phenothiazine antipsychotic drugs on acid secretion was investigated in the isolated toad gastric mucosa. The acid secretory responses induced by maximal doses of histamine, carbachol and theophylline were all inhibited in a similar fashion by chlorpromazine. The ID50 was between 300 and 600 microM. Histamine-stimulated H+ secretion was also inhibited by trifluoperazine. Soluble cyclic AMP-dependent protein kinase activity was not significantly affected by 300 microM chlorpromazine. Microsomal (H+ + K+)-ATPase activity was significantly reduced by chlorpromazine. The results indicate that phenothiazines can inhibit acid secretion in the toad gastric mucosa and that inhibition of the gastric (H+ + K+)-ATPase may be involved in the mechanism of action.

An attempt to increase the permeability of gastric mucosa to exogenous Krebs cycle intermediates seemed advisable for a better understanding their relationship with acid secretion. At pH 7.4, citrate, oxoglutarate, fumarate, and malate had no significant effect on oxygen uptake (QO2) nor on acid secretion (QH+) by toad gastric mucosa; succinate increased QO2 slightly and had no effect on QH+; but at pH 5.0, oxoglutarate and succinate increased QO2 by 18 and 21%, respectively. 14CO2 evolved by gastric mucosa incubated with [14C]oxoglutarate, succinate, malate, or citrate was 155, 92, 128, and 353%, respectively, greater at pH 5. Citrate, oxoglutarate, succinate, fumarate, and malate increased QH+ by theophylline-stimulated mucosa at pH 5.0 by 25, 39, 35, 17 and 28%, respectively. Oxoglutarate-dependent respiration was shown to correlate with oxoglutarate oxidation. Malonate and arsenite inhibited QO2 and QH+; malonate inhibition was reversed by washout or by succinate. Arsenite was reversed by washout and accelerated by addition of lipoate immediately after washout. The results suggest that the Krebs cycle has concomitant roles in the regulation of QH+ and oxidative metabolism in the toad gastric mucosa.

The role of extracellular Ca2+ in metabolic effects induced by theophylline and histamine was investigated in the isolated toad gastric mucosa. Primary and secondary effects on metabolism were differentiated by using K(+)-free solutions, which blocked the secretory responses but not the metabolic ones. The stimulation of respiration induced by theophylline and histamine was dose dependent and was significantly decreased by Ca2(+)-free solutions. In the presence of 1.8 mM Ca2+, the rate of glycogen breakdown was increased by theophylline in a dose-dependent manner and the dose-response curve was somewhat similar to that obtained with oxygen uptake. This effect was inhibited by incubation in Ca2(+)-free solutions. Ca2+ stimulated the rate of glycogen utilization in a concentration-dependent manner. The rates of oxidation of exogenous glucose and pyruvate were significantly inhibited by Ca2(+)-free solutions in theophylline- and histamine-stimulated mucosa, whereas the rates of oxidation of butyrate and acetate were not significantly affected. The Ca2+ ionophore A23187 significantly stimulated the rate of oxygen uptake and this response was not blocked by omeprazole and Sch 28080, two specific inhibitors of gastric H(+)-K(+)-ATPase. The results indicate that Ca2+ is required for optimal stimulation of carbohydrate catabolism in the toad gastric mucosa.

The role of extracellular Ca2+ in the effects and oxidation of metabolic substrates was investigated in the isolated toad gastric mucosa. In the presence of lipoate, the stimulating effect of 10 mM glucose on spontaneous acid secretion was significantly reduced by 76% in Ca2+-free solutions. The inhibition was overcome by addition of 5 mM Ca2+. The increment in respiration induced by glucose was also blocked in the absence of external Ca2+. The effect of 10 mM pyruvate on acid secretion was inhibited by 37% in Ca2+-free solutions. The secretory responses induced by 10 mM butyrate and 10 mM octanoate were not significantly affected by Ca2+-free solutions. The rates of oxidation of [14C]-glucose and [14C]pyruvate were significantly reduced by incubating in Ca2+-free solutions containing 0.1 mM of EGTA. When O2 uptake and glucose oxidation were measured simultaneously in the same preparation, the increment in the rate of glucose oxidation accounted for by 43% of the total increase of respiration observed in the presence of Ca2+. The rates of oxidation of [14C]butyrate and [14C]acetate were not significantly affected by Ca2+-free solutions. The rate of oxidation of [14C]glucose exhibited saturation kinetics versus concentration and was lower in the absence of external Ca2+ under a range of glucose concentrations. Similar results were observed when the experiments were performed in the absence of external potassium to block the acid secretory process. Ca2+ stimulated the rate of glucose oxidation in a dose-dependent manner. The kinetics of 45Ca2+ efflux and 45Ca2+ uptake were not significantly affected by glucose and butyrate.(ABSTRACT TRUNCATED AT 250 WORDS)

The substrate-level energy dependence of acid secretion was investigated in the human gastric mucosa in vitro using biopsy specimens obtained during fiberoptic gastroscopy in symptomatic patients. The oxygen consumption and the accumulation of aminopyrine were used as indexes of secretory activity. Basal and histamine-stimulated oxygen uptake by fundic biopsy specimens were not affected by medications (pethidine and diazepam) administered during gastroscopy. Under substrate-depleted conditions, the oxygen consumption and the aminopyrine accumulation of fundic mucosa were not significantly increased by histamine. Stimulation of functional activities by gastric secretagogues was observed only in the presence of exogenous substrates. The ability of various substrates to support acid formation in the presence of gastric secretagogues was evaluated. Carbohydrates were found to be effective substrates in supporting the functional responses of the tissue, with glucose being the most effective. Propionate, butyrate, beta-hydroxybutyrate, and octanoate were ineffective as substrates. Glucose by itself, but not butyrate, significantly increased oxygen uptake and aminopyrine accumulation. The results suggest that the human gastric mucosa, in vitro, has an absolute requirement for metabolic substrates to support secretory responses and that carbohydrates seem to be the preferential substrates.