Nutrients regulate diamine oxidase release from intestinal mucosa.

Diamine oxidase is continuously released from the intestinal mucosa and carried to the circulation by the lymphatics. The effect of nutrients on this release was examined. Rats were prepared with duodenal and intestinal lymph cannulas. Test mixtures of lipid emulsions containing triolein, oleic acid, or tricaprylin and solutions of carbohydrate and protein were infused into the duodenum. The enzyme release and triglyceride transport were determined and in some experiments were done in the presence and absence of Pluronic L-81, an inhibitor of chylomicron formation, and aminoguanidine, an inhibitor of diamine oxidase activity. The data indicate that nonlipid nutrients did not increase diamine oxidase activity in the intestinal lymph, but the mucosal tissue content was significantly reduced in the distal small intestine, particularly after protein infusion. Triglycerides and fatty acids increased diamine oxidase in the intestinal lymph, and the longer-chain triglyceride was more effective. Inhibition of triglyceride transport did not interfere with the enzyme release, and the inhibition of diamine oxidase activity had no significant effect on lipid absorption. According to our observations, only lipids increase intestinal lymph diamine oxidase. Nonfat nutrients appear to increase diamine oxidase in the intestinal lumen. Diamine oxidase is not directly required for lipid absorption.

Role of mast cell histamine in brown adipose tissue thermogenic response to VMH stimulation.

Electrical stimulation of the ventromedial hypothalamic area in rats caused a significant but transient increase in interscapular brown adipose tissue temperature. This response was markedly reduced by cimetidine, a histamine H2-receptor antagonist, but not by pyrilamine, an H1-receptor antagonist. Histamine is present in substantial amounts within mast cells in brown adipose tissue as injections of compound 48/80, which cause degranulation of connective tissue mast cells, reduced the tissue histamine content by > 85%. In contrast, histamine content in brown adipose tissue was not affected by loss of sympathetic neural input (with 6-hydroxydopamine) or sensory neural input (with capsaicin). Neither cimetidine nor histamine had any effect on basal and norepinephrine-stimulated rates of O2 consumption by isolated brown adipocytes. These results indicate that histamine released from mast cells acting on H2-receptors may play an important but indirect role in the thermogenic response of brown adipose tissue to stimulation of the ventromedial hypothalamic area.

Mucosal histamine elimination and its effect on acid secretion in rabbit gastric mucosa.

BACKGROUND: Rapid elimination of histamine near the oxyntic cells is important in the termination of the secretory response when the signal for histamine release is discontinued. The mechanism of this local process is still unclear. METHOD: Gastric mucosal histamine elimination was, therefore, examined in fundic mucosa mounted in flux chambers and in dispersed mucosal cells. RESULTS: [3H]histamine placed into the serosal chamber medium was transported across the mucosal tissue into the lumen, but a greater quantity was methylated to an inactive metabolite, Nt-methylhistamine, and preferentially released to the serosal chamber, the interstitial medium. Both processes were enhanced by increased substrate concentration. They were reduced by lowering the temperature and by sodium replacement. Inhibition of histamine methyltransferase suppressed histamine uptake and methylation and significantly increased histamine-stimulated acid secretion in the tissue preparation and in dispersed mucosal cells. The augmentation was reduced by an H2-receptor blocker. CONCLUSION: Mucosal histamine methylation and the secretion of histamine into the gastric lumen removes histamine from the extracellular space effectively, reducing the histamine concentration near the oxyntic cell surface.

Uptake and methylation of histamine by dispersed gastric mucosal cells and its possible influence on acid secretion.

Inactivation of histamine by gastric mucosal tissue was examined in dispersed rabbit gastric mucosal cells. Mucosal cells were incubated with [14C]histamine. The formed radioactive metabolites were separated and identified by thin layer co-chromatography and quantitated, in both the cellular and extracellular mediums. Gastric mucosal cells internalized histamine, most of which was immediately methylated primarily to N tau-methylhistamine and released. Cellular histamine product accumulation reached a plateau. The rate of histamine methylation increased with increasing extracellular histamine concentration, moving towards a plateau above 5 microM. Histamine methylation was greatly decreased but not abolished at 4 degrees C, in the absence of Na+ and by phlorizin (0.5 mM), an inhibitor of Na(+)-dependent co-transport. Inhibition of histamine N-methyltransferase decreased intracellular methylhistamine content dose dependently without increasing intracellular histamine. The secretagogues pentagastrin and carbachol did not influence histamine metabolism but ethanol inhibited methylation. The data suggest that gastric mucosal cells take up histamine by a Na(+)-dependent and Na(+)-independent process. The histamine uptake capacity appears to be linked to the methylation activity within the cell. The decrease in histamine uptake and metabolism caused by ethanol could potentially increase histamine concentrations near the target cells and be the reason for the stimulatory effect of ethanol on acid secretion.

Histamine methyltransferase in dispersed cells from rabbit fundic mucosa.

The cellular distribution of histamine N-methyltransferase was studied in rabbit gastric mucosa. The fundic mucosa was dispersed by collagenase treatment in Hanks' or calcium-free medium. In calcium-free medium, the number of dispersed cells/g wet tissue, as well as their viability was increased; histamine N-methyltransferase recovery was up to three-fold larger than in cells prepared in Hanks' medium. Furthermore, the calcium-free medium led to a greater acid secretory response, whereas the cellular pepsinogen content tended to be lower. Histamine N-methyltransferase activity was found in all cell fractions but was higher in the larger cell types. The enzyme activity showed only a partial correlation with either oxyntic or chief cells. These results indicate that the use of calcium-free medium to disperse and isolate rabbit mucosal cells improves cell quality. Histamine N-methyltransferase in the rabbit fundic mucosa, is found in more than one cell type, primarily the oxyntic and chief cells.

Histamine uptake and its methylation by isolated oxyntic cells.

The role of the oxyntic cells in the inactivation and elimination of histamine was studied in dispersed and isolated mucosal cells. Gastric mucosal cells from rabbits were incubated with 14C-labelled histamine (1 and 3.2 X 10(-6) M) at 37 degrees C. Histamine and the histamine metabolites were extracted, separated on thin layer chromatography, and quantitated. Both the intracellular and extracellular compartments were examined. Gastric mucosal cells were found to internalize histamine and methylate it to Nt-methylhistamine, a biologically inactive metabolite. This process was Na+-dependent and occurred primarily in the oxyntic cells. Ethanol in concentrations between 1 to 4% decreased histamine methylation. The histamine content associated with the intracellular compartment was unaffected by ethanol. Pentagastrin (10(-10) to 10(-6) M) had no significant effect on histamine methylation. The results substantiate that oxyntic cells take up and inactivate histamine, and thus are capable of modifying extracellular histamine concentration. Ethanol inhibits histamine methylation, potentially maintaining or increasing extracellular histamine, while pentagastrin appears to have no significant effect.

Regulation of gastric acid secretion at the cellular level.

Gastric acid secretion is controlled by neurocrine, endocrine, and paracrine pathways. At the organ level, the neurocrine and endocrine systems provide long-range regulation; and near the target cell the paracrine system appears to predominate. The integration of the regulatory commands from these various pathways is complex and, as a result, some pathways have not yet been clearly defined. Present evidence suggests that acetylcholine from mucosal nerve endings acts by 2 possible pathways. It interacts with muscarinic receptors on the oxyntic cell stimulating acid production. It is also capable of releasing histamine from the paracrine cell in the gastric glands, and histamine then acts on the oxyntic cells. The endocrine effect on acid secretion mediated by gastrin is less clear. Gastrin binds to oxyntic cell plasma membranes but has little or no direct stimulatory effect on the acid-secreting cell. It is assumed that its stimulatory action on acid secretion in vivo is mediated primarily by increasing histamine levels near the oxyntic cells. Histamine, released from paracrine cells near the oxyntic cells, is probably controlled by acetylcholine and gastrin, but other mechanisms are being explored. Histamine binds to the H2-receptors on the oxyntic cell plasma membrane, activating adenylate cyclase, which catalyzes the production of the intracellular messenger cyclic AMP. Cyclic AMP in turn activates a specific protein kinase, which phosphorylates a yet unknown substrate for the propagation of the stimulatory signal. The action of acetylcholine on the oxyntic cell receptors does not stimulate the production of cyclic AMP; instead, it acts on Ca++ channels, increasing the Ca++ entrance into the cell, which initiates the intracellular events.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative determination of histamine metabolites by capillary gas chromatography.

A method using capillary gas chromatography is described for the determination of histamine and eight of its basic and acid metabolites in a single biological sample of serum, urine, or gastric juice. Ion-exchange chromatography and extraction with organic solvents are used for isolation and purification, and gas chromatography for identification and quantitation. The heptafluorobutyryl derivatives of histamine and some basic metabolites are compatible with nitrogen-phosphorus and electron capture detection modes and offer an excellent sensitivity (detection limit 0.1 pmol with electron capture). The acid metabolites are quantitated after esterification. The linearity range, the sensitivity, a partial study of reproducibility and typical chromatograms show that the method is adaptable to a variety of applications.

Quantitation of histamine and some of its basic methylated metabolites in biological materials by gas-liquid chromatography.

A method which measures histamine, its basic metabolites, and some analogs in biological materials is described. The procedure consists of ion-exchange chromatography and chromatography on silicic acid for isolation and purification, and gas chromatography for identification and quantitation. The isolated compounds are prepared for gas chromatography by double derivatization with heptafluorobutyric anhydride and acetic anhydride. One of the synthetic histamine analogs, 2-methylhistamine, is used as an internal standard. The metabolites can be quantitated at a level as low as 1.5 nmol/100 microliters final concentration. The method is adaptable to a variety of applications, with good reproducibility and sensitivity. A number of different biological samples have been analyzed.

Carbonic anhydrase activity and aminopyrine uptake in isolated gastric mucosal cells.

The role of carbonic anhydrase in the regulation and production of gastric acid was examined. Studies were done on isolated rabbit fundic mucosal cells, in which carbonic anhydrase activity and [14C]aminopyrine uptake were measured. The oxyntic cell-enriched cell fractions had the largest carbonic anhydrase content (4.2 +/- 0.1 U/10(6) cells) compared with other mucosal cells. The cellular carbonic anhydrase content of all isolated cell fractions was primarily a soluble enzyme, accounting for 10% of the total mucosal enzyme quantity. The remainder was found in the incubation medium from the mucosal dispersion procedure. The remaining cellular carbonic anhydrase activity in the oxyntic cell fraction was not enhanced by secretagogues. [14C]aminopyrine uptake increased dose dependently in the presence of histamine and dibutyryl cAMP. Acetazolamide (0.2 mM) inhibited the cellular carbonic anhydrase activity (99%) but did not interfere with the cellular uptake of [14C]aminopyrine. The present data from isolated cells suggest that cellular carbonic anhydrase in the oxyntic cell does not appear to be an integral step in the initiation of secretory function of isolated oxyntic cells. The lack of interference by the carbonic anhydrase inhibitor with H+ production does not exclude a role for carbonic anhydrase at high levels of acid secretion as it may occur in vivo, since isolated oxyntic cells probably do not achieve maximal rates of acid secretion and aminopyrine uptake reflects acid gradients and not rate of acid secretion.

Acute necrosis of the intestinal mucosa with high serum levels of diamine oxidase.

A patient with acute necrosis of the intestinal mucosa and high serum diamine oxidase activity is described. The 71-year-old woman, with a history of hypertension and cardiovascular and peripheral arteriosclerotic disease, presented with acute epigastric pain, vomiting, and a deteriorating hemodynamic condition. Serum level of the intestinal enzyme diamine oxidase (DAO) obtained on admission, approximately 24 hr after the onset of symptoms, was 7.4 times above the normal value. An exploratory laparotomy performed 6 hr later revealed cyanosis and areas of transmural necrosis involving the entire small bowel. The bowel was not resected because of the extent of lesion. Thirty hours after the first sample was taken and 2 hr before death, the serum DAO level was only slightly above normal. It is suggested that this biochemical marker could provide a valuable tool for the early diagnosis of intestinal ischemia.

Release of intestinal diamine oxidase by histamine in rats.

Diamine oxidase activity was measured in the intestinal mucosa, lymph, and in the serum of rats, to determine whether histamine, a substrate of diamine oxidase, liberates this enzyme from its mucosal storage site(s). Histamine induced a sharp rise in intestinal lymph flow, lymph protein, and lymph diamine oxidase, lasting less than 1 h after the histamine injection. The rise in lymph diamine oxidase activity was dose dependent over a narrow concentration range (0.05-0.2 mmol/kg, i.v. and 0.15-0.6 mmol/kg i.d.). It did not correlate with the dose dependent increase in lymph flow or lymph protein. A single maximal intraduodenal dose of histamine caused a 41.6-fold increase in the lymph diamine oxidase activity and a 2.4-fold increase in the serum enzyme level temporarily. A second injection of histamine, 2 h after the first, resulted in a comparatively smaller increase in the lymph enzyme. The extent of the reduction was dependent on the magnitude of the first injection. The results suggest that histamine causes a limited liberation of diamine oxidase from the intestinal mucosa. The function of this enzyme release may be a protective response by the mucosa to reduce toxic levels of free histamine, either liberated by the mucosal tissue or absorbed from the intestinal lumen.

Effect of intestinal ischemia on diamine oxidase activity in rat intestinal tissue and blood.

This study examines the effect of increasing duration of intestinal ischemia on the mucosal integrity and the release of the enzyme diamine oxidase from the small intestine. Acute ischemia was produced by the occlusion of the superior mesenteric artery, and the subsequent changes in DNA and 125I-albumin content in the lumen were taken as indices of intestinal lesions. Diamine oxidase activity was measured in the intestinal lumen, mucosa, lymph, and serum. Occlusions of the superior mesenteric artery for periods of more than 60 min resulted in significant leakage of 125I-albumin (i.v.) into the lumen. In contrast, luminal DNA content rose significantly after 15 min of ischemia and continued to increase proportionally with the increased duration of the occlusion up to 120 min. Similarly, diamine oxidase activity was augmented in the lumen after 15 min of occlusion and rose sharply as the ischemic period was lengthened up to 60 min, leveling off thereafter. Increases in the diamine oxidase activity were also observed in the intestinal lymph and serum, reaching levels that were 2.6 and 3.6 times that of the control respectively after 60 min of ischemia. These findings suggest that intestinal ischemia reduces the diamine oxidase content in the intestinal mucosa by desquamation of the surface epithelial cells and by releasing the enzyme into the intestinal interstitial fluid, from which at least a portion is transported to the blood via the lymphatics. The early release of diamine oxidase seems to occur before the mucosal barrier is broken.

Actions of histamine, secretin, and PGE2 on cyclic AMP production by isolated canine fundic mucosal cells.

Cyclic AMP production was studied in isolated canine fundic gastric mucosal cells. Histamine, prostaglandin E2 (PGE2), and secretin increased cyclic AMP production by unenriched mucosal cells. In separated cell fractions, histamine stimulation of cyclic AMP production correlated with the parietal cell content of the fractions. Secretin in concentrations above 1 nM stimulated cyclic AMP production, and this effect correlated with the pepsinogen content of the separated cell fractions. At concentrations above 1 microM, PGE2 stimulated cyclic AMP production; this effect was found in all separated cell fractions and was not associated with any of the available cell markers. PGE2 stimulation of cyclic AMP production was, however, negatively correlated with the parietal cell content. Thus, histamine stimulated cyclic AMP production by parietal cells and secretin stimulated production of cyclic AMP by chief cells. PGE2 stimulation of cyclic AMP production could not be localized to a single cell type but occurred primarily in nonparietal cells.

Histamine and cyclic AMP in isolated canine parietal cells.

The relationship between cyclic AMP production and the response of isolated canine parietal cells to histamine has been examined. Histamine increased cyclic AMP generation, and this effect correlated with histamine stimulation of oxygen consumption and aminopyrine accumulation. Metiamide inhibited histamine-stimulated cyclic AMP generation and oxygen consumption in a parallel fashion. At concentrations below 100 microM, isobutyl AMP production and oxygen consumption in a similar fashion. However, with IMX above 100 microM, histamine caused no further increases in oxygen consumption, despite markedly enhanced cyclic AMP generation. Neither carbachol nor gastrin increased cyclic AMP production beyond that produced by IMX alone, and the combinations of histamine and carbachol and of histamine and gastrin produced no greater cyclic AMP generation than produced by histamine. These findings support a close relationship between cyclic AMP production and the action of histamine but not of carbachol or gastrin on isolated parietal cells. The mechanisms underlying the potentiating interactions between histamine, carbachol, and gastrin involve step(s) beyond stimulation of cyclic AMP generation.

Effect of histamine on canine gastric mucosal adenylate cyclase.

The effects of histamine, Nalpha-dimethylhistamine, 4,5-methylhistamine, Ntau-methylhistamine, pentagastrin, carbachol, and NaF on the adenylate cyclase activity from canine gastric mucosa were investigated in cell-free preparations. In gastric fundic mucosa, histamine (10(-4) M), Nalpha-dimethylhistamine (10(-4) M), 4,5-methylhistamine (10(-4 M), and NaF (10)-2) M) significantly (P less than 0.001) increased adenylate cyclase activity (means+/-SE) by 44.7+/-6.6, 49.4+/-6.7, 34.0+/-6.4, and 572.0+/-100%, respectively, above basal activity. The effect of histamine and Na-dimethyl histamine was dose-dependent. In contrast, other tested agents failed to stimulate the formation of cyclic AMP in gastric fundic mucosa. Metiamide (10(-4) M) blocked the stimulation of fundic mucosa adenylate cyclase by histamine and Nalpha-dimethylhistamine, without significantly altering basal and NaF-induced adenylate cyclase activity. Histamine, however, did not stimulate the adenylate cyclase activity from the gastric antral mucosa. The findings support the proposal that the canine gastric acid response to histamine may be mediated by cyclic AMP formed in response to stimulation of histamine H2-receptors.

Blocking of olive oil induced plasma protein escape from the intestinal circulation by histamine antagonists and by a diamine oxidase releasing agent.

Earlier studies have shown that feeding of olive oil to rats substantially increased the plasma protein in the intestinal lymph. The possibility of histamine mediating this response was examined. The plasma protein escape from intestinal circulation after olive oil feeding was measured in rats in terms of the amount of Evans Blue labelled plasma protein found in the intestinal lymph. Animals treated with histamine antagonists (H1-receptor antagonist pyrilamine, 16-22 mg/kg i.p., plus H2-receptor antagonist Burimamide, 12-16 mg/kg i.p.) did not show an increase in the quantity of lymphatic plasma protein. Heparin pretreatment which releases the histaminolytic enzyme, diamine oxidase, into the interstitial space also prevented the increased accumulation of labelled plasma protein in the lymph after olive oil ingestion. Based on these observations, histamine appears to act on the intestinal microcirculation during olive oil absorption and allows larger quantities of plasma proteins to leave the intestinal circulation.

Interaction of prostaglandins and histamine with enzymes of cyclic AMP metabolism from guinea pig gastric mucosa.

Prostaglandins (PGE1, PGE2, PGA1) and histamine have opposing effects on gastric HCl secretion, but we found that both stimulate adenylate cyclase activity in cell-free membrane preparations of guinea pig gastric fundic mucosa. The stimulatory effect of prostaglandins was found in this study to be specific and dose-dependent over a concentration range from 10(-7) to 10(-4) M. In similar preparations from antral regions of guinea pig gastric mucosa, the adenylate cyclase was stimulated only by PGE1, PGE2, and PGA1 and not by histamine. Maximum stimulating doses of PGE1, PGE2, or PGA1, and of histamine had an additive effect on the adenylate cyclase activity from fundic gastric mucosa. Metiamide, a histamine H2-receptor antagonist, inhibited the stimulation of fundic mucosa adenylate cyclase by histamine but did not interfere with the stimulation by prostaglandins. Cyclic AMP phosphodiesterase activity of guinea pig gastric mucosa was unaffected by PGE1 and PGE2 or by histamine, and was slightly depressed by PGA1. These results indicate that histamine and prostaglandins stimulate two different adenylate cyclase systems both present in guinea pig gastric mucosa tissue. Therefore, the known inhibitory effect of prostaglandins on gastric acid secretion is not related to the interference with the stimulation of the histamine H2-receptor-sensitive adenylate cyclase complex by histamine nor do prostaglandins accelerate cyclic AMP breakdown by cyclic AMP phosphodiesterase to reduce cyclic AMP levels.