Measurement of gastric bicarbonate secretion in the human stomach: different methods produce discordant results

Measuring pH and Buffer Capacity in Fluids Aspirated from the Fasted Upper Gastrointestinal Tract of Healthy Adults

PURPOSE

The design of biorelevant conditions for in vitro evaluation of orally administered drug products is contingent on obtaining accurate values for physiologically relevant parameters such as pH, buffer capacity and bile salt concentrations in upper gastrointestinal fluids.

METHODS

The impact of sample handling on the measurement of pH and buffer capacity of aspirates from the upper gastrointestinal tract was evaluated, with a focus on centrifugation and freeze-thaw cycling as factors that can influence results. Since bicarbonate is a key buffer system in the fasted state and is used to represent conditions in the upper intestine in vitro, variations on sample handling were also investigated for bicarbonate-based buffers prepared in the laboratory.

RESULTS

Centrifugation and freezing significantly increase pH and decrease buffer capacity in samples obtained by aspiration from the upper gastrointestinal tract in the fasted state and in bicarbonate buffers prepared in vitro. Comparison of data suggested that the buffer system in the small intestine does not derive exclusively from bicarbonates.

CONCLUSIONS

Measurement of both pH and buffer capacity immediately after aspiration are strongly recommended as "best practice" and should be adopted as the standard procedure for measuring pH and buffer capacity in aspirates from the gastrointestinal tract. Only data obtained in this way provide a valid basis for setting the physiological parameters in physiologically based pharmacokinetic models.

A physics-based model for maintenance of the pH gradient in the gastric mucus layer

It is generally accepted that the gastric mucus layer provides a protective barrier between the lumen and the mucosa, shielding the mucosa from acid and digestive enzymes and preventing autodigestion of the stomach epithelium. However, the precise mechanisms that contribute to this protective function are still up for debate. In particular, it is not clear what physical processes are responsible for transporting hydrogen protons, secreted within the gastric pits, across the mucus layer to the lumen without acidifying the environment adjacent to the epithelium. One hypothesis is that hydrogen may be bound to the mucin polymers themselves as they are convected away from the mucosal surface and eventually degraded in the stomach lumen. It is also not clear what mechanisms prevent hydrogen from diffusing back toward the mucosal surface, thereby lowering the local pH. In this work we investigate a physics-based model of ion transport within the mucosal layer based on a Nernst-Planck-like equation. Analysis of this model shows that the mechanism of transporting protons bound to the mucus gel is capable of reproducing the trans-mucus pH gradients reported in the literature. Furthermore, when coupled with ion exchange at the epithelial surface, our analysis shows that bicarbonate secretion alone is capable of neutralizing the epithelial pH, even in the face of enormous diffusive gradients of hydrogen. Maintenance of the pH gradient is found to be robust to a wide array of perturbations in both physiological and phenomenological model parameters, suggesting a robust physiological control mechanism.NEW & NOTEWORTHY This work combines modeling techniques based on physical principles, as well as novel numerical simulations to test the plausibility of one hypothesized mechanism for proton transport across the gastric mucus layer. Results show that this mechanism is able to maintain the extreme pH gradient seen in in vivo experiments and suggests a highly robust regulation mechanism to maintain this gradient in the face of dynamic lumen composition.

Netazepide, a gastrin/CCK2 receptor antagonist, causes dose-dependent, persistent inhibition of the responses to pentagastrin in healthy subjects

AIMS

To confirm by means of pentagastrin, a synthetic gastrin agonist, that netazepide is a gastrin/CCK2 receptor antagonist in healthy subjects, and that antagonism persists during repeated dosing.

METHODS

We did two studies in which we infused pentagastrin (0.6 μg kg(-1)  h(-1) intravenously), aspirated gastric secretion and measured the volume, pH and H(+) secretion rate of the gastric aspirate. First, we did a double-blind, five-way crossover study (n = 10) to assess the effect of single oral doses of netazepide (1, 5, 25 and 100 mg) and placebo on the response to pentagastrin. Then, we did a single-blind, placebo-controlled study (n = 8) to assess the effect of the first and last oral doses of netazepide (100 mg) twice daily for 13 doses on the response to pentagastrin.

RESULTS

Netazepide was well tolerated. After placebo, pentagastrin increased the volume and H(+) secretion rate and reduced the pH of gastric aspirate. Compared with placebo, single doses of netazepide caused dose-dependent inhibition of the pentagastrin response (P < 0.02); netazepide (100 mg) abolished the response. After 13 doses, the reduction in volume and H(+) secretion rate persisted (P < 0.001), but the pH effect was mostly lost.

CONCLUSIONS

Netazepide is an orally active, potent, competitive antagonist of human gastrin/CCK2 receptors. Antagonism is dose dependent and persists during repeated dosing, despite tolerance to the effect on pH. Further studies are required to explain that tolerance. Netazepide is a tool to study the physiology and pharmacology of gastrin, and merits studies in patients to assess its potential to treat gastric acid-related conditions and the trophic effects of hypergastrinaemia.

Comparison of oesophageal and gastric air tonometry in patients with circulatory failure

BACKGROUND

Gastric PCO2 measured by balloon tonometry can estimate the adequacy of splanchnic perfusion. However, enteral feeding and gastric content can interfere with gastric PCO2 assessment. Tonometry in other sites of the body could avoid these problems. We therefore tested the hypothesis that oesophageal air tonometry would give results similar to gastric tonometry.

METHODS

We studied 20 consecutive patients (mean age 68 (SD 9) [range 49-81] yr, 18 males, SAPS II score 55 (SD 18), ICU mortality 55%) with circulatory disorders during mechanical ventilation in the intensive care unit. Tonometer probes were placed via the nose, one into the stomach and the other in the oesophagus. PCO2 was measured with two automated gas analysers, at admission and 30 min, 1, 2, 3, 32, 40, and 48 h thereafter.

RESULTS

One hundred and forty-eight paired measurements were obtained. Gastric PCO2 was greater than oesophageal PCO2 on admission (7.19 (1.43) vs 5.89 (0.73) kPa, P < 0.01) and subsequently. Differences between the measures correlated (r = 0.67) with the mean absolute value, indicating that overestimation increased as gastric PCO2 increased.

CONCLUSIONS

Oesophageal PCO2 is less than gastric PCO2, and the difference is greater when gastric PCO2 levels are greater. Air tonometry may not measure regional PCO2 levels in the oesophagus satisfactorily. Other methods and sites for carbon dioxide tonometry should be examined.

Human duodenal mucosal brush border Na(+)/H(+) exchangers NHE2 and NHE3 alter net bicarbonate movement

The proximal duodenal mucosa secretes HCO that serves to protect the epithelium from injury. In isolated human duodenal enterocytes in vitro, multiple luminal membrane proteins are involved in acid/base transport. We postulated that one or more isoforms of the Na(+)/H(+) exchanger (NHE) family is located on the apical surface of human duodenal mucosal epithelial cells and thereby contributes to duodenal mucosal HCO transport. Duodenal biopsies were obtained from human volunteers, and the presence of NHE2 and NHE3 was determined by using previously characterized polyclonal antibodies (Ab 597 for NHE2 and Ab 1381 for NHE3). In addition, proximal duodenal mucosal HCO(3)(-) transport was measured in humans in vivo in response to luminal perfusion of graded doses of amiloride; 10(-5)--10(-4) M amiloride was used to inhibit NHE2 and 10(-3) M amiloride to inhibit NHE3. Both NHE2 and NHE3 were localized principally to the brush border of duodenal villus cells. Sequential doses of amiloride resulted in significant, step-wise increases in net duodenal HCO(3)(-) output. Inhibition of NHE2 with 10(-5) M and 10(-4) M amiloride significantly increased net HCO(3)(-) output. Moreover, there was an additional, equivalent increase (P < 0.05) in duodenal HCO(3)(-) output with 10(-3) M amiloride, which inhibited NHE3. We conclude that 1) NHE2 and NHE3 are localized principally to the brush border of human duodenal villus epithelial cells; 2) sequential inhibition of NHE2 and NHE3 isoforms resulted in step-wise increases in net HCO(3)(-) output; 3) NHE2 and NHE3 participate in human duodenal villus cell HCO(3)(-) transport; and 4) the contribution of NHE-related transport events should be considered when studying duodenal HCO(3)(-) transport processes.

Effect of gastric feeding on intragastric P(CO2) tonometry in healthy volunteers

PURPOSE

The tonometric detection of a high intragastric regional P(CO2) (PrCO2) reflecting an elevated intramucosal P(CO2) can be helpful to diagnose mucosal ischemia, if acid secretion is suppressed to avoid intragastric CO2 production through buffering of acid by bicarbonate in the stomach. It is recommended to perform tonometry in the fasting state, but this may hamper feeding of the critically ill. On the other hand, postfeeding tonometry could serve as a diagnostic stress test because feeding increases mucosal blood flow demand, provided that the meal itself does not hamper diffusion of CO2 from mucosa to tonometer balloon and does not generate intragastric CO2, independently from intramucosal P(CO2). We therefore studied the effect of a standard meal on intragastric PrCO2 tonometry in healthy volunteers with suppression of meal-stimulated gastric acid secretion and, presumably, with an adequate mucosal blood flow reserve.

MATERIAL AND METHODS

The gastric juice pH and tonometric PrCO2 were measured in 14 human volunteers, after gastric acid secretion suppression by either ranitidine (100-mg bolus, followed by 25 mg/h i.v., n = 7) or by ranitidine plus pirenzepine (10-mg bolus, followed by 3 mg/h i.v., n=7) to suppress any residual meal-stimulated gastric acid secretion, before and at 30-minute intervals until 120 minutes after oral ingestion of a standard liquid test meal (Pulmocare [Abbott, the Netherlands]; 500 mL, 750 kcal, P(CO2) 5 mm Hg, pH 7.50).

RESULTS

The gastric juice pH, which was >4.0 in all individuals throughout the study, and the PrCO2 did not depend on the regimen for gastric acid secretion suppression, and therefore the data were pooled. The PrCO2 (median [range]) after feeding was 69% (56% to 170%) of baseline (42 [37-51] mm Hg) from 0 to 30 minutes (P < .001), 85% (72% to 167%) of baseline from 30 to 60 (P < .05), 97% (57% to 193%) from 60 to 90 minutes, and 112% (97% to 189%) of baseline from 90 to 120 minutes with a rise above baseline in 10 of 14 patients. In vitro, the liquid test meal generated CO2 after adding bicarbonate but not after hydrochloric acid.

CONCLUSION

We recommend intragastric tonometry to be performed in the fasting state and discourage tonometry after feeding as a stress test, because a single test meal changes tonometric PrCO2 in a time-dependent manner until 2 hours after gastric feeding of healthy volunteers. The fall in PrCO2 directly after feeding can be attributed to dilution, whereas a rise above baseline in some patients may have been caused, as supported by CO2 production after adding bicarbonate to the test meal in vitro, by CO2 production through buffering of meal-derived acid by gastric bicarbonate, in the absence of stimulated gastric acid secretion by feeding.

Omeprazole promotes proximal duodenal mucosal bicarbonate secretion in humans

The proton pump inhibitor, omeprazole, surprisingly resulted in higher rates of proximal duodenal mucosal bicarbonate secretion than previously reported using an H2 receptor antagonist for gastric acid inhibition. Gastroduodenal perfusions were performed in healthy volunteers to evaluate whether this incidental finding is explained by more potent gastric acid inhibition by omeprazole or might be caused by the different mode of drug action. Basal and stimulated gastric and duodenal bicarbonate secretion rates were measured in the same subjects in control experiments (n = 17) and after pretreatment with high dose omeprazole (n = 17) and ranitidine (n = 9), respectively, by use of a technique permitting simultaneous measurements. Concentrations of bicarbonate were measured in the respective effluents by the method of back titration. Both omeprazole and ranitidine completely inhibited gastric acid secretion (pH 6.9 v 6.8; p > 0.05). Omeprazole caused higher rates of basal (mean (SEM)) (597 (48) v 351 (39) mumol/h; p < 0.02) and vagally stimulated (834 (72) v 474 (66) mumol/h; p < 0.02), but not acid stimulated (3351 (678) v 2550 (456) mumol/h; p > 0.05) duodenal bicarbonate secretion compared with control experiments. Also the combination of omeprazole and ranitidine increased (p = 0.05) duodenal bicarbonate secretion, while ranitidine alone caused no change in either basal or stimulated secretion. In the stomach basal as well as vagally stimulated bicarbonate secretion was independent of the means of acid inhibition. These results show that the proton pump inhibitor, omeprazole, promotes proximal duodenal mucosal bicarbonate secretion apparently independent of its gastric acid inhibitory effect. The mechanism of action remains speculative.

Gastric bicarbonate secretion and release of prostaglandin E2 are increased in duodenal ulcer patients but not in Helicobacter pylori-positive healthy subjects

BACKGROUND

Duodenal ulcer (DU) patients have impaired proximal duodenal mucosal bicarbonate secretion at rest and in response to luminal acid with higher acid-stimulated mucosal release of prostaglandin (PG) E2 than healthy subjects. Our purpose was to determine whether this abnormality was present also in the stomach of DU patients.

METHODS

Simultaneous determinations of gastric and duodenal bicarbonate secretion and luminal release of PGE2 were performed in 16 healthy volunteers (5 Helicobacter pylori-positive) and 8 inactive DU patients (all H. pylori-positive).

RESULTS

In healthy volunteers the rates of gastroduodenal bicarbonate secretion and the release of PGE2 were not influenced by H. pylori status. In inactive DU patients the rates of basal (704 +/- 84 versus 356 +/- 40 mumol/h; mean +/- SEM) and vagally stimulated (modified sham feeding) (1724 +/- 376 versus 592 +/- 52 mumol/h) gastric bicarbonate secretion were higher (p < 0.05) than in the health, whereas the corresponding rates (339 +/- 42 versus 591 +/- 51 mumol/h and 543 +/- 99 versus 778 +/- 69 mumol/h) in duodenal bicarbonate secretion were lower (p < 0.05). In addition, inactive DU patients had higher basal (148 +/- 32 versus 53 +/- 5 ng/h) and stimulated (291 +/- 84 versus 131 +/- 25 ng/h) gastric release of PGE2, but only the basal release of PGE2 into the duodenum was significantly increased (20 +/- 3 versus 5 +/- 1 ng/h; p < 0.05).

CONCLUSION

Increased mucosal production of PGE2 may be responsible for the abnormally high gastric secretion of bicarbonate in inactive DU patients. The defective duodenal secretion of bicarbonate observed in these patients may be a consequence of previous ulceration rather than the mere presence of H. pylori infection.

Indomethacin decreases gastroduodenal mucosal bicarbonate secretion in humans

BACKGROUND

Cyclooxygenase inhibitors reduce mucosal bicarbonate secretion in the duodenum, but the evidence for their effect on bicarbonate secretion in the stomach remains controversial. We have, therefore, studied how indomethacin influences gastroduodenal bicarbonate secretion and luminal release of prostaglandin (PG) E2 by means of a method that enables simultaneous measurements in the stomach and the duodenum.

METHODS

Gastric and duodenal perfusions were performed twice in random order during control conditions or after pretreatment with indomethacin (100 mg intravenously) in eight healthy volunteers. Bicarbonate and PGE2 were measured in the gastroduodenal effluents by back-titration and radioimmunoassay, respectively.

RESULTS

Vagal stimulation and duodenal luminal acidification (0.1 M HCl; 20 ml; 5 min) increased gastroduodenal bicarbonate secretion (p < 0.05). Indomethacin markedly inhibited both basal and stimulated gastric and duodenal mucosal bicarbonate secretion, and this reduction was similar to the degree of cyclooxygenase inhibition estimated by the luminal release of PGE2 (p < 0.05).

CONCLUSION

These results unequivocally demonstrate that endogenous PG modulates basal and stimulated bicarbonate secretion, both in the stomach and in the duodenum.

The pH/PCO2 method for continuous determination of human gastric acid and bicarbonate secretion. A validation study

BACKGROUND

The present paper describes and evaluates a methodologic approach for registration of the fast, interdigestive, motility-related changes in gastric acid and bicarbonate outputs seen in man.

METHODS

The technique is based on continuous gastric luminal perfusion and measurements of pH and PCO2 in gastric effluent and concomitant intragastric/duodenal manometry. Fourteen healthy volunteers participated.

RESULTS

Direct acid secretory estimations from pH recordings, corrected for hydrogen ion activity, correlated closely with values obtained by conventional titration. After intragastric infusion of bicarbonate, 96 +/- 5% of the newly measured steady-state value was registered virtually instantaneously provided that corrections for the PCO2 electrode time constant and the perfusion/aspiration time were made. In the neutral pH range (pH 5-7), practically full quantitative recovery of intragastrically infused bicarbonate was obtained. In the acid pH interval (pH 2-5) the recovery was significantly lower (53 +/- 6%; p < 0.01). With an aspirate without air admixture and during high perfusion rates (31 and 46 ml/min), full recovery of bicarbonate was obtained also at an acid pH, whereas a reduced perfusion rate (16 ml/min) significantly (p < 0.05) reduced the recovery rate.

CONCLUSIONS

With the pH/PCO2 technique both acid and bicarbonate assessments have a close to on-line time resolution. Acid output is measured accurately, but the method potentially underestimates actual bicarbonate levels in the acid pH range, a combined effect of diffusion of CO2 into air bubbles in the aspirate and into the gastric mucosa from the lumen. A high gastric perfusion rate minimizes this source of error. The pH/PCO2 technique is well suited for studies of the interaction between secretion and motility in the human stomach.

Review article: gastroduodenal bicarbonate secretion

The gastroduodenal epithelium is covered by an adherent mucus layer into which bicarbonate is secreted by surface epithelial cells. This mucus-bicarbonate barrier is an important first line of defence against damage by gastric acid and pepsin, and has been demonstrated in all species including human. Similar to gastric acid secretion, regulation of gastric and duodenal bicarbonate secretion can be divided into three phases: cephalic, gastric and duodenal. In humans, sham-feeding increases bicarbonate secretion in both the stomach and duodenum which is mediated by cholinergic vagal fibres in the stomach, but seems to be noncholinergic in the duodenum. Gastric distention and luminal acidification increases gastric bicarbonate production. Whereas there are no data relating to the gastric phase of human duodenal bicarbonate secretion, in animals, food and acid in the stomach independently stimulate duodenal bicarbonate output. To date, the duodenal phase of human gastric bicarbonate secretion has not been studied, but data from animals reveal that duodenal acidification augments bicarbonate secretion in the stomach. In all species tested, direct acidification of the duodenum is a potent stimulant of local bicarbonate production. In humans, the pH threshold for bicarbonate secretion is pH 3.0. Mediation of gastroduodenal bicarbonate secretion is provided by a variety of agonists and antagonists, tested mainly in animals, but some have been evaluated in humans. Prostaglandins of the E class and VIP are major factors that control bicarbonate secretion. Bicarbonate secretion, and the mucus-bicarbonate layer in general, is adversely effected by ulcerogenic factors such as aspirin, NSAIDs, bile salts, and cigarette smoking. Furthermore, duodenal ulcer patients have an impairment in bicarbonate production within the duodenal bulb, at rest and in response to stimulation. These findings indicate that the mucus-bicarbonate barrier is an important first line of defence in the pathogenesis of peptic ulcer disease.

Splanchnic tonometry: a review of physiology, methodology, and clinical applications

The objective of this article is to review splanchnic tonometry. The English literature, involving both animal and human studies, was used for review, with emphasis on papers on physiological and methodological principles and clinical applications. Tonometry involves the measurement of intraluminal PCO2 as a measure of mucosal PCO2 in the gastrointestinal tract via a catheter in, for instance, stomach or sigmoid colon, and the calculation, with help of the blood bicarbonate content and the Henderson-Hasselbalch equation, of the mucosal pH (pHi). The latter is considered as a relatively simple index of the adequacy of mucosal blood flow. Concerning methodology, it is still unclear whether acid secretion should be inhibited for proper assessment of PCO2 in the stomach. Buffering of bicarbonate by gastric acid may elevate the intraluminal PCO2 independently from mucosal PCO2, thereby confounding pHi as a measure of perfusion adequacy. This can be prevented by inhibition of acid secretion. Authors have raised doubts whether the composite variable pHi is of additive value to the acid-base status of arterial blood, so that it is unclear whether a subnormal pHi is a specific and sensitive indicator of mucosal ischemia, as suggested by others on the basis of a decline in the pHi along the gastrointestinal tract in animals subjected to vascular occlusion or circulatory shock. Moreover, tissue PCO2 depends on the PCO2 of supplying blood. Conversely, the bicarbonate concentration in ischemic mucosa may not equal that in arterial blood. Taken together, an elevated tonometer fluid arterial blood PCO2-gradient might be a more sensitive and specific indicator of mucosal ischemia than a decrease in the pHi, analogous to an increase in tissue PCO2 and widening of the venoarterial PCO2 gradient during various types of hypoperfusion, in animals and humans. Although splanchnic ischemia is an early event in shock, the sensitivity and specificity of this index for mucosal ischemia and its clinical value, relative to that of the pHi, have not been formally evaluated yet. Nevertheless, the pHi has been suggested to be of predictive value for gastrointestinal complications, multiple organ failure, success or failure of weaning from mechanical ventilation, and outcome in critically ill patients. Tonometry may be a useful monitoring technique to guide treatment and to improve survival. Splanchnic tonometry is a relatively simple, noninvasive, and thereby promising technique to monitor the critically ill. However, some aspects need further evaluation before the technique can be advocated for routine use.

Hypovolemia-induced cardiovascular effects on human gastric mucosal acid and HCO3- release

BACKGROUND

The bicarbonate ion seems to play a crucial role in mucosal acid-base regulation by generating a pH gradient that is regarded as a 'first line of defense' against acid back-diffusion. The aim of this study was to determine the effects of hypovolemia on gastric mucosal buffering capacity, as reflected by luminal HCO3- release, in human volunteers.

METHODS

Central hypovolemia was induced by lower-body negative pressure (LBNP), and HCO3- release was measured by using a perfusion system based on continuous recording of the pH and PCO2 of gastric aspirate. The response to LBNP was related to concomitant cardiovascular effects, to gastric pH, and to the current phase of the migrating motor complex (MMC).

RESULTS

At an acid gastric pH, LBNP induced a slight but statistically significant reduction in luminal HCO3- release (-27 +/- 10%, p < 0.05). The magnitude of the response was significantly correlated with the degree of reflex tachycardia. A larger and less variable response (-78 +/- 4%, p < 0.01 versus control group) was seen when luminal pH was increased by ranitidine pretreatment. The effect of LBNP on HCO3- release was statistically significant only during the early and middle parts of the MMC cycle.

CONCLUSIONS

The results indicate that hypotension may reduce gastric mucosal buffering capacity, probably by activation of a sympathetic reflex. The magnitude of this response seems to depend on: 1) the degree of baroreceptor unloading; 2) luminal pH; and 3) the current phase of the MMC.

Effect of ranitidine on basal and bicarbonate enhanced intragastric PCO2: a tonometric study

A high intragastric PCO2 (iPCO2), determined tonometrically, is the main factor participating in a low gastric intramucosal pH (pHi) and may point to gastric mucosal ischaemia. iPCO2 might also increase, however, after buffering of gastric acid by bicarbonate; the magnitude of this effect and the efficacy of H2 blockers to prevent it are unclear. Ten healthy volunteers (20-24 years) were studied at baseline and after oral ingestion of 500 mg sodium bicarbonate. The same test was carried out one hour after intravenous injection of 100 mg ranitidine. A glass pH electrode for continuous gastric juice pH measurements and a Tonomitor catheter were placed 10 cm distally from the gastro-oesophageal junction. iPCO2 was measured in saline boluses, infused at 30 minute intervals in the balloon at the tip of the Tonomitor. Before ranitidine was given, basal iPCO2 (mean (SD)) was 8.40 (2.53) kPa, and increased to 19.20 (5.87) kPa after sodium bicarbonate (p < 0.001). After ranitidine, the gastric juice pH increased from 1.8 (0.9) to 5.6 (1.3) (p < 0.05), while basal iPCO2 was 5.60 (0.67) kPa (p < 0.01) and did not change after sodium bicarbonate (6.27 (2.67) kPa)). iPCO2 values after acid secretion suppression were similar to those in capillary blood (5.60 (0.40 kPa)). The difference between intragastric and blood PCO2 during normal acid secretion probably results from buffering of gastric acid by gastric bicarbonate, rather than by duodenogastric reflux or saliva entering the stomach. During acid secretion suppression, intragastric equals blood PCO2, even after oral ingestion of sodium bicarbonate. Hence, acid secretion inhibition is mandatory for proper assessment of iPCO2 and pHi as specific measures of the adequacy of gastric mucosal blood flow.

Laboratory medicine in ulcer disease

The role of laboratory medicine in ulcer disease is poorly defined. However there is increasing evidence of the clinical usefulness of some laboratory tests that investigate secretory functions and defensive properties of the stomach, gastrointestinal hormones and Helicobacter pylori infection. These tests may modify the clinical management of patients with peptic ulcer by identifying H. pylori positive subjects, patients with high acid output, patients who do not respond to antisecretory therapy, and patients with high gastrin levels in whom Zollinger-Ellison syndrome may be suspected. Here we review the clinical value of laboratory tests in ulcer disease, particularly as concerns the cost/benefit ratio. The relative merits of these tests are described giving an indication of their possible role in the diagnostic algorithm.

Motility-related cyclic fluctuations of interdigestive gastric acid and bicarbonate secretion in man. A source of substantial variability in gastric secretion studies

The relationship between interdigestive gastric motility and secretion was studied in eight healthy volunteers. Acid and bicarbonate output rates were measured with a high time resolution, using a perfusion system based on continuous registration of pH and PCO2 of gastric effluent. Antral pressure was measured by manometry. The total duration of the interdigestive motility cycle (time between two phase-III complexes) was 96 +/- 12 min (mean +/- SE). In late migrating motor complex phase II, acid output, bicarbonate output, and bile reflux increased significantly. Acid secretion reached a peak in association with motor phase III. The gastric lumen was then rapidly alkalinized; this phenomenon was due to a simultaneous decrease in acid secretion and a short-lasting (15 +/- 2 min, mean +/- SE) phasic increase in bicarbonate output, which was not associated with bile reflux (bilirubin). After these phase-III-related events both acid and bicarbonate output rates reached a relatively stable level during phase I and early phase II. This period of stability constituted 47 +/- 3% (acid) and 41 +/- 6% (bicarbonate, means +/- SE), respectively, of the cycle. The peak to base line output ratio was 6.6 +/- 1.2 (p < 0.001) for acid and 2.8 +/- 0.3 (p < 0.001) for bicarbonate (means +/- SE). The results show a marked variability in acid and bicarbonate output rates during the interdigestive motility cycle. The magnitude of this variability has previously been underestimated owing to poor time resolution of the secretion measurements. If not taken into account, these 'spontaneous' secretory variations may constitute a considerable source of error in gastric secretion studies.