Measurement of Gastric Bicarbonate Secretion in the Human Stomach: Different Methods Produce Discordant Results

Abstract

Human gastric bicarbonate secretion has been measured by back-titration, from pH and pressure of carbon dioxide (PCO2) determinations (using the Henderson-Hasselbalch formula), and from equations based on gastric juice osmolality and [H+] (osmolality-[H+] method). Since these methods show large quantitative differences in their estimations of gastric bicarbonate secretion, we examined each to define the reasons for these discrepancies and establish guidelines for future work in this area. Bicarbonate recovery from 'non-parietal' secretions (0 to 80 mM HCO3) reacting with 'pure parietal secretion' (160 mM HCl) was studied both in vitro and in the pylorus-occluded healthy human stomach during acid suppression, exogenous acidification, and pentagastrin stimulation. The pH/PCO2 method estimated HCO3- accurately under anaerobic conditions in vitro, whereas the osmolality-[H+] method (with correction factors for osmolality incorporated by us) was accurate under aerobic conditions. In the acid-suppressed stomach back-titration was significantly more accurate than the pH/PCO2 method. In the exogenously acidified and pentagastrin-stimulated stomachs the pH/PCO2 method underestimated bicarbonates, and the osmolality-[H+] method was spuriously elevated in the low range and diminished at high bicarbonate concentrations. Estimates of 'basal' bicarbonate secretion (at zero added bicarbonate) were severalfold higher by the osmolality-[H+] method (5.26 +/- 0.33 mmol/h) than by the pH/PCO2 method (1.20 +/- 0.23 mmol/h) or back-titration (0.65 +/- 0.14 mmol/h). In conclusion, gastric bicarbonate was determined most correctly by back-titration in the acid-suppressed stomach, whereas measurement of bicarbonate in the acid-secreting stomach was not accurate with any method.

Gastric Bicarbonate Secretion and Release of Prostaglandin E2Are Increased in Duodenal Ulcer Patients But Not inHelicobacter pylori-Positive Healthy Subjects

“…The results of the present study indicate that the basal rates of gastric bicarbonate secretion observed in healthy volunteers, irrespective of their H. pylori antibody status, were in the same order of magnitude as those previously reported using the back-titration method in the acid-suppressed stomach (27). In contrast to other investigators (18, 32, 33), we observed higher rates of gastric bicarbonate secretion in inactive DU patients than in healthy volunteers.…”

“…The discrepancy probably reflects the methodologic constraints inherent in the choice of method for determination of bicarbonate in gastric effluents and means of acid inhibition. A single study used the osmolality-H+ method (32), which has been reported to overestimate gastric bicarbonate secretion at least fourfold (27). In two other studies (18,33) gastric bicarbonate secretion may have been underestimated, particularly in hypersecretory DU patients, because gastric acid secretion was insufficiently inhibited by a histamine-Hz-receptor antagonist.…”

“…This method corresponds to the backtitration method (26), which has previously been extensively validated and judged most accurate for determination of gastric bicarbonate (27). Before analysis the samples were gassed with C02-free nitrogen for 5 min to remove dissolved carbon dioxide.…”

Effects of Age on Gastric Alkaline and Nonparietal Fluid Secretion in Humans

“…We favor the latter explanation for three reasons. First, age had no effect on calculated gastric H + and parietal volume secretion rates, consistent with previous reports [1][2][3][4]18]. Second, age was inversely related to calculated gastric HCO -3 and nonparietal volume secretion rates.…”

“…The first is that our method for measuring gastric HCO -3 and nonparietal fluid secretion is indirect and derived from a two-component model of gastric secretion [9,11,18]. However, the inverse relationship between age and direct measurements of Na + output supports our basic conclusion.…”