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Secretion of Bicarbonate by Gastric and Duodenal Mucosa

Gunnar Flemström, Andrew Garner

10.1002/cphy.cp060316

Source: Supplement 18: Handbook of Physiology, The Gastrointestinal System, Salivary, Gastric, Pancreatic, and Hepatobiliary Secretion

Originally published: 1989

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 Methods of Measurement
1.1 Gastric Bicarbonate Secretion
1.2 Duodenal Bicarbonate Secretion
2 Mechanisms of Gastroduodenal Bicarbonate Secretion
2.1 Origin and Transport of Gastric Bicarbonate
2.2 Contribution of Bicarbonate Leakage
2.3 Duodenal Mucosal Transport of Bicarbonate
2.4 Gradient in Secretion Along the Duodenum
2.5 Biochemical Basis for Duodenal Bicarbonate Secretion
3 Physiological Control of Gastroduodenal Bicarbonate Secretion
3.1 Humoral Control
3.2 Neural Influence
3.3 Control by Mucosal Endogenous Prostaglandins
3.4 Relation to Gastric Acid Secretion and Blood Flow
4 Pharmacological Modulation
4.1 Inhibitors of Gastric Alkaline Secretion
4.2 Stimulation of Gastric Alkaline Secretion by Prostaglandins
4.3 Duodenal Mucosal Alkaline Secretion and cAMP
4.4 Stimulation of Duodenal Secretion by Prostaglandins
4.5 Other Drugs Affecting Duodenal Alkaline Secretion
5 Protective Role of Bicarbonate
5.1 Surface pH Gradient
5.2 Possible Therapeutic Implications
6 Summary and Perspectives
Figure 1. Figure 1.

Surface epithelia secretion of in bullfrog proximal duodenum based on in vitro studies. a, Cl‐‐ exchange stimulated by glucagon and inhibited by furosemide; b, transport independent of luminal Cl‐, stimulated by prostaglandins and cAMP but insensitive to furosemide; c, anion carrier that under some conditions displays affinity for Cl‐; d, passive migration of through shunt pathways sensitive to variations in transmucosal hydrostatic pressure. Similar inhibition of glucagon–stimulated secretion by furosemide occurs in rat duodenum in vivo 51.

From Flemström and Garner 45
Figure 2. Figure 2.

Humoral mediation of rise in secretion in response to luminal acid, based on experiments where isolated amphibian mucosae were mounted in parallel 82. Exposure of fundic mucosa to pH 2 releases agents that simulate secretion in parallel (non‐acid‐exposed) fundus and antrum. Exposure of duodenal mucosa to pH 4 releases agents that stimulate secretion in both duodenum and fundus. Experiments with fundic, antral, and duodenal pouches in conscious dog 109,110 suggest that similar stimulation of mucosa alkaline secretions operates in mammals.

From Heylings et al. 84
Figure 3. Figure 3.

Sham feeding (SH) stimulates gastric secretion in healthy volunteers. Means ± SE; n = 6, where n is number of experiments.

From Forssell et al. 58. Copyright 1985 by The American Gastroenterological Association
Figure 4. Figure 4.

Effects of bilateral vagal stimulation (shaded area, 10 Hz for 10 min) on gastric and duodenal secretion in anesthetized cats with intact (closed circles, n = 5) and cut (open circles, n = 6) splanchnic nerves; n, number of experiments. Note much greater response after splanchnicotomy.

From Fändriks 30
Figure 5. Figure 5.

Brief 10‐min exposures of duodenal segments devoid of Brunner's glands in anesthetized rat to 10 mM hydrochloric acid increase the secretion titrated at neutral luminal pH 7.4. Pretreatment with ganglionic blocking agent hexamethonium 10 mg/kg) or muscarinic antagonist atropine 40 μg/kg) decreases response to luminal acid. Data are means ± SE of normalized secretion; n = 8 in all groups, where n is the number of rats.
Figure 6. Figure 6.

Model for protection of gastric mucosa. Stimulation of the H+ secretory process in the parietal cells increases the amount of available for secretion by surface epithelial cells. Direct stimulation of secretory process by neural stimuli and the subsequent effect of low luminal pH generated by H+ secretion further increase protection.

From Flemström 43. In: Physiology of the Gastrointestinal Tract 2nd ed.), © 1987, Raven Press, New York
Figure 7. Figure 7.

Inhibitory action of various nonsteroidal, anti‐inflammatory drugs on gastric fundic secretion in vitro. Frog tissues were pretreated with a histamine H2‐receptor antagonist, and drugs were added to serosal side (Closed circles, exposed to an anti‐inflammatory agent; open circles, exposed to histamine H2‐receptor antagonist alone.

Adapted from Garner 63; aspirin results), and from Garner et al. 67; fenclofenac and indomethacin results)
Figure 8. Figure 8.

Stimulation of gastric alkaline secretion by 16,16‐dimethyl prostaglandin E2 in frog fundus, rabbit fundus, and canine Heidenhain pouches and by PGE2 in human stomach. Compounds were applied to serosal side of isolated preparations and to luminal side in vivo

Adapted from Garner and Heylings 68; frog data), Rees et al. 133; rabbit data), Kauffman et al. 98; dog data), and Johansson et al. 95; human data)
Figure 9. Figure 9.

In the isolated proximal duodenum, prostaglandin E2 and forskolin (serosal side) show comparable activity as stimulants of secretion, suggesting that prostaglandins act by elevating intracellular cAMP levels. Sensitivity of tissues to a standard agonist (PGE2) was established at the beginning of experiments. Data are means ± SE; n = 8 for both where n is number of experiments.


Figure 1.

Surface epithelia secretion of in bullfrog proximal duodenum based on in vitro studies. a, Cl‐‐ exchange stimulated by glucagon and inhibited by furosemide; b, transport independent of luminal Cl‐, stimulated by prostaglandins and cAMP but insensitive to furosemide; c, anion carrier that under some conditions displays affinity for Cl‐; d, passive migration of through shunt pathways sensitive to variations in transmucosal hydrostatic pressure. Similar inhibition of glucagon–stimulated secretion by furosemide occurs in rat duodenum in vivo 51.

From Flemström and Garner 45


Figure 2.

Humoral mediation of rise in secretion in response to luminal acid, based on experiments where isolated amphibian mucosae were mounted in parallel 82. Exposure of fundic mucosa to pH 2 releases agents that simulate secretion in parallel (non‐acid‐exposed) fundus and antrum. Exposure of duodenal mucosa to pH 4 releases agents that stimulate secretion in both duodenum and fundus. Experiments with fundic, antral, and duodenal pouches in conscious dog 109,110 suggest that similar stimulation of mucosa alkaline secretions operates in mammals.

From Heylings et al. 84


Figure 3.

Sham feeding (SH) stimulates gastric secretion in healthy volunteers. Means ± SE; n = 6, where n is number of experiments.

From Forssell et al. 58. Copyright 1985 by The American Gastroenterological Association


Figure 4.

Effects of bilateral vagal stimulation (shaded area, 10 Hz for 10 min) on gastric and duodenal secretion in anesthetized cats with intact (closed circles, n = 5) and cut (open circles, n = 6) splanchnic nerves; n, number of experiments. Note much greater response after splanchnicotomy.

From Fändriks 30


Figure 5.

Brief 10‐min exposures of duodenal segments devoid of Brunner's glands in anesthetized rat to 10 mM hydrochloric acid increase the secretion titrated at neutral luminal pH 7.4. Pretreatment with ganglionic blocking agent hexamethonium 10 mg/kg) or muscarinic antagonist atropine 40 μg/kg) decreases response to luminal acid. Data are means ± SE of normalized secretion; n = 8 in all groups, where n is the number of rats.



Figure 6.

Model for protection of gastric mucosa. Stimulation of the H+ secretory process in the parietal cells increases the amount of available for secretion by surface epithelial cells. Direct stimulation of secretory process by neural stimuli and the subsequent effect of low luminal pH generated by H+ secretion further increase protection.

From Flemström 43. In: Physiology of the Gastrointestinal Tract 2nd ed.), © 1987, Raven Press, New York


Figure 7.

Inhibitory action of various nonsteroidal, anti‐inflammatory drugs on gastric fundic secretion in vitro. Frog tissues were pretreated with a histamine H2‐receptor antagonist, and drugs were added to serosal side (Closed circles, exposed to an anti‐inflammatory agent; open circles, exposed to histamine H2‐receptor antagonist alone.

Adapted from Garner 63; aspirin results), and from Garner et al. 67; fenclofenac and indomethacin results)


Figure 8.

Stimulation of gastric alkaline secretion by 16,16‐dimethyl prostaglandin E2 in frog fundus, rabbit fundus, and canine Heidenhain pouches and by PGE2 in human stomach. Compounds were applied to serosal side of isolated preparations and to luminal side in vivo

Adapted from Garner and Heylings 68; frog data), Rees et al. 133; rabbit data), Kauffman et al. 98; dog data), and Johansson et al. 95; human data)


Figure 9.

In the isolated proximal duodenum, prostaglandin E2 and forskolin (serosal side) show comparable activity as stimulants of secretion, suggesting that prostaglandins act by elevating intracellular cAMP levels. Sensitivity of tissues to a standard agonist (PGE2) was established at the beginning of experiments. Data are means ± SE; n = 8 for both where n is number of experiments.

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Article Title: Secretion of Bicarbonate by Gastric and Duodenal Mucosa
 

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Gunnar Flemström, Andrew Garner. Secretion of Bicarbonate by Gastric and Duodenal Mucosa. Compr Physiol 2011, Supplement 18: Handbook of Physiology, The Gastrointestinal System, Salivary, Gastric, Pancreatic, and Hepatobiliary Secretion: 309-326. First published in print 1989. doi: 10.1002/cphy.cp060316