Gastric secretion elicited by conditioning in rats

Risk factors for gastroesophageal reflux disease and analysis of genetic contributors

Gastroesophageal reflux disease (GERD) is a common gastrointestinal disorder with an increasing prevalence. GERD develops when the reflux of stomach contents causes troublesome typical and atypical symptoms and/or complications. Several risk factors of GERD have been identified and evaluated over the years, including a considerable amount of genetic factors. Multiple mechanisms are involved in the pathogenesis of GERD including: (1) motor abnormalities, such as impaired lower esophageal sphincter (LES) resting tone, transient LES relaxations, impaired esophageal acid clearance and delayed gastric emptying; and (2) anatomical factors, such as hiatal hernia and obesity. Genetic contribution seems to play a major role in GERD and GERD- related disorders development such Barrett’s esophagus and esophageal adenocarcinoma. Twin and family studies have revealed an about 31% heritability of the disease. Numerous single-nucleotide polymorphisms in various genes like FOXF1, MHC, CCND1, anti-inflammatory cytokine and DNA repair genes have been strongly associated with increased GERD risk. GERD, Barrett’s esophagus and esophageal adenocarcinoma share several genetic loci. Despite GERD polygenic basis, specific genetic loci such as rs10419226 on chromosome 19, rs2687201 on chromosome 3, rs10852151 on chromosome 15 and rs520525 on the paired related homeobox 1 gene have been mentioned as potential risk factors. Further investigation on the risk genes may elucidate their exact function and role and demonstrate new therapeutic approaches to this increasingly common disease.

Simultaneous detection of gastric acid and histamine release to unravel the regulation of acid secretion from the guinea pig stomach

Gastric acid secretion is regulated by three primary components that activate the parietal cell: histamine, gastrin, and acetylcholine (ACh). Although much is known about these regulatory components individually, little is known on the interplay of these multiple activators and the degree of regulation they pose on the gastric acid secretion mechanism. We utilized a novel dual-sensing approach, where an iridium oxide sensor was used to monitor pH and a boron-doped diamond electrode was used for the detection of histamine from in vitro guinea pig stomach mucosal sections. Under basal conditions, gastrin was shown to be the main regulatory component of the total acid secretion and directly activated the parietal cell rather than by mediating gastric acid secretion through the release of histamine from the enterochromaffin-like cell, although both pathways were active. Under stimulated conditions with ACh, the gastrin and histamine components of the total acid secretion were not altered compared with levels observed under basal conditions, suggestive that ACh had no direct effect on the enterochromaffin-like cell and G cell. These data identify a new unique approach to investigate the regulation pathways active during acid secretion and the degree that they are utilized to drive total gastric acid secretion. The findings of this study will enhance our understanding on how these signaling mechanisms vary under pathophysiology or therapeutic management.

Gastric secretion

PURPOSE OF REVIEW

This review summarizes the past year's literature regarding the regulation of gastric exocrine and endocrine secretion at the central, peripheral, and cellular levels.

RECENT FINDINGS

Gastric acid secretion is an intricate and dynamic process that is regulated by neural (efferent and afferent), hormonal (e.g., gastrin), and paracrine (e.g., histamine, ghrelin, somatostatin) pathways as well as mechanical (e.g., distension) and chemical (e.g., protein, glutamate, coffee, and ethanol) stimuli. Secretion of hydrochloric acid by the parietal cell involves recruitment and fusion of HK-adenosine triphosphatase (HK-ATPase)-containing cytoplasmic tubulovesicles with the apical membrane with subsequent electroneutral transport of hydronium ions in exchange for potassium; the source of the latter is the potassium channel, KCNQ1. Concomitantly, chloride exits via the cystic fibrosis transmembrane regulator. Inhibition of the HK-ATPase by proton pump inhibitors leads to a compensatory hypergastrinemia which, if prolonged, results in parietal and enterochromaffin-like cell hyperplasia. The clinical consequence is rebound acid secretion which may induce dyspeptic symptoms in healthy individuals and exacerbate reflux symptoms in patients with gastroesophageal reflux disease.

SUMMARY

We continue to make progress in our understanding of the regulation of gastric acid secretion in health and disease. A better understanding of the pathways and mechanisms regulating acid secretion should lead to improved management of patients with acid-induced disorders as well as those who secrete too little acid.