Oesophageal Intraluminal Nitric Oxide Facilitates the Acid-Induced Oesophago-Salivary Reflex

Abstract

Background: The present study explores some aspects of the triggering of the acid-induced oesophagosalivary reflex. In addition to hydrogen ions, there are two acid-dependent molecules with messenger potential in the oesophageal lumen: CO₂ and NO. The aim of this study was to clarify whether oesophageal NO and CO₂ participate in the regulation of salivary neutralizing capacity in response to acid exposure. Methods: Healthy volunteers received oesophageal acidification composed of HCl, with NO₃⁻, or HCO₃⁻ or NO₃⁻ and HCO₃⁻ in combination. In a second series of experiments, the exposure period was divided into 2 separate 10-min events. Saliva volume and titratable buffering capacity were used to calculate alkaline secretion. Results: Salivary alkaline secretion increased markedly following 20 min intraluminal exposure to HCl. The initial part of this response was 22% ± 2.2% larger (P < 0.05) if NO₃⁻ was present. When HCO₃ was added, or if NO₃ and HCO₃⁻ were given simultaneously, the secretory response tended to be lower. The accumulated responses over 70 min to 2 short HCl exposures (10 min each separated by a 30 min ‘rest’) compared to one long one lasting 20 min were similar regardless of the presence of NO₃⁻. Conclusion: The data suggest that oesophageal intraluminal NO facilitates initiation of the oesophago-salivary reflex. CO₂ seems to have a negligible effect on alkaline salivation, and repeated stimulation does not influence the magnitude of the response over time.

Key words:

• Alkaline secretion
• carbon dioxide
• nitric oxide
• oesophago-salivary reflex
• oesophagus
• salivary