Effects of esophageal acidification on esophageal reflexes controlling the upper esophageal sphincter

Esophageal acid exposure can alter upper esophageal sphincter (UES) function, but the mechanism is unknown. The aim of this study was to determine the effects of esophageal acid exposure on esophago-UES relaxation (EURR) and contractile (EUCR) reflexes. Cats, decrebrate ( n = 27) or chronic ( n = 4), were implanted with electromyographic electrodes on pharynx, larynx, and esophagus. The esophagus was infused with either NaCl (0.9%) or HCl (0.1 N). The EUCR was activated by balloon distension in acute cats and slow air injection in chronic cats, and the EURR was activated by rapid air injection in both sets of cats. We found that NaCl infused for 15 or 30 min had no effect on EUCR or EURR in acute cats. HCl infused for 15, 30, or 45 min significantly ( P < 0.05) decreased the sensitivity to activate EUCR. HCl infused for 15 min significantly ( P < 0.05) increased and for 45 min significantly ( P < 0.05) decreased sensitivity to activate EURR. In chronic cats, HCl infused for 15 min/day increased sensitivity to activate EURR and decreased ( P < 0.05) sensitivity to activate EUCR after 4 days of infusion. EURR occurred spontaneously during HCl infusions on the 3rd and 4th ( P < 0.05) days of HCl infusion. We conclude that esophageal acid exposure initially sensitizes the esophagus to activation of EURR and desensitizes to activation of EUCR, but with longer exposure desensitizes to both. The alteration in sensitivity to activate EURR and EUCR caused by gastroesophageal reflux may play a role in the generation of supraesophageal reflux. NEW & NOTEWORTHY In acute studies, short-term esophageal acid exposure sensitizes esophagus to activation of esophago-upper esophageal sphincter relaxation response (EURR), whereas longer-term exposure inhibits EURR. Short- or long-term esophageal acid exposure decreases sensitivity to activation of esophago-upper esophageal sphincter contractile response (EUCR). In chronic studies, short-term esophageal acid exposure has the same effects on EURR and EUCR as occur acutely, but these effects take days to develop. Alteration in EURR and EUCR caused by gastroesophageal reflux may play a role in reflux disease.