Role of duodenal reflux in nonglandular gastric ulcer disease of the mature horse.

Gastric contents were sampled in horses via nasogastric tube to determine changes in pH and bile salt concentrations during feeding and fasting periods. The horses were rotated through 4 feeding protocols. (1) hay; (2) hay with twice daily grain meals; (3) and (4) fasting preceded by either hay only or hay and grain. Sequential, hourly samples were collected from 3 horses prepared with gastric cannulas. Horses were fed hay twice daily and grain mix either twice daily or in small aliquots dispensed every 90 min. The horses were sampled during normal feeding or after 14 h of feed deprivation. Gastric pH values varied with time, but there was no significant difference between the feeding protocols or the fasting period on mean pH. Bile salt concentrations in fasted animals averaged 0.23-0.44 mmol/l with individual samples greater than 0.9 mmol/l. The bile salt concentrations in fed animals were consistently below 0.2 mmol/l. The effect of bile salt and acid on the stratified squamous gastric mucosa was tested in vitro. Mucosa, stripped of muscle and serosal layers, was mounted in Ussing chambers and the electrical potential difference (PD) across the tissue recorded. Sodium taurocholate or deoxycholate (0.3 mmol/l, bile salt) and/or HCl were added to the mucosal bathing solutions. The bile salt alone had no significant effect. Addition of acid (pH 2.5) to control tissues caused a decrease in the PD, which recovered within 20 min. Addition of acid to tissues exposed to bile salts resulted in a significant decrease in the PD, which did not recover. We conclude that combinations of bile salts and acid are more injurious to the stratified squamous gastric mucosa of the equine than acid alone. Concentrations of bile salts and acid sufficient to alter the electrolyte transport function of this mucosa can be found in the gastric contents of horses deprived of feed for as little as 14 h.