Gastric ulcers of the nonglandular (NG) squamous mucosa are common in horses. Volatile fatty acids (VFAs), byproducts of carbohydrate fermentation by resident bacteria, have been implicated in causing NG gastric ulcers. Lactic acid (LA), also produced by bacteria, may cause ulcers when exposed to the equine NG mucosa.
The purpose of this study was to investigate the in vitro effects of LA on tissue NG mucosal bioelectric properties, sodium transport and tissue resistance. Gastric tissues obtained from 13 horses were studied in Ussing chambers. Short-circuit current (Isc) and potential difference (PD) were measured and electrical resistance (R) and conductance (G) calculated for tissues after addition of HCl and various concentrations of LA (5, 10, 20, or 40 mM) in normal Ringer's Solution (NRS). Permeability to [14C] Mannitol was measured in 2 additional horses. Tissues were examined for histopathologic changes after routine staining with H&E.
Mucosa exposed to HCl in NRS at pH 1.5 and 4.0 had a significant decrease in Isc and PD; whereas or tissues exposed to LA (5, 10, and 20 mM) in NRS did not show a significant decrease in Isc and PD, more than what was seen with HCl exposure alone. However, mucosa exposed to 40 mM lactic acid in NRS, at pH 1.5, tended to show an increased G, decreased R and increased permeability to [14C] Mannitol. Histologic changes were consistent with HCl-induced (pH < 4.0) acid damage.
HCl induced alteration in bioelectric properties of equine NG mucosa, whereas addition of LA (5, 10, 20 mM) did not induce alter tissue bioelectric properties NG mucosa, other than that seen with HCl exposure alone. However, a high concentration of LA (40 mM) exposure at pH 1.5, increased NG tissue permeability, without significantly altering sodium transport in tissues. Lactic acid, produced by resident bacteria in the stomach of horses fed a high-grain diet, may increase equine NG mucosal permeability by a different mechanism than VFAs, which may be important in the pathogenesis of Equine Gastric Ulcer Syndrome (EGUS).