Mixture of volatile fatty acids effect on bioelectric properties of acid injury in the equine non-glandular stomach

The purpose of this study was to expose viable non-glandular (NG) mucosa from recently euthanized horses to Normal Ringers solution (NRS) and VFA mixtures (sub-threshold VFA mixture and VFA mixtures containing high acetic acid, high butyric acid and high propionic acids in NRS), at different pHs (1.5, 4.0, 7.0) in an in vitro Ussing Chamber system and to measure their effects on tissue bioelectric properties. After tissue exposure to NRS or VFA mixtures in NRS, tissue was examined under light microscopy for histopathologic evidence of cell swelling and necrosis. Horses (n=11) were euthanized and gastric tissue obtained. Tissues, except from one horse with severe ulcers, were then mounted in Ussing Chambers and NRS or VFA mixtures were added to the mucosal side of the chamber and NRS at pH 7.0 was added to the serosal side. The pH of the mucosal side was dropped at 30 minutes to pH 1.5, 4 or 7 and exposed for 330 minutes.Tissue short circuit current (lsc) and potential difference (PD) was measured and resistance and conductance calculated every 15 minutes throughout the study. At the conclusion of the study, tissues were removed from the Ussing Chamber and placed in 10% formalin and stained with hematoxylin and eosin for histopathologic examination. NG mucosa exposed to HCl alone (pH 4.0 and 1.5) caused an immediate significant decrease in PD, followed by a decrease in lsc. NG mucosa when exposed to the sub-threshold VFA mixture caused no significant change in PD or lsc, when compared to NRS at the same pH. However, NG mucosa exposed to above-threshold VFA mixtures caused an immediate significant decrease in PD and lsc. Results suggest that a sub-threshold mixture of VFAs do not cause bioelectric changes in the equine NG mucosa other than that caused by HCl alone.However, if the concentrations of VFAs exceed the threshold level of propionic and butyric acids at pH <4.0, changes in the barrier function occured. This study confirms that when stomach VFA concentrations are at or below threshold, tissue barrier function is maintained; whereas when stomach VFA concentrations exceed threshold concentrations, as found with high grain diets, at pH < [less than or including] 4.0, cause damage to the NG mucosa which may lead to the formation of ulcers.