Production of amines in equine cecal contents in an in vitro model of carbohydrate overload.

Acute laminitis can be induced experimentally in horses by the administration of carbohydrate, resulting in fermentation within the cecum and ischemia-reperfusion of the digits. The products of fermentation that trigger acute laminitis are as yet unknown; however, compounds such as amines might play a role due to their potential vasoactive properties. The objectives of this study were to quantify the amines present in equine cecal contents and to use a model of carbohydrate overload in vitro to test the hypothesis that carbohydrate fermentation is associated with increased amine production. Cecal contents from each horse were divided into aliquots and incubated anaerobically with either cornstarch or inulin (a form of fructan carbohydrate; both 1 g/100 mL). The pH was measured and samples were taken at the same time for amine measurement by HPLC at 2-h intervals over a 24-h period. In a second set of experiments, the effects of the antibiotic virginiamycin (1 mg/100 mL), calcium (CaPO4; 0.3 g/100 mL), and plant steroidal saponin (Yucca schidigera extract; 0.1 g/100 mL) were examined on pH and amine concentrations in cecal contents incubated with starch or inulin. Both starch and inulin caused significant time-dependent falls in pH, from 6.7 +/- 0.1 at 0 h to 5.2 +/- 0.1 (starch) and 5.0 +/- 0.1 (inulin) at 24 h. Fermentation of carbohydrate was also associated with increased production of phenylethylamine and isoamylamine (two- to threefold increases) as well as putrescine and cadaverine (1.5- to twofold increases). Virginiamycin inhibited the fall in pH and increases in production of phenylethylamine and isoamylamine, while calcium phosphate moderated the changes in pH only. Yucca schidigera extract was without effect. These data show that fermentation of carbohydrate by equine cecal microbiota may lead to increased production of amines.