Use of indomethacin to demonstrate enterotoxic activity in extracts of Entamoeba histolytica trophozoites

Abstract

Animal models for the assay of enterotoxic activity in extracts of E. hisolytica trophozoites were studied. Marked water and electrolyte secretion occurred in both in vivo rabbit ileal loops and rat colon loops exposed to clarified sonic fluids of E. histolytica strain HM-1 trophozoites (106/ml) when the animals were first administered indomethacin (0.1 mg/kg). No effect on intestinal absorption was observed in animals exposed to Entamoeba extracts alone or after administration of a lower (0.01 mg/kg) dose of indomethacin. Higher doses (.gtoreq. 1 mg/kg) of indomethacin inhibited extract-induced secretion. No enterotoxic activity was detected with or without indomethacin, using extracts from the nonpathogenic E. histolytica-like Laredo strain, even at 10-fold-higher cell concentrations. The HM-1 enterotoxic activity was heat labile. Prior exposure of the loop lumen to fetuin (100 .mu.g/ml) blocked the secretory response to subsequent HM-1 extract exposure, but postexposure of the loop to fetuin did not block secretion already established by the amoeba extract. No histological changes were seen associated with the amoeba extract-induced secretion. Evidently, E. histolytica HM-1 strain elaborates an enterotoxic activity capable of causing consistent secretion in the mammalian intestine that has had its mucosal cytoprotection impaired by indomethacin.