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Effect of Ingested Toxic Bean Lectins on the Gastrointestinal Tract in the Rat1

Shinobu Nakata and Toshizo Kimura

Laboratory of Food and Nutrition, Department of Home Economics, Osaka Kyoiku University, Ikeda, Osaka 563 Japan

The present study was undertaken to provide further evidence for the mechanisms proposed for the toxicity of ingested bean lectins in animals: 1) to show the stability of concanavalin A (Con A) in the gastrointestinal tract so that it has enough time to interact with some enzymes localized in the intestinal membrane and 2) to find its effect on the activities of those enzymes that have been adopted as criteria for adaptive changes in response to altered diets, namely intestinal sucrase, alkaline phosphatase and leucine aminopeptidase. Significant amounts of ingested Con A were recovered unaltered (as seen from affinity chromatography and electrophoresis) from the cecal content of rats 4 h after its oral administration and from feces (90% recovery) 4 d later. This indicated that Con A is quite stable during its passage through the gastrointestinal tract. Con A, given at a level of 0.3 or 0.5% in the diet, completely prevented adaptive changes in the activities of those enzymes. These results substantiate the mechanisms proposed earlier by other investigators that the toxicity of ingested bean lectins involves their binding to the luminal surface of the small intestine, where they disturb the function of the brush border membrane.

KEY WORDS: • bean lectins • concanavalin A • sucrase • alkaline phosphatase • leucine aminopeptidase • small intestine

1 This study was supported in part by a Grant from the Ministry of Education, Science and Culture of Japan (No. 59560083).

Manuscript received 31 August 1984. Revision accepted 14 August 1985.






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