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

Abstract

The present study was undertaken to provide further evidence for the mechanisms proposed for the toxicity of ingested bean lectins in animals: 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 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.

Effect of ingested winged bean lectin on gastrointestinal function in the rat.

“…The effects of WBLF, observed in the present study, added to the high sucrose diet on the hydrolase activities of enzymes localized in the brush border membrane of the small intestine were similar to those of Con A observed in the previous study (7).…”

“…However, adaptive changes observed in these enzyme activities of rats given a high sucrose diet were prevented by the addition of WBLF to the diet. The time-course changes in the hydrolase activities in rats given the high-sucrose diet were similar to those observed in the previous study (7), this restraining effect of WBLF diet feeding on enzyme activities being consistent with that of the Con A diet feeding (7) .…”

“…Our previous study (7) demonstrated that: 1) Ingested Con A is unaltered during its passage through the gastrointestinal tract and is rapidly excreted.…”

Behavior of Ingested Concanavalin A in the Gastrointestinal Tract of the Rat

“…On the basis of the findings previously reported 5 ) and those obtained in the present study, the behavior of ingested Con A in the gastrointestinal tract could be concluded to be as follows: 1. Ingested Con A inertly passes through the lumen of the stomach.…”

Effects of Diets on Hydrolase Activities Localized in the Brush Border Membrane of the Small Intestine in Rats

“…4 . 5 ) On the other hand, sucrosemediated changes in jejunal sucrase activity in these rats were initiated at the level of the crypt cell and were expressed after a latent period of 18 to 20 hr, during which these cells matured and migrated toward the villus tip.4,6-S) Cezard et al,9,!O) thereafter, reported that the maximal increase in sucrase activity caused by sucrose feeding in rats given a carbohydratefree diet occurred by 12 hr after giving the sucrose diet, and separation of villus and crypt cells 12 hr after giving the diet revealed a parallel increase of sucrase activity along the villus-crypt axis. They proposed that the sucrose-mediated increase in sucrase actIvIty, rather than acting preferentially on the crypt, occurred over the entire villus-crypt unit.…”