Phytohemagglutinin from red kidney bean (Phaseolus vulgaris) inhibits sodium and chloride absorption in the rabbit ileum

Abstract

Phytohemagglutinin (PHA), derived from red kidney bean (Phaseolus vulgaris), can induce malabsorption and diarrhea when fed to rats. In this study, we determined the effect of PHA on ion transport in the rabbit ileum in vitro. Compared with control tissues, PHA (1 mg/ml) added to the mucosal solution increased short-circuit current (1.1 +/- 0.2 microEq/cm2 X h, p less than 0.001), decreased net Na (-1.0 +/- 0.5 microEq/cm2 X h, p less than 0.02) and Cl (-1.2 +/- 0.6 microEq/cm2 X h, p less than 0.025) absorption, and decreased tissue conductance (-1.8 +/- 0.5 mS/cm2, p less than 0.001). Serosal addition of PHA had no effect on the short-circuit current or tissue conductance. Mucosal PHA did not increase mucosal levels of cyclic adenosine monophosphate or cyclic guanosine monophosphate. Removal of serosal calcium did not affect the increase in short-circuit current induced by mucosal PHA. Utilizing fluorescent microscopy, rhodamine-labeled PHA was found to bind to the luminal border of villus cells, but not to crypt cells, in the ileum. In the descending rabbit colon, PHA did not affect either the short-circuit current or conductance, and rhodaminated PHA did not bind to the epithelial surface. Using the increase in short-circuit current as an indicator of absorption, PHA did not affect Na-coupled glucose or amino acid absorption in the ileum. This study suggests that dietary lectins may play a role in regulating intestinal fluid and electrolyte transport.