Effects of ricin, a protein toxin, on glucose absorption by rat small intestine. Biochemical studies on oral toxicity of ricin. II.

Abstract

The effects of ricin, a proteinous toxin from castor bean seeds, on glucose absorption by rat small intestine have been examined by the everted sac method. Glucose absorption was affected by ricin poisoning at 1 h after oral administration, and the inhibition reached the maximum at 5h, whereas very slight impairment of glucose absorption was observed at 5h after intraperitoneal injection of ricin. The dose required for 50% impairment of glucose absorption was 10mg ricin/kg body weight of rat when determined at 5 h after oral administration. This inhibition of glucose absorption was found only when ricin or ricin B-chain had been in contact with the mucosal membrane of the small intestine of the normal rats. The inhibition was prevented by the presence of a galactose-containing sugar, lactose. The effect of ricin on glucose absorption under physiological conditions was analyzed in situ, and the increase in blood glucose level was inhibited in ricin-intoxicated rats. These results suggest that ricin, especially its B-chain, interacts primarily with the intestinal mucosa and inhibits sugar absorption of the rat small intestine. It was also inferred that ricin B-chain is cytotoxic to the epithelial absorptive cells of the small intestine, but that impairment of sugar absorption by the small intestine alone is not the direct cause of death of animals following oral administration of ricin.