Comparison of the rate of absorption and proteolysis of [14C]choleragen and [14C]bovine serum albumin in the rat jejunum.

[14C]choleragen was used to study the rate of disappearance of choleragen enterotoxin from the jejunum of rats. [14C]bovine serum albumin (BSA) was studied in a similar manner. Almost one-third of the labeled toxin had disappeared from the intestine after 6 h. Its rate of disappearance was the same in germfree rats as in conventional rats. The rate of proteolysis of [14C]choleragen and [14C]BSA by intestinal mucodal lysosomal enzymes was also studied. Neither was significantly degraded by neutral proteases; however, heat-inactivated toxin was. They were all degraded by acid proteases; however, the rate of BSA proteolysis was only one-third of that of toxin. Soybean trypsin inhibitor had no effect on the in vivo disappearance of toxin nor on the acid proteases. It did inhibit the neutral protease digestion of heat-treated toxin. Aprotinin and protamine inhibited disappearance in loops of gut but had no effect to inhibit degradation rates. Gangliosides inhibited both rates of disappearance and proolysis of toxin. These agents had some different effects on disappearance rates and proteolysis of BSA. The data indicate that cholera enterotoxin is absorbed by intestinal mucosal cells and is degraded by acid proteases in the cells.