POSTSECRETORY CHANGES OF PANCREATIC JUICE TRYPSINOGEN IN THE DUODENUM

I. Partial Activation and Effect of Bile (In Vitro Study)

Abstract

Although pancreatic juice trypsinogen is generally understood to be activated totally and completely into trypsin in the duodenum, intraduodenal conditions are also suited for degradation as well as for activation. In vitro experiments of trypsinogen activation at 37°C using rabbit pancreatic juice, duodenal juice and bile revealed the simultaneous occurrence of activation and degradation processes, resulting in partial activation of the original trypsinogen with the degree of 30 to 60%, dependent on bile content in the mixture. Bile accelerated the activation and inhibited the degradation chiefly by means of calcium ion. In in vitro incubation of solutions of crystallized enzymes at 37°C, pH 8, Ca²⁺ below 3mM, being approximated the intraduodenal conditions, trypsinogen was activated almost entirely by enterokinase and not by trypsin, which reversely provoked degradation both of trypsinogen and of trypsin. It is suggested that pancreatic juice trypsinogen is simultaneosly activated into trypsin and degradated into inert protein immediately after being secreted into the duodenal lumen, resulting in the partial activation, and that bile increased the degree of activation to about 60% at the maximum.