Effect of synthetic trypsin inhibitor on plasma immunoreactive cholecystokinin in rats

A sensitive and specific radioimmunoassay system for rat plasma cholecystokinin (CCK) was employed to study the effect of trypsin inhibitor on plasma CCK levels. Feeding the trypsin inhibitor, FOY-305 200 mg/kg, to rats for 10 days stimulated the pancreatic growth. However, there was no significant difference in fasting plasma concentrations and duodenal contents of CCK and secretin. On the other hand, acute ingestion of same dosage of FOY-305 caused a marked (20-fold) and sustained elevation of plasma CCK levels. The principal form of circulating CCK was CCK-22 like on Sephadex G-50, in contrast to that of the cerebrum and duodenum where CCK-8 like form, or CCK-8 and CCK-22 like forms were main components, respectively. A significant rise in plasma levels of immunoreactive secretin was also found. These results suggest that the pancreatic growth observed by feeding the trypsin inhibitor to rats is caused by an excessive amount of CCK in conjunction with secretin.