Non-parallel enzyme secretion from rat pancreas: in vivo studies.

The secretion of amylase, lipase and chymotrypsinogen was measured in the pancreatic juice of anaesthetized rats. 1. Stimulation of the protein secretion by I.V. cholecystokinin-pancreozymin (8 IDU kg-1) given together with secretin (5 CU kg-1) resulted in a change in the enzyme proportions in pancreatic juice, characterized by decreases in the amylase to chymotrypsinogen and amylase to lipase ratios. 2. The same phenomenon was elicited by pilocarpine (15 mg kg-1) associated with secretin (5 CU kg-1) but not by secretin alone. 3. Blockade of protein synthesis by cycloheximide did not suppress the induction of non-parallelism by stimulation. 4. It was concluded that the exocrine proteins are stored in two pools in which the proportions of enzymes are different. 5. With the help of a mathematical model it is proposed that one pool which corresponds to less than 0.35% of total enzyme storage, is responsible for basal secretion and is not sensitive to stimulation. The second (preponderant) pool provides secretion with a protein output increasing with stimulation.