The kinetics of pancreatic amylase secretion and its relationship to volume flow and electrical conductance in the anaesthetized cat

Abstract

1. Enzyme secretion in response to short duration vagal stimulation or to rapid I.V. injections of cholecystokinin-pancreozymin (CCK-PZ) or gastrin or to intra-arterial injections of acetylcholine is a function of the volume of juice secreted and not primarily a function of time.2. The output of amylase in response to each stimulus occurred in a constant volume of approximately 15 drops (0.5 ml.) regardless of the rate of background secretin stimulated flow of water and electrolyte.3. It is argued that because amylase secretion occurs in this constant volume, it is due to the rapid secretion of enzyme into the duct system from the acini, and subsequently the secretin stimulated secretion of water and bicarbonate washes the enzyme from the duct system.4. When enzyme secretion is stimulated an increase in the electrical conductance (measured at 1.592 kHz) occurs across the tail of the pancreas. This increased conductance has two components. An early peak associated with the extrusion of enzyme from the acinar cell and a later peak which is probably due to vasodilatation.5. Atropine was without effect on both enzyme secretion and the conductance record when the stimulant was CCK-PZ. Atropine blocked enzyme secretion and both peaks of the conductance record in response to stimulation by acetylcholine. Atropine blocked enzyme secretion and abolished the early phase of the conductance record, on vagal stimulation. It was without effect on the later peak which probably indicates an atropine resistant vasodilation of the pancreatic vessels.6. When the vagus is stimulated on a background of submaximal electrolyte secretion caused by the intravenous infusion of secretin, the volume rate of secretion and the rate of amylase secretion follow a similar time course. The maximal volume response occurred between 7 Hz and 15 Hz and the maximal amylase output per impulse was at 5 Hz.