Enzyme secretion in the absense of zymogen granules.
Pure pancreatic juice was collected from the cannulated common bile duct of anesthetized rats after an overnight fast. Digestive enzyme secretion was followed in these animals during and after the progressive degranulation of acinar cells produced by sequentially applied cholinergic stimuli. The kinetics of degranulation, a progressive decrease in the number of zymogen granules in acinar cells, was estimated from the relative cell volume occupied by electron-opaque granules at various times using a random pointcount stereological technique to examine tissue sections. Three hourly injections of methacholine chloride were sufficient to produce the almost complete disappearance of electron-opaque granules from secretory cells. Greatly augmented enzyme secretion was still observed in their absence, 7-25 times greater than control values: 10-fold for protein output overall, 7-fold for trypsinogen, and 25-fold for chymotrypsinogen. Secretion in the absence of zymogen granules is discussed relativeto exocytosis and three-compartment (intracellular storage, cytoplasm, and duct lumen)secretory models.