Digestive end products mobilize secretory proteins from subcellular stores in the pancreas

Two digestive end products, D-glucose and L-lysine, produced substantial concentration-dependent release of amylase and trypsinogen, respectively, from subcellular storage pools into a postmicrosomal supernatant fraction of rat pancreatic tissue homogenate. This process was selective in that D-glucose did not lead to trypsinogen release, while L-lysine did not effect amylase. An analogue of D-glucose, 2-deoxy-D-glucose, was much less potent than D-glucose on an equimolar basis. Half-maximal release for both end-product enzyme pairs occurred at concentrations within the range of normal plasma values for these end products in the rat. Although amylase release reached an apparent plateau when the concentration of glucose was increased beyond the maximally effective level, lysine concentrations higher than that maximally effective resulted in a fall in trypsinogen release that ultimately returned (at 3.0 mM L-lysine) to the level seen in its absence. When isolated zymogen granules were exposed to the same concentrations of D-glucose or L-lysine, a similar pattern of release was seen, indicating that the zymogen granules are a source of the enzymes released from the particulate phase of the homogenates. These findings can be explained most simply by the selective movement of digestive enzymes across zymogen granule membranes in response to the presence of appropriate end products. They are also consistent with the concept that digestive end products can act rapidly and directly on the pancreatic acinar cell to regulate the mixture of enzymes secreted in response to the specific hydrolytic needs of a meal.