Factors Regulating Biosynthesis, Intracellular Transport and Secretion of Amylase and Lipase in the Rat Exocrine Pancreas

The purpose of this study was to evaluate some of the parameters involved in the biosynthesis, intracellular transport and secretion of two pancreatic hydrolases. The kinetics of amylase and lipase were followed by several procedures including short-term dietary adaptations of enzymatic levels in the gland, in vivo labelling with L-[1- 14 C] leucine, intracellular distribution, in vivo secretion in the biliary duct under pilocarpine, and in vitro secretion by perfused fragments of pancreas. It was demonstrated that the intake of carbohydrates and fats and their subsequent utilization influenced the levels of amylase and lipase in opposite directions. The quality of the diet was also a determining factor. Glucose was a better inducer of amylase than fructose or galactose, while oils rich in unsaturated fatty acids were more efficient than saturated fats in increasing the level of lipase. These differential adjustments of the levels of pancreatic hydrolases were mostly due to proportional adjustments of their rates of biosynthesis. In general, the duration of amylase transport across the acinar cell was probably longer than that of lipase. On the other hand, the turnover (secretion) time of amylase and lipase, once agglomerated in zymogen granules, was the same in a given physiological situation. This common turnover time with respect to different hydrolases decreased when dietary proteins were the limiting factor. The abbreviations used in this study are: Chtg: chymotrypsinogen; Tgs 1 + 2: trypsinogens 1 and 2; PCPase B: procarboxypeptidase B.