Liver Amylase. Iii. Synthesis by the Perfused Liver and Secretion into the Perfusion Medium.

The presence of ar-amylase in liver tissue has been reported previously by several investigators (l-3). In the liver from rats deprived of food, the enzyme is found primarily in the microsomal fraction (4) whereas in fed animals a considerable proportion is bound to glycogen (5). In perfused liver systems, amylase activity is secreted into the perfusion medium under conditions in which other enzymes, normally released on liver damage, remain within the tissue (6). On the basis of these facts and supplementary experimental information, several physiological functions of liver amylase have been postulated (6). Of these, the possible role of the liver as a prominent source of serum amylase under normal physiological conditions is of particular interest because it implies a specific metabolic process directed toward the synthesis and secretion of a serum enzyme. The experimental observations reported to date provide only circumstantial evidence for the synthesis of amylase by the liver. 1. The immunochemical evidence of McGeachin and Reynolds (7,8) that liver amylase is different from salivary and pancreatic amylase is based upon the action of antibodies on the amylase activity in crude extracts. Since the liver enzyme is primarily bound to glycogen or microsomal particles, it is possible that its interaction with antibodies is modified. 2. The accumulation of amylase in the perfusion medium during the course of perfusion of rat liver is not unequivocal evidence for synthesis by this organ because of the following alternatives. (a) There may be a release of intracellular bound amylase under the conditions normally employed in the perfusion studies. (b) There may be a conversion of an inactive to an active form of this enzyme. (c) Perfused rat liver systems are usually contaminated with small quantities of pancreas, which is a diffuse organ in this animal. Since the specific activity of amylase is approximately three orders of magnitude higher in the pancreas than in the liver, the accumulation during perfusion may be of pancreatic and not hepatic origin. The experiments presented in the present paper demonstrate that amylase accumulation during perfusion of liver tissue is not the result of bound amylase or of contaminating pancreatic tissue. Evidence is presented for the synthesis de novo of amylase by liver tissue and for its release into the medium under normal