The plasma amylase: Source, regulation and diagnostic significance

Abstract

The total amylolytic activity of the blood appears to be the sum of the activities of several alpha amylases of diverse origin. The salivary glands, pancreas and liver are the likely important tissue sources of the normal blood amylase, although the fallopian tubes, striated muscle and even adipose tissue may possibly contribute in varying degrees. Until methods for specifically labeling the amylase of these tissues are developed this remains conjectural. However, under physiologic conditions the contribution of the pancreas and salivary glands is probably smaller than has been hitherto considered, that of the liver considerably greater. The serum amylase responds quickly and transiently to a variety of substances and hormones which affect carbohydrate metabolism in the liver. As a rough generalization, states of increased carbohydrate utilization are associated with lowered plasma amylase levels. These alterations are not dependent on pancreatic function. In pathologic states of the salivary glands and pancreatic glands, the serum amylase is increased by contributions from these organs. Secretion against obstruction, rupture of ductular apparatus and glandular tissue result in the appearance of variable amounts of amylase in the peripheral blood by way of the venous drainage of the pancreas, and by lymphatic absorption from the peritoneum. Plasma amylase determinations remain the most important laboratory aid in the diagnosis of acute pancreatitis or of acute exacerbations of chronic pancreatitis. The peripheral levels of amylase do not accurately mirror the severity of the pathologic process. Administration of opiates may contribute to the elevation. The role of renal clearance of the enzyme is not completely elucidated. Perforated peptic ulcer and intestinal obstruction with some necrosis of bowel wall may occasionally result in elevated serum amylase levels derived from the peritoneal absorption of enzyme.