Aging changes of pancreatic isoamylases and the appearance of "old amylase" in the serum of patients with pancreatic pseudocysts.

Human serum and pancreatic secretions contain at least three isoamylases of pancreatic origin. As determined by gel electrophoresis and saccharogenic amylase assay, P1, P2, and P3 designate isoenzymes with slow, intermediate, and rapid electrophoretic mobilities, respectively. The P1 isoamylase normally accounts fo 80-90% of total amylase activity, P2 for 10-20%, and P3 for 0-4% in both serum and pancreatic juice. When pancreatic amylase is incubated at 37 degrees C, P1 decreases, and P2 and P3 increase within hours. Whereas P2/P1 is always < 0.25 in fresh pancreatic juice, normal serum, acute pancreatitis serum, chronic pancreatitis serum, or pancreatic cancer serum, the ratio was elevated in 11 of 12 pseudocyst contents (mean P2/P1 = 0.51) and in 14 of 16 sera from patients with proven pseudocysts (mean P2/P1 = 0.43) (P < 0.001). After pseudocysts were surgically drained, the proportions of the pancreatic isoamylases in serum reverted to normal. The precise, characteristic, and predictable changes in electrophoretic mobility, presumably a result of specific spontaneous chemical alterations of the isoenzyme molecules, allow identification of "old amylase" in the serum of patients with pancreatic pseudocysts. This finding may be a useful adjunct for diagnosis, but whether the amount of "old amylase" can be used to estimate the age of a pseudocyst is not yet known.