The mechanism of increased renal clearance of amylase in acute pancreatitis.

Amylase isoenzymes, separated by polyacrylamide gel electrophoresis, were measures in 25 normal persons (mean amylase to creatinine clearance ratio 3.0%), 15 patients with acute pancreatitis (mean clearance ratio 9.5%, P less than 0.0001), and 6 patients with hyperamylasemia due to common duct stones (mean clearance ratio 4.1%). Two isoamylases (P1, P2) resembling pancreatic isoenzymes and three isoamylases (S1, S2, S3) resembling salivary isoenzymes appeared regularly in normal serum and urine. Salivary amylases predominated in serum, but pancreatic amylases predominated in urine. This finding is consistent with renal clearance of pancreatic amylases exceeding that of salivary amylases under normal conditions. In patients with pancreatitis or common duct stones, essentially all of the increased amylase activity in serum and urine was due to pancreatic isoamylases (P1 and P2) in their normal proportions. No new or altered amylase isoenzymes were detected. The fraction of pancreatic amylases in the serum or urine was identical for the two diseases. Whereas the difference in amylase to creatinine clearance ratios observed between the two groups of patients is not a function of different amylase isoenzymes presented to the kidney, we conclude that the increased amylase clearance in acute pancreatitis is caused by an alteration of renal transfer of amylase, either at the glomerulus or tubule.