Sources of the serum isoamylases and their normal range of variation with age.

The isoamylases in various human tissue homogenates and body fluids were separated by agarose gel electrophoresis. Nothing suggested any significant production of amylase in the liver. Minute amounts of amylase belonging to the pancreatic group of isoamylases might be produced by the glands of the proximal duodenum. The specific group of isoamylases produced in the female genital tract could not be demonstrated in serum or urine. The activity of amylase in serum was derived from two groups of isoenzymes, one group originating from the salivary glands, the other from the pancreatic gland. The contribution of each of these two sources to the total serum amylase was determined from early foetal life to adult age. A very low activity of the salivary isoamylases was regularly found in serum from 14-week-old foetuses. The activity increased steadily with age and reached the normal adult level, about 80 U/l, at the age of 5 years. The pancreatic group of isoamylases in serum developed later; the majority of children below 3 months had no demonstrable pancreatic isoamylase activity. The activity rose slowly to reach adult level, about 80 U/l, at the age of 10 to 15 years. The activity did not vary with sex, and the diurnal variation of the isoamylase was negligible. In children with cystic fibrosis of the pancreas the activity of pancreatic isoamylases in serum was low.