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. 