Mammary Amylase: a Possible Alternate Pathway of Carbohydrate Digestion in Infancy

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Abstract
Summary: Mammary amylase is a possible alternate pathway of digestion of glucose polymers and starches, that is most important in early infancy when pancreatic amylase is low or absent in duodenal fluid and responds poorly to stimuli. Human breast milk contains 1000–5000 units of amylase/liter. In order to evaluate the likelihood that a significant proportion of mammary amylase activity would withstand passage through the stomach, purified and unpurified mammary anylase were exposed to acid and pepsin in vitro to simulate the gastric environment found in young infants. Both purified and unpurified enzymes were stable at pH 7.5 with little or no activity lost after 4 h, and approximately 80% retained at 6 h. When incubated at pH 3.5, one-third of unpurified enzyme activity was retained for 6 h; in contrast, the purified enzyme was acid labile losing 80% by 2 h. Addition of bovine serum albumin or breast milk proteins to purified enzyme protected the activity. When unpurified enzyme was exposed to a stepwise decline in pH from 6.5 to 3.5 over 4 h, 50% of the original activity was retained. Unless the concentration was >3750 units/ml, the addition of varying concentrations of pepsin to defatted breast milk incubated at pH 3.5 did not affect any greater decay of enzyme activity despite evidence of peptic digestion of proteins in the reaction mixture. This study supports the possibility that ingested mammary amylase could retain a significant proportion of its original activity after exposure to acid and pepsin in the stomach of young infants. Speculation: Mammary amylase may be an enzyme important to carbohydrate digestion in infancy. The amount that would survive passage through the stomach of a young infant is most probably greater than would be contained in the pancreatic secretions of infants less than approximately 4-6 months of age. The physiologic importance of mammary amylase may be analogous to that of the bile salt stimulated lipase found in human milk.

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