The contribution of salivary amylase to glucose polymer hydrolysis in premature infants

To determine whether salivary amylase of premature infants can function as a surrogate for pancreatic amylase, we evaluated its production in the infant, acid resistance, and hydrolytic potency in a simulated oropharyngeal, gastric, and intestinal environment. The activity of salivary amylase in 11 prematures varied between 1 and 33 U/ml; the isozymic profile and acid resistance of the premature salivary amylase were identical to those of the enzyme of adults. A "modular" formula containing 7 g/dl of a 14C labeled long chain glucose polymer with degrees of polymerization ranging between 18 and 29 glucose units was prepared. Salivary amylase, 1.1 U/ml, was added to this formula. The progressive breakdown of the 14C polymers as the milk was subjected to oropharyngeal, gastric, and intestinal phase environments was evaluated by quantifying the liberation of short-chain oligomers from the 14C labeled substrates. The gastric pH was varied between 2 and 5 and the gastric incubation time was either 5 or 180 min. Substantial gastric phase breakdown only occurred after 3 h of exposure at the higher pHs of 4 (12%) and 5 (32%). During the intestinal phase, salivary amylase activity resumed. Prior gastric phase pH affected ultimate intestinal phase breakdown, p less than 0.001; after 5-min gastric phases at pHs ranging from 2 to 5, the intestinal phase breakdown ranged from 17 to 55%. We conclude that the limited salivary amylase in the saliva of premature infants can produce significant glucose polymer digestion in both the stomach and small intestine but the digestion falls substantially short of that accomplished by usual concentrations of pancreatic amylase.