Some aspects of gastric function in the newborn.

Gastric digestion of protein is dependent on the hydrogen ion concentration of the stomach contents. Human gastric juice will digest casein optimally in the pH ranges 1 * 8 to 2 2 and 3 * 5 to 3 * 6. Between and above these ranges hydrolytic activity rapidly declines and is minimal between pH 2-5 and 3*2 (Taylor, 1959). Pepsin is the main enzyme concerned, but others, i.e. parapepsins, have been demonstrated (Ryle and Porter, 1959). At any given time the pH of the stomach contents will be the result of several factors. Under physiological conditions these will include free hydrochloric acid, ingested food, swallowed saliva and regurgitated duodenal contents. Other factors, such as gastric mucus, may also play a part. During infancy gastric acidity is low, especially so in the newborn period (Miller, 1941). This low acidity together with the high buffering capacity of milk seems an unlikely combination for the production of a medium of a sufficiently low pH to digest protein. The present study is concerned essentially with the pH changes in the newborn infant's stomach during the whole interval between feeds under as near physiological conditions as possible. In a number of cases the presence or absence of hydrolysed protein has been determined.