Potential role of galactokinase in neonatal carbohydrate assimilation.

Glucose given to the newborn human may result in hyperglycemia, suggesting that its utilization is impaired at this developmental stage. Galactose is thought to be a more appropriate carbohydrate source for the newborn. The enzymes involved in hexose phosphorylation may, in part, be responsible for these observations. A key regulatory enzyme of hepatic glucose assimilation, glucokinase, is diminished in newborns compared to adults, whereas galactokinase activity is increased. When newborn dogs were fasted and then fed either glucose or galactose, their plasma insulin responses to glucose were similar, but the pups fed galactose demonstrated an attenuated systemic appearance rate of glucose. Hexose incorporation into hepatic glycogen and net glycogen synthesis was augmented in the galactose-fed dogs. In vitro, liver from neonatal dogs showed enhanced galactokinase activity relative to that for hexokinase or glucokinase. Neonatal hexose assimilation may be independent of insulin action and, instead, be related to the developmental presence of hexose phosphorylating enzymes.