Adaptation of glucose production and gluconeogenesis to diminishing glucose infusion in preterm infants at varying gestational ages

In preterm infants low plasma glucose concentrations are frequently observed. We hypothesized that the infants' ability to adapt endogenous glucose production to diminishing exogenous supply is disturbed, but will improve with increasing gestational age. Glucose production rate and gluconeogenesis were measured using stable isotope techniques with [6,6-H-2(2)]glucose and [2-C-13]glycerol in 19 preterm infants (10 less than or equal to 30 wk and nine >30 wk gestational age) on d 5.0 +/- 1.4 of life. Exogenous glucose was administered at a rate of 33 mumol(.)kg(-1.)min(-1) followed by 22 mumol(.)kg(-1.)min(-1). In the first 2 h after the decrease in exogenous supply, plasma glucose concentration declined comparably in both groups: less than or equal to30 wk, from 4.3 +/- 1.2 to 3.2 +/- 0.9 mM; >30 wk, from 3.7 +/- 0.7 to 3.0 +/- 0.6 mM. Thereafter, only in infants >30 wk an increase was observed, to 3.4 +/- 0.8 mM. Glucose production rate increased comparably in both groups: less than or equal to 30 wk, from 6.0 +/- 4.1 to 8.8 +/- 3.4 mumol(.)kg(-1.)min(-1); >30 wk, from 7.8 +/- 4.6 to 11.6 +/- 5.2 mumol(.)kg(-1.)min(-1). This increase was equivalent to approximately 30% of the decline in exogenous glucose. Gluconeogenesis increased comparably in both groups: <30 wk, from 3.2 +/- 1.2 to 4.5 +/- 1.3 mumol(.)kg(-1.)min(-1); >30 wk, from 4.3 +/- 1.9 to 6.8 +/- 2.9 mumol(.)kg(-1.)min(-1). We conclude that preterm infants can only partly compensate a decline in exogenous glucose supply by increasing endogenous glucose production rate, probably because of limitations in the final common pathway of intracellular glucose metabolism (i.e. glucose-6-phosphatase). The ability to maintain the plasma glucose concentration after a decrease in exogenous supply is better preserved in infants >30 wk owing to more efficient adaptation of peripheral glucose utilization