Estimation of Glucose Turnover and13C Recycling in the Human Newborn by Simultaneous l-13CGlucose and 6,6-2H2Glucose Tracers*

To compare two methods of estimating systemic glucose production rates and to quantify carbon tracer recycling, six newborn infants, aged 2 h to 3 days, were infused simultaneously with 1-13Cglucose and 6,6-2H2glucose tracers. The older infants were studied 6 h after a meal. 1-13CGlucose was infused at 6 microgram/kg.min. Systemic glucose production rates were calculated from tracer dilution, assuming steady state kinetics. Although 13C was expected to randomize away from the C-1 of glucose, recycling occurred and was estimated from the difference in the rate of systemic glucose production quantified by the dilution of the two tracers. Systemic glucose production rates ranged from 4.2--5.4 mg/kg.min. Recycling on the glucose C-1 was 3--20% of the systemic glucose production rate and did not change with the age of the infant. Because recycling of glucose carbon signifies gluconeogenesis from lactate or pyruvate, it is concluded that the human newborn is able to initiate gluconeogenesis soon after birth.