Glucose turnover and glucose-lactate inter-relations in the newborn rat

A technique of continuous infusion of labelled glucose and lactate was developed in the 1-day-old suckling rat, allowing the calculation of true and apparent glucose turnover and glucose-lactate inter-relations under steady-state conditions. True glucose turnover rate in suckling newborns (16.9 +/- 0.4 mg min-1 per kg body weight) was 50% higher than in fasted adult rats. A 20 +/- 3% glucose recycling was found which corresponded approximately to the Cori cycle activity. Although lactate was contributing for 25% of glucose turnover rate, this did not represent a net glucose synthesis, since more lactate was formed from glucose than glucose from lactate. However, recycling from lactate may be physiologically important as it could be the expression of a glucose sparing effect of the elevated circulating concentrations of non-esterified fatty acids and ketone bodies found in the 1-day-old suckling rat.