Glycerol metabolism in humans: validation of²H- and¹³C-labelled tracers

For a tracer to be valid it must follow the metabolism of the tracee without distortion. Especially when the tracer contains several deuterium substitutions, the tracer can be altered or degraded differently from the metabolite it is to trace or be subject to distorting isotope effects. To determine whether²H₅-glycerol is a valid tracer for following glycerol kinetics,²H₅-glycerol and [2-¹³C] glycerol tracers were infused simultaneously in six healthy postabsorptive adult subjects. After 90 min of tracer infusion, epinephrine was also infused for 60 min to stimulate lipolysis and increase glycerol flux. Glycerol flux increased from 2.2±0.3 to 6.7±0.4 μmol/kg per minute (with the¹³C tracer) and from 2.2±0.3 to 6.7±0.3 μmol/kg per minute (with the²H tracer) when epinephrine was infused. There was no significant difference in glycerol flux measured with the²H tracer compared to the¹³C tracer either under basal or a stimulated flux condition. These results indicate that²H₅-glycerol is a valid tracer for measuring glycerol metabolism in humans.