Glucose production during exercise in humans: a-hv balance and isotopic-tracer measurements compared

The present study compared the arteriohepatic venous (a-hv) balance techniq ue and the tracer-dilution method for estimation of hepatic glucose product ion during both moderate and heavy exercise in humans. Eight healthy young men (aged 25 yr; range, 23-30 yr) performed semisupine cycling for 40 min a t 50.4 +/- 1.5(SE)% maximal O-2 consumption, followed by 30 min at 69.0 +/- 2.2% maximal O-2 consumption. The splanchnic blood flow was estimated by c ontinuous infusion of indocyanine green, and net splanchnic glucose output was calculated as the product of splanchnic blood flow and a-hv blood gluco se concentration differences. Glucose appearance rate was determined by a p rimed, continuous infusion of [3-H-3]glucose and was calculated by using fo rmulas for a modified single compartment in non-steady state. Glucose produ ction was similar whether determined by the a-hv balance technique or by th e tracer-dilution method, both at rest and during moderate and intense exer cise (P > 0.05). It is concluded that, during exercise in humans, determina tion of hepatic glucose production can be performed equally well with the t wo techniques.