CONSTANT INFUSION AND BOLUS INJECTION OF STABLE-LABEL TRACER GIVE REPRODUCIBLE AND COMPARABLE FASTING HGO

We have investigated the reproducibility of fasting hepatic glucose ou tput (HGO) estimates by use of isotope dilution methodology of stable- label tracers. Six normal subjects were studied on two occasions 1 wk apart. After an overnight fast, the subjects received a bolus injectio n of 7 mg/kg of [U-C-13]glucose and, simultaneously a primed constant infusion of 0.05 mg.kg(-1).min(-1) of [6,6-H-2]glucose. The bolus inje ction provided one estimate of HGO (HGO(BOL)), and the constant infusi on provided two estimates of HGO, namely, HGO at 2 h (HGO(INF2)) and H GO at 4 h (HGO(INF4)), both with the assumption of steady-state condit ions. All estimates mere similar in value; HGO(BOL) was highest, follo wed by HGO(INF2) and HGO(INF4) [2.30 +/- 0.11 (SE), 2.17 +/- 0.12, and 2.01 +/- 0.13 mg.kg(-1).min(-1)]. The constant infusion gave highly r eproducible results. In the case of HGO(INF2), the within-subject coef ficient of variation (CV) was only 3% compared with 5% of HGO(INF4) Th e reproducibility of HGO(BOL) was comparable with the within-subject C V of 7%. We conclude that a constant infusion and a bolus injection of stable-label tracer give reproducible and comparable estimates of HGO .