Constant infusion and bolus injection of stable-label tracer give reproducible and comparable fasting HGO

We have investigated the reproducibility of fasting hepatic glucose output (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 injection of 7 mg/kg of [U-13C]glucose and, simultaneously, a primed constant infusion of 0.05 mg.kg-1.min-1 of [6,6(-2)H]glucose. The bolus injection provided one estimate of HGO (HGOBOL), and the constant infusion provided two estimates of HGO, namely, HGO at 2 h (HGOINF2) and HGO at 4 h (HGOINF4), both with the assumption of steady-state conditions. All estimates were similar in value; HGOBOL was highest, followed by HGOINF2 and HGOINF4 [2.30 +/- 0.11 (SE), 2.17 +/- 0.12, and 2.01 +/- 0.13 mg.kg-1.min-1]. The constant infusion gave highly reproducible results. In the case of HGOINF2, the within-subject coefficient of variation (CV) was only 3% compared with 5% of HGOINF4. The reproducibility of HGOBOL was comparable with the within-subject CV of 7%. We conclude that a constant infusion and a bolus injection of stable-label tracer give reproducible and comparable estimates of HGO.