title: Partitioning glucose distribution/transport, disposal, and endogenous production during IVGTT.
abstract: We have separated the effect of insulin on glucose distribution/transport, glucose disposal, and endogenous production (EGP) during an intravenous glucose tolerance test (IVGTT) by use of a dual-tracer dilution methodology. Six healthy lean male subjects (age 33 +/- 3 yr, body mass index 22.7 +/- 0.6 kg/m(2)) underwent a 4-h IVGTT (0.3 g/kg glucose enriched with 3-6% D-[U-(13)C]glucose and 5-10% 3-O-methyl-D-glucose) preceded by a 2-h investigation under basal conditions (5 mg/kg of D-[U-(13)C]glucose and 8 mg/kg of 3-O-methyl-D-glucose). A new model described the kinetics of the two glucose tracers and native glucose with the use of a two-compartment structure for glucose and a one-compartment structure for insulin effects. Insulin sensitivities of distribution/transport, disposal, and EGP were similar (11.5 +/- 3.8 vs. 10.4 +/- 3.9 vs. 11.1 +/- 2.7 x 10(-2) ml small middle dot kg(-1) small middle dot min(-1) per mU/l; P = nonsignificant, ANOVA). When expressed in terms of ability to lower glucose concentration, stimulation of disposal and stimulation of distribution/transport accounted each independently for 25 and 30%, respectively, of the overall effect. Suppression of EGP was more effective (P < 0.01, ANOVA) and accounted for 50% of the overall effect. EGP was suppressed by 70% (52-82%) (95% confidence interval relative to basal) within 60 min of the IVGTT; glucose distribution/transport was least responsive to insulin and was maximally activated by 62% (34-96%) above basal at 80 min compared with maximum 279% (116-565%) activation of glucose disposal at 20 min. The deactivation of glucose distribution/transport was slower than that of glucose disposal and EGP (P < 0.02) with half-times of 207 (84-510), 12 (7-22), and 29 (16-54) min, respectively. The minimal-model insulin sensitivity was tightly correlated with and linearly related to sensitivity of EGP (r = 0.96, P < 0.005) and correlated positively but nonsignificantly with distribution/transport sensitivity (r = 0.73, P = 0.10) and disposal sensitivity (r = 0.55, P = 0.26). We conclude that, in healthy subjects during an IVGTT, the two peripheral insulin effects account jointly for approximately one-half of the overall insulin-stimulated glucose lowering, each effect contributing equally. Suppression of EGP matches the effect in the periphery.
authors.affiliation: Centre for Measurement and Information in Medicine, City University, London EC1V 0HB. r.hovorka@city.ac.uk
authors.forename: Roman
authors.initials: R
authors.lastname: Hovorka
authors.forename: Fariba
authors.initials: F
authors.lastname: Shojaee-Moradie
authors.forename: Paul V
authors.initials: PV
authors.lastname: Carroll
authors.forename: Ludovic J
authors.initials: LJ
authors.lastname: Chassin
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Gowrie
authors.forename: Nicola C
authors.initials: NC
authors.lastname: Jackson
authors.forename: Romulus S
authors.initials: RS
authors.lastname: Tudor
authors.forename: A Margot
authors.initials: AM
authors.lastname: Umpleby
authors.forename: Richard H
authors.initials: RH
authors.lastname: Jones
mesh_terms: D019325:3-O-Methylglucose / Q000493:pharmacokinetics; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002247:Carbon Isotopes; D005947:Glucose / Q000493:pharmacokinetics*; D005951:Glucose Tolerance Test / Q000379:methods*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D008954:Models, Biological
chemical_list: D001786:Blood Glucose; D002247:Carbon Isotopes; D007328:Insulin; D019325:3-O-Methylglucose; D005947:Glucose