Diabetes 54:1934-1941, 2005 © 2005 by the American Diabetes Association, Inc. A Multicompartmental Model of In Vivo Adipose Tissue Glycerol Kinetics and Capillary Permeability in Lean and Obese Humans
1 Diabetes & Metabolic Medicine, St. Bartholomews and The London School of Medicine, London, U.K
Lipolysis of adipose tissue triglycerides releases glycerol. Twenty-four volunteers, of whom 6 were obese and 13 were women, received a primed-constant infusion of 2H5-glycerol for 120 min during postabsorptive steady-state conditions. Arterial, abdominal venous, and interstitial (microdialysis) samples were taken, and a four-compartment model was applied to assess subcutaneous abdominal adipose tissue glycerol kinetics. Adipose tissue blood flow was measured using 133Xe washout. Venous glycerol concentrations (median 230 µmol/l [interquartile range 210–268]) were consistently greater than those of arterial blood (69.1 µmol/l [56.5–85.5]), while glycerol isotopic enrichments (tracer-to-tracee ratio) were greater in arterial blood (8.34% [7.44–10.1]) than venous blood (2.34% [1.71–2.69], P < 0.01). Microdialysate glycerol enrichment was 1.44% (1.11–1.79), indicating incomplete permeability of glycerol between capillary blood and interstitium. Calculated interstitial glycerol concentrations were between 270 µmol/l (256–350) and 332 µmol/l (281–371) (examining different boundary conditions). The calculated capillary diffusion capacity (ps) was between 2.21 ml · 100 g tissue–1 · min–1 (1.31–3.13) and 3.09 ml · 100 g tissue–1 · min–1 (1.52–4.90) and correlated inversely with adiposity (Rs
Address correspondence and reprint requests to Simon W. Coppack, MD, Academic Medical Unit, The London Hospital, Whitechapel, London E1 1BB, U.K. E-mail s.w.coppack{at}qmul.ac.uk
Abbreviations: ATBF, adipose tissue blood flow; IBW, ideal body weight; LPL, lipoprotein lipase; TTR, tracer-to-tracee ratio
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