A multicompartmental model of in vivo adipose tissue glycerol kinetics and capillary permeability in lean and obese humans.
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 micromol/l [interquartile range 210-268]) were consistently greater than those of arterial blood (69.1 micromol/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 micromol/l (256-350) and 332 micromol/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< or = -0.45, P < 0.05). Our results support previous estimates of interstitial glycerol concentration within adipose tissue and reveal capillary diffusion capacity is reduced in obesity.
Coppack
Simon W
SW
Diabetes & Metabolic Medicine, St. Bartholomew's and The London School of Medicine, London, UK. s.w.coppack@qmul.ac.uk
Chinkes
David L
DL
Miles
John M
JM
Patterson
Bruce W
BW
Klein
Samuel
S
D000273:Adipose Tissue / Q000098:blood supply / Q000378:metabolism*; D000328:Adult; D001783:Blood Flow Velocity; D015992:Body Mass Index; D005260:Female; D005990:Glycerol / Q000378:metabolism*; D006801:Humans; D008066:Lipolysis / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009765:Obesity / Q000378:metabolism*; D013851:Thinness; D014280:Triglycerides / Q000097:blood*; D014316:Tritium
D014280:Triglycerides; D014316:Tritium; D005990:Glycerol