Analogue tracers and lumped constant in capillary beds

Bass, Ludvik, Sorensen, Michael, Munk, Ole Lajord and Keiding, Susanne (2011) Analogue tracers and lumped constant in capillary beds. Journal of Theoretical Biology, 285 1: 177-181. doi:10.1016/j.jtbi.2011.06.034

Author Bass, Ludvik
Sorensen, Michael
Munk, Ole Lajord
Keiding, Susanne
Title Analogue tracers and lumped constant in capillary beds
Journal name Journal of Theoretical Biology   Check publisher's open access policy
ISSN 0022-5193
Publication date 2011-09
Sub-type Article (original research)
DOI 10.1016/j.jtbi.2011.06.034
Volume 285
Issue 1
Start page 177
End page 181
Total pages 5
Place of publication London, United Kingdom
Publisher Academic Press
Collection year 2012
Language eng
Formatted abstract
The lumped constant is a proportionality factor for converting a tracer analogue's metabolic rate to that of its mother substance. In a uniform system, it is expressed as the ratio of the tracer analogue's extraction fraction (E*) to the extraction fraction of its mother substance (E).

Here we show that, in capillary beds perfused by unidirectional blood flow, unequal concentration gradients of the tracer analogue and of the mother substance influence extraction fractions both locally and across the organ and that the direct proportionality of E* and E must be replaced by ln(1−E*)/ln(1−E) to yield Λ, i.e. the lumped constant derived from first principles of bi-substrate enzyme and membrane kinetics. In other words, at a given capillary blood flow (F), the ratio of systemic clearances (FE*/FE), often used in compartmental kinetic analysis, must be replaced by the ratio of the intrinsic clearances, [−F ln(1−E*)]/[−F ln(1−E)].

The conclusion is supported by 2-[18F]fluoro-2-deoxy-d-galactose removal kinetics in pig liver in vivo from previous publications by the dependence of E*/E and the independence of Λ, on blood galactose concentration. Moreover, our corrections to the results of compartmental kinetics are quantified for comparing extraction fractions in different regions of interest (e.g. by positron emission tomography) and for calculating Λ using whole-organ E* and E measured by arteriovenous concentration differences.
Keyword Microvascular tracer kinetics in vivo
Intrinsic clearance
2-[F-18]Fluoro-2-deoxy-D-glucose PET
Positron emission tomography
Bi-substrate enzyme kinetics
Galactose elimination
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2012 Collection
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Citation counts: TR Web of Science Citation Count  Cited 4 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 5 times in Scopus Article | Citations
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