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- Title
L-Glucose: A Superior Tracer for Microdialysis Assessment of Microvascular Flow Response to Exercise or Insulin in Muscle.
- Authors
Newman, John M.; Ross, Renee M.; Richards, Stephen M.; Rattigan, Stephen; Clark, Michael G.
- Abstract
The microdialysis O/I ratio technique has been used to monitor microvascular blood flow as a consequence of change in blood flow and/or capillary recruitment within muscle. An increase in microvascular flow lowers the probe O/I ratio of microdialysis tracers. However, highly diffusible tracers such as ethanol or labeled water have low O/I ratios that prevent accurate assessment of change in microvascular flow. Herein we compare ³H[sub 2]O and a novel tracer, [[sup 14]C]-L-glucose using muscle contraction and insulin as stimuli for increased microvascular flow. Anaesthetized rats were used to assess the changes in Oh ratio following increased muscle blood flow in response to exercise (field stimulation of the lower leg, 0.1msec pulses at 2Hz) or insulin (10mU/min/kg, euglycemic clamp). A comparison of the O/I ratio of two radioactive tracers (³H[sub 2]O and [[sup 14]C]-L-glucose -- an extra-cellular marker) was conducted. Field stimulation and insulin each increased femoral blood flow (FBF, Transonic flow probe) approximately 1.6-fold. The O/I ratio of ³H[sub 2]O decreased during field stimulation, but was unaffected by insulin. In contrast, the O/I ratio of [[sup 14]C]-L-glucose decreased in response to both field stimulation and insulin. Mathematical models were used to calculate muscle diffusion coefficients for ³H[sub 2]O and [[sup 14]C]-L-glucose as well as blood flow around the probe (Q[sub b]) using microdialysis O/I ratio data. For ³H[sub 2]O the calculated Q[sub b] was unaffected by insulin, but Q[sub b] calculated from [[sub 14]4C]-L-glucose increased 2-fold (P<0.05) and by a greater amount compared to the measured increase in FBF. For ³H[sub 2]O the calculated Q[sub b] during field stimulation was increased to the same degree as FBF (1.6-fold). In contrast, the calculated Q[sub b] using [[sup 14]C]-L-glucose during field stimulation increased 2.6-fold. It is concluded that [[sup 14]C]-L-glucose is superior to ³H[sub 2]O as a tracer for determining changes in muscle microvascular blood flow following exercise or insulin. Microdialysis using [[sup 14]C]-L-glucose in conjunction with our mathematical model allows calculation of the proportion of total flow that is nutritive.
- Subjects
GLUCOSE; BLOOD flow; MICRODIALYSIS; EXERCISE; INSULIN; MUSCLES
- Publication
Diabetes, 2007, Vol 56, pA398
- ISSN
0012-1797
- Publication type
Article