Key result
In anaesthetized rats, both contraction and insulin significantly increased the nutritive fraction of total muscle blood flow from a basal level of 0.38 to 0.82 and 0.52, respectively (P < 0.05).
A novel microdialysis method using L-[14C]glucose demonstrates that both muscle contraction and insulin significantly increase the nutritive fraction of total muscle blood flow in rats.
Requires human validation before clinical consideration; leaves open the role of nutritive blood flow in insulin resistance and exercise.
In the present study, a mathematical model using the microdialysis outflow: inflow (O/I) ratio of the novel analogue L-[14C]glucose has been developed which allows the calculation of the nutritive (and non-nutritive) flow in muscle as a proportion of total blood flow. Anaesthetized rats had microdialysis probes carrying L-[14C]glucose inserted through a calf muscle group (tibialis/plantaris/gastrocnemius). The nutritive fraction of total blood flow was determined under basal conditions and in response to contraction (electrical field stimulation), insulin (hyperinsulinaemic euglycaemic clamp with 10 mU min(-1) kg(-1) insulin) or saline control from limb blood flow and the microdialysis O/I ratio of L-[14C]glucose. Both contraction and insulin infusion decreased the O/I ratio of L-[14C]glucose and increased total limb blood flow. Calculations based on mathematical models using L-[14C]glucose O/I and limb blood flow revealed that during basal conditions, the nutritive fraction of total flow was 0.38 +/- 0.06, indicating that basal flow was predominantly non-nutritive. Contraction and insulin increased the nutritive fraction to 0.82 +/- 0.24 (P < 0.05) and 0.52 +/- 0.12 (P < 0.05). Thus the increase in limb blood flow from insulin was fully accommodated by nutritive flow, while contraction increased nutritive flow at the expense of non-nutritive flow. This novel method using microdialysis and the O/I ratio of L-[14C]glucose allows the determination of the nutritive fraction of total flow in muscle as well as the proportion of total flow that may be redistributed in response to contraction and insulin.
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Newman et al. (2007) studied this question. Contraction and insulin vs. Basal conditions and saline control was evaluated on Nutritive fraction of total blood flow (p=< 0.05). In anaesthetized rats, both contraction and insulin significantly increased the nutritive fraction of total muscle blood flow from a basal level of 0.38 to 0.82 and 0.52, respectively (P < 0.05).
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