Estimation of rat muscle blood flow by microdialysis probes perfused with ethanol, [14C]ethanol, and 3H2O.

We used the perfused rat hindquarter to evaluate whether the microdialysis ethanol technique can be used to qualitatively estimate nutritive skeletal muscle blood flow. Four microdialysis probes were inserted in different hindlimb muscles in each of 16 rats. Hindquarters were perfused at blood flow rates ranging from 0 to 21 ml. 100 g-1. min-1. The microdialysis probes were perfused at 2 microliter/min with perfusate containing ethanol, [14C]ethanol, and 3H2O. Within and between experiments outflow-to-inflow ratios (o/i) generally varied inversely with blood flow. When a low flow or no flow was maintained in hindquarters, o/i ratios first increased with time (for at least 60 min) and then leveled off. The long time constant impaired detection of rapid oscillations in blood flow, especially at low blood flow rates. Contractions per se apparently decreased o/i ratios independent of blood flow. Ethanol and [14C]ethanol o/i ratios did not differ. 3H2O o/i paralleled ethanol and [14C]ethanol o/i ratios but it was significantly lower. In conclusion, differences in skeletal muscle blood flow can be detected by the microdialysis technique. However, the slow changes in o/i, in particular at low blood flow rates, limit the usefulness of the technique for measuring dynamic changes in blood flow; caution must also be exerted during muscle contractions. 3H2O and [14C]ethanol are good alternatives to ethanol in the determination of blood flow by microdialysis.