Principle of In Vivo Microdialysis

Microdialysis is an in vivo bioanalytical sampling technique for monitoring local chemistry in the extracellular fluid of an organ and in body fluids. The sampling principle is quite simple: Molecules diffuse from the body compartment through a semipermeable membrane of the sampling cannula into the perfusion medium flowing inside the probe (Delgado et al., 1972; Ungerstedt and Pycock, 1974). The driving force for this molecular movement is passive diffusion down the concentration gradient between the two compartments. Thus, the technique works in both directions: for recovering substances from a living body, and for delivering substances into this organism.

In practice, a microdialysis probe is implanted into the tissue with tubing connecting it to external components: a perfusion pump and a fraction collector. The probe is perfused continually at low flow rate (0.1-10 juL/min) with an artificial physiological solution. As the perfusate emerges from the probe, fractions are collected and samples of each fraction analyzed.

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