The Linear Probe: A Flexible Choice for In Vivo Microdialysis Sampling in Soft Tissues

ysis sampling in pharmacokinetics research has proven to have many benefits such as clean samples, more frequent samples, conservation of body fluid, and fewer animals per study. In addition, it provides a direct profile of pharmacokinetics within the tissue of interest instead of traditional methods which calculate the tissue concentration indirectly from serial blood samples. Microdialysis sampling was originally developed by neuroscientists for CNS studies, but during the past several years its suitability for sampling from other sites has been demonstrated. The applications of microdialysis sampling in the neurosciences have been extensively reviewed (1,2). Various designs of microdialysis probes have been developed for particular sites or types of tissue. For example, the rigid cannula probe, most suitable for sampling from the brain, has also been used to sample from adipose tissue (3), muscle (3-5), and liver (3,6). A flexible cannula probe has proven most appropriate for sampling from blood (7,8), but has also been used in liver (9). A flow-through or shunt probe design has been used in the bile duct (9-11). As previously reported, linear design probes have been used for pharmacokinetics and metabolism studies of dermal tissue (12), muscle and tumor (13), and liver (14). The linear design has the advantages of minimizing tissue damage, being totally flexible (and therefore more comfortable), and sufficiently durable for use in awake, freely moving animals. Recently, we developed a new linear microdialysis probe (F1) with an even smaller profile and additional strength and flexibility. It samples the interstitial fluid of a variety of soft tissues including dermis, muscle, adipose and subcutaneous tissue, liver and tumors. Long lengths of highly flexible tubing in the probe make it possible to implant in tissues that are distant from the exit site for the inlet and outlet tubing. This feature also makes the probe inherently more comfortable for the animal than a probe that must be anchored to skin proximal to the implant site. This linear probe moves with the tissue and does not jab or tear tissue during normal respiration, digestion, or movement by the animal. Implanting a probe in the thigh muscle of an active free-moving rat is a good test of ruggedness and stability. Linear probes in this muscle remained functional for up to 6 The Linear Probe: A Flexible Choice for In Vivo Microdialysis Sampling in Soft Tissues