Historically, most information about the distribution and concentration of endogenous and exogenous compounds has been based on blood sampling or homogenized tissue. In the case of endogenous compounds, sampling plasma or homogenized tissue only provides data on concentrations and provides little or no insight into the physiology of temporal release patterns or release stimuli. While blood sampling can provide multiple serial samples from a single animal, it sums analyte concentrations from all tissues and offers no anatomical specificity. While sampling tissue does provide anatomical specificity, it usually permits only one sample per tissue/animal and thus can dramatically increase the number of animals required in a study.
In Vivo Microdialysis and Ultrafiltration Sampling address these limitations and are two of the very few sampling techniques that allows for direct sampling in the interstitial fluid, allowing investigators to measure free analyte concentrations along with temporal and spatial release and concentration patterns. While both are semi-permeable membrane based sampling techniques, the applications and features of these two techniques differ.