Recovery as a function of the osmolality of the perfusion medium in microdialysis experiments Original Research Article

The effect of varying perfusion medium osmolality on the in vivo microdialysis recovery of caffeine and 5-chloro-2′,3′-dideoxy-3′-fluorouridine (FCdU) was investigated. The microdialysis probes were implanted in rats into the corpus striatum of the brain. Each probe was perfused with a solution containing 10 μM FCdU (in distilled water, Ringerʹs solution or in 20% sucrose in Ringerʹs solution) or with a solution containing 10 μM caffeine (in distilled water, Ringerʹs solution, in 20% sucrose in distilled water or in 20% sucrose in Ringerʹs solution). Recovery was calculated as the proportion of concentration loss over the microdialysis membrane to the perfusion medium (i.e. from 10 μM). The recovery was significantly dependent on the composition of the perfusion medium. The recoveries of FCdU were 0.097 (55%) for water solution, 0.176 (100%) for Ringerʹs solution and 0.292 (166%) for sucroseʹs solution. The recoveries of caffeine were 0.196 (73%) for water solution, 0.270 (100%) for Ringerʹs solution and 0.335 (124%) for sucroseʹs solution in water and 0.303 (112%) for sucroseʹs solution in Ringer. A linear correlation between the recovery over microdialysis membrane and osmolality of perfusion medium was demonstrated for FCdU. The model describing the change of the recovery of caffeine with osmolality of perfusion medium fitted a polynomial function of second order. It is concluded that the osmolality of the perfusion medium influences the recovery in microdialysis experiments. A possible mechanism for this phenomenon is an increase in the extracellular volume fraction with increasing osmolality, thereby increasing the effective diffusion in the tissue.