RECOVERY AS A FUNCTION OF THE OSMOLALITY OF THE PERFUSION MEDIUM IN MICRODIALYSIS EXPERIMENTS

The effect of varying perfusion medium osmolality on the in vivo micro dialysis recovery of caffeine and 5-chloro-2',3'-dideoxy-3'-fluorourid ine (FCdU) was investigated. The microdialysis probes were implanted i n rats into the corpus striatum of the brain. Each probe was perfused with a solution containing 10 mu M FCdU (in distilled water, Ringer's solution or in 20% sucrose in Ringer's solution) or with a solution co ntaining 10 mu M caffeine (in distilled water, Ringer's solution, in 2 0% sucrose in distilled water or in 20% sucrose in Ringer's solution). Recovery was calculated as the proportion of concentration loss over the microdialysis membrane to the perfusion medium (i.e. from 10 mu M) . The recovery was significantly dependent on the composition of the p erfusion medium. The recoveries of FCdU were 0.097 (55%) for water sol ution, 0.176 (100%) for Ringer's solution and 0.292 (166%) for sucrose 's solution. The recoveries of caffeine were 0.196 (73%) for water sol ution, 0.270 (100%) for Ringer's solution and 0.335 (124%) for sucrose 's solution in water and 0.303 (112%) for sucrose's solution in Ringer . A linear correlation between the recovery over microdialysis membran e and osmolality of perfusion medium was demonstrated for FCdU. The mo del describing the change of the recovery of caffeine with osmolality of perfusion medium fitted a polynomial function of second order. It i s 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 in creasing osmolality, thereby increasing the effective diffusion in the tissue. (C) 1998 Elsevier Science B.V. All rights reserved.