Adenosine deaminase activity in rat intestine: assay with a microdialysis technique

Using microdialysis, we measured adenosine deaminase activity in rat intestine by detecting inosine, a breakdown product of adenosine. The dialysis probe consisted of a 3 x 0.22 mm dialysis fiber with a 50,000 mol wt cut off. When the probe was perfused at 1 microl/min in vitro, the average relative recovery rate of inosine was 22.1+/-0.9%). The dialysis probe was implanted in the intestinal mucosa and perfused with Tyrode solution containing adenosine at 1 microl/min. The dialysate samples were analyzed for inosine by high-performance liquid chromatography with ultraviolet (HPLC-UV) detection at 260 nm. When adenosine (100-1000 microM) was perfused, the level of inosine increased dose-dependently and was saturatable at about 1 mM adenosine. The ED50 of adenosine was 192.6 microM, with a maximum attainable inosine concentration of 59.7 microM. In the presence of aminoguanidine, a adenosine deaminase inhibitor (10 mM or 10 n mol/microl/min), the elevation of inosine was not observed. The dialysis technique makes it possible to measure adenosine deaminase activity in intestinal mucosa.