A new method of sampling blood for measurement of plasma adenosine

The half-life of adenosine in human blood is 1-2 s at 37 degrees C. To measure plasma adenosine concentration accurately, it is necessary to inhibit adenosine metabolism during transit of blood through the sampling catheter. We have tested a double-lumen catheter and a solution of compounds that inhibit adenosine metabolism (stop solution) for this purpose. Stop solution and radiolabeled adenosine were delivered via an inner lumen, mixed with blood at the catheter tip, and withdrawn to a collection syringe in an outer lumen. Extracellular recovery of label was 89 +/- 5% and proportional to the quantity of label added to blood. In contrast, when blood and radiolabel were mixed with stop solution in the collecting syringe only after passage through the catheter, recovery of radiolabel was 7 +/- 3%. The importance of inhibiting pathways of adenosine formation and degradation or uptake during transit of blood through the catheter was demonstrated. The results suggest that a double-lumen catheter and stop solution are both necessary and suitable for collection of human blood to determine the concentration of plasma adenosine.