Propentofylline reinforces adenosine actions by blocking its cellular reuptake via
nucleoside transporters. Adenosine, which is present in the normal brain at concentra-
tions between 30 and 100 nM, acts as a homeostatic neuromodulator (62,65). Adeno-
sine is rapidly inactivated by adenosine deaminase and by an eflicient cellular reup-
take system utilizing nucleoside transporters. During brain ischemia, large quantities
of adenosine are formed during ATP catalysis and are subsequently released into the
extracellular space. Inhibitors of adenosine transport into cells (e.g., dipyridamole and