Intrathecal adenosine does not relieve allodynia-like behavior in spinallyinjured rats

THE intrathecal (i.t.) administration of the adenosine Al-receptor agonist R-phenylisopropyl-adenosine (R-PIA) reduced pain-related behaviors after pe ripheral nerve or spinal cord injury in rats. The endogenous ligand adenosi ne is clinically available and has been tested i.t. as an analgesic. Thus, we set out to investigate whether i.t. adenosine could reduce allodynia in a model of central pain in spinally injured rats. I.t. adenosine did not re duce mechanical and cold allodynia-like behaviors at doses of 10, 100 and 1 87 nmol, whereas i.t. R-PIA at 10 nmol markedly alleviated allodynia in the same animals. The lack of effect by exogenous adenosine may be due to phar macokinetic or pharmacodynamic reasons. Alternatively, adenosine may have r educed affinity and selectivity towards the A(1)-receptors which may be imp ortant for the antiallodynic effect. (C) 1999 Lippincott Williams & Wilkins .