Morphine enhances adenosine release from the in vivo rat cerebral cortex.

Morphine (1 and 5 mg/kg), administered intravenously, increased the rate of efflux of purines from intact rat cerebral cortices prelabelled with 3H-adenosine. Naloxone antagonized morphine's action. It is suggested that the depressant actions of morphine on transmission in the central nervous system may be related to this enhancement of extracellular levels of adenosine and the adenine nucleotides.