Metabolism of ( 14 C)adenine and derivatives by cerebral tissues, superfused and electrically stimulated.

1. Uptake of [(14)C]adenine and [(14)C]adenosine from surrounding fluids to guinea-pig cerebral tissues was measured during incubation in vitro. Output of (14)C-labelled compounds from the loaded tissues to superfusion fluids occurred on continued incubation, at about 0.2% of the tissue's content/min, and this rate was increased about fourfold by electrical excitation of the tissue. 2. The compounds released from the tissue to superfusion fluids included adenine, adenosine, inosine and hypoxanthine with small amounts of nucleotides. Output of all these compounds, except adenine, increased on excitation. Media depleted of oxygen or glucose also increased the output of (14)C-labelled derivatives from [(14)C]adenine-loaded tissues, and this augmented output was further increased by electrical stimulation. 3. [(14)C]Adenosine was found as the main product from [(14)C]ATP when this was added at low concentrations to fluids superfusing cerebral tissue. Metabolic and neurohumoural explanations of the liberation and action of adenosine derivatives in the tissue are discussed.