Cyclic AMP‐Generating Systems in Cell‐Free Preparations from Guinea Pig Cerebral Cortex: Loss of Adenosine and Amine Responsiveness Due to Low Levels of Endogenous Adenosine

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Abstract
The accumulations of radioactive cyclic[c]AMP elicited by adenosine, norepinephrine and histamine in adenine-labeled vesicular entities of a particulate fraction from guinea pig cerebral cortex are greatly reduced as a result of prolonged preincubation. The presence of adenosine deaminase during preincubations largely prevents the loss of adenosine, norepinephrine and histamine responses. Adenosine deaminase was inactivated by deoxycoformycin prior to stimulation of cAMP accumulation by adenosine or amines. If adenosine deaminase is not inactivated, responses to norepinephrine are not significant and histamine responses are reduced by 50%. Adenosine deaminase cannot restore responsiveness of the cAMP-generating systems. In particulate fractions of guinea pig cerebral cortex, low levels of adenosine may cause a slow loss of receptors and/or of coupling of receptors to cAMP-generating systems.

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