IN VIVO CHANGES OF CEREBRAL CYCLIC ADENOSINE 3′,5′‐MONOPHOSPHATE INDUCED BY BIOGENIC AMINES: ASSOCIATION WITH PHOSPHORYLASE ACTIVATION

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Abstract
—The intravenous injection of adrenaline, isoprenaline and histamine to 4‐6‐day‐old chicks resulted in a rapid increase in the cyclic AMP content of cerebral hemispheres that had been removed and frozen within 0·5 s using a freeze‐blowing technique. Noradrenaline, dopamine, adenosine, 5‐HT and acetylcholine did not significantly alter the nucleotide concentration in vivo. Addition of adrenaline, isoprenaline and histamine to incubated chick cerebral cortex slices also increased the cyclic AMP content of the tissue. Noradrenaline was considerably less potent than these amines and adenosine was ineffective.Low phosphorylase a levels (16 per cent of total activity) were observed in instantaneously frozen cerebral hemispheres of untreated chicks. The injection of adrenaline, isoprenaline and histamine resulted in a rapid conversion of phosphorylase b to a and a significant fall in tissue glycogen. Administration of noradrenaline was without effect on the relative forms of phosphorylase and also failed to influence cerebral glycogen. Phosphorylase activation was not observed in chick cerebral slices under conditions producing large increases in cyclic AMP.It is suggested that in vivo phosphorylase activation and subsequent glycogenolysis may occur, at least in part, in glia and that these cells may be damaged during preparation of cerebral slices. The results provide evidence of a metabolic role for cyclic AMP in cerebral tissue.