Direct and indirect stimulations of cyclic AMP formation in human brain.

1. Adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation, by use of an [3H]-adenine prelabelling assay, was measured in fragments of human cerebral cortex, taken in the course of various neurosurgical procedures. 2. Large accumulations of [3H]-cyclic AMP due to isoprenaline, noradrenaline and adenosine and small effects due to forskolin were observed. Histamine, 5-hydroxytryptamine (5-HT) and the excitatory amino acids glutamate and quisqualate were ineffective. 3. The response to noradrenaline consisted of two components; a direct beta-adrenoceptor response and an enhancement mediated by an alpha-adrenoceptor which appears to be similar to that in rat cerebral cortex. 4. The response to isoprenaline was also potentiated by histamine H1 receptor stimulation but the direct effect of 2-chloroadenosine was not altered by histamine, 5-HT or quisqualate. 5. It is concluded that some, but not all, of the indirect modulations of cyclic AMP formation previously observed in experimental animal brain exist in human cerebral cortex.