Adenylate cyclase activation by noradrenaline in a cell-free system of rat cerebral cortex

Basal and noradrenaline stimulated adenylate cyclase activity was measured in a hypoosmotic homogenate of rat cerebral cortex. During incubation the basal enzyme activity declined, whereas noradrenaline caused a near linear activation of the enzyme within the observation period. The stimulation by noradrenaline was higher in percentage after preincubation with ATP than in the cases when noradrenaline was given simultaneously with ATP to the system. It was therefore assumed that homogenization resulted in an apparent activation of the enzyme activity. The activity declined only in the presence of ATP and was accompanied by a diminished augmentation by noradrenaline of adenylate cyclase activity.