Stimulation of adenosine 3',5'-monophosphate formation in guinea-pig cerebral cortical slices in a calcium free medium.

In guinea-pig cerebral cortical slices cyclic AMP concentrations increase during incubation with histamine+noradrenaline. After 10 min of incubation the levels of cyclic AMP start to decline. When calcium ions are omitted from the incubation medium, cyclic AMP levels do increase to a greater extent under the same conditions and do not drop during 30 min incubation. In the presence of calcium ions cyclic AMP synthesis can not be elicited by noradrenaline alone. In calcium-free Krebs-Ringer solution a pronounced effect of noradrenaline on cyclic AMP levels is observed. This effect of noradrenaline is shown to be mediated by a classical alpha-type receptor. 5-Hydroxytryptamine, prostaglandin E1 and dopamine do not significnatly enhance cyclic AMP formation in guinea-pig brain slices in either the presence in, or the absence of calcium ions from the incubation medium. Under depolarizing conditions of incubation the stimulatory effect of ouabain or 125 mM K+ is blocked in a calcium-free medium, while with the depolarizing agent veratridine no significant reduction of cyclic AMP formed during incubation in a calcium-free medium is obtained.