Abstract
1. The mechanism of stimulation of cyclic adenosine 3',5'-monophosphate (cyclic AMP) accumulation by adrenaline and ouabain and the effect of Mn(++) substitution for Mg(++) as the metal ion requirement of this system was studied in cell-free preparations of adenyl cyclase from rat brain.2. In the rat cerebral cortex preparation, substitution of Mn(++) for Mg(++) significantly increased cyclic AMP accumulation while significantly inhibiting adenosine triphosphate (ATP) and adenosine diphosphate (ADP) hydrolysis and adenosine 5'-monophosphate (AMP) accumulation. In the synaptic membrane preparation, in the absence of NaF, the highest amount of ATP hydrolysis was obtained in tissue prepared with Mn(++) and incubated with Mg(++); under these conditions cyclic AMP accumulation was equal to that produced under any other condition and significantly higher than that observed in the presence of Mg(++) prepared and Mg(++) incubated tissue.3. Preparation and/or incubation of tissue with Mn(++) significantly reduced phosphodiesterase (PDE) activity compared to that observed in Mg(++) prepared tissue.4. Adrenaline and ouabain both significantly increased cyclic AMP accumulation in the rat cerebral cortex preparation but did not inhibit ATP or ADP hydrolysis. In the synaptic membrane preparation, in the presence of 0.01 mM Ca(++), adrenaline but not ouabain significantly increased cyclic AMP accumulation. Phenoxybenzamine (0.1 mM) and pronethalol (0.1 mM) significantly inhibited adrenaline-induced cyclic AMP accumulation in both these preparations.5. Ouabain and adrenaline both failed to stimulate cyclic AMP accumulation in the presence of Mn(++) prepared and/or incubated tissue.6. Ouabain and adrenaline had no effect on PDE activity in either of these preparations.7. It was concluded that Mn(++) increased cyclic AMP accumulation in part by indirect inhibition of ATP and ADP hydrolysis which provides inhibitors of cyclic AMP destruction, by direct stimulation of adenyl cyclase and by inhibition of cyclic AMP destruction in a way unrelated to nucleotide inhibition of PDE. Adrenaline and ouabain appeared tp stimulate cyclic AMP accumulation in a more direct manner.