[Inhibition of rat heart and brain cyclic 3',5'-adenosine monophosphate phosphodiesterase under the influence of neurohormone "C"].

In vitro studies of the effect of neurohormone C on cyclic AMP phosphodiesterase activity of heart and brain showed that amounts of neurohormone equal to 5 ng inhibited significantly the activity of phos-phodiestherase in heart and even more strongly in brain. A comparison of the effect of the neurohormone with that of theophylline (10 mM) showed that very small amounts of the neurohormone brought about inhibition of enzyme activity that was equal to that observed from much larger concentrations of the theophylline. It is proposed that the inhibition of phosphodiestherase activity is of importance in the mechanism of the action of the neurohormone.