PHENYLEPHRINE-INDUCED INCREASES IN CARDIAC CONTRACTILITY, CYCLIC ADENOSINE MONOPHOSPHATE AND PHOSPHORYLASE a

¹ Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver Canada

Both norepinephrine and phenylephrine increased cardiac cyclic adenosine monophoshate (AMP), contractility and phosphorylase a; in the isolated guinea-pig heart. Cyclic AMP increased prior to the other two events in both cases. Dose-response data revealed that phenylephrine was less potent and less effective than norepinephrine when either the biochemical or mechanical events were measured. The data indicate that phenylephrine is a weak beta adrenergic agonist and provide evidence that cyclic AMP is involved in the positive inotropic effect of the amine.