Lack of Interaction between Norepinephrine or Histamine and Theophylline on Cardiac Cyclic AMP

Abstract

The hypothesis that theophylline can enhance the cardiac effects of norepinephrine and histamine by inhibiting phosphodiesterase was tested in isolated perfused hearts of rats and guinea pigs. Theophylline did enhance the inotropic and phosphorylase-activating effect of both amines. Cyclic AMP, increased by the injection of the amines, was not further increased when the hearts were perfused concomitantly with theophylline. When theophylline was injected into the heart, an increase in contractility and phosphorylase a was noted but cyclic AMP values were not affected. The data do not support phosphodiesterase inhibition as the mechanism by which theophylline produces its cardiac effects.