Relationship between the tonus of the walls of the internal carotid artery and cyclic adenylmonophosphate

Experiments were carried out in dogs with the use of resistography of circulatory-isolated internal carotid artery. Both activation of adenyl cyclase by adenosine and inhibition of phosphodiesterase by theophylline in the vascular wall result in a significant decrease in the vasoconstrictor effect of prestaglandin E2. On the contrary, inhibition of adenyl cyclase by the beta-blocker propranolol or activation of phosphodiesterase by imidazol in the vascular wall causes potentiation of vasoconstriction brought about by prostaglandin E2. Thus the endogenous cyclic AMP either antagonizes the vasoconstrictor effect of prostaglandin E2, or the latter affects vascular smooth muscles by influencing the activity of enzymes that are responsible for the cyclic AMP level in the vascular wall.