The role of cyclic AMP in mesenteric vasodilation

We tested the hypothesis that one mechanism regulating vasodilation in the mesenteric arterial circulation involves an increase in the cyclic AMP (cAMP) content of vascular smooth muscle. In anesthetized dogs, mesenteric blood flow measured with an electromagnetic flowmeter increased during intra-arterial infusion of isoproterenol, prostaglandin E₁, papaverine, and cAMP. Propranolol blocked the vasodilator response to isoproterenol but not the dilatory effects of the other drugs. Segments of mesenteric arteries were incubated with the preceding drugs (except cAMP), and tissue concentrations of cAMP were measured. Mesenteric artery cAMP content was increased by isoproterenol, prostaglandin E₁, and papaverine. The effect of isoproterenol on tissue cAMP was blocked by propranolol. For comparison we studied the effect of oxygen tension on arterial cAMP content. Varying the pO₂ of the bathing solution from 680 to 0 mm Hg did not significantly alter mesenteric artery cAMP content except for a small reduction at zero pO₂. The present results are consistent with the concept that isoproterenol, prostaglandin E₁, and papaverine induce dilation of mesenteric arteries via increases in intracellular cAMP.