Role of Cyclic AMP and Ca++ in Mechanical and Metabolic Events in Isometrically Contracting Vascular Smooth Muscle

Abstract

In bovine mesenteric artery catecholamines stimulated simultaneously adrenergic α‐and β‐receptors. The relaxation induced by a specific adrenergic β‐receptor stimulation was associated with an increased content of cyclic AMP, a phosphorylase a activation and a decrease of the content of ATP and creatinephosphate (CrP). No effect on the high energy phosphate compounds was present in the Ca⁺⁺‐poor artery, but the effect on cyclic AMP and phosphorylase was still evident. Sotalol blocked all the actions induced by adrenergic β‐receptor stimulation. The contracting action induced by selective adrenergic α‐receptor stimulation was initially associated with a decrease of the cyclic AMP content, but when the tension was maximally developed, after 120 s, the cyclic AMP content was increased and the phosphodiesterase activity reduced. In Ca⁺⁺‐poor artery a cyclic AMP decreasing effect was still present after 120 s and there was no reduction of the phosphodiesterase activity. The mechanical and metabolic effects induced by α‐receptor stimulation were blocked by dibenamine. Histamine, which increased the artery tension, significantly reduced the cyclic AMP content after 15 s, but after 5 min the level of cyclic AMP had increased and phosphorylase a was activated. The mechanical and metabolic effects of histamine were blocked by promethazine, an antihistaminic drug. The role of cyclic AMP in relaxation and contraction of vascular smooth muscle is discussed.