Coronary artery cyclic AMP content during adrenergic receptor stimulation

The purpose of this study was to test the hypothesis that the mechanical response of coronary smooth muscle following adrenergic receptor stimulation was mediated by changes in cyclic AMP content. Dibutyryl cyclic AMP caused relaxation of coronary artery strips. Aminophylline caused relaxation and a 254% elevation of cyclic AMP content (P < 0.005). Phenylephrine caused contraction but no significant change in cyclic AMP content (P>0.4). Epinephrine alone caused contraction and a 99% elevation of cyclic AMP content (P < 0.001). The alpha blocker, phentolamine, reversed the mechanical response to epinephrine, but it did not significantly (P > 0.15) reduce the effect of epinephrine on cyclic AMP content. Propranolol enhanced the contractile response to epinephrine and attenuated the epinephrine induced increase in cyclic AMP content. These results suggest that the contraction of coronary arteries associated with alpha receptor stimulation is not mediated by changes in cyclic AMP content; however, relaxation associated with beta receptor stimulation may be mediated by an increase in cyclic AMP content.