Effect of propranolol on cyclic nucleotides of ischemic dog heart

The effects of ischemic and beta-blocker on myocardial cyclic nucleotides (cyclic AMP and cyclic GMP) of dogs were studied. The concentration of cyclic AMP in both infarcted and noninfarcted area 60 min after the ligation of the proximal part of the left anterior descending coronary artery to significantly higher than in sham-operated control animals. The concentration of cyclic GMP in infarcted area is also significantly elevated compared with control 15 min after the ligation. The cAMP/cGMP (A/G) ratio in the infarcted group was also elevated at 60 min and returned to control level after 5 hr. When propranolol was given, the concentration of cyclic AMP of both infarcted and noninfarcted area remained at control level. In propranolol-treated animals, the concentration of cyclic GMP in both infarcted and noninfarcted area increased significantly compared with control at 15 min and 60 min. The A/G ratio was also decreased below control level after the administration of propranolol. These results suggest that the stability of the ischemic cardiac muscle was enhanced by the administration of beta-blockers.