Myocardial concentration of norepinephrine and cyclic AMP in ventricular fibrillation during acute myocardial ischemia.

To clarify the relationship between the concentrations of norepinephrine (NE) and cyclic AMP (c-AMP) in the myocardium and the incidence of ventricular fibrillation (VF), we studied 48 dogs in which VF was induced by the ligation of the left anterior descending coronary artery. The animals were divided into two groups of equal size: The first received no drugs, the second received d,l-propranolol (0.5 mg/kg) 15 min before coronary ligation. Myocardial samples were taken at regular intervals from normal and ischemic areas to determine NE and c-AMP concentrations. In the untreated group, no significant change in the concentrations of NE and c-AMP was observed in 12 dogs that did not develop VF. In the other 12 dogs that developed VF, there was a significant increase in c-AMP in the ischemic area immediately after the onset of the dysrhythmia. A significant increase in NE concentration both in normal and ischemic myocardium was observed in only 8 of these latter 12 dogs. Premedication with propranolol significantly reduced the incidence of VF, but it still occurred in 5 out of 24 dogs. Increase in c-AMP without an increase in NE in ischemic area was observed in these five dogs. These results suggest that c-AMP may play a role in the development of VF during acute ischemia.