Myocardial norepinephrine and cyclic AMP concentration following myocardial ischemia-Relation to ventricular fibrillation and sudden death.

This study was designed to investigate the relationships of myocardial concentrations of norepinephrine (NE) and cyclic AMP (c-AMP) to the development of ventricular fibrillation (VF) with reference to the effects of a premedication of dibutyryl cyclic AMP (DBC-AMP) and propranolol in dogs with experimental myocardial infarction. Myocardial specimens were obtained serially from the ischemic and the non-ischemic zones by mini-drill biopsy, and NE and c-AMP levels were determined by high-performance liquid chromatography and radioimmunoassay, respectively. Before the occurrence of VF, myocardial NE increased in both the ischemic and the non-ischemic zones, and c-AMP increased significantly in the ischemic zone but did not in the non-ischemic zone. In dogs premedicated with DBC-AMP an increase of c-AMP was observed in both the ischemic and the non-ischemic zones in association with an increased incidence of VF. On the other hand, no significant increase of myocardial c-AMP was observed in both the ischemic and the non-ischemic zones of propranolol-premedicated dogs which were free from VF. A significant increase of myocardial c-AMP in the ischemic zone was observed in dogs which suffered from VF in spite of the premedication of propranolol. The incidence of VF was significantly reduced by 26.5% in dogs pretreated with propranolol. No significant changes in myocardial norepinephrine and c-AMP were observed in dogs which were free from VF throughout the experiments.