The relation between myocardial tissue cyclic AMP (cAMP) and the vulnerability to ventricular fibrillation was assessed in the isolated perfused rat heart by measurement of ventricular fibrillation threshold (VFT) and vulnerable period duration (VP). Exogenous dibutyryl cyclic AMP (DBcAMP) reduced VFT and increased VP by a concentration-related action whereas exogenous cAMP did not. Theophylline (1.0 mmol/liter) increased the tissue content of cAMP by 58% (P < 0.001) and caused a leftward shift in the concentration-response curve to DBcAMP. An effect of cAMP on VFT and VP could be shown in the presence of phosphodiesterase inhibition by theophylline. β-1-Adrenergic receptor blockade with atenolol did not alter the concentration-response curve for VFT when DBcAMP was administered. Epinephrine (100 nmol/liter to 1 μmol/liter) also increased vulnerability to VF; this effect was accompanied by a concentration-related increase in tissue cAMP, but inconsistent changes in tissue ATP, phosphocreatine and potassium. The concentration-response curve of VFT to epinephrine was shifted leftward by theophylline and rightward by atenolol.
W. F. Lubbe, Th. Podzuweit, P. S. Daries, L. H. Opie