Cyclic AMP as a determinant of vulnerability to ventricular fibrillation in the isolated rat heart.

Ventricular fibrillation threshold and vulnerable period were measured in the isolated perfused rat heart to assess the influence of dibutyryl cyclic AMP on ventricular vulnerability. Doses of dibutyryl cyclic AMP of 0.6-1.6 mumol/min caused an increase in coronary flow but had no effect on vulnerability, whereas doses of 2.6-4.2 mumol/min resulted in an increase in coronary flow, a decrease in VF threshold, and an increase in the width of the vulnerable period. These experiments support the concept of a local myocardial action of catecholamines, mediated by cyclic AMP, whereby vulnerability to ventricular fibrillation is increased.