Individual and combined effects of cafeine and nicotine on responses of the isolated rat heart

In order to assess whether the cardiotoxic effects of caffeine and nicotine are caused by direct action on the heart, the individual and combined effects of caffeine and nicotine on responses df the isolated rat heart were monitored using an in vitro heart chamber. Perfusion of caffeine at 10 to 5000 μM caused dose-dependent effects on the heart responses. Following perfusion with 10 to 5000 μM caffeine, the mean heart rate was reduced by 3.1 to 28.4%, the P-R interval was increased by 2.5 to 31.5%, and the QRS amplitude was decreased by 8.5 to 51.0%. The left ventricular (LV) pressure was increased by 8.3% after 10 μM and decreased by 71.5% after 5000 μM caffeine Following perfusion with 1 to 100 μM nicotine, the mean heart rate was reduced by 2.0 to 33.0%, the P-R interval was increased by 2.6 to 30.6%, the QRS amplitude was decreased by 6.0 to 46.4%, and LV pressure was increased by 5.9 to 69.0%. The combination of caffeine at 100 μM and nicotine at 1 to 10 μM, did not cause significant effects on heart responses. These results indicate that caffeine and nicotine acting individually or jointly do not exert significant direct effects on the heart at clinically relevant concentrations, but exert marked direct effects on the heart at higher concentrations.