One-to-one synchronization between the cardiac sympathetic nerve stimuli and heart beats in rats

One-to-one synchronization of heart rate to the cardiac sympathetic nerve stimuli was observed in Sprague-Dawley rats. Propranolol and L-propranolol, but not D-propranolol, blocked 1:1 synchronization evoked by the nerve stimulation. Thus, 1:1 synchronization is entirely ascribable to neurally released norepinephrine. When a single volley was applied to the cardiac sympathetic nerve, there was a significant abbreviation of the respective cardiac cycle at which the stimulus fell. The mean latency was 33.1 +/- 2.29 ms (mean +/- SE). The extent of the abbreviation of the cardiac cycle was linearly correlated to the interval between P wave and a nerve stimulus. These results ensure that the effect of the sympathetic nerve stimulation is phase dependent and that the sympathetic nerve can entrain the heart beat as well as the parasympathetic nerve can.