VULNERABILITY TO ARRHYTHMIAS DURING SOCIAL STRESS IN RATS WITH DIFFERENT SYMPATHOVAGAL BALANCE

An increased activity of the sympathetic nervous system is an importan t factor in the genesis of ventricular arrhythmias. Changes in average R-R, interval, R-R interval variability (indirect measure of sympatho vagal balance), occurrence of arrhythmias, and plasma norepinephrine c oncentrations were measured during asocial stress episode (defeat) in two strains of rats, Wistar and wild type, which were supposed to diff er in their autonomic stress responsiveness. Electrocardiograms were t elemetrically recorded, and blood samples were withdrawn through jugul ar vein catheters from healthy, freely moving animals. R-R interval va riability was estimated by the following time-domain parameters: the s tandard deviation of the mean R-R interval, the coefficient of varianc e, and the root mean square of successive differences in R-R interval. Average R-R interval and R-R interval variability measures, as well a s plasma norepinephrine concentrations, indicated a higher sympathetic tone, a larger sympathetic responsiveness, and a lower parasympatheti c antagonism after sympathetic activation in wild-type animals, which also showed a much higher incidence of arrhythmias (ventricular premat ure beats). compared with Wistar rats. These two strains might represe nt a valuable experimental model for studying the mechanisms (cellular /electrophysiological) responsible for the susceptibility to arrhythmi as in healthy individuals exposed to stressful situations.