Aim: 

It is known that physical training depresses intrinsic chronotropism and dromotropism. However, the role that postganglionic parasympathetic neurons could exert on this effect is less known. Therefore, the aim of this study was to determine if the changes on intrinsic cronotropism and dromotropism are influenced by postganglionic neuron activity.

Methods: 

The study was performed in 17 New Zealand rabbits which were assigned to a control (n=5), a sham operated (n=6) and a trained (n=6) groups. The trained group exercised during 6 weeks of physical training on treadmill, while the other groups were housed during the same period. After the 6 weeks, rabbits were anaesthetized, sacrificed and the heart excised and isolated in a Langendorff system. Pacing and recording electrodes were positioned on left atria and ventricle. RR interval was used to measure cronotropism, and dromotropism was determined with Wenckebach cycle length (WCL) and retrograde Wenckebach cycle length (RWLC). Paired and unpaired t-tests were applied to analyze the corresponding comparisons.

Results: 

Chronotropism and dromotropism were not modified by time in the sham operated group. RR interval was longer in trained animals than in controls (345.534.2 versus 283.834.2,p<0.05) and, although WCL was not significantly modified, it tended to be longer in the trained group (129.610 versus 118.510, p=0.07). No differences were obtained in RR, WCL and RWCL after atropine in both groups.

Conclusion: 

Chronotropism and dromotropism depression produced by physical training does not seem to be dependent on parasympathetic postganglionic neurons activity in isolated heart.

Supported by MEC (DEP2007-73234-C03-01) and Generalitat Valenciana (BFPI/2008/003).