Effects of chronic exercise on myocardial refractoriness: a study on isolated rabbit heart.
OBJECTIVE
To determine whether chronic physical training increases atrial and ventricular refractoriness in isolated rabbit heart.


METHODS
Trained rabbits were submitted to a protocol of treadmill running. The electrophysiological parameters of refractoriness investigated in an isolated heart preparation were: (1) atrial effective refractory period (AERP) and atrial functional refractory period and ventricular effective and functional refractory periods (VERP and VFRP) using the extrastimulus technique at four different pacing cycle lengths; (2) the dominant frequency (DF) of ventricular fibrillation (VF). A multi-electrode plaque containing 256 electrodes and a spectral method were used to obtain the mean, maximum and minimum DF of VF. Sinus cycle length of the isolated hearts was determined as an electrophysiological parameter of training. In vivo heart rate, myocardial heat shock proteins (HSP60) and inducible nitric oxide synthase were also determined in some animals as electrophysiological and biochemical markers of training respectively.


RESULTS
VERP and VFRP were longer in the trained group than in the control group. The mean DF of VF was lower in the trained group than in the control group. Despite the fact that training did not significantly modify the AERP, it tended to be longer in the trained group (P = 0.09).


CONCLUSIONS
Training seems to increase the electrical stability of ventricular myocardium. As the electrophysiological modifications were exhibited in hearts not submitted to extrinsic nervous system or humoral influences, they are, at least in part, intrinsic modifications. These electrophysiological data also suggest that training could protect against reentrant ventricular arrhythmias.
Such
L
L
Department of Physiology, University of Valencia, Valencia, Spain. luis.such@uv.es
Alberola
A M
AM
Such-Miquel
L
L
López
L
L
Trapero
I
I
Pelechano
F
F
Gómez-Cabrera
M C
MC
Tormos
A
A
Millet
J
J
Chorro
F J
FJ
D000818:Animals; D016275:Atrial Function / Q000502:physiology; D018834:Chaperonin 60 / Q000378:metabolism; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D009043:Motor Activity / Q000502:physiology; D009206:Myocardium / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D009924:Organ Culture Techniques; D009929:Organ Size; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011817:Rabbits; D012032:Refractory Period, Electrophysiological / Q000502:physiology*; D014693:Ventricular Fibrillation / Q000503:physiopathology; D016276:Ventricular Function / Q000502:physiology
D018834:Chaperonin 60; D052247:Nitric Oxide Synthase Type II