Effects of endurance training on left ventricular performance: a study in anaesthetized rabbits

Endurance training is known to increase ventricular performance during exercise and to decrease resting heart rate. The aim of this study was to evaluate a model for endurance training in rabbits and to study the effects of endurance training on local myocardial performance in the left ventricle during resting conditions. One group of rabbits underwent a 10-week exercise training programme. The rabbits trained 5 days a week on a treadmill. Training periods increased gradually from 15 min to 1 h with increments in speed from 0.5 to 1.2 km h-1. After the training programme the rabbits were anaesthetized and studied as acute open-chest preparations. A micro-tip pressure transducer was introduced via apex to the left ventricle and two pairs of ultrasonic crystals were implanted in the left anterior wall to measure segment lengths. One pair measured shortening in the circumferential direction whereas the other pair measured shortening in the longitudinal direction. Heart rate was lower in the trained group (n = 5), 172 +/- 9 beats min-1 (mean +/- SEM), compared with 235 +/- 19 beats min-1 in the control group (n = 8) (P < 0.02). Stroke volume, measured by radio-nuclidelabelled microspheres, was greater in the trained rabbits compared with controls (P < 0.03). Shortening in both segments was of similar magnitude for the trained and control groups. End-systolic pressure-length relations (ESPLR) obtained by occlusion of the descending aorta (balloon catheter) showed reduced slopes for longitudinal segments in the trained group compared with the control group (P < 0.05). We conclude that this endurance training programme in rabbits can be used to study myocardial effects of endurance training. Furthermore, the less steep slope of ESPLRs for the longitudinal segment in the trained animals might indicate a structural myocardial remodelling and increased contractile reserve that might be recruited during adrenergic stimulation in the trained group.