EFFECTS OF ENDURANCE TRAINING ON LEFT-VENTRICULAR PERFORMANCE - A STUDY IN ANESTHETIZED RABBITS

Endurance training is known to increase ventricular performance during exercise and to decrease resting heart rate. The aim of this study wa s to evaluate a model for endurance training in rabbits and to study t he effects of endurance training on local myocardial performance in th e left ventricle during resting conditions. One group of rabbits under went a 10-week exercise training programme. The rabbits trained 5 days a week on a treadmill. Training periods increased gradually from 15 m in 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 acut e open-chest preparations. A micro-tip pressure transducer was introdu ced via apex to the left ventricle and two pairs of ultrasonic crystal s 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. Hea rt 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 contro l group (n = 8) (P < 0.02). Stroke volume, measured by radio-nuclidela belled microspheres, was greater in the trained rabbits compared with controls (P < 0.03). Shortening in both segments was of similar magnit ude for the trained and control groups. End-systolic pressure-length r elations (ESPLR) obtained by occlusion of the descending aorta (balloo n catheter) showed reduced slopes for longitudinal segments in the tra ined group compared with the control group (P < 0.05). We conclude tha t this endurance training programme in rabbits can be used to study my ocardial effects of endurance training. Furthermore, the less steep sl ope of ESPLRs for the longitudinal segment in the trained animals migh t indicate a structural myocardial remodelling and increased contracti le reserve that might be recruited during adrenergic stimulation in th e trained group.