Exercise training improves left ventricular contractile response to β- adrenergic agonist

To determine whether endurance exercise training can improve left ventricular function in response to β-adrenergic stimulation, young healthy sedentary subjects (10 women and 6 men) were studied before and after 12 wk of endurance exercise training. Training consisted of 3 days/wk of interval training (running and cycling) and 3 days/wk of continuous running for 40 min. The training resulted in an increase in maximal O₂ uptake from 41.0 ± 2 to 49.3 ± 2 ml · kg^-1 · min^-1 (P < 0.01). Left ventricular function was evaluated by two-dimensional echocardiography under basal conditions and during β-adrenergic stimulation induced by isoproterenol infusion. Fractional shortening (FS) under basal conditions was unchanged after training (36 ± 1 vs. 36 ± 2%). During the highest dose of isoproterenol, FS was 52 ± 1% before and 56 ± 1% after training (P < 0.05). At comparable changes in end-systolic wall stress (σ(es)), the increase in FS induced by isoproterenol was significantly larger after training (13 ± 1 vs. 17 ± 2%, P < 0.01). Furthermore there was a greater decrease in end-systolic dimension at similar changes in σ(es) in the trained state during isoproterenol infusion (-4.6 ± 0.1 mm before vs. -7.0 ± 0.1 mm after training, P < 0.01). There were no concurrent changes in end-diastolic dimension between the trained and untrained states during isoproterenol infusion, suggesting no significant changes in preload at comparable levels of σ(es). Under basal conditions, end-diastolic dimension was increased (46 ± 0.5 vs. 50 ± 0.5 mm, P < 0.03) after training (P < 0.03), with no significant change in left ventricular wall thickness-to-radius ratio after training, consistent with volume-overload hypertrophy. The results indicate that endurance exercise training enhances the left ventricular contractile response to β-adrenergic stimulation without affecting basal contractility in young subjects.