Moderate Continuous Aerobic Exercise Training Improves Cardiomyocyte Contractility in Β(1) Adrenergic Receptor Knockout Mice

BACKGROUND: The lack of cardiac β(1)-adrenergic receptors (β(1)-AR) negatively affects the regulation of both cardiac inotropy and lusitropy, leading, in the long term, to heart failure (HF). Moderate-intensity aerobic exercise (MCAE) is recommended as an adjunctive therapy for patients with HF. OBJECTIVE: We tested the effects of MCAE on the contractile properties of left ventricular (LV) myocytes from β(1) adrenergic receptor knockout (β(1)ARKO) mice. METHODS: Four- to five-month-old male wild type (WT) and β(1)ARKO mice were divided into groups: WT control (WTc) and trained (WTt); and β(1)ARKO control (β(1)ARKOc) and trained (β(1)ARKOt). Animals from trained groups were submitted to a MCAE regimen (60 min/day; 60% of maximal speed, 5 days/week) on a treadmill, for 8 weeks. P ≤ 0.05 was considered significant in all comparisons. RESULTS: The β(1)ARKO and exercised mice exhibited a higher (p < 0.05) running capacity than WT and sedentary ones, respectively. The β(1)ARKO mice showed higher body (BW), heart (HW) and left ventricle (LVW) weights, as well as the HW/BW and LVW/BW than WT mice. However, the MCAE did not affect these parameters. Left ventricular myocytes from β(1)ARKO mice showed increased (p < 0.05) amplitude and velocities of contraction and relaxation than those from WT. In addition, MCAE increased (p < 0.05) amplitude and velocities of contraction and relaxation in β(1)ARKO mice. CONCLUSION: MCAE improves myocyte contractility in the left ventricle of β(1)ARKO mice. This is evidence to support the therapeutic value of this type of exercise training in the treatment of heart diseases involving β(1)-AR desensitization or reduction.