Exercise capacity and cardiac hemodynamic response in female ApoE/LDLR(−/−) mice: a paradox of preserved V’O(2max) and exercise capacity despite coronary atherosclerosis

We assessed exercise performance, coronary blood flow and cardiac reserve of female ApoE/LDLR(−/−) mice with advanced atherosclerosis compared with age-matched, wild-type C57BL6/J mice. Exercise capacity was assessed as whole body maximal oxygen consumption (V’O(2max)), maximum running velocity (v(max)) and maximum distance (DIST(max)) during treadmill exercise. Cardiac systolic and diastolic function in basal conditions and in response to dobutamine (mimicking exercise-induced cardiac stress) were assessed by Magnetic Resonance Imaging (MRI) in vivo. Function of coronary circulation was assessed in isolated perfused hearts. In female ApoE/LDLR(−/−) mice V’O(2max), v(max) and DIST(max) were not impaired as compared with C57BL6/J mice. Cardiac function at rest and systolic and diastolic cardiac reserve were also preserved in female ApoE/LDLR(−/−) mice as evidenced by preserved fractional area change and similar fall in systolic and end diastolic area after dobutamine. Moreover, endothelium-dependent responses of coronary circulation induced by bradykinin (Bk) and acetylcholine (ACh) were preserved, while endothelium-independent responses induced by NO-donors were augmented in female ApoE/LDLR(−/−) mice. Basal COX-2-dependent production of 6-keto-PGF(1α) was increased. Concluding, we suggest that robust compensatory mechanisms in coronary circulation involving PGI(2)- and NO-pathways may efficiently counterbalance coronary atherosclerosis-induced impairment in V’O(2max) and exercise capacity.