Exercise capacity of rats remains unaffected by a chronic pressure overload

OBJECTIVE: The aim was to determine if the adaptive responses of the myocardium to a chronic pressure overload affected cardiovascular performance when evaluated under conditions of increased functional demand. METHODS: Selected female rats were made hypertensive by abdominal aortic constriction. After eight weeks of aortic constriction, cardiovascular responses and work performance were measured during a maximal treadmill exercise bout. RESULTS: Aortic constriction increased mean arterial pressure and the relative quantity of the slow ATPase myosin isoform, V3, relative to untreated controls (p < 0.05). Both groups had similar oxygen consumptions (VO2), heart rates (HR), and oxygen pulses (VO2/HR) at rest and throughout the exercise test. Both groups reached their VO2 max at the same exercise duration and exercise intensity (40.4 m.min-1). Soleus citrate synthase activity was not different between the groups. CONCLUSIONS: These similarities in work capacity, VO2, oxygen pulse, and muscle oxidative capacity suggest (1) that cardiovascular and exercise capacity can both be maintained in spite of the presence of a chronic pressure overload; (2) that after two months of aortic constriction the heart appears to be in a compensated stage of adaptation; and (3) that the cardiac myosin isoenzyme profile may have little direct effect on cardiovascular functional capacity.