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Exercise capacity of rats remains unaffected by a chronic pressure overload
G S Morris1, D P Fitzsimons, K M Baldwin
1Department of Physiology and Biophysics, University of California, Irvine.
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.