The hemodynamic response to maximal exercise was determined in sedentary and trained rats with a chronic myocardial infarction (MI) produced by coronary artery ligation and in rats that underwent sham operations (SHAM). Infarct size in the MI groups of rats comprised 28-29% of the total left ventricle and resulted in both metabolic and hemodynamic changes that suggested that these animals had moderate compensated heart failure. The training regimen used in the present study produced significant increases in maximal O2 uptake (V̇O(2max)) when expressed in absolute terms (ml/min) or when normalized for body weight (ml·min-1·kg-1) and consisted of treadmill running at work loads that were equivalent to 70-80% of the animal's V̇O(2max) for a period of 60 min/day, 5 days/wk over an 8- to 10-wk interval. This training paradigm produced two major cardiocirculatory adaptations in the MI rat that had not been elicited previously when using a training paradigm of a lower intensity. First, the decrement in the maximal heart rate response to exercise (known as 'chronotropic incompetence') found in the sedentary MI rat was completely reversed by endurance training. Second, the downregulation of cardiac myosin isozyme composition from the fast ATPase V1 isoform toward the slower ATPase (V2 and V3) isoforms in the MI rat was partially reversed by endurance training. These cardiac adaptations occurred without a significant increase in left ventricular pump function as an increase in maximal cardiac output (Q̇(max)) and maximal stroke volume (SV(max)) did not occur in the trained MI rat. These data suggest that central cardiac adaptations can be produced in the MI rat through a training program that would be considered as moderately severe in its intensity. Whether or not increases in Q̇(max) and SV(max) can be produced in the MI rat through training paradigms that are of a greater intensity and duration than that found in the present study remains to be answered.
All Science Journal Classification (ASJC) codes
- Physiology (medical)