Cardiocirculatory adjustments to exercise following myocardial infarction in rats

The sequential changes of the cardiocirculatory response to exercise over time in rats with myocardial infarction and failure were studied. Hemodynamics and regional blood flow (RBF, radioactive microspheres) were determined at rest and during exercise either at 1, 10 or 42 days after infarction (MI, infarct size 41.4 +/- 2.6% of LV) or sham procedures (SH). Whereas the response to exercise was attenuated one day after surgery in MI and SH, cardiocirculatory recovery was present in SH at 10 days and LV systolic and end-diastolic pressures separated SH and MI groups. Renal vasoconstriction during exercise occurred 10 days after MI and BF to working muscle during exercise was significantly lower in MI as compared to SH. At 42 days after MI manifest heart failure was present and despite significant blood flow redistribution (p less than 0.05 MI vs SH in renal and cutaneous beds) impaired skeletal muscle flow was observed along with increased vascular resistance in working muscle during exercise. We conclude that the cardiocirculatory response to exercise following large MI follows a distinctive time-dependent pattern, which differs from that observed at rest. Besides exaggerated sympathetically mediated vasoconstriction during exercise, impaired vasodilatation in skeletal muscle at exercise emerged.