Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat

These experiments examined the independent effects of short-term exercise a nd heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O-2 uptake ((V) over dot O-2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% (V) over dot O-2 max), and 4) whole body heat stress (15 min at 42 degreesC). Twent y-four hours after heat stress or exercise, animals were anesthetized and m echanically ventilated, and the chest was opened by thoracotomy. Coronary o cclusion was maintained for 30-min followed by a 30-min period of reperfusi on. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pre ssure (LVDP), maximum rate of left venticular pressure development (+dP/dt) , and maximum rate of left ventricular pressure decline (-dP/dt) at all mea surement periods during both ischemia and reperfusion. No differences exist ed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise res ulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increas ed (P < 0.05) myocardial glutathione levels and manganese superoxide dismut ase activity. These data indicate that 3-5 consecutive days of exercise imp roves myocardial contractile performance during in vivo I/R and that this e xercise-induced myocardial protection is associated with an increase in bot h myocardial HSP72 and cardiac antioxidant defenses.