Protective effects of high-intensity versus low-intensity interval training on isoproterenol-induced cardiac injury in wistar rats

Background: Cardiovascular diseases are among the major causes of mortality in industrialized countries. Prevention of cardio- vascular diseases and increasing stress tolerance are two of the main goals of physical training. Objectives: This study was designed to compare the effects of two exercise programs of different intensities on rat hearts with isoproterenol-induced myocardial injuries. Methods: Animals were randomly divided into four groups (n = 8 per group): control group (CTL); ISO group, administered iso- proterenol (85 mg/kg subcutaneously) for two consecutive days; low-intensity interval training + isoproterenol group (LIIT+ ISO: 5 minutes warm up at 40% VO2 max,5 x 10 minutes at50% -60% VO2 max [about 20-24 m/min]); and high-intensity interval training + isoproterenol group (HIIT+ ISO: 5 minutes warm-up at 40% VO2 max, 5 x 5 min at 95% -105% VO2 max [45 -50 m/min]). The train- ing groups performed high- and low-intensity interval training programs (5 days/week) on a motor-driven treadmill for 16 weeks. Seventy-two hours after the last training session, isoproterenol (85 mg/kg) was injected on two consecutive days. On the third day, hemodynamic parameters were recorded, blood samples were taken, and hearts were removed for laboratory analysis. Results: ISO-induced heart injury raised cardiac troponin I levels, significantly decreased + dp/dt max(P< 0.05) and-dp/dt max(P < 0.05), and significantly increased serum CTnI and tissue TNF α levels (P < 0.05). Exercise training had no significant effects on HR, LVSP, and LVEDP. Impairments of + dp/dt max and-dp/dt max were significantly improved in the HIIT+ ISO and LIIT+ISO groups (P < 0.05 for both groups versus ISO). In addition, exercise training groups especially HIIT + ISO to some reduce exacerbated the myocardial lesions induced by ISO (P < 0.05). Conclusions: These biochemical and histopathological findings suggest there is a protective role provided by both high- and low- intensity interval training protocols on ischemic hearts.