The effect of the chronic and acute
antioxidant tempol (
superoxide dismutase mimetic) treatment on cardiac ischemic tolerance was investigated in adult male Wistar rats. The first experimental group was given
tempol (1 mM) in
drinking water for three weeks, the second group received
tempol (100 mg/kg, i.v.) 10 min before test
ischemia, and control rats received the same volume of
solvent. Anesthetized open-chest animals (
pentobarbitone 60 mg/kg, i.p.) were subjected to 20-min coronary artery occlusion and 3-h reperfusion for
infarct size determination. Ventricular arrhythmias were monitored during
ischemia and at the beginning (5 min) of reperfusion. Acute
tempol administration shifted the time profile of ischemic arrhythmias to the later phase and significantly increased the number of ischemic and reperfusion premature ventricular complexes, respectively (504 +/- 127 and 84 +/- 21) as compared with the chronically treated group (218 +/- 36 and 47 +/- 7) or controls (197 +/- 26 and 31 +/- 7). Acute
tempol-treated rats exhibited a tendency to decrease
infarct size (P = 0.087). The mechanism of proarrhythmic
tempol action during
ischemia and reperfusion remains to be elucidated.