Methods : Mitochondria isolated from the ischemic rabbit hearts were incubated in the reaction conditions with different oxygen tensions. Generation of superoxide anion and activities of defensive enzymes aginst oxidative stress were mesured.

Results : Superoxide anion genertion by mitochondria incubated in 21% oxygen condition were 0.54±0.09 and 0.27±0.04(O₂·/min/mg protein) in ischemic mitochondria and in control respectively(P<0.05). Activites of defensive enzymes against oxidative stress, superoxide dismutase and glutathione peroxidase, were significantly reduced in mitochondria isolated from either ischemic or reperfused hearts. With the lapse of respiration in 21% oxygen condition, ADP-stimulated state 3 oxygen consumption(306.4±31.5 vs 214.4±11.4n atoms O/min/mg protein) at 30 minutes, P : O ratio and phosphorylation rate were significantly decreased in ischemic mitochondria.

Conclusions : Elevation of oxygen free radical generation as well as the reduction of defensive enzyme activities in ischemic reperfused mitochondria are injurious to mitochondrial respiratory function. It may contribute to the mechanism of cellular damage in ischemic reperfused hearts.