No abstract

We investigated the effects of ischemia duration on the functional response of mitochondria to reperfusion and its relationship with changes in mitochondrial susceptibility to oxidative stress. Mitochondria were isolated from hearts perfused by the Langendorff technique immediately after different periods of global ischemia or reperfusion following such ischemia periods. Rates of O2 consumption and H2O2 release with complex I- and complex II-linked substrates, lipid peroxidation, overall antioxidant capacity, capacity to remove H2O2, and susceptibility to oxidative stress were determined. The effects of ischemia on some parameters were time dependent so that the changes were greater after 45 than after 20 min of ischemia, or were significantly different to the nonischemic control only after 45 min of ischemia. Thus, succinate-supported state 3 respiration exhibited a significant decrease after 20 min of ischemia and a greater decrease after 45 min, while pyruvate malate-supported respiration showed a significant decrease only after 45 min of ischemia, indicating an ischemia-induced early inhibition of complex II and a late inhibition of complex I. Furthermore, both succinate and pyruvate malate-supported H2O2 release showed significant increases only after 45 min of ischemia. Similarly, whole antioxidant capacity significantly increased and susceptibility to oxidants significantly decreased after 45 min of ischemia. Such changes were likely due to the accumulation of reducing equivalents, which are able to remove peroxides and maintain thiols in a reduced state. This condition, which protects mitochondria against oxidants, increases mitochondrial production of oxyradicals and oxidative damage during reperfusion. This could explain the smaller functional recovery of the tissue and the further decline of the mitochondrial function after reperfusion following the longer period of oxygen deprivation.

Whole mitochondrial population and three mitochondrial fractions were resolved by differential centrifugation from liver homogenates from euthyroid, hyperthyroid (ten daily i.p. injections of triiodothyronine (T₃), 10 μg/100 g body weight) and hyperthyroid vitamin E-treated (ten daily i.m. vitamin E injections, 20 mg/100 g body weight) rats. Homogenates and mitochondrial preparations were examined for their protein content, oxidative capacity, lipid peroxidation, antioxidant status, and susceptibility to oxidative stress. In all groups, antioxidant level was smaller and oxidative capacity, lipid peroxidation, and susceptibility to oxidants were greater in the heavy mitochondrial fraction. T₃ treatment was associated with increased oxidative capacity, lipid peroxidation, and susceptibility to oxidative stress, and decreased antioxidant levels in all preparations. It was also associated with increased mitochondrial protein content of homogenate and altered quantitative presence of the mitochondrial fractions. The vitamin E effects on the T₃-induced changes were different for the different parameters. Vitamin E did not modify the mitochondrial protein content in liver and oxidative capacity of the various preparations, reduced the changes in both susceptibility to oxidants and contribution of each fraction to the whole mitochondrial population, and reinstated euthyroid values for antioxidant capacity and lipid peroxidation. The incomplete recovery of euthyroid resistance to oxidants in vitamin E-treated rats is due to the vitamin inability to reinstate the levels of both antioxidants and hemoproteins, on which such a resistance depends. The vitamin E effect on the composition of the mitochondrial population is more difficult to explain, because of the complexity of the mechanisms underlying the mitochondrial population modulation by thyroid hormone. However, available data suggest that such a modulation occurs through changes in the turnover of the mitochondrial fractions to which an induction of mitochondrial protein synthesis and accelerated antioxidant-sensitive degradation contribute in different measure.

No abstract

No abstract