Age-dependent production of mitochondrial hydrogen peroxide, lipid peroxides and fluorescent pigments in the rat heart.

Mitochondria were prepared from hearts of 3-, 14-, 18-, and 24-month-old male Wistar rats. Respiratory control ratio (RCR) values did not change with age in the glutamate or succinate-induced respiration except at 24 months in which RCR values significantly increased with both the substrates. Using still glutamate or succinate as substrates the production of H2O2 was measured in the presence of antimycin. A 70% and 25% increase in H2O2 formation was observed at 14 and 18 months of age, respectively, in comparison to the youngest group. Only in the presence of succinate was a 25% elevation in H2O2 found at 24 months of age. These observations parallel with the decrease of the ratio between tissue levels of reduced and oxidized glutathione that was observed at 14 and 18 months of age. The concentration of myocardial malondialdehyde, a secondary product of lipid peroxidation, remained the same at all ages measured, most probably because it is readily metabolized in vivo. On the contrary the myocardial level of lipofuscin, which is not degraded by the cell, progressively increased beginning from 18 months of age.