Mitochondrial activities of rat heart during ageing.

Some analytical and functional parameters of rat heart mitochondrial have been investigated at six different periods of ageing from 2 to 26 months. The fatty acid composition of the mitochondrial membranes reveals a percentage increase of polyunsaturated fatty acids (20:4 n-6, 22:6 n-3) up to 12 months, followed by a decrease; however, fluorescence polarization of the membrane probe diphenylhexatriene is not changed, revealing that membrane fluidity is not significantly affected. No major change in ubiquinone-9 and in cytochrome content is apparent, indicating that the relative ratio of the respiratory chain components is unmodified. Nevertheless, significant changes in enzyme specific activities are detected: NADH cytochrome c reductase and cytochrome oxidase activities increase up to 12 months, then decrease at 18-26 months; ubiquinol cytochrome c reductase exhibits a peak at 18 months, followed by a decrease. All these activities follow a similar trend during the whole life span of the rat, even though the 'maximum' is different. No significant changes have been found in ATP synthase. Succinate-cytochrome c reductase steadily increases over the whole life span. The results, showing activity decreases in the respiratory enzymes having subunits encoded by mitochondrial DNA, are compatible with the 'mitochondrial' theory of ageing.