Age dependency of mitochondrial DNA decrease differs in different tissues of rat

: Mitochondrial DNA contents were measured using non-radioactive DNA probes for specific mtDNA sequences. The nuclear repetitive DNA sequence, LINE, was used as an internal standard marker. Age-dependent decreases in the mtDNA/nucDNA ratio in rat hepatic cells were confirmed with this method and, furthermore, a similar decrease was found in cardiac muscles. On the other hand, in thigh skeletal muscles such a decrease was not observed, slight increases being rather found in 18- to 24-month-old rats. The possible relationship of the decrease in mtDNA and the mechanism underlying animal senescence was discussed.