Changes in content of cytochromes c and a (a3) in liver mitochondria of hyperthyroid rats

Male Wistar rats aged 1, 3, 12, and 24 months were given thyroxine in a dose of 250 μg/100 g body weight daily. After 9 days the content of cytochromes c and a (a3) was considerably increased. An appreciable increase in the cytochrome c content was observed as early as after 24 h, whereas the content of cytochromes a (a3) did not exceed normal even after 2 days. The content of cytochromes a (a3) in rats aged 3, 12, and 24 months was little lower after 24 h than normally. A significant temporary increase in the ratio c/a (a3) after 1–2 days was observed only in rats aged 12 and 24 months. An increase in the ratio c/a (a3) with age also was demonstrated. The prospects for the use of thyroid hormones in the study of regulation of biogenesis of the mitochondria are suggested.