[Age-related characteristics of thyroxine action on the cytochrome content in rat liver mitochondria and on body weight].

Content of cytochromes a (a3) was decreased and the ratio c/a/a3/ was increased in rat liver mitochondria depending on animal age. Administration of thyroxine incresased the level of cytochromes. These phenomena were especially distinct in 12- and 24-month old rats. The latent period, manifested as a decrease in body mass, was the characteristic property of the tyroxine effect in the young animals. Age differences in the effect of thyroxine depend also on the dose of the hormone.