[Effect of thyroid hormones on cytochrome concentration on the liver and heart tissues of chickens during ontogenesis].

Changes in the concentration of cytochromes c, c1 and a in the liver and heart homogenates during chick pre- and postnatal development were detected by means of low temperature differential spectrometry. At the early stages of development the high content of respiratory enzymes comparable with that in the adult organism is noted. By the end of embryogenesis the content of cytochromes decreased and, subsequently, increased. The injection of thyroxine in the 16-17 days old embryos and 9-10 days old chickes resulted in more distinct changes in the content of respiratory enzymes in mitochondria of the heart, as compared with those of the liver. No changes in the content of cytochromes were recorded after the injection of 6-methyl thiouracyl in the 10 days old embryos, thus suggesting the inactive state of thyroid parenchyma during this period of development.