Postnatal development of the circadian rhythm of rat liver tyrosine aminotransferase activity.

The rhythm of tyrosine aminotransferase (TAT) activity in 2-day old rats is characterized by a maximum at the beginning and a further one at the end of light-time. In 7-day old animals, the rhythm is much less pronounced than in 2-day old pups. At the 21st day of life, the rats already exhibit the rhythmic pattern of the adults, although the absolute values are still somewhat below those of the adults. The TAT rhythm in neonates is obviously generated by periodic variations in cyclic AMP-dependent release of TAT from polysomes.