Variations in free amino acids in tissues of rats from birth to puberty.

Variations in concentrations of free amino acids and total protein in tissues of rats have been studied from birth to puberty. In the first 10 days after birth the concentrations of free amino acids in peripheral tissues increased. Only in the liver there was an increase in concentration of essential amino acids. When nutrition changed at weaning, concentration of amino acids decreased. This may be associated with high protein synthesis rates and increased catabolism of amino acids. Even after weaning, when the young rat became nutritionally independent, concentrations of free amino acids in the tissues had not become constant.