Early postnatal metabolism of amino acids in rat.

The production of 14CO2 from glutamate and alanine studied in the newborn rat after injection of labeled precursors was intense and revealed an important catabolism from 130 nmol/hr in a 0-hr neonate to 2000 nmol/hr in 3-week-old rat. The degradative metabolism of leucine was low at birth (10 nmol/hr), but increased up to 500 nmol/hr in 3-week-old rat. Phenylalanine was practically not metabolized into CO2, but its incorporation into protein was higher than leucine, alanine, and glutamate incorporation. Glucose is the major fuel utilized by newborn rat for its energy supply (300-560 nmol/hr). However, the relative part of amino acids in energy production is important in the early neonate (0 and 1 hr after birth).