Ascorbic acid and tyrosine metabolism in preterm and small-for-dates infants.

Ascorbic acid levels in plasma and leucocytes and urinary excretion of tyrosyl derivatives (TD) were determined in 11 normal, 18 preterm, and 4 small-for-dates infants. Concentrations of ascorbic acid in both plasma and leucocytes were found to be similar in the 3 groups. There was no difference in the basal levels of TD between normal and small-for-dates infants, but preterms showed higher basal excretion of TD than the other two groups. After protein load the excretion of TD was higher than the basal level in preterms. It was concluded that the altered metabolism of tyrosine observed in preterms is not the result of poor ascorbic acid status; and that tyrosine metabolism is influenced by the period of gestation rather than the body weight of the infant.