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

Abstract

Hyderabad, IndiaMohanram, M., and Kumar, A. (1975). Archives of Disease in Childhood, 50, 235. Ascorbic acid and tyrosine metabolism in preterm and small-fordates infants. Ascorbic acid levels in plasma and leucocytes and urinary excretion of tyrosyl derivatives (TD) were determined in 11 normal, 18 preterm, and 4 smallfor-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.It has been reported that scorbutic subjects given a load of L-tyrosine excrete large amounts of tyrosine and its metabolites-a defect that is eliminated by administration of ascorbic acid (Rogers and Gardner, 1949a, b;Morris, Harpur, and Goldbloom, 1950;Huisman and Jonxis, 1957;Mohanram and Reddy, 1974). A transient defect in tyrosine oxidation has also been commonly observed in preterm infants fed on high protein diets (Levine, Marples, and Gordon, 1939; Levine, Gordon, and Marples, 1941; Matthews and Partington, 1964;Rizzardini and Abeliuk, 1971;Prasad, Sinha, and Sen, 1972). Rizzardini and Abeliuk (1971) showed that both plasma and urinary tyrosine levels were markedly increased when high protein diets were given to infants of gestational age below 38 weeks. However, it is not clear whether this abnormality observed in preterm infants is due to altered ascorbic acid status. A study was therefore undertaken to determine the levels of ascorbic acid in leucocytes, which is now accepted as a reliable index of ascorbic acid nutritional status, and urinary excretion of tyrosyl derivatives (TD) in normal, preterm, and small-for-dates infants. Materials and methodsEleven normal term infants with body weights more than 2400 g, 4 small-for-dates infants (term infants with body weights < 2400 g), and 18 preterm infants were studied. The gestational ages of the 18 preterm infants ranged from 28 to 34 weeks. Samples of blood and random samples of urine were collected from all the infants within 48 hours of birth. For the first 24 hours after birth all the infants were fed 5% glucose solution orally and thereafter the normal and small-for-dates infants were started on breast milk. In the case of preterms, expressed breast milk was fed orally until they were able to suckle. Levels of ascorbic acid in plasma and leucocytes, and urinary excretion of creatinine and TD were determined. The infants were then fed 4 g/kg milk protein. Random samples of urine were again collected at 24 and 48 hours and the levels of creatinine and TD were determined.Plasma ascorbic acid was estimated by the method of Roe and Ku...

Human Growth

“…Early studies suggested that supplementation with ascorbate or folate, or both, would alleviate these biochemical abnormalities. Systematically controlled studies performed more recently (Bakker et al, 1975;Partington and Mathews, 1967;Mohanram and Kumar, 1975), however, indicate that the tyrosinemia and tyrosyluria found in preterm infants fed high-protein diets is not corrected by massive doses of either vitamin. Plasma concentrations of phenylalanine as high as those found in phenylketonuria were observed in a few preterm infants fed a formula providing 4.5 protein/kg-day of a caseinpredominant formula .…”