Metabolism of Intravenous Phenylalanine by Babies Born before 33 Weeks of Gestation

Abstract

Random urine samples collected weekly from 22 infants of 25–32 weeks of gestation were analyzed by capillary gas chromatography-mass spectrometry to define the normal organic acid profile. Increased excretion of phenolic acid derivatives of phenylalanine and tyrosine was found in 21 samples from 13 babies during established parenteral nutrition. Compared with 53 samples collected during milk feeding, phenyllactic acid, 4-hydroxy-3-methoxyphenyllactic acid, and N-acetyltyrosine were excreted significantly more often and 4-hydroxyphenyllactic and 4-hydroxyphenylpyruvic acids at significantly higher concentrations. The mean daily intake of phenylalanine (197 mg/kg) was significantly higher and that of tyrosine (22 mg/kg) significantly lower during parenteral nutrition. Three cyclohexanediol isomers were identified which might have derived from phenylalanine or one of its metabolites.

Effects of Birth Asphyxia on Urinary Organic Acid Excretion

“…Asphyxia did not lead to excessive excretion of medium chain dicarboxylic acids from incomplete fatty acid oxidation. Production of these metabolites by microsomal cytochrome P450 monooxy genase requires molecular oxygen [15], Fi nally, increased excretion of 4-hydroxyphenyllactic acid, an intermediate of tyrosine degradation [16], can be attributed to he patic disturbance associated with severe as phyxia [3]. …”