The effects of post-natal age on the whole body protein metabolism and the urinary 3-methyl-histidine excretion of premature infants

Abstract

The effects of post-natal age were examined on whole body protein turnover and urinary 3-methyl-histidine in 24 premature neonates. The infants were each studied twice (Studies A & B). The first study was conducted when the infants were clinically stable and receiving a total oral energy intake of at least 500 kJ/kg/d. The second study was started about 2 weeks later. No effect of post-natal age on whole body nitrogen flux, protein synthesis or breakdown was demonstrated. The values obtained for the two studies were similar and lend support to the reproducibility of the methods used to study protein turnover. Mean values were: nitrogen flux, 2.76±0.71 gN/kg/d; protein synthesis, 16.1±4.5 g/kg/d; protein breakdown, 12.4±4.3 g/kg/d. Protein and energy intakes were significantly correlated to whole body amino nitrogen flux (p<0.01). Energy intake was also correlated to urine 3-methyl-histidine excretion (p<0.05). No change was seen in either urinary 3-methyl-histidine (3MH) excretion or in the 3MH/creatinine ratio with increasing post-natal age. The value for the ratio of 0.029 μmol 3MH/μmol creatinine is comparable to previous reported values for neonates. Urinary creatinine excretion increased by 19.3% (p<0.05) with increasing post-natal age.