PROTEIN TURNOVER INCREASES IN PARENTERALLY FED PREMATURE INFANTS - A STUDY WITH |[lsqb]|13C|[rsqb]|LEUCINE

摘要

There are few studies of protein turnover in premature infants (PMI). Most have used [15N]glycine which may be criticised for two reasons: the high concentration of urea in breast milk and the possibility that glycine is essential for PMI. Both lead to tracer dilution and overestimation of flux. We have used an intravenous (iv) infusion of [13C]leucine to measure whole body leucine flux in PMI. Leucine oxidation was derived from urinary nitrogen excretion, enabling protein synthesis and degradation to be calculated. Enrichment of plasma leucine was measured by gas chromatography/mass spectrometry. Baseline data were obtained for protein turnover in PMI on iv glucose and the studies repeated if total parenteral nutrition (TPN) was introduced. Fifteen PMI, gestational ages 27-33 weeks and mean weight 1.42 +/- 0.29 kg, were studied on the 2nd, 3rd, or 4th postnatal days while receiving iv glucose: mean rates (+/- SD) of protein synthesis and breakdown were 141 +/- 42 μmoles/kg/hr and 150 +/- 40 μmoles/kg/hr respectively (NS). Five infants started TPN and were studied on 5 consecutive days: there was a mean increase in protein synthesis between day 1 and day 5 of 152 +/- 28 μmoles/kg/hr (p = 0.005) and a simultaneous rise in breakdown of 54 +/- 23 μmoles/kg/hr (p = 0.03). Synthesis rose significantly more than breakdown (p = 0.003). In conclusion, TPN results in a greater increase in protein synthesis than in breakdown with a consequent improvement in protein retention.