Similarity of protein synthesis rate measured with 1-13C) leucine and (1-13C) phenylalanine

p.131 RRPRATABILITY OF 'IWE MSASUFDEIW Ur' AlYIN0 ACLU iti) I&U 11\1 ?HE HIND LlN8 OF PATIENTS RECEIVING IWI'RAVEKUS NUTRITICN (I'&). A.J. Kee, P.B. Lader, R.C. Smith, University kpartmsnt of Surgery at Royal North Showtal, Sydney. Australia.

Peripheral mni.110 acid flux may be used to assess anabolism in peripheral tissues. In order to determine the size of smtple required to catpare peripheral anabolism during different IVN regimens, the precision of peripheral amino acid flux measurements must be known.

Eighteen lower lti amino acid flux measurements were performed in seven surgical patients receiving IVN. All patients were given a glucose based solution with a Cal:iJ ratio of 135:l supplying 0.29 gN/kg/day. They ens clinically stable and had been receiving IVN at a constant infusion rate for at least 48 hours prior to the initial study. Flux was calculated as the difference in M concentrations in the arterial and femoral plasma, multiplied by the plasma flow, determined by duplex ultrasound. Each patient was studied on at least 2 occasions.

The coefficients of variation, both within (%CV ) and between patients (%CV ) for the arteriovenous difference and the flux of se?eral amino acids are shown bul the table.

(%CVw)A-V (%CVb)A-V (%CVw)Flux (%CV,) Flux

E 7.1 12.9 3.2 13.5 5.0 9.4 3.0 10.0

Ala 8.7 11.9 5.4 11.5

We conclude that with an arbitary group of 10 patients we can demonstrate a 3.5% difference in flux within patients and a 5-158 difference in flux between groups of patients for nkxt AA if a crossover method is used.

P.132 SIMILARITY OF PROTEIN SYNTHESIS RATE MEASURED WITH (I- 13 C) LEUCBJE AND (l- ‘3 C) PHENYTALANINE

M. A. MC Nurlan, P. Es&n, E. Milne, V. Buchan, G. E. Calder, J. Wernerman, P. J. Garlick, and E. Vinnars. The Rowett Research Institute, Aberdeen, UK and Dept. of Anesthesiology and Intensive Care at Huddinge University Hospital, Karolinska Institute, Sweden.

In animal studies branchedchain amino acids, and particularly leucine, stimulated protein synthesis in incubated muscle. The suggestion that leucine stimulates protein synthesis has serious implications for measurements of protein synthesis rate which involve a flooding amount of this amino acid. Measurement of muscle protein synthesis rate with leucine has been compared with an estimate of synthesis rate based on phenylalanine.

Twelve healthy subjects were studied after an overnight fast. An intravenous infusion of (l- 13Cl leucine (n=6) or (l- ‘SC) phenylalanine (n=6) was given over 3 minutes (0.05 g/kg, 19.4 APE). Percutaneous muscle biopsies were taken from the quadriceps femoris muscle before and after the infusion of the specific amino acid. Synthesis rate was estimated from the increase in enrichment in muscle proteins between 0 and 90 min, determined by gas isotope-ratio mass spectrometer following isolation and decarboxylation of the respective amino acid. Plasma phenylalanine enrichment and plasma keto-isocaproate (the ketoacid of leucine), determined by GC-mass spectrometry, were similar to the enrichment of the respective amino acid within the tissue and were, therefore, used as precursor enrichment. Protein synthesis rate in muscle expressed as %/d f SD was 1.95 f 0.37 measured with leucine and 1.89 f 0.45 from labelled phenylalanine.

The flooding technique was developed to improve the accuracy of estimates of protein synthesis rate by ensuring that all pools of free amino acid were enriched to a similar degree. The results obtained using leucine and phenylalanine incorporation into muscle proteins in the overnight fasted state were similar.

123