The measurement of muscle protein synthesis in broilers with a flooding dose technique:: Use of 15N-labelled phenylalanine, GC-MS and GC-C-IRMS

An experiment was carried out to measure fractional muscle protein synthesis rates (k(s)) in broilers with injection of a flooding dose of phenylalanine (I ml/100 g body weight of 150 mM phenylalanine; 38 atom percent excess (APE) [N-15]phenylalanine). K-s was calculated from the [N-15] enrichment in phenylalanine of tissue-free and protein-bound phenylalanine using both gas chromatography mass spectrometry (GC-MS) and gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) for measurements after a 10 min isotope incorporation period. The tertiary-butyldimethylsilyl (t-BDMS) derivatives of phenylalanine were used for gas chromatographic separation in both systems. GC-MS and GC-C-IRMS were calibrated for a range of 7 to 37 [N-15]APE and 0 to 0,62 [N-15]APE, respectively, and for sample sizes of 0.45 to 4.5 nmol phenylalanine and 7 to 40 nmol phenylalanine, respectively. Reproducibility of standards as a measure of precision varied from 0.06 to 0.29 [N-15]APE and from 0.0004 to 0.0018 [N-15]APE in GC-MS and GC-C-IRMS, respectively. K-s was measured in the in. pectoralis major of broilers fed rye based diets (56%) which were provided either unsupplemented (-) or supplemented (+) with an enzyme preparation containing xylanase. K-s in breast muscles was significantly increased from 21.80%/d to 23.90%/d due to enzyme supplementation. It can be concluded from the study that the measurement of protein synthesis in broilers with the flooding dose technique can be carried out by using [N-15]phenylatanine, GC-MS and GC-C-IRMS.