title: Measurement of muscle protein fractional synthesis and breakdown rates from a pulse tracer injection.
abstract: We have developed a new method to determine the fractional synthesis rate (FSR) and breakdown rate (FBR) of muscle protein. This method involves a pulse tracer injection and measurement of enrichment in the arterial blood and muscle at three time points. The calculations of FSR and FBR are based on the precursor-product principle. To test this method, we gave a pulse injection of L-[ring-(13)C(6)]phenylalanine of 4-6 mg/kg in five rabbits. The measured FBR value (0.233 +/- 0.060%/h) was almost identical (P = 0.35) to that (0.217 +/- 0.078%/h) estimated from a leg arteriovenous balance model (Biolo G, Chinkes D, Zhang X-J, and Wolfe RR. J Parenter Enteral Nutr 16: 305-315, 1992). The measured FSR value tended to be lower than that estimated from the leg model (0.125 +/- 0.036 vs. 0.185 +/- 0.086%/h; P = 0.14), possibly because the new method measures only muscle FSR, whereas the leg balance model also includes skin and bone contributions. The pulse tracer injection did not affect muscle protein kinetics as measured by leucine and phenylalanine kinetics in the leg. In another five rabbits, we demonstrated that sampling could be reduced to either one or two muscle biopsies when multiple pulse injections were used. This method can be completed in 1 h with one muscle biopsy and has technical advantages over currently used methods.
authors.affiliation: Metabolism Unit, Shriners Hospitals for Children, and Departments of Surgery and Anesthesiology, The University of Texas Medical Branch, Galveston, Texas 77550, USA.
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Zhang
authors.forename: David L
authors.initials: DL
authors.lastname: Chinkes
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D008401:Gas Chromatography-Mass Spectrometry; D007930:Leucine / Q000493:pharmacokinetics; D008297:Male; D008954:Models, Biological; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010649:Phenylalanine / Q000493:pharmacokinetics; D011817:Rabbits; D015203:Reproducibility of Results
chemical_list: D002247:Carbon Isotopes; D009124:Muscle Proteins; D010649:Phenylalanine; D007930:Leucine