title: Comparison of bolus injection and constant infusion methods for measuring muscle protein fractional synthesis rate in humans.
abstract: BACKGROUND
  The use of stable isotope tracer techniques to measure muscle protein fractional synthesis rate (FSR) has been well established and widely used. The most common method that has been utilized so far is a primed constant infusion (CI) method, which requires 3-4 h of tracer infusion. However, recently our group has developed a bolus injection (BI) method, which requires an injection of bolus of tracer and can be completed within 1 h. In this study, we compared calf (gastrocnemius) muscle protein FSR measured using these two different methods--CI and BI.
  
  
  METHODS
  FSRs were measured in eight people (5 men and 3 women; age: 62.3±6.9 years (mean±SD); body weight: 75.4±21.5 kg) at basal, postabsorptive state using L-[ring-2H5]-phenylalanine. In the CI protocol, a primed continuous infusion was given for 4 h, and muscle biopsies were taken at 120 and 240 min; in the BI, a bolus injection of the tracer was given at 0 min and biopsies were taken at 5 and 60 min. Tracer enrichments in blood and muscle tissue were determined by gas chromatography-mass spectrometry. Data are expressed as mean±SE; t-test, linear regression and Levene Median equal variance test analyses were performed.
  
  
  RESULTS
  CI FSR was 0.066±0.006%/h, whereas BI FSR was 0.058±0.008%/h, p=NS. The linear regression analysis showed a significant relationship between BI and CI, p=0.038. The intra-class correlation coefficient was 0.83. The standard deviation of the differences in the measurements was 0.015%/h. The Levene Median equal variance test demonstrated no difference in variance between the CI and BI measurements (p=0.722).
  
  
  CONCLUSIONS
  No difference could be detected in calf muscle protein FSR measured by CI and BI methods; the BI method can be used for the measurement of muscle protein FSR in humans.
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX; Shriners Hospitals for Children, Galveston, TX. Electronic address: detuvden@utmb.edu.
authors.forename: Demidmaa
authors.initials: D
authors.lastname: Tuvdendorj
authors.affiliation: Department of Surgery, University of Texas Medical Branch, Galveston, TX; Shriners Hospitals for Children, Galveston, TX.
authors.forename: David L
authors.initials: DL
authors.lastname: Chinkes
authors.affiliation: Sulpizio Cardiovascular Center, University of California, San Diego, CA.
authors.forename: John
authors.initials: J
authors.lastname: Bahadorani
authors.affiliation: Department of Surgery, University of Texas Medical Branch, Galveston, TX; Shriners Hospitals for Children, Galveston, TX.
authors.forename: Xiao-jun
authors.initials: XJ
authors.lastname: Zhang
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX.
authors.forename: Melinda
authors.initials: M
authors.lastname: Sheffield-Moore
authors.affiliation: Department of Surgery, University of Texas Medical Branch, Galveston, TX.
authors.forename: Lois A
authors.initials: LA
authors.lastname: Killewich
authors.affiliation: University of Arkansas for Medical Sciences, Little Rock, AR.
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000368:Aged; D003903:Deuterium; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000235:genetics; D010649:Phenylalanine / Q000008:administration & dosage*; D019275:Radiopharmaceuticals / Q000008:administration & dosage*
chemical_list: D009124:Muscle Proteins; D019275:Radiopharmaceuticals; D010649:Phenylalanine; D003903:Deuterium
keywords: Bolus injection method; Constant infusion method; Fractional synthesis rate; Muscle protein; Stable isotope tracer techniques