Table 2.
Comparison of leg phenylalanine kinetics derived by using individual subjects’ data summarized in Table1 and the newly proposed and six different previously published approaches
| Difference in mean values | ||||
|---|---|---|---|---|
| compared to mean values derived | ||||
| Condition | by newly developed equations | |||
| Postabsorptive | HECP + Whey | |||
| (μmol min−1) | (μmol min−1) | Postabsorptive | HECP+Whey | |
| Net balance | ||||
| (CTA – CTV) × PF | −0.63 ± 0.10 | 0.96 ± 0.20* | 0.00 (0.0%) | 0.00 (0.0%) |
| (CUA – CUV) × PF | −0.80 ± 0.12 | 0.74 ± 0.20* | −0.17 (26.5%) | −0.22 (−23.1%) |
| Phe release from protein breakdown | ||||
| Newly developed equations | 2.18 ± 0.24 | 1.47± 0.24* | — | — |
| Wolfe & Chinkes (2005) | ||||
| Synthesis (MPE + CT) − Net balance (CT) | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| Synthesis (MPE + CU) − Net balance (CU) | 1.99 ± 0.22 | 1.35 ± 0.22* | −0.19 (−8.6%) | −0.12 (−8.0%) |
| Synthesis (TTR + CT) − Net balance (CT) | 2.38 ± 0.27 | 1.59 ± 0.26* | 0.20 (9.4%) | 0.13 (8.7%) |
| Synthesis (TTR + CU) − Net balance (CU) | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| Gelfand & Barrett (1987) | ||||
| PF × CTV × [1 − (MPEV/MPEA)] | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| PF × CUV × [1 − (MPEV/MPEA)] | 1.99 ± 0.22 | 1.35 ± 0.22* | −0.19 (−8.6%) | −0.12 (−8.0%) |
| PF × CTV × [1 − (TTRV/TTRA)] | 2.38 ± 0.27 | 1.59 ± 0.26* | 0.20 (9.4%) | 0.13 (8.7%) |
| PF × CUV × [1 − (TTRV/TTRA)] | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| Barrett et al. (1987) with extraction ratio | ||||
| {[(MPEA / MPEV) − 1] × CTA × PF} × [1 − (CLA − CLV)/CLA)] | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| {[(MPEA / MPEV) − 1) × CUA × PF} × [1 − (CLA − CLV)/CLA)] | 1.94 ± 0.21 | 1.33 ± 0.22* | −0.24 (−10.8%) | −0.14 (−9.4%) |
| {[(TTRA / TTRV) − 1] × CTA × PF} × [1 − (CLA − CLV)/CLA)] | 2.44 ± 0.27 | 1.62 ± 0.27* | 0.26 (12.2%) | 0.15 (10.3%) |
| {[(TTRA / TTRV) − 1] × CUA × PF} × [1 − (CLA − CLV)/CLA)] | 2.18 ± 0.24 | 1.47± 0.24* | 0.00 (0.0%) | 0.00 (0.0%) |
| Barrett et al. (1987) without extraction ratio, and Bennet et al. (1990) and Thompson et al. (1989) | ||||
| [(MPEA / MPEV) − 1] × CTA × PF | 2.58 ± 0.29 | 1.82 ± 0.31 | 0.40 (18.4%) | 0.35 (24.0%) |
| [(MPEA / MPEV) − 1] × CUA × PF | 2.30 ± 0.26 | 1.65 ± 0.28 | 0.12 (5.6%) | 0.18 (12.3%) |
| [(TTRA / TTRV) − 1] × CTA × PF | 2.89 ± 0.33 | 2.01 ± 0.34* | 0.72 (32.8%) | 0.54 (36.8%) |
| [(TTRA / TTRV) − 1] × CUA × PF | 2.58 ± 0.29 | 1.82 ± 0.31 | 0.40 (18.4%) | 0.35 (24.0%) |
| Greenhaff et al. (2008) | ||||
| [(MPEA / MPEV) − 1] × CTV × PF | 2.74 ± 0.32 | 1.71 ± 0.29* | 0.57 (26.0%) | 0.25 (16.9%) |
| [(MPEA / MPEV) − 1] × CUV × PF | 2.51 ± 0.29 | 1.58 ± 0.27* | 0.33 (15.1%) | 0.11 (7.6%) |
| [(TTRA / TTRV) − 1] × CTV × PF | 3.08 ± 0.36 | 1.89 ± 0.33* | 0.90 (41.3%) | 0.43 (29.0%) |
| [(TTRA / TTRV) − 1] × CUV × PF | 2.81 ± 0.33 | 1.74 ± 0.30* | 0.64 (29.2%) | 0.27 (18.7%) |
| Phe used for protein synthesis | ||||
| Newly developed equations | 1.55 ± 0.17 | 2.43 ± 0.21* | — | — |
| Wolfe & Chinkes (2005) | ||||
| (CTA × MPEA − CTV × MPEV) × (PF/ MPEA) | 1.55 ± 0.17 | 2.43 ± 0.21* | 0.00 (0.0%) | 0.00 (0.0%) |
| (CUA × MPEA − CUV × MPEV) × (PF/ MPEA) | 1.20 ± 0.13 | 2.09 ± 0.18* | −0.35 (−22.8%) | −0.34 (−14.0%) |
| (CTA × TTRA − CTV × TTRV) × (PF/ TTRA) | 1.75 ± 0.19 | 2.55 ± 0.23* | 0.20 (13.2%) | 0.13 (5.3%) |
| (CUA × TTRA − CUV × TTRV) × (PF/ TTRA) | 1.38 ± 0.15 | 2.21 ± 0.19* | −0.17 (−10.8%) | −0.22 (−9.1%) |
| Gelfand & Barrett (1987) | ||||
| [(CLA − CLV)/CLA] × CTA × PF | 1.55 ± 0.17 | 2.43 ± 0.21* | 0.00 (0.0%) | 0.00 (0.0%) |
| [(CLA − CLV)/CLA] × CUA × PF | 1.38 ± 0.15 | 2.21 ± 0.19* | −0.17 (−10.8%) | −0.22 (−9.1%) |
| Barrett et al. (1987) with extraction ratio | ||||
| Breakdown (MPE + CT) + Net Balance (CT) | 1.55 ± 0.17 | 2.43 ± 0.21* | 0.00 (0.0%) | 0.00 (0.0%) |
| Breakdown (MPE + CU) + Net Balance (CU) | 1.15 ± 0.13 | 2.07 ± 0.17* | −0.40 (−26.0%) | −0.36 (−14.8%) |
| Breakdown (TTR + CT) + Net Balance (CT) | 1.81 ± 0.20 | 2.58 ± 0.23* | 0.26 (17.1%) | 0.15 (6.2%) |
| Breakdown (TTR + CU) + Net Balance (CU) | 1.38 ± 0.15 | 2.21 ± 0.19* | −0.17 (−10.8%) | −0.22 (−9.1%) |
| Barrett et al. (1987) without extraction ratio and Bennet et al. (1990) | ||||
| Breakdown (MPE + CT) + Net Balance (CT) | 1.95 ± 0.22 | 2.78 ± 0.26* | 0.40 (25.9%) | 0.35 (14.5%) |
| Breakdown (MPE + CU) + Net Balance (CU) | 1.50 ± 0.17 | 2.39 ± 0.22* | −0.04 (−2.9%) | −0.04 (−1.7%) |
| Breakdown (TTR + CT) + Net Balance (CT) | 2.26 ± 0.25 | 2.97 ± 0.29* | 0.72 (46.2%) | 0.54 (22.2%) |
| Breakdown (TTR + CU) + Net Balance (CU) | 1.78 ± 0.20 | 2.56 ± 0.24* | 0.23 (15.2%) | 0.14 (5.3%) |
| Thompson et al. (1989) | ||||
| [(MPEA × CTA − MPEV × CTV) / MPEV] × PF | 1.95 ± 0.22 | 2.78 ± 0.26* | 0.40 (25.9%) | 0.35 (14.5%) |
| [(MPEA × CUA − MPEV × CUV) / MPEV] × PF | 1.50 ± 0.17 | 2.39 ± 0.22* | −0.04 (−2.9%) | −0.04 (−1.7%) |
| [(TTRA × CTA − TTRV × CTV) / TTRV] × PF | 2.26 ± 0.25 | 2.97 ± 0.29* | 0.72 (46.2%) | 0.54 (22.2%) |
| [(TTRA × CUA − TTRV × CUV) / TTRV] × PF | 1.78 ± 0.20 | 2.56 ± 0.24* | 0.23 (15.2%) | 0.14 (5.3%) |
| Greenhaff et al. (2008)** | ||||
| [(MPEA / MPEV) – 1] × CTA – (CTA – CTV) × PF | 17.57 ± 1.43 | 9.60 ± 1.94* | 16.02 (1034%) | 7.17 (296%) |
| [(MPEA / MPEV) – 1] × CUA – (CUA – CUV) × PF | 15.89 ± 1.26 | 8.83 ± 1.75* | 14.34 (925%) | 6.40 (264%) |
| [(TTRA / TTRV) – 1] × CTA – (CTA – CTV) × PF | 19.65 ± 1.65 | 10.70 ± 2.11* | 18.10 (1168%) | 8.27 (341%) |
| [(TTRA / TTRV) – 1] × CUA – (CUA – CUV) × PF | 17.74 ± 1.45 | 9.82 ± 1.93* | 16.19 (1045%) | 7.40 (305%) |
Data are means ± SEM. *Value significantly different from corresponding postabsorptive value (P < 0.05). **Synthesis rates calculated using the equation presented by Greenhaff et al. (2008) were ∼5- to 10-fold different from those derived by any of the other methods and therefore appear to be attributable to typos in the published equation. Abbreviations: CT, total (i.e. tracer and tracee) concentration; CTA, total arterial concentration; CTV, total venous concentration; CU, unlabelled (i.e. tracee) concentration; CUA, unlabelled arterial concentration; CUV, unlabelled venous concentration; CLA, labelled arterial concentration; CLV, labelled venous concentration; HECP+Whey, hyperinsulinaemic–euglycaemic clamp procedure with concomitant whey protein ingestion; MPEA, mole percent excess in the artery; MPEV, mole percent excess in the vein; PF, plasma flow; TTRA, tracer-to-tracee ratio in the artery; TTRV, tracer-to-tracee ratio in the vein. Leg phenylalanine kinetics were calculated by using the arterial concentrations and enrichments obtained during the AV balance study described in the methods section. The equations presented by Barrett et al. (1987) and Gelfand & Barrett (1987) were originally described for radioactive tracers and have been adapted for use with stable isotope labelled tracers as described by Nair et al. (1992) (i.e. total and labelled Phe concentrations in the artery and vein and enrichments expressed as MPE). Furthermore, Barrett et al. (1987) present a commonly used equation to calculate protein breakdown that includes contribution from arterial inflow as well as an extraction ratio that corrects for this; therefore, we present breakdown rates for Barrett et al. (1987) using both approaches.