Table 4 Arginine and related amino acids plasma concentrations, whole body production rates, and clearance rates in COPD non-depressed and COPD depressed
|  | COPD non-depressed (CN) (n = 51) | COPD depressed (CD) (n = 27) | Estimated difference (t-test) | ANCOVA p value |
|---|---|---|---|---|
Plasma concentrations (μmol/L) | ||||
 Arginine | 69.46 [62.83, 76.10] | 68.22 [54.30, 75.72] | − 0.54 [10.00, − 11.08] | 0.943 |
 Citrulline | 34.54 [31.00, 38.08] | 31.12 [22.98, 37.61] | − 3.07 [− 11.54, 5.40] | 0.438 |
 Ornithine | 55.70 [51.75, 59.66] | 51.89 [44.19, 63.77] | − 5.066 [− 11.49, 1.35] | 0.140 |
Whole body production rates (μmol/h) | ||||
 Arginine | 9405.40 [7503.03, 11,307.80] | 9394.86 [8228.46, 10,561.30] | 5.67 [− 3398.25, 3409.58] | 0.855 |
 Citrulline | 1028.99 [950.60, 1107.42] | 1124.34 [989.04, 1259.63] | 70.86 [− 76.83, 218.60] | 0.334 |
 Ornithine | 2031.62 [1856.21, 2207.03] | 2277.54 [1954.20, 2600.88] | 81.64 [− 386.24, 549.71] | 0.544 |
 Citrulline to arginine (ARG de novo production) | 1075.75 [951.58, 1199.93] | 1311.09 [1072.80, 1549.37] | 164.97 [− 93.01, 422.81] | 0.224 |
 Arginine to citrulline (NO production) | 389.80 [154.50, 625.20] | 372.80 [82.24, 247.60] | − 1.67 [− 108.32, 105.00] | 0.974 |
 Arginine to ornithine | 2258.60 [1631.89, 2885.32] | 2706.34 [1709.68, 3702.99] | 85.26 [602.25, − 431.73] | 0.819 |
 Ornithine to citrulline | 116.50 [97.74, 135.20] | 145.00 [118.10, 187.70] | 24.12 [− 59.20, 107.42] | 0.555 |
 Citrulline to ornithine | 292.80 [195.40, 390.10] | 364.30 [206.2, 522.30] | 14.57 [184.66, − 155.53] | 0.902 |
Clearance rates (L h−1) | ||||
 Arginine | 3.00 [2.51, 3.49] | 2.843 [2.52, 3.34] | − 0.172 [2.66, − 3.00] | 0.879 |
 Citrulline | 0.67 [0.62, 0.71] | 0.75 [0.66, 0.80] | 0.10 [0.03, 0.17] | 0.006 |
 Ornithine | 0.79 [0.73, 0.84] | 0.86 [0.71, 1.00] | 0.08 [− 0.002, 0.16] | 0.075 |