Whole-body protein turnover in metabolically stressed patients and patients with cancer as measured with [¹⁵N] glycine

The whole-body protein synthesis rate (PSR) was measured in 5 control patients (group I) and 38 patients in various clinical states (group II). A single pulse of [¹⁵N]glycine was given and the PSR calculated from the ¹⁵N enrichment in the urinary ammonia excreted over the next 10 hr. The patients' results fell into three separate groups: group IIa patients were nonstressed and had uneventful recoveries (3.1 ± 0.6 g prot./kg/day), their PSRs were the same as the control group I, (3.1 ± 1.0 g prot./kg/day); group IIb patients were stressed, had higher PSRs (6.3 ± 0.9 g prot./kg/day), one of whom died, and the rest had more complications than group IIa; group IIc patients had very high PSRs (15.4 ± 6.1 g prot./kg/day), all of whom were seriously ill, and 8 out 12 died; Data are ± 1 SD. The PSR correlated with the serum glutamate oxaloacetate transferase (SGOT, P < 0.01). We concluded: (i) [¹⁵N]glycine cannot be used to measure the PSR in patients with evidence of liver disease; the results are best interpreted in terms of glycine metabolism; (ii) the "apparent" PSR correlated with clinical status; and (iii) an elevated PSR in a patient with a malignancy is not necessarily due to protein metabolism by the tumor.