PROTEIN-SYNTHESIS MEASUREMENT IN CANCER-PATIENTS WITH C-13 VALINE

The flooding dose technique is a method that uses tracer amino acids t o measure the rate of protein synthesis in tissues in vivo. This techn ique involves the injection of a large amount of unlabelled amino acid together with the tracer to minimize difference in isotopic enrichmen t of the free amino acid in plasma and tissue compartments which repre sent the precursor pool of protein synthesis. Seven patients with loca lized colorectal carcinoma received a total parenteral nutrition befor e surgery and protein synthesis was measured in tumour and colon after administration of a large dose of valine (20% atom percent excess). T he enrichment of free valine in plasma and tissues was measured by GCM S and the enrichment of protein-bound valine into tumour and colon by IRMS. The fractional synthesis rate in tumours was 13.44 +/- 6.9%/day compared to a value of 10.9 +/- 8.1%/day in healthy colon. The lack of significant difference probably relates to the low number of patients and the variability of protein synthesis rate in tumours.