This method for estimating clinically important amino acids in serum or urine within 40 min involves o-phthalaldehyde/2-mercaptoethanol derivatization and reversed-phase "high-pressure" liquid chromatography. Homocysteic acid is an internal standard, and homoserine and norvaline are reference peaks. For all the amino acids estimated, the between-run coefficients of variation ranged from 2.0 to 13.5%, and the mean analytical recoveries from both serum and urine samples was 101%. Peak areas vary linearly with concentration up to 1500 mumol/L for all the amino acids assayed. The limit of detection for each amino acid was estimated to be 38 fmol.

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Concentrations of several metabolites in deproteinized blood and plasma were determined in 100 subjects after an overnight fast, to establish reference ranges. Blood glycerol, nonesterified fatty acids, and ketone body concentrations and the 3-hydroxybutyrate/acetoacetate ratio increased with age while blood alanine concentrations delined. Serum insulin and blood alanine concentrations were also related to weight. No marked sex-related differences were found, although blood glycerol concentration was slightly higher in women. Distribution of all metabolite concentrations was positively skewed, except for glucose, but skewness could be corrected by logarithmic transformation. Skew was particularly marked for blood ketone body concentrations. Concentrations of all metabolites in plasma exceeded those in whole blood, but this was significant for only lactate and pyruvate when concentrations in plasma were compared with calculated concentrations in erythrocyte water.

The relation of lipid metabolism to nitrogen balance was studied in patients having undergone abdominal surgery and was compared with control subjects who had fasted for a similar period. The patients had lower circulating concentrations of glycerol, non-esterified fatty acids and ketone bodies. There were inverse correlations between blood alanine and ketone body concentrations in both patients (r = -0.64, P less than 0.01) and controls (r = -0.58, P less than 0.01). Nitrogen excretion by patients (12.7 mmol/kg body weight/day +/- 1.4 s.e. mean) was greater than by controls (9.2 mmol kg(-1)d(-1) +/- 0.8, P less than 0.05), but a more marked difference was noted for urinary methyl histidine excretion of 5.1 +/- 0.5 mmumol kg(-1) d(-1) by patients and only 2.5 +/- 0.3 mumol kg(-1) d(-1) by controls (P less than 0.01), a disparity indicative of more active protein turnover after surgery.