The end-product method of measuring whole-body protein turnover: a review of published results and a comparison with those obtained by leucine infusion

The present review summarizes the results of all published papers on whole-body protein turnover in man measured by [15N]glycine and the end-product method using both urea and ammonia. It begins with a short account of the underlying assumptions and the justification for the use of [15N]glycine. The results are then compared with those of a large sample of measurements by the 'gold standard' precursor method with continuous infusion of [13C]leucine. The pros and cons of the two methods are compared and it is suggested that there is a place for further work by the less invasive end-product method, particularly for population studies of the genetic, environmental and functional determinants of whole-body rates of protein synthesis.

Stable isotopes in obesity research

Obesity is recognized as a major public health problem. Obesity is a multifactorial disease and is often associated with a wide range of comorbidities including hypertension, non-insulin dependent (Type II) diabetes mellitus, and cardiovascular disease, all of which contribute to morbidity and mortality. This review deals with stable isotope mass spectrometric methods and the application of stable isotopes to metabolic studies of obesity. Body composition and total energy expenditure (TEE) can be measured by mass spectrometry using stable isotope labeled water, and the metabolism of protein, lipid, and carbohydrate can be measured using appropriate labeled tracer molecules.

Metabolic effects of adjuvant recombinant human growth hormone in patients with continuing sepsis receiving parenteral nutrition

BACKGROUND

Adjuvant growth hormone is advocated for treating the catabolism of prolonged sepsis not corrected by parenteral nutrition alone.

METHODS

An open study was performed in which eight patients whose postabsorptive resting energy expenditure was persistently elevated by a mean of 19% as a result of continuing sepsis were randomized to receive 0.03 or 0.06 mg/kg recombinant human growth hormone (rhGH) each evening for 7 days adjuvant to total parenteral nutrition. Plasma concentrations of growth hormone, insulin, insulin-like growth factors 1 and 2 (IGF-1 and -2) and their binding proteins IGFBP-1 and -3 were measured before and after rhGH, and their relationship with rates of whole-body protein turnover was determined in the morning in the postabsorptive state by using L-[1-13C]leucine.

RESULTS AND CONCLUSIONS

Before rhGH, the patients were hyperinsulinemic (mean, 44.4 mU/L) but had growth hormone levels within the normal range (< 10 mU/L). After the seventh dose of rhGH, nocturnal growth hormone concentrations rose to a mean of 35.3 +/- 26.1 and 61.3 +/- 21.05 mU/L for the low and higher dose groups, respectively. Morning IGF-1 concentrations showed a small increase during treatment, rising from a mean of 241.3 +/- 99.0 to 301.7 +/- 167.3 ng/mL for the low-dose group and from 214.5 +/- 74.6 to 294.1 +/- 116.9 ng/mL for the higher-dose group. IGF-2 increased slightly by 89 +/- 39 and 75 +/- 49 ng/mL for the low and higher doses, respectively. IGFBP-1 and -3 and insulin did not change. The balance between nitrogen input and urinary urea nitrogen increased after rhGH by a mean of 5.3 g/d with no differences between the two dosage groups (4.74 +/- 1.56 g/d for the higher dose, 5.94 +/- 3.70 g/d for the lower). No significant changes were observed in whole-body protein turnover after a 1-week course of rhGH.

Protein Turnover, Energy Expenditure and Body Composition in Patients with Acute Leukaemia Undergoing Chemotherapy

1. Measurements of whole body protein turnover using the (13)C-leucine tracer technique, of body composition using anthropometric measurements and DEXA scanning, and of resting energy expenditure (REE) assessed by indirect calorimetry were made in 8 patients with acute leukaemia undergoing a single course of chemotherapy. Measurements were made in the post absorptive state immediately before chemotherapy and were repeated close to the time of discharge from hospital (mean days in hospital 31 ± 4.3, range 22-35), a mean of 23 ± 4.8 days after completion of chemotherapy. 2. The mean weight loss was 3.63kg (P < 0.001) with significant reductions in the mean non dominant mid arm circumference (1.29cm, P < 0.01), biceps (0.7mm, P < 0.01) and triceps (1.9mm, P < 0.05) skinfold thicknesses. DEXA scanning showed a reduction of mean body fat (1.22kg, P < 0.05) and lean tissue (1.85kg, P < 0.01). 3. There was a reduction in whole body leucine flux (Q) by 35% (P < 0.01) and synthesis (S) by 40% (P < 0.001) with no change in catabolism (C) over the course of admission. 4. There were no significant changes in REE.