The place of some newer techniques in studies of nutrition in the hospitalized patient

Nutrient utilisation in muscle and in the whole body of patients receiving total parenteral nutrition

Forearm metabolite exchange was assessed by the arterio-venous catheterization technique in 5 parenterally fed patients (weight 55.22 kg +/- 4.18 kg; height 1.71 m +/- 0.04 m), who received an 'all-in-one' nutrition regimen whilst in remission from Crohn's disease. All patients received 12.8 g N, 4725 kJ from carbohydrate and 4200 kJ from fat (10416 kJ total energy). The exchanges were related to nutrient oxidation and nutrient balances in the whole body as assessed by indirect calorimetry and nitrogen excretion. At rest, the subjects were found to be in positive balances for carbohydrate (+0.78 +/- 0.13 kJ/min), fat (+1.85 +/- 0.26 kJ/min) and protein (+0.240 +/- 0.04 kJ/min). Resting forearm muscle was also in positive amino acid balance and positive carbohydrate balance. Despite the large estimated uptake of glucose by forearm muscle (+1860 +/- 84 nmol/100 ml tissue/min) there was no net release of pyruvate and lactate. Glutamate and the branched chain amino acids (BCAA) were the dominant amino acids taken up by muscle (26% and 30% of total uptake respectively) and glutamine was the dominant amino acid carrying nitrogen out of muscle (78% of total amino acid nitrogen release). The energy taken up by muscle as non-esterified fatty acids, triacylglycerol and ketone bodies was small relative to that associated with glucose uptake. The results suggest that during the hypercaloric parenteral nutrition regimen, a) increased peripheral glucose uptake is not necessarily associated with increased release of glycolytic products, b) in the absence of glutamine intake for at least 10 days, muscle retains enough capacity to synthesise and release sufficient quantities of glutamine so that it remains the dominant amino acid carrying nitrogen out of muscle, c) despite the use of the intravenous route for administration of nutrients, and unusual amino acid composition of the regimen, the overall pattern of forearm metabolism bears many similarities to that which occurs after a mixed meal in normal subjects.

The effect of severe dietary restriction on intramuscular glutamine concentrations and protein synthetic rate

An investigation was carried out to examine the relationship between fractional muscle protein synthetic rate (FSR) and intramuscular glutamine concentration ({GLN}(i)) in rats that had a dietary intake which was deficient in both protein and energy. Young male rats (38 days old) were fed for 48 h on either 1) 25% of the ad lib intake of a 20% protein diet, or 2) glucose alone, sufficient to provide the same energy intake as in 1). In a separate study, 33 day old rats were starved completely for 48 h. Appropriate controls were included in both studies. Muscle FSR, which was reduced by 40% in both groups of energy restricted rats (P<0.001), was associated with a small increase in {GLN}(i) (P<0.05). Starvation produced a 60% reduction in FSR (P<0.01) and a 45% (P<0.05) reduction in {GLN}(i). It is concluded that reductions in muscle protein synthesis can occur by mechanisms independent of intramuscular glutamine concentration.