Plasma concentrations and tissue uptake of free amino acids in dogs in sepsis and starvation: effects of glucose infusion--some effects of low alimentation

Seconds-Resolved, In Situ Measurements of Plasma Phenylalanine Disposition Kinetics in Living Rats

Current knowledge of the disposition kinetics of endogenous metabolites is founded almost entirely on poorly time-resolved experiments in which samples are removed from the body for later, benchtop analysis. Here, in contrast, we describe real-time, seconds-resolved measurements of plasma phenylalanine collected in situ in the body via electrochemical aptamer-based (EAB) sensors, a platform technology that is independent of the reactivity of its targets and thus is generalizable to many. Specifically, using indwelling EAB sensors, we have monitored plasma phenylalanine in live rats with a few micromolar precision and a 12 s temporal resolution, identifying a large-amplitude, few-seconds phase in the animals' metabolic response that had not previously been reported. Using the hundreds of individual measurements that the approach provides from each animal, we also identify inter-subject variability, including statistically significant differences associated with the feeding status. These results highlight the power of in vivo EAB measurements, an advancement that could dramatically impact our understanding of physiology and provide a valuable new tool for the monitoring and treatment of metabolic disorders.

A pilot study of protein sparing in healthy dogs using peripheral parenteral nutrition

Total parenteral nutrition is the standard nutritional support of dogs when the enteral route is contraindicated, but it can be difficult because of cost, technical difficulties, and potential complications. Peripheral parenteral nutrition (PPN) may be a feasible option for short-term support in some cases. The objectives of this study were to determine the effect of PPN on nitrogen balance (as an indicator of the effect on protein sparing), serum folate concentrations and serum insulin-like growth factor-I (IGF - I) concentrations in fasting dogs. The effect of PPN on these parameters has not previously been reported in dogs. Using a cross-over design, three healthy adult fasting dogs were randomly assigned to three treatments: 5 per cent amino acid solution, 5 per cent glucose solution, and a control electrolyte solution. The solutions were administered into a peripheral vein at 60 ml kg(-1)per day for 4 days. The amino acid infusion resulted in a positive nitrogen balance and the glucose infusion produced less nitrogen loss than the control. Amino acid, but not glucose or electrolyte infusions, decreased serum folate concentrations. Amino acid and glucose infusions resulted in higher serum IGF -I concentrations than electrolyte infusions, although the differences were small and IGF -I decreased in all cases. In conclusion, these findings suggest that PPN increases nitrogen balance in healthy dogs undergoing short-term fasting.

Nutritional management of liver disease

The provision of adequate nutrition to the patient with liver disease is a challenge. The practitioner must avoid overwhelming the remaining metabolic capabilities of the damaged organ. The ability of the liver to regenerate and the patient to recover depends on the availability of sufficient nutrients. There is no default diet for the patient with liver disease. Each patient must be evaluated individually, with consideration given to the type and origin of the liver disease, the current extent of hepatic dysfunction, and the patient's previous dietary history. Efforts should be directed at the provision of an energy intake adequate to maintain body weight and a protein intake as close to normal as can be tolerated without precipitating signs of hepatic encephalopathy.

Plasma and skeletal muscle amino acids following severe burn injury in patients and experimental animals

This study describes and analyzes sequential changes in plasma and skeletal muscle free amino acids following severe burn injury. Plasma free amino acids were determined in children (n = 9) with burns averaging 60% total body surface area and were compared with laboratory beagles (n = 44) which received a flame burn totaling 30% of their body surface area. In addition, needle biopsy specimens were obtained from the semitendonosus muscle in the animals to determine free intracellular amino acids. In both patients and animals the amount of total free amino acids in plasma fell following burn, suggesting relative protein deficiency. This drop was primarily due to a 47% drop in nonessential amino acids. However, plasma phenylalanine was consistently higher than normal following burn, and was strongly associated with death and weight loss in both animals and patients, especially when analyzed as a ratio with tyrosine. This finding suggested excessive catabolism, hepatic dysfunction, or both. Plasma levels of several amino acids correlated significantly with weight loss. Alterations in muscle free amino acids generally were similar to plasma amino acids. Exceptions were muscle alanine and glycine which strongly correlated with weight loss. However, the determination of muscle free amino acid profiles did not yield clinically useful information not available from plasma profiles. Plasma levels of liver enzymes suggested progressive hepatic dysfunction. These studies show that the laboratory beagle is a good model for studying the metabolic alterations of amino acids that accompany burn injury, since they mimic humans in many parameters which appear to be most useful with respect to clinical evaluation.

Rapid glucose disappearance in infants with infection

Altered carbohydrate metabolism has been reported during episodes of neonatal infection. To document that there is more rapid glucose disappearance during infection, intravenous glucose tolerance tests (IVGTT) and serial plasma growth hormone and insulin levels were determined in eight full-term neonates during the first three days of an acute episode of infection and during convalescence, 5 to 15 days later. Eight healthy infants were each studied once using the same study protocol. Glucose disappearance rates, measured as K1 of glucose, were increased (p less than 0.01) during both the acute septic period (3.7 +/- 0.3% disappearance/min; mean +/- S.E.M.) and convalescent period (2.5 +/- 0.2% min) when compared with values in control infants (1.3 +/- 0.3%/min). Gram-negative, gram-positive, and viral infections were all associated with rapid glucose disposal. The abnormality in carbohydrate homeostasis persisted for at least 5 to 15 days after treatment was begun. Baseline and stimulated (20-minutes post bolus glucose infusion) plasma insulin and growth hormone levels did not differ among the groups. Thus, there is no evidence that hyperinsulinism produced the rapid glucose disappeared rate and enhanced glucose utilization. The reason for the disturbed carbohydrate metabolism in neonatal infections remains unknown.

Blood-brain barrier derangement in sepsis: cause of septic encephalopathy?

Patients with sepsis often manifest disorientation, somnolence, asterixis and coma, symptoms also seen in portasystemic encephalopathy. Altered plasma concentrations of the neutral amino acids and in creased blood-brain transport of these acids may play a role in portasystemic encephalopathy. Plasma amino acids and blood-brain barrier transport of neutral amino acids were investigated in a rat model of abdominal sepsis, cecal ligation and puncture. The blood-brain transport was studied by the technique of Oldendorf with carbon-14-amino acids 12 and 24 hours after the induction of sepsis. In similar groups of animals, isolation of brain capillaries was carried out by the technique of Hjelle and the capillaries were incubated with carbon-14-amino acids to study transport activity. Plasma and brain amino acids were deranged in a fashion similar to the derangements seen in portasystemic encephalopathy, with a decrease in plasma branched chain amino acids and an increase in most neutral amino acids in brain. The changes were most pronounced after 24 hours. The brain uptake of several neutral amino acids was increased in the septic rats, while the uptake of lysine, a basic amino acid, was normal. In the brain capillaries isolated from septic rats, tyrosine and leucine transport was also greater than in sham-operated animals. Elevated neutral amino acids may play a role in the encephalopathy encountered in septic patients similar to its role in patients with portasystemic encephalopathy, as similar mechanisms appear to be operating.