The effect of burn subeschar tissue fluid on skeletal muscle and hepatic amino acid uptake in an experimental system in vitro

The effect of burn plasma on skeletal muscle proteolysis in rats

We studied the effects of plasma from burned rats on skeletal muscle proteolysis. Major burn injury (40% total body surface area (TBSA)) was produced in male Sprague-Dawley rats. Fluid resuscitation was given with intraperitoneal Ringer's solution (4cm(3)/(kg%) TBSA). Plasma was harvested daily for 5 days after burn injury from the tail blood vessel. This plasma was added in vitro to incubated soleus muscles from healthy animals. The incubation medium was assayed for amino acids by HPLC. Glutamine, glutamate, leucine and alanine were tested to monitor the amino acid profile in the medium. Results showed there was no significant change during the initial 4 days after injury, except that glutamine and alanine increased significantly on the first day. However, all of them had a tendency to increase on the fifth day after injury. Present results suggest that the humoral effect on muscle proteolysis did not exist during the initial days after burning. The humoral effect on skeletal muscle proteolysis may have been present 5 days post-burn.

Inverse regulation of protein turnover and amino acid transport in skeletal muscle of hypercatabolic patients

We have investigated the relationships between the rates of muscle protein synthesis and degradation and of transmembrane transport of selected amino acids in leg skeletal muscle of 19 severely burned patients and 18 normal controls in the postabsorptive state. Patients were studied on the 14 +/- 5 postburn day, and their mean burn size was 66% +/- 18% of total body surface area. Methods were based on the leg arteriovenous balance technique in combination with biopsies of the vastus lateralis muscle and infusions of isotopic tracers of amino acids. Net muscle protein breakdown was greater in the patients because of an 83% increase in the rate of muscle protein degradation. The rate of muscle protein synthesis was also increased in the patients but to a lesser extent than protein degradation, i.e. by 50% with the arteriovenous phenylalanine balance technique and by 49% with the direct tracer incorporation method. The absolute values of inward transport of phenylalanine, leucine, and lysine were not significantly different in the two groups. However, the ability of transport systems to take up amino acids from the bloodstream, as assessed by dividing inward transport by amino acid delivery to leg muscle, were 50-63% lower in the patients. In contrast, outward phenylalanine and lysine transport were 40% and 67% greater in the patients than in the controls, respectively. We conclude the primary alteration in muscle protein metabolism is an acceleration of protein breakdown, and the increase in protein synthesis likely is due to increased intracellular amino acid availability as a result of accelerated breakdown. Transmembrane transport in the outward direction is accelerated, presumably to facilitate the export of amino acids from muscle to other tissues. In contrast, transmembrane transport in the inward direction is impaired relatively to the increased delivery of circulating amino acid to skeletal muscle secondary to accelerated blood flow.