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Burn trauma to the extremities can produce marked systemic effects in mice. Burn injury to the dorsal surface of mice is also associated with changes in glucose metabolism ([18F] 2-fluoro-2-deoxy-D-glucose [18FDG] uptake) by brown adipose tissue (BAT) and nuclear factor (NF)-κB activity in several tissues including skeletal muscle. This study examined the effect of a single hind limb burn in mice on 18FDG uptake by NF-κB activity in vivo, and blood flow was determined by laser Doppler techniques. Male NF-κB luciferase reporter mice (28-30 g) were anesthetized, both legs were shaven, and the right leg was subjected to scald injury by immersion in 90°C water for 5 seconds. Sham-treated animals were used as controls. Each burned and sham mouse was resuscitated with saline (2 mL, i.p.). The individual animals were placed in wire bottom cages with no food and free access to water. After 24 hours, the animals were imaged with laser Doppler for measuring blood flow in the hind limb. The animals were then unanesthetized with 50 μCi of FDG or luciferin (1.0 mg, i.v.) via tail vein. Five minutes after luciferin injection, NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. One hour after 18FDG injection, the animals were killed with carbon dioxide overdose, and 18FDG biodistribution was measured. Tissues were also analyzed for NF-κB luciferase activity. The scalding procedure used here produced a full-thickness burn injury to the leg with sharp margins. 18FDG uptake by the burned leg was lower than that in the contralateral limb. Similarly, luciferase activity and blood flow in the burned leg were lower than those in the contralateral leg. 18FDG uptake by BAT and heart increased, whereas that by brain decreased. In conclusion, the present study suggests that burn injury to a single leg decreased FDG uptake by skeletal muscle but increased 18FDG uptake by BAT. The injury to the leg reduced NF-κB expression compared with the contralateral leg and the uninjured skeletal muscle of the sham but activated NF-κB expression in a number of other organs. These findings are consistent with the hypothesis that burn trauma to the extremities can produce marked systemic effects, including activation of NF-κB expression and activation of 18FDG uptake by BAT.

Exercise is a component of the clinical management for burn patients, to help reduce muscle wasting associated with prolonged hospitalization. In the present study the authors examined 2-deoxy-2-[18F] fluoro-D-glucose (18FDG) uptake in mice subjected to burn injury with and without exercise. Mice had their the dorsums shaven, were placed in molds, and the exposed area was immersed in 90°C water for 9 seconds followed by resuscitation with saline (2 ml) to produce a 30% full-thickness burn injury. Twenty-four hours later, the mice were subjected to treadmill exercise for 1 hour. Before exercise, mice were injected with ~50 μCi 18FDG. Mice were killed after running and a complete biodistribution was performed. Exercise produced a stimulation of 18FDG update by skeletal muscle and heart, while reducing 18FDG accumulation in brain. Burn injury had no significant effect on 18FDG update by skeletal muscle, but did increase 18FDG accumulation in heart, while reducing 18FDG accumulation in brain. However, exercise combined with a burn injury produced a significant increase in 18FDG uptake in the skeletal muscle compared with the burned mice, as great as that produced in the sham animals subjected to exercise. The combination of burn plus exercise appeared to prevent the stimulation of 18FDG uptake by the heart produced by burn injury alone. Exercise treatment did not correct the changes in 18FDG uptake in the brain produced by burn injury. Separately, exercise and burn injury significantly increased serum interleukin-6 levels, increases that were higher when exercise was combined with the burn injury. These findings suggest that exercise may exert some therapeutic effects in burn patients by tissue-specific modulation of glucose metabolism, and these changes may be related to interleukin-6.

Background: Burn injury (BI) is associated with insulin resistance (IR) and hyperglycemia which complicate clinical management. We investigated the impact of BI on glucose metabolism in a rabbit model of BI using a combination of positron emission tomography (PET) and stable isotope studies under euglycemic insulin clamp (EIC) conditions., Materials and Methods: Twelve male rabbits were subjected to either full-thickness BI (B) or sham burn. An EIC condition was established by constant infusion of insulin, concomitantly with a variable rate of dextrose infusion 3 d after treatment. PET imaging of the hind limbs was conducted to determine the rates of peripheral O(2) and glucose utilization. Each animal also received a primed constant infusion of [6,6-(2)H(2)] glucose to determine endogenous glucose production., Results: The fasting blood glucose in the burned rabbits was higher than that in the sham group. Under EIC conditions, the sham burn group required more exogenous dextrose than the B group to maintain blood glucose at physiological levels (22.2 ± 2.6 versus 13.3 ± 2.9 mg/min, P < 0.05), indicating a state of IR. PET imaging demonstrated that the rates of O(2) consumption and (18)F 2-fluoro-2-deoxy-D-glucose utilization by skeletal muscle remained at similar levels in both groups. Hepatic gluconeogenesis determined by the stable isotope tracer study was found significantly increased in the B group., Conclusions: These findings demonstrated that hyperglycemia and IR develop during the early "flow phase" after BI. Unsuppressed hepatic gluconeogenesis, but not peripheral skeletal muscular utilization of glucose, contributes to hyperglycemia at this stage., (Published by Elsevier Inc.)

Radiation exposure and burn injury have both been shown to alter glucose utilization in vivo. The present study was designed to study the effect of burn injury combined with radiation exposure on glucose metabolism in mice using [¹⁸F] 2-fluoro-2-deoxy-D-glucose (¹⁸FDG). Groups of male mice weighing approximately 30 g were studied. Group 1 was irradiated with a ¹³⁷Cs source (9 Gy). Group 2 received full thickness burn injury on 25% TBSA followed by resuscitation with saline (2 ml, IP). Group 3 received radiation followed 10 minutes later by burn injury. Group 4 were sham-treated controls. After treatment, the mice were fasted for 23 hours and then injected (IV) with 50 μCi of ¹⁸FDG. One hour postinjection, the mice were sacrificed, and biodistribution was measured. Positive blood cultures were observed in all groups of animals compared to the shams. Increased mortality was observed after 6 days in the burn plus radiated group as compared to the other groups. Radiation and burn treatments separately or in combination produced major changes in ¹⁸FDG uptake by many tissues. In the heart, brown adipose tissue, and spleen, radiation plus burn produced a much greater increase (P < .0001) in ¹⁸FDG accumulation than either treatment separately. All three treatments produced moderate decreases in ¹⁸FDG accumulation (P < .01) in the brain and gonads. Burn injury, but not irradiation, increased ¹⁸FDG accumulation in skeletal muscle; however, the combination of burn plus radiation decreased ¹⁸FDG accumulation in skeletal muscle. This model may be useful for understanding the effects of burns plus irradiation injury on glucose metabolism and in developing treatments for victims of injuries produced by the combination of burn plus irradiation.

In mice, it has been demonstrated that at 7 days after burn injury, injection of lipopolysaccharide (LPS) is more lethal than the same dose at 1 day after injury. In the present study, we examined the effect of LPS injection to mice burned 7 days previously on glucose metabolism ([(18)F] 2-fluoro-2-deoxy-D-glucose [(18)FDG] uptake) in vivo. CD-1 male mice (25-28 g, Charles River Breeding Laboratories, Wilmington, MA) were anesthetized, backs shaven, and subjected to dorsal full thickness burn on 25% TBSA. Sham-treated animals were used as controls. Six days after burn injury, all mice were fasted overnight. One half of the burned and sham controls were subsequently injected IP with LPS (10 mg/kg; Escherichia coli). The remaining animals were injected with saline IP. Two hours later, all mice were injected IV with 50 μCi of (18)F FDG. One hour later, the animals were euthanized, and biodistribution was measured. Tissues were weighed, and radioactivity was measured with a well-type γ counter. Results were expressed as %dose/g tissue, mean ± SEM. The combination of burn 7 days previously and LPS significantly increased mortality compared to animals with burn alone, LPS alone, or sham controls. Burn injury 7 days previously caused a significant decrease in (18)FDG uptake by the brain compared to sham controls. The combination of LPS and burn injury 7 days previously produced a significant increase in (18)FDG uptake by brown adipose tissue and heart compared with either treatment separately. LPS produced a significant increase in (18)FDG uptake by lung, spleen, and gastrointestinal tract of the sham animals, changes that were different in mice burned 7 days previously and injected with LPS. The present results suggest that burn injury 7 days previously predisposes mice to alterations in (18)FDG uptake produced by LPS. These changes may relate, in part, to the increased lethality of LPS injection in previously burned mice.

It has been demonstrated that restoration of function to compromised tissue can be accomplished by transplantation of bone marrow stem cells and/or embryonic stem cells (ESCs). One limitation to this approach has been the lack of noninvasive techniques to longitudinally monitor stem cell attachment and proliferation. Recently, murine ESC lines that express green fluorescent protein (GFP), luciferase (LV), and herpes simplex thymidine kinase (HVTK) were developed for detection of actively growing cells in vivo by imaging. In this study, the authors investigated the use of these ESC lines in a burned mouse model using Integra® as a delivery scaffolding/matrix. Two different cell lines were used: one expressing GFP and LV and the other expressing GFP, LV, and HVTK. Burn wounds were produced by application of a brass block (2 × 2 cm kept in boiling water before application) to the dorsal surface of SV129 mice for 10 seconds. Twenty-four hours after injury, Integra® with adherent stem cells was engrafted onto a burn wound immediately after excision of eschar. The stem cells were monitored in vivo by measuring bioluminescence with a charge-coupled device camera and immunocytochemistry of excised tissue. Bioluminescence progressively increased in intensity over the time course of the study, and GFP-positive cells growing into the Integra® were detected. These studies demonstrate the feasibility of using Integra® as a scaffolding, or matrix, for the delivery of stem cells to burn wounds as well as the utility of bioluminescence for monitoring in vivo cellular tracking of stably transfected ESC cells.

Firefighters receive significant training and are outfitted with state-of-the-art protective equipment. However, given the unpredictable nature of their work environment, injuries still occur. The National Burn Repository (NBR) was viewed as a resource for defining the epidemiology of these injuries on a national level and to identify predictive factors for outcomes in this population. The NBR was queried for the occupation of "firefighter" for the years 1990-2008. Records were screened for completeness, and 597 patients were identified for analysis. Data examined included demographics, %TBSA burn, length of stay (LOS), injury circumstance, and disposition. Multiple linear regression models were created to determine factors related to outcome measures. The majority of patients were white (84%) and male (96%). The mean age was 35 years. Most injuries were caused by fire/flame (73%). Only six deaths (1%) were reported. Most injuries were work-related (86%), and most patients were discharged home (92%). Inhalation injury was documented in 9% of patients. The mean LOS was 6.5 ± 11.3 days (median 2 days), and few patients had critical care requirements. The average %TBSA was 6 ± 11.7%. Patients with larger injuries had increased LOS. The presence of inhalation injury, elevated carboxyhemoglobin levels, and advancing age were significantly associated with larger burns. From the NBR data, most firefighter burn injuries were small, and few firefighter burn patients required critical care resources or had significant disability. Firefighters comprise a small number of burn center admissions each year, yet they are an important population to consider for burn prevention efforts.

After severe burn injury and other major traumas, glucose tolerance tests demonstrate delayed glucose disposal. This 'diabetes of injury' could be explained by insulin deficiency, and several studies have shown that soon after trauma (ebb phase) insulin concentrations are reduced in the face of hyperglycemia. After resuscitation of trauma patients (flow phase), β-cell responsiveness normalizes and plasma insulin levels are appropriate or even higher than expected, however, glucose intolerance and hyperglycemia persist. In the acute care setting, several approaches have been used for treating insulin resistance, including insulin infusion, propranolol and glucagon-like-peptide-1 (GLP-1). Recently, it was demonstrated that a tetrapeptide with antioxidant properties D-Arg-Dmt-Lys-Phe-NH2 (SS31), but not its inactive analogue Phe-D-Arg-Phe-Lys-NH2 (SS20) attenuates insulin resistance in mice maintained on a high fat diet. In this report the effects of SS31 and SS20 on burn-induced insulin resistance was studied in mice. Oral glucose tolerance tests (OGTT) were performed in 4 groups of 6 mice with thermal injury with or without pre-treatment with SS31 or SS20 and sham controls. In addition, biodistribution of 18FDG was measured in burned mice with and without SS31 treatment and shams (subsets of these animals were also studied by µPET). For comparison purposes, groups of 6 cold-stressed mice with and without SS31 treatment were also studied. The results of these studies demonstrate that SS31 but not SS20 ameliorated burn-induced insulin resistance. In addition, SS31 treatment resulted in marked reduction in the increased 18FDG uptake by brown adipose tissue (BAT) in burned but not cold-stressed animals; suggesting that the stressors act by different mechanisms. Overall, these studies confirmed that SS31 can be used to reverse burn-induced insulin resistance and provide a firm pre-clinical basis for future clinical trials of SS31 for the treatment of insulin resistance in patients with burn injury.

Aims: Cold stress has been shown to produce dramatic increases in 2-fluoro-2-deoxy-D-Glucose ((18)FDG) accumulation by brown adipose tissue (BAT) in rodents. However, neither the effects of other types of stress on (18)FDG accumulation nor the effects of stressors on the accumulation of tracers of other aspects of energy metabolism have been evaluated. In this report we studied the effects of cold stress, burn injury and cutaneous wounds on murine BAT at the macroscopic, microscopic and metabolic level., Main Methods: Glucose metabolism was studied with (18)FDG, fatty acid accumulation was evaluated with trans-9(RS)-(18)F-fluoro-3,4(RS,RS)-methyleneheptadecanoic acid (FCPHA) and tricarboxcylic acid cycle (TCA) activity was evaluated with (3)H acetate., Key Findings: All three stressors produced dramatic changes in BAT at the macroscopic and microscopic level. Macroscopically, BAT from the stressed animals appeared to be a much darker brown in color. Microscopically BAT of stressed animals demonstrated significantly fewer lipid droplets and an overall decrease in lipid content. Accumulation of (18)FDG by BAT was significantly (p<0.01) increased by all 3 treatments (Cold: ~16 fold, burn ~7 Fold and cutaneous wound ~14 fold) whereas uptake of FDG by white fat was unchanged. This effect was also demonstrated non invasively by μPET imaging. Although less prominent than with (18)FDG, BAT uptake of FCPHA and acetate were also significantly increased by all three treatments. These findings suggest that in addition to cold stress, burn injury and cutaneous wounds produce BAT activation in mice., Significance: This study demonstrates brown fat activated by several stressors leads to increased uptake of various substrates., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Infection is the most common and most serious complication of a major burn related to burn size. Recent studies have demonstrated that statin treatment can decrease mortality in murine or human sepsis. In the current study mice were anesthetized and subjected to a dorsal 30% TBSA scald burn. Simvastatin or placebo were administered by intraperitoneal injection once daily or every 12h. On post burn day 7 cecal ligation and puncture with a 21-gauge needle (CLP) was performed under ketamine/xylazine anesthesia, the two different dosing schedules were continued and survival was monitored. In other groups of mice, interleukin-6 (IL-6) levels in blood were measured in mice at 7 days after injury. A simvastatin dependent improvement in survival was observed in the burn sepsis model. This protection was found to be dose and time dependent. In addition, statin treatment reduced the elevation in IL-6 levels of mice burned 7 days previously. However, IL-6 levels in burned mice with or without statin treatment were elevated by CLP to the same degree. The results of these studies suggest that statin treatment reduces mortality in mice with burns and CLP and that this effect may not be mediated via IL-6 levels., (Copyright © 2010 Elsevier Ltd and ISBI. All rights reserved.)

In addition to their primary role in lowering plasma cholesterol, statins have a variety of other actions. We studied the effect of simvastatin treatment on burn injury-induced changes in regional glucose metabolism. Groups of six CD-1 mice (male, approximately 25 g) were subjected to full thickness 30% total body surface area (TBSA) burn injury. The animals were treated with simvastatin at various doses (0.02, 0.2 and 2.0 microg/kg, i.p.) for seven days. The following morning, mice were injected with 18F labeled 2-fluoro-2-deoxy-D-glucose (18FDG) (50 microCi) via the tail vein. Approximately 60 min after tracer injection, the animals were sacrificed and biodistribution was measured. A sub-set of burned mice with and without statin treatment and sham controls was injected with approximately 1.0 mCi of FDG and tracer distribution was evaluated by microPET. In addition, oral glucose tolerance tests (OGTT) were performed in other groups of burned mice with and without statin treatment and sham controls. In the heart and brown adipose tissue (BAT), burn injury produced a highly significant increase in 18FDG accumulation (p<0.01), whereas tracer accumulation in brain was markedly reduced (p<0.01). In the heart and BAT, simvastatin treatment produced dose-dependent reductions in 18FDG accumulation. In contrast, simvastatin did not affect 18FDG accumulation in the brain. There was no effect of simvastatin treatment on 18FDG accumulation in the heart, BAT or brain of sham-treated mice. Less pronounced effects were detected in other tissues that were studied. All animals had normal plasma glucose levels (approximately 90 mg/dl). The OGTTs demonstrated insulin resistance in burn injured mice which was reversed by statin treatment. Our results indicate that simvastatin reverses burn-induced increases in 18FDG accumulation by the heart and BAT in a dose-dependent manner but does not affect burn-induced reductions of 18FDG accumulation by the brain. These findings suggest that statins exert some of their effects by tissue specific modulation of glucose metabolism.

Brown adipose tissue (BAT) contains numerous mitochondria and is characterized by the presence of uncoupling protein 1 (UCP1). UCP1 is the main mediator of thermogenesis that plays an important role in the modulation of energy balance. The authors hypothesize that alterations in the expression of UCP1 might be involved in the major metabolic disorders occurring during burn trauma. The present study is designed to explore the potential role of the UCP1 in metabolic disorders after burn injury. The authors have used the real-time reverse transcription-polymerase chain reaction to quantify UCP1 mRNA expression in the mice BAT and white adipose tissue (WAT). UCP1 mRNA expression was up-regulated in BAT, especially at 24 hours after burn. UCP1 mRNA expression was detectable and also up-regulated by burn injury in WAT. The authors provide evidence that one of the mechanisms mediating hypermetabolism and increased energy expenditure in burn injury is a pronounced increase in thermogenic capacity, as illustrated by robust gene expression of UCP1 in BAT and WAT.

Postburn alterations in the morphology and metabolism of brain tissue have been previously reported. It was demonstrated in our previous study that thermal injury decreased glucose usage in rat brain during the ebb phase. The cellular and molecular signaling events that trigger the pathophysiologic alterations, however, have not yet been characterized. In the present report, the authors have examined the effect of burn injury on mitogen-activated protein kinases (MAPKs) activities and insulin signaling in the brain tissue. Rats were subjected to 50% total body surface area full thickness scald injury. Brain samples were collected at 6 hours after injury. Tissue lysates were analyzed for MAPKs activities, insulin receptor substrate (IRS)-1 expression, and Akt activity which were determined by western blot and immunoprecipitation. Burn injury stimulated the stress-responsive components, SAPK/JNK, p38 MAP kinase and p44/42 MAP kinase, and increased IRS-1 expression and Akt activity. There was no change, however, on the phosphorylation of Ser307 of IRS-1 in brain tissue. The present data is consistent with the hypothesis that activation of the three major MAPKs pathways appears to be events involved in the mechanisms of burn injury induced insulin resistance and encephalopathy. Changes in signal transduction pathways in the brain after burn injury provide the underlying molecular mechanism of neurologic abnormalities (burn encephalopathy) that occur in burn patients.

A rapid method for measuring 3-methylhistidine (3MH) in rat and human urine with higher sensitivity and precision than any previously reported method is described using internal standard [1-(13)C]3MH (M+1) and negative chemical ionization (NCI) gas chromatography/mass spectrometry (GC/MS). Internal standard [1-(13)C]3MH (M+1) was added to rat and human urine samples, hydrolyzed, and absorbed onto cation exchange columns. The column eluent was dried and derivatized for GC/MS analysis. Quantification of 3MH levels was accomplished by monitoring the m/z 204 fragment. The m/z 204 fragment was chosen due to the fragment's abundance and stability as determined by analysis of [methyl-(2)H(3), (18)O(2)]3MH (M+7) and [methyl-(13)C]3MH (M+1) fragmentation patterns under NCI conditions. This method shows excellent linearity (0.9989) over the range studied (0-0.5 mol), high recovery (95.9%), and low coefficient of variation (4.7%). The described method is sensitive enough to detect 6.8 pmol amount of urinary 3MH with a precision of 9.1%. The in vivo utility of this method to quantify urinary 3MH was tested in a burn injury rat model and on urine specimens from pediatric burn patients. Data obtained from the urine of burn-injured rats and pediatric burn patients match previously reported trends and validate the in vivo utility of this method.

Hyperglycemia, glucose intolerance and elevated insulin levels frequently occur in burned patients; however, the mechanism(s) for this insulin resistance has not been fully elucidated. One possible mechanism could involve alterations in the phosphorylation of serine 307 of the insulin receptor substrate-1 (IRS-1) via activation of stress kinase enzymes, including SAPK/JNK. In the present study we examined the time course of the effect of burn injury to mice on: levels of IRS-1 protein, phosphorylation of serine 307 of IRS-1, SAPK/JNK kinase levels and activity and Akt kinase activity in hind limb skeletal muscle. Burn injury produced a reduction in hind limb muscle mass 24 h after injury, and, which persisted for 168 h. At 24 h after injury, there was a dramatic ( approximately 9-fold) increase in phosphorylation of IRS-1 serine 307 followed by a more moderate elevation thereafter. Total IRS-1 protein was slightly elevated at 24 h after injury and decreased to levels below sham treated animals at the later times. Burn injury did not appear to change total SAPK/JNK protein content, however, enzyme activity was increased for 7 days after injury. Akt kinase activity was decreased in skeletal muscle following burn injury; providing a biochemical basis for burn-induced insulin resistance. These findings are consistent with the hypothesis that burn-induced insulin resistance may be related, at least in part, to alterations in the phosphorylation of key proteins in the insulin signaling cascade, including IRS-1, and that changes in stress kinases, such as SAPK/JNK produced by burn injury, may be responsible for these changes in phosphorylation.

Several of the possible molecular mechanisms that contribute to the insulin resistance associated with burn injury were examined in a rat model of thermal injury. Rats were subjected to full thickness scald injury (25% total body surface area, 10 sec burn) and resuscitated with saline. After 1, 2 and 3 weeks, urinary C-peptide excretion was measured in burned and sham-treated control animals. At 3 weeks after injury, glucose production by the liver and utilization by skeletal muscle was measured under insulin clamp conditions, insulin receptor binding was measured in skeletal muscle, liver and adipose tissue membranes and IRS-1 expression was measured by Western blot methods. Urinary C-peptide excretion was significantly elevated at 1, 2 and 3 weeks after injury. At 3 weeks after injury, several key metabolic processes were blunted, including the ability of insulin infusion to stimulate glucose uptake by skeletal muscle, the potency of insulin infusion for inhibiting hepatic glucose production, and the ability of a bolus injection of insulin to simulate phosphorylation of IRS-1 in liver, skeletal muscle or adipose tissue. In contrast, there were no apparent alterations in the binding of insulin to membranes from liver, skeletal muscle or adipose tissue. These findings support the concept that the burn injury stimulates insulin production 3 weeks after burn injury, and produces insulin resistance in skeletal muscle, adipose tissue and liver by processes that are associated with post-receptor alterations in the absence of changes in insulin receptor binding.

Burn injury produces a marked and prolonged hypermetabolic state, which is characterized by accelerated hepatic amino acid metabolism and negative nitrogen balance. The effect of burn injury on hepatocyte transport of glutamine, a key substrate in gluconeogenesis and ureagenesis, was examined following the administration of a full thickness 20% total body surface scald injury. The burn injury was induced in wild-type mice, as well as two types of knockout mice: a CD-14 knockout and an interleukin-6 (IL-6) knockout. In both the wild-type and CD-14 knockout mice a latent and profound 2-fold increase in hepatocyte glutamine transport was seen. In contrast, hepatocytes isolated from IL-6 knockout mice failed to show an induction of glutamine transport after burn injury. Hepatocytes isolated from burned wild-type and CD-14 knockout mice produced significantly higher levels of IL-6 as compared to hepatocytes isolated from sham burned mice. Histologic analysis of skin isolated from wild-type mice showed a robust inflammatory response whereas skin from IL-6 deficient mice showed minimal inflammation and decreased granulation tissue. The results of this study suggest that IL-6 may play a key role in the stimulation of hepatic glutamine transport following burn injury.

Increased nitrogen loss in the form of urea is a hallmark of the metabolic aberrations that occur after burn injury. As the immediate precursor for urea production is arginine, we have conducted an investigation on the metabolic fate of arginine in the liver to shed light on the metabolic characteristics of this increased nitrogen loss. Livers from 25% total surface burn (n = 8) and sham burn rats (n = 8) were perfused in a recycling fashion with a medium containing amino acids and stable isotope labeled l-[(15) N(2)-guanidino, 5,5-(2)H(2)]arginine for 120 minutes. The rates of glucose and urea production and oxygen consumption were measured. The rate of unidirectional arginine transport and the intrahepatic metabolic fate of arginine in relation to urea cycle activity were quantified by tracing the disappearance rate of the arginine tracer from and the appearance rate of [(15)N(2)]urea in the perfusion medium. Perfused livers from burned rats showed higher rates of total urea production (mean +/- SE, 4.471 +/- 0.274 v 3.235 +/- 0.261 mumol. g dry liver(-1). min(-1); P <.01). This was accompanied by increased hepatic arginine transport (1.269 +/- 0.263 v 0.365 +/- 0.021 mumol. g dry liver(-1). min(-1)) and an increased portion of urea production from the transported extrahepatic arginine (12.9% +/- 2.9% v 3.5% +/- 0.4%, P <.05). The disposal of arginine via nonurea pathways was also increased (0.702 +/- 0.185 v 0.257 +/- 0.025 mumol/g dry weight(-1)/min(-1); P <.05). We propose that increased inward transport and utilization of extrahepatic arginine by the liver contributes to the accelerated urea production after burn injury and accounts, in part, for its conditional essentiality in the nutritional support of burn patients.

A difficulty that has emerged in the development and preclinical evaluation of adjuvant therapies for gram-negative sepsis is the lack of easily studied animal models that closely mimic human infection. An objective of this study was to adapt a previously described model of infection in burned mice to rats with a defined bacterial strain of Escherichia coli. Challenge with two colonies of live E. coli O18:K1:H7 bacteria into an 8% full-thickness burn of the dorsal skin surface of rats produced predictable bacteremia at 24 to 48 h and 80 to 100% mortality at 3 to 4 days. E. coli O18:K1:H7 was approximately 10-million-fold more virulent than several other gram-negative bacterial strains. The model should be a useful tool in studying the pathogenicity of burn wound infections and in evaluating the efficacy of novel adjuvant therapies for gram-negative sepsis.

Thermal injury in animal models clearly alters glucose metabolism. Insulin resistance results, with the wound in the skin receiving increased glucose, presumably to be used for wound healing and fighting invasion by foreign organisms. Using the whole-body imaging capacities of PET, it may now be possible to explore in greater detail the mechanism(s) responsible for the skeletal muscle wasting that is associated with burn and trauma patients, and possibly to develop strategies to prevent muscle atrophy without interfering with wound healing.

The effects of thermal injury in rats on glucose utilization (Rg) by skin, wound, small intestine, and muscle in vivo has been determined using 2-[18F]-fluoro-2-deoxy-D-glucose (18FDG) 6 hours, 24 hours, and 3 weeks after injury. These results were compared with serum glucose and insulin levels at the same time points and with hexokinase activity in the tissues. Thermal injury had no significant effects on serum glucose levels; however, serum insulin levels were lower than sham values 6 hours after injury, the same as sham values 24 hours after injury, and significantly higher than sham values 3 weeks after injury. Rg of unburned skin was not changed at 6 or 24 hours after injury, but was increased at 3 weeks after injury. The Rg of the wound was almost zero at 6 and 24 hours after injury; however, at 3 weeks after injury, the wound area had a Rg two to three times higher than that of the normal skin of sham animals. Small intestine Rg was decreased 6 and 24 hours after injury, but was essentially normal by 3 weeks after injury. The Rg of muscle was unchanged at all of the time points tested. Total Rg was significantly higher in the animals 3 weeks after injury, with the increase primarily due to the increases in skin and wound. The increases in Rg were associated with changes in tissue hexokinase activity. The present data suggest that thermal injury to rats results in dramatic alterations in glucose utilization by the skin and wound, changes that may contribute to the overall alterations in carbohydrate metabolism during burn trauma.

Objective: Thermal injury is associated with the development of encephalopathy. The mechanism(s) for the development of this condition have not been established. In the present study, the effects of thermal injury were determined on rat brain glucose utilization (Rg), using 2-[18F]fluoro-2-deoxy-D-glucose (18FDG)., Design: Four types of studies were performed. In one group of rats, the effect of thermal injury on total rat brain glucose utilization (Rg) was determined at 6 hours, 24 hours, and 3 weeks after injury. The brains of thermally injured rats were also assayed for hexokinase and glucose-6-phosphatase activities, since these enzyme activities are responsible for the phosphorylation and dephosphorylation of the 18FDG. We also measured total body oxygen consumption in the thermally injured rats. We wanted to compare the changes produced by thermal injury on rat brain glucose utilization (Rg) with the effects produced by compounds known to modify energy metabolism and/or rat brain glucose utilization (Rg). For that reason, in a second group of rats, an inflammatory state was produced by lipopolysaccharide injection, and rat brain glucose utilization (Rg) was determined. In the third group of rats, overall metabolism in rats was reduced by pentobarbital injection, followed by hypothermia, and rat brain glucose utilization (Rg) was determined. In the fourth group of rats, overall metabolism in rats was stimulated by 2,4-dinitrophenol injection, and rat brain glucose utilization (Rg) was determined., Materials and Methods: Glucose utilization (Rg) by the brains of these treated rats was determined using 18FDG. Oxygen consumption in vivo, as well as glucose-6-phosphatase and hexokinase activity in vitro, were measured by standard procedures., Measurements and Main Results: Glucose utilization (Rg) by rat brain was significantly reduced (p < 0.01) at 6 and 24 hours after injury, but returned to normal values 3 weeks after injury. These reductions were associated with decreases in rat brain hexokinase activity, increases in rat brain glucose-6-phosphatase activity, and decreased oxygen consumption by rats in vivo. Pentobarbital injection followed by hypothermia reduced rat brain glucose utilization (Rg) (p < 0.01), while 2,4-dinitrophenol treatment elevated rat brain glucose utilization (Rg) (p < 0.01). In contrast, LPS treatment had no effect on rat brain glucose utilization (Rg)., Conclusions: These data indicate that thermal injury decreases glucose utilization (Rg) in rat brain during the hypometabolic phase. This effect can be explained, at least in part, by alterations in hexokinase and glucose-6-phosphatase activities, as well as reductions in oxygen consumption. Thus, the changes in brain glucose utilization (Rg) appear to be associated with the ebb phase of the thermal injury. The present results observed in burned rats may provide evidence to explain the encephalopathy observed in burned patients.

NO is a major messenger molecule which regulates immunity and vascular tone, serves as a neurotransmitter and participates in wound healing. It has also been known to be increased in vivo by thermal injury. Urinary nitrate excretion and tissue levels of NO synthase activity were measured after a non-lethal thermal injury. Urinary nitrate excretion decreased by 90% 24-48 h after injury, but dramatically increased by 10-fold thereafter for 30-40 days after injury and remained elevated until the wound healed. This response was inhibited by a competitive inhibitor of NO synthase. These rates of urinary nitrate excretion suggest that NO production is dramatically affected by injury in a pattern that is distinct from that observed after lipopolysaccharide administration. On the basis of these findings, we suggest that the hyperdynamic cardiovascular and hypermetabolic responses seen to continue weeks after thermal injury could be a result of the autocrine and paracrine effects of NO generated locally within the tissues in addition to that generated by inflammatory cells.

Background: Cytokines are putative mediators of thermal injury-induced systemic changes. We studied the effects of thermal injury on cytokine activation in vivo with a sensitive radioimmunoassay specific for rat interleukin-1 alpha (IL-1 alpha)., Methods: We characterized the organ distribution and expression kinetics of IL-1 alpha in rats submitted to either 20% total body surface area cutaneous burn, muscle burn, or endotoxic shock. Rats were killed at various time points, and liver, lung, spleen, ileum, thymus, kidney, skin, and plasma were harvested. Tissues were homogenized, and the supernates were assayed for rat IL-1 alpha. The assay detection limit was 1.5 ng/gm wet tissue (WT)., Results: Thermal injury induced marked elevations of IL-1 alpha levels in the liver and lung, and maximal levels were reached at 2.5 hours when compared with controls. In the liver mean IL-1 alpha levels in cutaneous burn injury were 16.5 +/- 6.2 ng/gm WT, whereas in sham injury they were 1.7 +/- 0.1 ng/gm WT, p < or = 0.05; in the lung IL-1 alpha levels with cutaneous burn injury were 10.3 +/- 1.3 ng/gm WT, whereas sham injury levels were 1.9 +/- 0.8 ng/gm WT, p < or = 0.002). Levels in all other organs and plasma were below detection limits. Muscle burn injury had similar elevated levels of IL-1 alpha in the liver at 1 hour, indistinguishable from cutaneous burn. In contrast, endotoxin challenge resulted in dramatic elevation of IL-1 alpha levels in all organs tested except for the kidney, whereas the skin maintained its usual large amounts of IL-1 alpha., Conclusions: These data indicate that thermal or mechanical injury induce very early and organ-specific association of IL-1 alpha in vivo by mechanisms other than endotoxemia.

Mean arterial blood pressure was measured in anesthetized rats. The duration that the rats were under anesthesia with ether or methohexital was brief, and the animals were allowed to awaken early after injury. Three hemodynamic measurements were compared: (1) lowest mean arterial blood pressure, (2) duration at lowest mean arterial blood pressure, and (3) time to recover initial mean arterial blood pressure. In these studies the anesthetic agents reduced mean arterial blood pressure by 36%, recovering to normal pressures within 24 to 39 minutes. During the hemodynamic observation period, no significant additional hemodynamic effects as a result of the thermal injury were seen. Administration of resuscitation fluid did not significantly affect hemodynamics during the observation period in this study. These studies demonstrate that anesthesia dominates the short-term cardiovascular effects of thermal injury, and therefore caution is required in the interpretation of acute cardiovascular effects immediately after thermal injuries with patients under general anesthesia.

Objective: To determine the effects of burn size and burn wound infection on gut permeability to the macromolecule polyethylene glycol 3350 (PEG 3350; molecular weight, 3350 d)., Design: Randomized, controlled study using 36 male Sprague-Dawley rats., Setting: Hospital research laboratory., Interventions: Animals received scald burns to 0%, 20%, or 35% of their total body surface area. Half of the animals in each group were infected with Pseudomonas aeruginosa., Main Outcome Measures: Gut permeability was measured using the intestinal absorption and renal excretion of enterally administered PEG 3350 and mannitol (molecular weight, 182 d)., Results: There were dramatic increases in PEG 3350 excretion and in the PEG 3350/mannitol ratios (P = .0001 in both instances) that were seen in relation to burn size. Significant increases in PEG 3350 excretion and in the PEG 3350/mannitol ratios (P = .017 and P = .045, respectively) were also seen in animals in which infection was present. This was in addition to the effects of burn size already noted., Conclusions: A direct relationship between gut permeability and the extent of burn injury was found, which is consistent with the results from a previous study in humans. In addition, this study found that further separate increases in gut permeability occur in the presence of P aeruginosa in burn wound infections.

Burn injury inhibits lipoprotein lipase, which leads to an impeded clearance of triglycerides from the plasma and an increase in serum triglycerides. Intestinal brush border lipase, which hydrolyzes triglyceride to free fatty acids and is essential for absorption of triglycerides from the gastrointestinal tract, could also be inhibited by burn injury. In thermally injured rats, the absorption and oxidation of enterally administered 14C-palmitate triglyceride, brush border lipase activity, and small-intestinal and colonic content of fat were determined. Absorption of 14C-palmitate triglyceride and production of 14CO2 were reduced 50% 18 hours after injury (p < 0.01). In addition, brush border lipase activity was reduced 50% (p < 0.01). Because brush border lipase function is essential to the proper absorption of enterally administered fat, inhibition of intestinal lipase could be an important factor in enteral diet effectiveness.

In response to severe injury, extraordinary quantities of lactate that are released from the peripheral tissues serve as substrate for hepatic gluconeogenesis. It is possible that as a result of burn injury, reaction kinetics involving lactate could be directly changed within the liver. The metabolic fate of [U-14C]lactate was examined in vitro in fresh liver slices after a 20 per cent total body surface area injury. Glucose and CO2 were produced in vitro by the liver tissues after the injury and no differences were seen in the metabolism of these substrates between the injured and control animals. These findings suggest that the intrinsic enzymatic processes within the liver are not directly altered by injury itself or by any of the associated inflammatory mediators which appear early after burns.

The effect of interleukin (IL)-1 beta on proteoglycan (PG) synthesis and secretion, into culture medium by normal human skin and post-burn human normal scar using tissue explants in culture, was investigated. Following exposure of different tissues to labeling with Na2[35SO4] in the presence and absence of IL-1 beta, the extractable [35SO4]PG (isolated from 0.15 M NaCl and 4 M Gdm. Cl extracts), non-extractable [35SO4]PG (isolated after papain treatment of residual tissue), and [35SO4]PG secreted into culture medium were analyzed for contents and distribution. The contents of [35SO4]PG as measured by [35SO4] incorporation indicate differences in [35SO4]PG production of extractable and non-extractable PGs and also in the PGs released into the culture medium. Examination of the sizes of [35SO4]PGs on Sepharose CL-6 beta columns with and without treatment of IL-1 beta shows that the size of non-extractable [35SO4]PG decreases after IL-1 beta treatment. Cellulose acetate plate electrophoresis of these [35SO4]PG fractions shows that the distribution of PGs alters after treatment with IL-1 beta. These results indicate that burn wound healing abnormalities (scarring) is related to a change in the level of PGs, and may be modified by IL-1 beta treatment.

Background: The brush border cytoskeleton maintains the selective absorptive surface of the intestine epithelium. Increased intestinal permeability caused by cutaneous thermal injury may be the result of changes in the organization of the brush border cytoskeleton., Methods: In this study we used electron and laser confocal microscopy to examine the temporal and spatial organization of the rat brush border cytoskeleton after thermal injury., Results: Vesiculation of microvilli and disruption of core actin filament bundles were observed in rats with burns covering 20% total body surface area (TBSA). In rats with 40% TBSA burns changes in the brush border cytoskeleton were more pronounced, resulting in increased vesiculation of microvilli and disruption of terminal web actin filaments. Confocal microscopy of corresponding areas of the gut epithelium after staining with rhodamine-phalloidin showed rearrangement of brush border actin filaments. Although tight junctions were intact, the apical region of the gut epithelium in rats with 40% TBSA burns was constricted, possibly because of contraction of brush border actin filaments. Changes in brush border structure and cytoskeletal organization were most pronounced in the ileum of rats 18 hours after injury., Conclusions: These findings suggest that disruption of the brush border cytoskeleton may, in part, be responsible for the loss of intestinal barrier function after thermal injury in animal models.

The biodistribution of the plasma expander colloidal solution, heta-starch (HES), has been examined in rats, subjected to thermal injury or sepsis. The ability of these solutions to alter RES phagocytic function of [99mTc]-sulphur colloid ([99mTc]SC) uptake in vivo has been examined. The biodistribution of radiolabelled HES has been determined in normal rats. The HES colloidal solution has no deleterious effect upon RES function in vivo in the thermally injured animals or the septic animals as compared to sham controls. In addition, the HES colloidal solution seemed to be distributed primarily within the liver, spleen and kidney, with a small amount residing in the lung. Thermal injury did not increase the uptake of this material by the lung. These results suggest that the use of HES in thermally injured and septic individuals has no deleterious effects on RES function, nor does it accumulate in the lungs, and hence, should be advocated for use in these situations.

Internal temperatures were continuously measured in rats that received 20% or 40% body surface area cutaneous scald injuries in 25 degrees C and 38.5 degrees C environments. In animals that received thermal injuries in the 25 degrees C environment, intraperitoneal, intraesophageal, and intrarectal temperatures rapidly rose to 40 degrees C within 5 minutes but returned to normal values within 15 minutes after injury. When 20% body surface area injuries were induced in a 25 degrees C environment, all of the animals survived. In the 25 degrees C environment, neither acute core body temperature elevations nor use of fluid resuscitation predicted survival. In contrast, in a 38.5 degrees C environment core body temperatures rapidly exceeded 41 degrees C with the 20% injury, and all of the animals died within minutes in spite of fluid resuscitation. These studies suggest that the ambient environmental temperature may significantly influence a thermally injured animal's ability to rapidly eliminate absorbed heat of injury and result in an elevated core body temperature, which may contribute to the immediate lethality of the injury.

We previously observed a 75-90% decrease in concentration of biliary IgA after thermal injury to rat skin. Decrease in biliary IgA might result from an alteration in supply of polymeric IgA delivered to the hepatocyte or from an alteration in hepatocyte transfer of polymeric IgA into bile. In the present study, we examined the transfer of intravenously administered 125I-IgA into bile. Purified IR22 rat IgA myeloma protein consisting of both monomeric and polymeric IgA was labelled with 125I. Sprague-Dawley rats (140-180 g) received a 20-30% body surface area scald-burn or sham treatment. The bile duct was cannulated 18-24 h later and 125I-IgA preparations were injected into the tail vein. Bile was collected under light ether anesthesia for 3 h. In rats injected with 125I-IR22 IgA myeloma protein there were no significant differences in total, TCA-precipitable, or immunoprecipitable radioactivity in bile from burn-injured or sham-treated animals. On Bio-Gel A-1.5 m gel permeation, the radioactivity in bile from sham-treated animals eluted in the region of polymeric IgA as expected; the radioactivity in the bile from burn-injured animals eluted equally in the same regions as polymeric IgA and monomeric IgA. In sham-treated rats injected with isolated polymeric IgA only, bile contained primarily polymeric IgA. In burn-injured rats injected with polymeric IgA only, bile contained a mixture of polymeric IgA and monomeric IgA. These findings suggest that hepatocyte processing of polymeric IgA is altered after thermal injury, resulting in the transformation of some polymeric IgA into its monomeric form.

The concentration of biliary IgA is greatly reduced after scald burn injury in the rat, thereby contributing to a deficiency in upper intestinal immune defense. This reduction in biliary IgA might have several explanations, including failure of the transhepatic transport of polymeric IgA (pIgA) from the circulation, decreased delivery of pIgA to the hepatocyte, or decreased local synthesis of IgA in the liver. The authors examined whether burn injury reduces circulating pIgA available for delivery to the hepatocyte. In initial studies, they demonstrated that burn injury induces a decrease in circulating pIgA in bile-duct-ligated rats. They then sought to determine whether this decrease in pIgA was due to increased loss from the circulation or to a decreased supply of pIgA to the circulation through the thoracic duct. After injection of purified 125I-pIgA into bile duct-ligated rats, radioactivity was removed more rapidly from the circulation of burn-injured compared with control rats. The radioactivity localized in the skin and muscle at the site of burn injury. In another group of rats with patent bile ducts, the thoracic duct was cannulated and lymph collected for 12 hours. The total amount of IgA protein in lymph was found to be reduced in burn-injured compared with control animals. Thus, burn injury is accompanied by reduced circulating pIgA, which may be attributed to its enhanced loss from the circulation and to decreased delivery of pIgA from the intestinal mucosa to the systemic circulation via the thoracic duct.

The pathway which results in a loss of intestinal barrier function and transepithelial transfer of macromolecules after cutaneous thermal injury is unknown. To determine the enhanced absorption pathway, transepithelial transport of horseradish peroxidase (HRP) was examined ultrastructurally after a thermal injury. Within 6 h after the injury, increased HRP uptake was seen in the portal and systemic blood with the maximal increase in uptake measured at 18 h postinjury; permeability returned to normal by 72 h postinjury. Morphologically, the increased uptake was found to be transcellular through ultrastructurally normal intestinal absorptive cells. Occasional focal regions of enhanced HRP uptake were found and this enhanced uptake was attributed to focal intestinal epithelial disruptions. This increase in intestinal permeability represents a transient loss of intestinal barrier function and potentially allows absorption of macromolecules such as endotoxin from the intestinal lumen into the portal circulation early after thermal injury.

The effect of injection or chronic infusion of lipopolysaccharide (LPS) into unanaesthetized rats on the distribution of [99Tcm-]SC has been determined. At a dose of 2.5 mg/kg, LPS injection caused a marked alteration in the distribution of the radiolabelled material, with more uptake being achieved in the lung while less was taken up by the spleen. Kidney and liver uptake were also changed. Chronic infusion of LPS at a similar dose (3 mg/kg in 24 h) caused a marked increase in the uptake of the radioactive material by the lung only. These data are consistent with a working hypothesis that the alterations in RES phagocytic activity of the lung observed in rats subjected to burn trauma could be related in part to LPS, either coming as a bolus, or being continuously presented.

The synthesis of proteoglycans (PG) by normal human skin, and normal and hypertrophic scars were compared using tissue explants in culture. Newly synthesized PG were labelled with [35S]Na2SO4. Significant differences were found in the proportion of [35S]-radio-labelled incorporation of PG in the tissue and accumulation of [35S]PG in culture medium in the different tissues. The rate of PG biosynthesis in all three tissue types occurred in two phases. There was an initial phase of PG synthesis occurring at 0-3 h and a later phase that occurred at 3-18 h [35S]-labelled PG were isolated and characterized by Sepharose CL-6B chromatography and cellulose acetate electrophoresis. The results showed that the hypertrophic scar tissue and its culture medium contained higher proportions of dermatan sulphate (DS), chondroitin sulphate (CS) and DS' PG than the normal skin fractions. These results suggest that abnormal scarring is related to a change in the level of PG synthesis during the burn injury repair process.

The role of haemolysis of blood in the alterations in the uptake of [99mTc]SC ([99mTc]-sulphur colloid) in vivo in the rat has been examined. When the haemolysed blood (produced by first freezing the blood in liquid nitrogen) was infused into synergenic Lewis rats via the tail vein, there was a significant reduction in the uptake of the [99mTc]SC by the spleen, but lung, liver and kidney uptake remained constant. These results suggest that haemolysis of the blood may play a role in the alterations in RES phagocytic activity observed in the spleen following thermal injury.

A model of full-thickness dermal necrosis was produced in rats by the application of liquid nitrogen to a 20% total body surface area of the dorsal skin surface. In this model there was an alteration of reticuloendothelial system phagocytic activity of the lung and spleen as measured by the uptake of technetium 99m-labeled sulfur colloid in vivo. The present results suggest that marked alterations in reticuloendothelial system phagocytic activity can be produced by full-thickness dermal necrosis in the absence of heat.

We have examined the role of neutrophils in the alterations observed in the intestines of rats subjected to 40 per cent surface area scald injury. Histologically, there was no evidence of neutrophilia in the intestinal tissue, and myeloperoxidase activity in mucosal scrapings was not elevated. The distribution of labelled human neutrophils injected into the burned rats showed no enhancement of uptake in the intestines, although there was increased uptake by the lung. The present data suggest that neutrophil migration may not play a role in the alterations in small intestinal function and morphology seen in burn trauma in the rat, but may be a factor in lung damage associated with thermal injury.

The uptake of radiolabelled colloid or bacteria was compared in normal rats and animals subjected to acute burn trauma. The uptake of colloid by the liver was unaffected by burn trauma, but uptake of the labelled bacteria was reduced. Spleen uptake of both colloid and bacteria was reduced by burn trauma while lung uptake was increased. These data are consistent with the hypothesis that acute burn trauma alters reticuloendothelial system phagocytic activity in the rat towards both inert particles and live bacteria.

Small intestinal mucosal weight and nutrient absorption are significantly diminished early after cutaneous thermal injuries. Because these intestinal properties are highly dependent on rates of nucleic acid and protein synthesis, in vivo incorporation of thymidine, uridine, and leucine into small intestinal deoxyribonucleic acid, ribonucleic acid, and proteins were measured. Deoxyribonucleic acid synthesis was markedly decreased with the lowest thymidine incorporation in the jejunum (p less than 0.01); these findings were confirmed by autoradiographic identification of radiolabeled nuclei in the intestinal crypts. Protein synthesis was decreased by 6 h postinjury (p less than 0.01) but had returned to normal by 48 h. Consistent with a decreased rate of protein synthesis, ribonucleic acid synthesis was also decreased 18 h postinjury (p less than 0.01). These decreased deoxyribonucleic acid, ribonucleic acid, and protein synthesis rates are not likely a result of ischemia because in other studies of this injury model, intestinal blood flow was not significantly changed by the burn injury. Potentially, factors initiating the acute inflammatory reaction may directly inhibit nucleic acid and protein synthesis and lead to alterations in nutrient absorption and intestinal barrier function after injury.

The intestinal epithelium normally provides a barrier function that prevents absorption of potentially harmful materials from the intestinal lumen. It has been postulated but never demonstrated that a cutaneous thermal injury will result in increased small-intestinal permeability. In a standardized 20% body surface area full-thickness scald injury, with polyethylene glycol 3350 and horseradish peroxidase used as permeability probes, small-intestinal permeability was examined regionally in an everted intestinal sac model. In the normal animals, the upper (proximal) and lower (distal) small intestine were less permeable to these probes than the middle segment. Within 6 hours after the injury, an increase in the mucosal uptake and transmural permeability was seen in all three small-intestinal segments; the most dramatic increase in permeability occurred in the ileum, p less than 0.01. The maximum increase in permeability was seen at 18 hours, and permeability was normal by 72 hours after the injury. This increase in intestinal permeability may represent a transient failure of the intestinal barrier function and may allow absorption of potentially toxic macromolecules from the intestinal lumen into the portal circulation early after thermal injury. Absorption of these macromolecules, such as endotoxin, may be potentially harmful by direct toxic actions or potentially helpful by activation of the immune system.

Acute burn trauma has been demonstrated to depress reticuloendothelial system (RES) phagocytic activity, which could partially explain the development of septicaemia in burn patients. In the present study we have attempted to determine the role that skin plays in the depression of the RES. One group of Lewis rats was subjected to a 100 degrees C scald burn for 10 s. Eschar was then removed and implanted onto the backs of a second group of normal controls. A third group of Lewis rats were subjected to sham treatment; the eschar of these animals was removed and implanted onto the back of a fourth group of normal rats. The excision sites of the donor animals were immediately covered with Biobrane. Twenty-four hours later the technetium-99m sulphur colloid [( 99mTS]SC) method described earlier (Trop et al., 1989) was used to determine phagocytosis in these four groups of animals. Acute burn trauma produced a marked reduction in colloid uptake by the spleen and a marked increase in the uptake of colloid material by the lung, although no effect was observed on liver or kidney uptake. Implantation of the burn eschar into normal control rats had no statistically significant effect upon colloid uptake. These data suggest that alterations in phagocytic activity of the spleen and lung occur within minutes after burn injury and may be unrelated to the presence of the burn eschar itself.

Because cardiac output decreases after burn injuries, investigators have assumed, based upon dye clearance techniques, that hepatic and intestinal blood flow are also decreased following these injuries. Blood flow to the liver, stomach, small intestine, and kidney was determined by the uptake of 201thallium and 125I-labeled fatty acid (para-125I-phenyl-3-methyl pentanoic acid) in a 20% body surface area scald injury that also included plasma volume replacement resuscitation. Uptake of these radioisotopes was determined 15 minutes, 18 hours, and 72 hours after injury. The uptake of the 201thallium and 125I-labeled fatty acid by the gastrointestinal tissues was not statistically different at any of the time periods after comparison of the injured and control (sham-treated) animals. 201Thallium uptake by the kidney was significantly diminished 15 minutes after the burn injury (P less than 0.01). Based on these blood flow measurement techniques, the data suggest that the 20% body surface area scald injury did not alter blood flow to the liver or gastrointestinal tract within the initial 72 hours after the burn injury even though a decrease in renal blood flow was easily detected. These results suggest that the dysfunction of the gastrointestinal system or hepatic system observed after an acute burn injury is not simply the result of hypovolemic shock, which reduces both renal and mesenteric blood flow. These gastrointestinal and hepatic alterations may be related to a factor or factors other than intestinal ischemia.

The effect of acute burn trauma on phagocytic activity of the reticuloendothelial system measured in vivo with technetium 99m sulfur colloid was examined in rats subjected to acute burn trauma. After the scald injuries (10-second, full-thickness burns) were induced, a reduction in phagocytic activity by the spleen took place with an accompanying increase in the uptake of colloid material by the lungs. Uptake of colloid material by the liver was essentially unchanged. These uptake changes, observed within hours after the inducement of acute burn trauma and apparently continuing for 7 days after burn injury, may explain, in part, the development of septicemia in patients with burns because altered phagocytic activity of the reticuloendothelial system can result in subsequent overabundance of microorganisms and bacteria in the blood.

Diminished mucosal mass and a diminished rate of DNA synthesis by the intestinal mucosa have been identified in the rat after thermal injury. Because these changes may be associated with ischemia, the distribution of intestinal blood flow was studied after a thermal injury and compared with the blood flow distribution after hemorrhagic shock. For the thermal injury, anesthetized animals received a standardized 20% body surface area, full-thickness injury and were given intraperitoneal saline resuscitation. By the use of 46Sc- or 141Ce-labeled microspheres, no changes in intestinal and hepatic blood flow occurred after thermal injury. In contrast, a marked redistribution of blood flow was identified after hemorrhagic shock in which a decrease in arterial blood flow was identified to the stomach and to the small and large intestine. Although clinical shock was not present, the cardiac output decreased to a comparable degree in the hemorrhagic shock and the thermal injury. These studies indicate that although physiological changes in intestinal mucosa can be demonstrated after burn injury, these changes are not due to decreases in mesenteric arterial blood flow.

Hepatic repair and regeneration which is extremely important after thermal injuries can be inhibited by the acute inflammatory reaction. Since thermal injury initiates this acute inflammatory reaction, DNA synthesis was studied in the regenerating liver following this injury. In vivo incorporation of [3H]-thymidine into hepatic DNA, autoradiographic determination of a labeling index, and thymidine kinase activity were determined. Incorporation of [3H]-thymidine into hepatic DNA and labeling indices were markedly diminished at 24 hours if partial hepatectomy and thermal injury were carried out concurrently. After partial hepatectomy, the expected elevations in thymidine kinase activity were inhibited by the thermal injury (p less than 0.01) and elevation of serum fibrinogen, a marker of the acute phase reaction that normally follows thermal injury, was blunted by the partial hepatectomy (p less than 0.05). The combination of thermal injury and partial hepatectomy resulted in a greatly diminished DNA replicative response as compared to partial hepatectomy alone and suggests that multiplicative injury is more likely to result in multi-system failure.

The effect of acute burn trauma, produced by scalding hot water, on rat small intestinal nutrient absorption and DNA synthesis has been examined. Burned rats showed decreased small-intestine mucosal weight and altered small-intestine transport of nutrients (calcium, glucose, or amino acid) in vitro. In addition, there was decreased 3H-thymidine incorporation into intestinal DNA in vivo and decreased intestinal thymidine kinase activity in vitro 18 hours after acute burn. These data suggest that after the severe stress produced by acute burn trauma, there is altered small-intestine nutrient absorption and DNA synthesis. These alterations may affect delivery of nutrients by the gut to the burn patient.

Following acute thermal injury to rats produced by scalding water, there was marked elevation of a number of plasma enzyme activities, including GOT, GPT, and 5'-nucleotidase, suggesting hepatic dysfunction. Changes in plasma enzyme activities were observed within minutes following application of acute burn trauma, and remained elevated for at least one month. The magnitude of the elevations of the plasma enzyme activities was dependent upon the length of time the acute burn trauma was applied to the skin and/or the percentage of skin surface area burned. These changes in plasma enzyme activity correlated with histologic examination of the hepatic tissue, indicating single cell necrosis. These data suggest that acute burn trauma to rats is associated with altered hepatic function.