Arterial blood pressure immediately after thermal injury: the role of anesthesia

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.

Additive effects of thermal injury and infection on gut permeability

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.

Injury-induced inhibition of fat absorption

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.

Absence of change in hepatic lactate metabolism after burn injury

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.

Comparison of the effects of interleukin-1 beta on proteoglycan synthesis by human skin and post-burn normal scar explant cultures

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.

Influence of prenatal corticosteroids on bacterial colonization in the newborn rat

The interactions between bacteria and the host's intestinal barrier appear to be important regulators of bacterial colonization. In this study we investigated the effect of prenatal corticosteroids, known to accelerate the intestinal maturation of newborn rats, on bacterial colonization in the rat pup. Pregnant rats were treated with either cortisone acetate or normal saline on days 18-21 of gestation and were allowed to deliver spontaneously. The pups, after normal delivery, were sacrificed at different times during the first 10 days of life. The entire small intestine was removed, and each lumen was flushed to exclude nonadherent, transient organisms and homogenized. Tenfold dilutions were plated on horse-blood agar (total bacteria) and MacConkey's medium (gram-negatives). Quantitation and bacterial typification was determined after 24 h of incubation at 37 degrees C. Total bacteria and gram-negatives found in association with the mucosa were significantly lower in pups prenatally treated with steroids. These changes were not related to any changes in motility or intraluminal digestion. This suggests that the developmental condition of the host's intestinal barrier may be an important regulator of the bacterial microenvironment of the newborn small intestinal mucosa.

Ontogeny of Ia messenger RNA in the mouse small intestinal epithelium is modulated by age of weaning and diet

BACKGROUND

Exogenous antigenic peptides are presented to T cells by class II major histocompatibility complex (Ia) molecules on the surface of antigen-presenting cells. Class II-associated invariant chain (Ii) is also required for effective antigen presentation. Because messenger RNAs (mRNAs) for Ii chain and for class II I-A beta chain appear in the mouse intestinal epithelium after weaning, experiments were conducted to test the effect of age of weaning and diet on the appearance of Ia and Ii mRNA.

METHODS

Four litters were split at day 17; one half was weaned and the other remained with the mother until day 24. On day 23, 25, 27, and 29, enterocytes were isolated from full-length small intestine by vascular perfusion with 30 mmol/L ethylenediaminetetraacetic acid, and the RNA was extracted.

RESULTS

Appearance of Ii and I-A beta was significantly delayed by late weaning, as judged by RNA hybridization blots (Ii chain) and complementary DNA amplification (I-A beta chain). In mice on elemental diets, the appearance of Ii and I-A beta chain was delayed compared with littermates reared on standard chow. Ii mRNA failed to appear in mice maintained on the elemental diet by day 40, despite normal growth.

CONCLUSIONS

Appearance of mRNA for both Ia and Ii depends on the introduction of a complex diet and not the "stress" of weaning or elimination of breast milk. Introduction of foreign dietary antigens or development of an altered intestinal flora may contribute to this process.

Thermal injury-induced changes in the rat intestine brush border cytoskeleton

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.

Differential regulation of B7 mRNA in enterocytes and lymphoid cells

To investigate the molecular details of antigen presentation by cells of lymphoid or epithelial origin, we compared B7 mRNA regulation in intestinal epithelium with that in spleen, since both cell types express class II major histocompatibility complex (MHC) and present antigen. As measured by cDNA amplification using sequence-specific primers, I-A beta mRNA content was found to be similar in mouse full-thickness small intestine, isolated intestinal epithelial cells and spleen. However, in contrast to I-A beta, B7 mRNA intestinal epithelial cell content was markedly lower than in spleen and whole small bowel; cardiac RNA was negative for both sequences. Administration of intraperitoneal interferon-gamma (IFN-gamma) (10(5) U daily for 2 days) to adult mice resulted in an increase in I-A beta mRNA in epithelial cells, but did not alter levels of B7 mRNA. In addition, exposure of the IEC-6 rat cell line to the IFN-gamma resulted in a dose-dependent increase in I-A beta mRNA without altering levels of B7 mRNA. Thus, an apparent dichotomy exists in regulation of B7 and I-A beta gene expression in rodent intestinal epithelial cells. Since maximal T-cell response to splenocytes depends on B7, the absence of B7 mRNA in intestinal epithelium may be a factor in determining why antigen-presenting enterocytes normally do not elicit damaging T-cell proliferative responses.

Isolation and long-term culture of human hepatocytes

Pressure-controlled perfusion of specimens of surgical hepatic resection produced improved yields of human hepatocytes for studies of long-term cultures. The effect of an extracellular matrix configuration on albumin secretion was evaluated by culture on a single layer of collagen or between double layers of collagen gel with Dulbecco's modified Eagle and Williams E media. Hepatocytes from 12 patients were maintained for more than 30 days, and in five of 12 experiments cells were cultured beyond 2 months. In the double gels the cells demonstrated typical polygonal liver cell morphology and higher albumin secretion (p < 0.01) up to 65 days; in contrast, in the single gels cells spread horizontally, and albumin secretion declined rapidly within 3 weeks. A comparison of media formulations showed that maximum albumin secretion occurred 5 days later but was maintained significantly longer with Dulbecco's medium (p < 0.01). The simple addition of a second layer of gelled collagen forming a collagen sandwich significantly stabilizes and supports the long-term culture of human hepatocytes.

Effect of heta-starch colloidal solutions on reticuloendothelial phagocytic system (RES) function in burned and infected rats

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.

Core body temperature responses immediately after cutaneous thermal injury in rats

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.

Effect of chronic interleukin-2 treatment on RES phagocytic activity in the rat

The effect of chronic interleukin-2 (IL-2) injection upon reticuloendothelial system (RES) function in the rat has been determined. Seven-day treatments with two doses of human recombinant IL-2 resulted in a dramatic reduction in the phagocytic uptake of the liver and spleen, while increasing the weight of both organs. There were dramatic histological changes in the intestine, liver and spleen as well. These results suggest that the chronic use of IL-2 can result in hepatic dysfunction, which is associated with altered RES phagocytic function.

Ontogeny of class II MHC mRNA in the mouse small intestinal epithelium

MHC Class II (Ia) and invariant chain cooperate in the presentation of exogenous antigen by antigen presenting cells to T-helper cells. Both glycoproteins have been identified in the small intestine of the mature mouse. In this study, we examine the ontogeny of mRNA for three molecules; (Ii31, Ii41 and I-A beta) in whole intestine and in isolated epithelial cells. When RNA from whole intestine was analysed in northern blots using cDNA probe, Ii31 mRNA was present in Day 10 mice and at each 5 day time point thereafter; Ii41 and I-A beta were not detected by this technique. To examine ontogeny of Ii chain mRNA in enterocytes, RNA was purified from an enriched population of epithelial cells isolated after systemic perfusion with 30 mM EDTA in Day 21 and Day 28 and adult mice. Ii chain mRNA was not detected until Day 28 by blot hybridization. Reverse transcription of mRNA and amplification of the resultant cDNA by PCR revealed Ii41 and I-A beta as well as Ii31. RNA from Day 21 epithelial cells required five additional amplification cycles to attain cDNA levels equivalent to those found in Day 28 cells for Ii chain, and 10 additional cycles for I-A beta. In conclusion, Ii31, Ii41 and I-A beta mRNA increase rapidly in the enterocyte after weaning.

Case report: complete lung collapse--an unusual presentation of cryptococcosis

Cryptococcosis presenting as an intrabronchial mass is not a recognized cause of complete lung collapse. This case report illustrates this extremely rare manifestation of pulmonary cryptococcosis, which mimicked primary pulmonary carcinoma clinically, radiologically and bronchoscopically.

Percutaneous drainage of a thigh haematoma: case report of an unusual radiographic appearance

We present a case of fat necrosis in the thigh of a ten year old girl, resulting in unusual multiple, ovoid filling defects seen in the residual cavity following drainage of a subcutaneous haematoma. No similar cases have been found on review of the literature. The appearance is described to aid diagnosis at the time of initial cavity drainage, avoiding the need for further investigation.

Effect of thermal injury on transfer of IR22 IgA myeloma protein into bile in the rat

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.

Effect of acute and chronic lipopolysaccharide (LPS) administration on reticuloendothelial system (RES) phagocytic activity in vivo

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.

Reduction in biliary IgA after burn injury. Role of diminished delivery via the thoracic duct and of enhanced loss from the systemic circulation

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.

Increased transcellular permeability of rat small intestine after thermal injury

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.

Effect of ethanol administration on plasma glycerol levels in the rat

Many mechanisms have been postulated as being responsible for the fatty liver resulting from ethanol ingestion. Lipid mobilization has been strongly implicated in both acute and chronic ethanol administration--the difference between the two lying in the source of the fat. In the acute situation, the lipid is mobilized from depot fat, whereas in the chronic situation, it apparently comes from the diet. One possibility not explored is the mobilization of glycerol. This substance is the backbone of triglyceride. Hence, an influx of glycerol to the liver coupled with increased amounts of fatty acids could help explain, in part, the fatty liver resulting from alcohol administration. The purpose of the following study was to determine if such an effect does occur.