The influence of burn trauma on the hypothalamus-pituitary axis in normal female subjects

Women are more than twice as likely to die from burns as men in Australia and New Zealand: an unexpected finding of the Burns Evaluation And Mortality (BEAM) Study

While the risk of death after nonthermal trauma and sepsis may be higher for men, sex differences in outcome after burns are inconsistently reported. The Burns Evaluation And Mortality Study examined the outcomes of all patients admitted after thermal injury to the intensive care unit (ICU) at 8 of 9 burn referral centers in Australia and New Zealand between January 1, 2005, and December 31, 2011. There were 348 women and 1367 men treated for acute burns. Women were older, had more extensive burns, and higher severity of illness scores. Women spent longer in hospital and in ICU than men. Mortality among women was higher than in men (21% vs 8.3%, P<.001). Trends toward a survival disadvantage for women were seen across all ages, at all levels of severity of illness, at every proportion of body surface area burnt, and across all centers. After adjusting for confounding factors, women had more than double the risk of death compared with men (odds ratio, 2.35; 95% confidence interval, 1.38-4.01; P=.002). Our study conclusively shows worse outcomes for women with burns admitted to ICUs in Australia and New Zealand. Further research is required to determine why this is happening.

The endocrine response to severe burn trauma

The endocrine system is frequently altered after a major burn trauma. Besides the endocrine response to stress characterized by hypercortisolism, several hypothalamus-hypophysis-target gland axes are rapidly perturbed within a few days. These alterations can persist in the long term and deserve an appropriate treatment. Disturbances in water clearance and glucidic metabolism are also common and need to be diagnosed and corrected to decrease morbidity in such patients. Bone and mineral metabolism is deeply compromised and requires correction of mineral abnormalities in order to improve symptoms and prevent bone loss. No large prospective and/or intervention trials are available to date to elaborate age-related, evidence-based recommendations to monitor and treat burn-related endocrine alterations.

Profound effects of burn and ethanol on proinflammatory cytokines of the reproductive axis in the male mouse

Thermal injury is often associated with previous ethanol exposure, and close to 50% of patients admitted to a burn unit have a potentially high blood ethanol level. Cellular mechanisms by which ethanol and/or burn affect the hypothalamic-pituitary-gonadal (HPG) axis are not entirely understood. However, it is known that the proinflammatory cytokines, tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 influence negatively on the endocrine functions of the HPG. We report a time course study (6, 12, 24, and 48 hours) of the effects of ethanol, burn, or the combination of burn/ethanol on proinflammatory cytokines of the hypothalamus, pituitary and testes of male C57Bl/6 mice. We found that there were highly significant increases in each of these cytokines caused by ethanol, burn, and burn/ethanol compared with sham/vehicle (P < .001). This was true in hypothalamus, pituitary, and testes. Because these cytokines generally reduce reproductive function, it may be that proinflammatory cytokines of HPG axis mediate the deleterious effects of burn and/or ethanol on mammalian reproduction.

Gender differences in mortality following burn injury

Clinical and experimental studies have demonstrated higher mortality following nonthermal trauma among males compared with females. To date, few clinical retrospective studies have focused on gender differences in outcome following burn injury with respect to age. All patients admitted to the University of Alabama at Birmingham (UAB) Burn Center between January 1994 and December 2000 were selected for inclusion in the study. Gender differences in demographic, clinical, and outcome characteristics were compared. Unadjusted and adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for the association between mortality and gender, both overall and stratified by age. Over the 7-year study period, 1229 males and 382 females were admitted to the UAB Burn Center, and mortality rates were 7.2% and 13.4%, respectively (P = 0.0002). Female patients were more likely to be older, of the black race, and in poorer health. In addition, females were more likely to suffer flame and scald burns. The association between mortality and gender was modified by age. Up to age 60, mortality rates among females were over twice that of males (OR 2.3, 95% Cl 1.4-3.8); however, no difference was noted among those 60 and older (OR 0.9, 95% Cl 0.5-1.6). These associations persisted following adjustment for potentially confounding variables. Causes and timing of death were similar for males and females. Women less than 60 years of age who sustain burn injuries have an increased risk of death compared with males. Differences in the natural history of nonthermal trauma and burn injury may provide insight regarding these divergent findings.

Estrogen regulation of immune responses after injury

There is a naturally occurring gender difference in immune responses which persists after traumatic injury. Physiological levels of 17beta-estradiol (E(2)) are immunostimulatory, whereas high pregnancy and superphysiological levels are immunosuppressive. In contrast, at all concentrations, testosterone suppresses immune responses. Evidence from this laboratory and others suggest that the gender difference in immune responses after injury is mediated in part by alterations in the circulating levels of gonadal steroid hormones through modulation of production of inflammatory and immunoregulatory cytokines, including interleukin-6 (IL-6). Aberrant production of IL-6 is known to be an important mediator of immunity after injury. Since E(2) is a critical regulator of IL-6 production and overall immune function, it suggests gender specific therapies should be considered for the treatment of patients.

Testosterone administration in severe burns ameliorates muscle catabolism

OBJECTIVE

To assess the effects of testosterone administration on muscle protein metabolism after severe burn injury. We hypothesized that restoration of blood testosterone concentrations would restore an important anabolic stimulus to skeletal muscle, and would further increase the anabolic response of muscle to amino acid supplementation.

DESIGN

Pre- and postintervention trial conducted between September 1997 and July 1999.

SETTING

Burn intensive care unit.

PATIENTS

Six severely burned male patients (>70% total body surface area).

INTERVENTION

Testosterone enanthate, 200 mg/wk (intramuscularly), for 2 wks.

MEASUREMENTS AND MAIN RESULTS

Muscle protein synthesis, breakdown, and amino acid kinetics were determined. After a basal period in each study, we subsequently investigated the response to acute amino acid supplementation during enteral feeding. Total testosterone increased significantly from baseline to the low normal range after 1 wk, and to upper normal range after two injections (p <.001). Protein synthesis was unchanged, however, protein synthetic efficiency increased 2-fold (p <.01). Protein breakdown decreased almost 2-fold after testosterone enanthate (p <.05), resulting in an improvement in net amino acid balance to a value that was approximately zero (p <.0001). Amino acid supplementation at either time point provided no additional effects.

CONCLUSIONS

Restoration of blood testosterone can ameliorate the muscle catabolism of severe burn injury with normal feedings.

Decreased cerebral glucose utilization in rats during the ebb phase of thermal injury

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.

Hormonal dysregulations in severe burns

Measurements of the concentrations of pituitary, thyroid and gonadal hormones have been made under both basal conditions and after adequate stimulation using a combined arginine TRH-LHRH stimulation test in 10 patients with deep burns covering between 30 and 70 per cent of the body surface during the first 20 days after injury. The most remarkable changes were found in the pituitary-gonadal system with testosterone concentrations significantly decreased at all times during the periods of study. Stimulation with LHRH resulted in a prompt response of FSH and LH during the first 10 days after burning whereas between 10 and 20 days after injury the basal concentrations for both hormones were significantly lower and showed a delayed response to stimulation. During the period of early fluid therapy large amounts of glucose without additional insulin were given, resulting in elevated blood glucose and high plasma insulin levels. It is concluded that normal pancreatic insulin production is sufficient to avoid excessive hyperglycaemia even during the period soon after burning. Compared with the findings in control patients the HGH levels in burned patients were not significantly different at any time during the periods of study.

Burn encephalopathy in children

Among 287 children with burns treated over a recent two-year period, 13 (5%) showed evidence of encephalopathy. The major clinical symptoms were an altered sensorium and seizures. The majority of symptoms began later than 48 hours after the burn and were accompanied by multiple metabolic aberrations including hypocalcemia. Three children had a relapsing course, and 1 had temporarily enlarged cerebral ventricles. Eleven children improved to normal. In the majority of instances, burn encephalopathy probably reflects central nervous system dysfunction resulting from complex metabolic, hematological, and hemodynamic abnormalities rather than from a single metabolic abnormality.