Phase-related changes in tissue energy reserves during hemorrhagic shock

Ringer's lactate solution enhances the inflammatory response during fluid resuscitation of experimentally induced haemorrhagic shock in rats

INTRODUCTION

Hemorrhagic shock leads to systemic oxygen deficit (hypoxaemia) that results in systemic inflammatory response syndrome (SIRS), a recognised cause of late mortality in this case. The aim of this study was to analyse the impact of fluid resuscitation, using two Ringer solutions, on the microcirculation changes that take place during experimentally induced haemorrhagic shock.

MATERIAL AND METHODS

A model of the rat cremaster muscle was used to assess microcirculation in vivo. The experimental groups (n = 10 each) included: control (CTRL); shock (HSG); Ringer's acetate (RAG); and Ringer's lactate (RLG). Microhaemodynamic parameters were measured during the experiment.

RESULTS

A statistically significantly higher level of leukocytes, both those attached to the endothelium and those located in the extravascular space (p < 0.05), was reported in the lactate Ringer (LR) group compared with the AR group. There were significant differences in the activity of A3 arterioles compared with A1 and A2 arterioles. Ringer's lactate solution seemed to the inflammation response during fluid resuscitation from haemorrhagic shock. A3 arterioles are likely to play a role as a pre-capillary sphincter in the skeletal muscle.

CONCLUSIONS

The present study revealed that fluid resuscitation with Ringer's lactate solution exacerbates inflammation in the skeletal muscle. It is worth noting that Ringer's acetate solution reduces local inflammation and could therefore be recommended as the "first line" crystalloid of the fluid resuscitation during haemorrhagic shock.

Mitochondrial function in hypoxic ischemic injury and influence of aging

Mitochondria are a major target in hypoxic/ischemic injury. Mitochondrial impairment increases with age leading to dysregulation of molecular pathways linked to mitochondria. The perturbation of mitochondrial homeostasis and cellular energetics worsens outcome following hypoxic-ischemic insults in elderly individuals. In response to acute injury conditions, cellular machinery relies on rapid adaptations by modulating posttranslational modifications. Therefore, post-translational regulation of molecular mediators such as hypoxia-inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), c-MYC, SIRT1 and AMPK play a critical role in the control of the glycolytic-mitochondrial energy axis in response to hypoxic-ischemic conditions. The deficiency of oxygen and nutrients leads to decreased energetic reliance on mitochondria, promoting glycolysis. The combination of pseudohypoxia, declining autophagy, and dysregulation of stress responses with aging adds to impaired host response to hypoxic-ischemic injury. Furthermore, intermitochondrial signal propagation and tissue wide oscillations in mitochondrial metabolism in response to oxidative stress are emerging as vital to cellular energetics. Recently reported intercellular transport of mitochondria through tunneling nanotubes also play a role in the response to and treatments for ischemic injury. In this review we attempt to provide an overview of some of the molecular mechanisms and potential therapies involved in the alteration of cellular energetics with aging and injury with a neurobiological perspective.

Arterial blood gases, electrolytes, and metabolic indices associated with hemorrhagic shock: inter- and intrainbred rat strain variation

We have previously shown interstrain variation (indicating a genetic basis), and intrastrain variation in survival time after hemorrhage (STaH) among inbred rat strains. To assist in understanding physiological mechanisms associated with STaH, we analyzed various arterial blood measures (ABM; pH, Paco2, oxygen content, sodium, potassium, glucose, bicarbonate, base excess, total CO2, and ionized calcium) in inbred rats. Rats from five inbred strains (n = 8-10/strain) were catheterized and, ≈ 24 h later, subjected to a conscious, controlled, 47% hemorrhage. ABM were measured at the start (initial) and end (final) of hemorrhage. Inter- and intrainbred strain variations of ABM were quantified and compared, and correlations of ABM with STaH were determined. All final ABM values and some initial ABM values were different among strains. Most ABM changed (Δ) during hemorrhage, and these changes differed among strains (P <0.03). Some strain-dependent correlations (r ≥ 0.7; P ≤ 0.05) existed between ΔABM and STaH (e.g., BN/Mcwi, ΔK(+), r = -0.84). Dark Agouti rats (longest STaH) had the smallest ΔPaco2, ΔHCO3(-), and Δbase excess, and the highest final glucose. High coefficients of variation (CVs, >10%), strain-specific CVs, and low intraclass correlation coefficients (rI < 0.5) defined the large intrastrain ABM variation that exceeded interstrain variation for most ABM. These results suggest that some ABM (K(+), Paco2, glucose, oxygen content) could predict subsequent STaH in an inbred rat strain-dependent manner. We speculate that whereas genetic differences may be responsible for interstrain variation, individual-specific epigenetic processes (e.g., DNA methylation) may be partly responsible for both inter- and intrastrain ABM variation.

Geldanamycin inhibits hemorrhage-induced increases in caspase-3 activity: role of inducible nitric oxide synthase

Hemorrhage has been shown to increase inducible nitric oxide synthase (iNOS) and deplete ATP levels in tissues and geldanamycin limits both processes. Moreover, it is evident that inhibition of iNOS reduces caspase-3 and increases survival. Thus we sought to identify the molecular events responsible for the beneficial effect of geldanamycin. Hemorrhage in mice significantly increased caspase-3 activity and protein while treatment with geldanamycin significantly limited these increases. Similarly, geldanamycin inhibited increases in proteins forming the apoptosome (a complex of caspase-9, cytochrome c, and Apaf-1). Modulation of the expression of iNOS by iNOS gene transfection or siRNA treatment demonstrated that the level of iNOS correlates with caspase-3 activity. Our data indicate that geldanamycin limits caspase-3 expression and protects from organ injury by suppressing iNOS expression and apoptosome formation. Geldanamycin, therefore, may prove useful as an adjuvant in fluids used to treat patients suffering blood loss.

The influence of hemorrhagic shock on etomidate: a pharmacokinetic and pharmacodynamic analysis

We studied the influence of hemorrhagic shock on the pharmacology of etomidate in swine. Sixteen swine were randomly assigned to control and shock groups. The shock group was bled to a mean arterial blood pressure of 50 mm Hg and held there until 30 mL/kg blood was removed. Etomidate 300 micro g x kg(-1) x min(-1) was infused for 10 min to both groups. Fifteen arterial samples were collected until 180 min after the infusion began to determine drug concentration. Pharmacokinetic variables for each group were estimated by using a three-compartment model. The bispectral index scale was used as a measure of drug effect. The pharmacodynamics were characterized by using a sigmoid inhibitory maximal effect model. The raw data revealed a 25% increase in the plasma etomidate concentration at the end of the 10-min infusion which resolved after termination of the infusion in the shock group. The pharmacokinetic analysis revealed subtle changes in the variable estimates between groups. The etomidate infusion produced a similar Bispectral Index Scale change in both groups. These results demonstrated that, unlike the influence of hemorrhagic shock on other sedative hypnotics and opioids, moderate hemorrhagic shock produced minimal changes in the pharmacokinetics and no change in the pharmacodynamics of etomidate.

IMPLICATIONS

Hemorrhagic shock produced minimal changes in the pharmacokinetics and no change in the pharmacodynamics of etomidate in swine. These results suggest that, unlike other sedative hypnotics and opioids, minimal adjustment in the dose of etomidate is required to achieve the same drug effect during hemorrhagic shock.

Intraperitoneal, but not enteric, adenosine administration improves survival after volume-controlled hemorrhagic shock in rats

OBJECTIVE

To circumvent the potential adverse systemic side effects of adenosine, this study explored the potential benefit of intraperitoneal or enteric adenosine on survival and inflammatory responses after volume-controlled hemorrhagic shock.

DESIGN

Prospective, randomized, and blinded. A three-phase, volume-controlled hemorrhagic shock model was used: hemorrhagic shock phase (120 mins), resuscitation phase (60 mins), and observation phase (72 hrs). Three groups were compared: controls, intraperitoneal adenosine, and enteric adenosine.

SETTING

Animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Starting at 20 mins of hemorrhagic shock and continuing through the resuscitation phase, all three groups received both intraperitoneal lavage and repeated bolus injections into the ileum of vehicle (normal saline) or adenosine. In the intraperitoneal adenosine group (n = 10), adenosine solution (0.1 mM) was used for intraperitoneal lavage. In the enteric adenosine group (n = 10), adenosine (1.0 mM) was injected into the ileum. Blood cytokine concentrations and leukocyte infiltration in lungs and liver were studied in 12 separate rats (control and intraperitoneal adenosine, n = 6 each) with the same hemorrhagic shock model at resuscitation time 1 hr or 4 hrs.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and heart rate were similar between the three groups during hemorrhagic shock and resuscitation. Potassium, lactate, and blood urea nitrogen concentrations were lower and arterial pH was higher in the intraperitoneal and enteric adenosine groups compared with the control group (both p <.05). Survival time to 72 hrs was longer in the intraperitoneal adenosine group than in the control group(p <.05). Neither plasma interleukin-1beta, interleukin-6, interleukin-10, and tumor necrosis factor-alpha concentrations nor leukocyte infiltration in the lungs and liver was different between the control and intraperitoneal adenosine groups.

CONCLUSIONS

The administration of adenosine via the intraperitoneal route improves survival time after severe volume-controlled hemorrhagic shock in rats without worsening hypotension or bradycardia. This beneficial effect may not be attributable to effects of adenosine on the inflammatory response.

Adrenergic blockade reduces skeletal muscle glycolysis and Na(+), K(+)-ATPase activity during hemorrhage

BACKGROUND

Recent evidence suggests that hyperlactatemia in shock may reflect accelerated aerobic glycolysis linked to activity of the Na(+), K(+)-ATPase rather than hypoxia. Epinephrine stimulates glycolysis in resting muscle largely by stimulating Na(+), K(+)-ATPase activity. This study evaluates the effects of hemorrhagic shock, with and without combined alpha- and beta-adrenergic receptor blockade, on lactate production, glycogenolysis, Na(+)-K(+) pump activity, and high-energy phosphates in rat skeletal muscle.

METHODS

Male Sprague-Dawley rats in four treatment groups were studied: unhemorrhaged control not receiving blockers (CN), controls receiving blockers (CB), shocked animals not receiving blockers (SN), and shocked rats receiving blockers (SB). Shocked rats (SN and SB) were bled to a MAP of 40 mm Hg, maintained for 60 min. Blocker groups (CB and SB) received propranolol and phenoxybenzamine. Arterial blood was drawn for plasma lactate, epinephrine, norepinephrine, and gas analysis. Lactate, glycogen, glucose 6-phosphate, ATP, phosphocreatine, and intracellular Na(+) and K(+) were determined in extensor digitorum longus and soleus muscles. For comparison, muscles were exposed to epinephrine and/or ouabain in vitro.

RESULTS

With the exception of P(a)CO(2), HCO(3), and base excess in the SN group, no significant differences in arterial blood gas parameters were noted. Adrenergic blockade significantly reduced plasma lactate concentration. In shocked rats, adrenergic blockade significantly reduced muscle lactate and glucose 6-phosphate accumulation. Intracellular Na(+):K(+) ratio was decreased in SN rats, implying increased Na(+)-K(+) pump activity. Adrenergic blockade raised the intracellular Na(+):K(+) ratio in shocked animals, implying decreased pump activity. Epinephrine exposure in vitro stimulated muscle lactate production, raised glucose 6-phosphate content, and significantly reduced soleus phosphocreatine stores.

CONCLUSIONS

Neither hypoxia nor defective oxidative metabolism appeared responsible for increased glycolysis during hemorrhagic shock. Adrenergic blockade concurrently reduced plasma lactate, muscle levels of lactate and glucose 6-phosphate, and muscle Na(+)-K(+) pump activity during shock. Rapid skeletal muscle aerobic glycolysis in response to increased plasma epinephrine levels may be an important contributor to increased glycolysis in muscle and increased plasma lactate during hemorrhagic shock.

Is gut the "motor" for producing hepatocellular dysfunction after trauma and hemorrhagic shock?

BACKGROUND

Although studies suggest that the gut may be the "motor" responsible for producing sepsis and multiple organ failure after injury, it is not known whether enterectomy prior to the onset of hemorrhage alters proinflammatory cytokines TNF and IL-6 and, if so, whether hepatocellular dysfunction and damage are prevented or attenuated under such conditions.

MATERIALS AND METHODS

Under methoxyflurane anesthesia, an enterectomy in the rat was performed by excision of the duodenum, jejunum, and ileum. The rats were then bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximal shed volume was returned in the form of Ringer's lactate. The animals were then resuscitated with four times the volume of shed blood with Ringer's lactate over 1 h. At 1.5 h after the completion of resuscitation, hepatocellular function [i.e., the maximal velocity (Vmax) and transport efficiency (Km) of indocyanine green (ICG) clearance] was assessed by an in vivo ICG clearance technique. Blood samples were taken for the measurement of TNF, IL-6, and liver enzymes (i.e., SGPT and SGOT). Cardiac output and microvascular blood flow were determined by ICG dilution and laser Doppler flowmetry, respectively.

RESULTS

The increase in circulating levels of TNF but not IL-6 was prevented by enterectomy prior to hemorrhage. The reduced Vmax and K(m) and elevated SGPT and SGOT following hemorrhage and resuscitation, however, were not significantly affected by prior enterectomy. Moreover, enterectomy before hemorrhage further reduced hepatic perfusion.

CONCLUSION

Since enterectomy prior to the onset of hemorrhage does not prevent or attenuate the reduced ICG clearance and elevated liver enzymes despite downregulation of TNF production, it appears that the small intestine does not play a significant role in producing hepatocellular dysfunction and injury following trauma and hemorrhagic shock.

Improvement of survival from hemorrhagic shock by enterectomy in rats: finding to implicate the role of the gut for irreversibility of hemorrhagic shock

OBJECTIVE

This study used a Wiggers shock model to investigate the effect of the removal of the intestines on the outcome of hemorrhagic shock.

METHODS

Rats were subjected to laparotomy for the removal of the entire small and large intestines (experimental group) or a sham operation (control group) before bloodshedding. During the period of shock, animals were maintained at 30-35 mm Hg arterial pressure for 2 hours. After reinfusion of the shed blood, rats were observed for over 3 hours for survival. The average volumes (mean +/- SEM) of shed blood were 6.84 +/- 0.23 mL (experimental group) and 6.49 +/- 0.39 mL (control group), with no significant difference between the two (p > 0.05).

RESULTS

This protocol resulted in a 42% mortality (11 of 26) in the control group and 0% mortality (0 of 25) in the experimental group (p < 0.005, chi2). Moreover, in the survivors, the mean arterial pressure was significantly lower in the control (65.7 +/- 4.3 mm Hg) than in the experimental group (78.2 +/- 3.5 mm Hg) at the end of the experiment (p < 0.05). Comparing volume status, neither serial hematocrit values nor body weight changes through the experiment had a significant difference between the two groups (p's > 0.05). Serial quantitation of blood levels of tumor necrosis factor-alpha (TNF-alpha) revealed that systemic TNF-alpha concentrations peaked at 4 hours after shock in both groups. TNF-alpha levels were not reduced by enterectomy. Instead, the peak concentrations were significantly higher in the enterectomized (387.5 +/- 36.5 pg/mL, n = 13) than in the sham-enterectomized group (175.7 +/- 35.9 pg/mL, n = 12,p < 0.001). Limulus assay, used to detect endotoxins in the blood at 2 hours after restoration of blood volume, showed no endotoxemia in any specimen from either group. Four hours after hemorrhagic shock, blood levels of platelet-activating factor, quantitated by the radioimmunoassay method, were 2.88 +/- 0.18 ng/mL (experimental group, n = 8) and 2.32 +/- 0.32 ng/mL (control group, n = 6). The difference between these two means was not significant (p > 0.05). Measurement of hepatic adenosine triphosphate (ATP) by the luminometric method showed that hepatic ATP contents were significantly reduced in both groups after shock (p's < 0.05). However, a higher magnitude of hepatic ATP depletion occurred in the control group; significantly lower amounts of ATP in the liver tissues of the sham-enterectomized group (367 +/- 95 nmol/g, n = 7) than in that of the enterectomized group (870 +/- 100 nmol/g, n = 13) were observed at 5 hours after shock (p < 0.05).

CONCLUSIONS

These experimental findings show that, in the absence of the intestines, hemorrhagic shock is associated with both an improved outcome and higher hepatic ATP levels in rats, suggesting the importance of intestinal participation in the process leading to hepatic ATP depletion as well as irreversibility in shock.