A Role for Angiotensin II in the Activation of Extracellular Signal-Regulated Kinases in the Liver During Hemorrhagic Shock

Inhaled, nebulized sodium nitrite protects in murine and porcine experimental models of hemorrhagic shock and resuscitation by limiting mitochondrial injury

OBJECTIVE

The cellular injury that occurs in the setting of hemorrhagic shock and resuscitation (HS/R) affects all tissue types and can drive altered inflammatory responses. Resuscitative adjuncts hold the promise of decreasing such injury. Here we test the hypothesis that sodium nitrite (NaNO2), delivered as a nebulized solution via an inhalational route, protects against injury and inflammation from HS/R.

METHODS

Mice underwent HS/R to a mean arterial pressure (MAP) of 20 or 25 mmHg. Mice were resuscitated with Lactated Ringers after 90-120 min of hypotension. Mice were randomized to receive nebulized NaNO2 via a flow through chamber (30 mg in 5 mL PBS). Pigs (30-35 kg) were anesthetized and bled to a MAP of 30-40 mmHg for 90 min, randomized to receive NaNO2 (11 mg in 2.5 mL PBS) nebulized into the ventilator circuit starting 60 min into the hypotensive period, followed by initial resuscitation with Hextend. Pigs had ongoing resuscitation and support for up to four hours. Hemodynamic data were collected continuously.

RESULTS

NaNO2 limited organ injury and inflammation in murine hemorrhagic shock. A nitrate/nitrite depleted diet exacerbated organ injury, as well as mortality, and inhaled NaNO2 significantly reversed this effect. Furthermore, NaNO2 limited mitochondrial oxidant injury. In porcine HS/R, NaNO2 had no significant influence on shock induced hemodynamics. NaNO2 limited hypoxia/reoxia or HS/R-induced mitochondrial injury and promoted mitochondrial fusion.

CONCLUSION

NaNO2 may be a useful adjunct to shock resuscitation based on its limitation of mitochondrial injury.

Resuscitation after hemorrhagic shock: the effect on the liver--a review of experimental data

The liver is currently considered to be one of the first organs to be subjected to the hypoxic insult inflicted by hemorrhagic shock. The oxidative injury caused by resuscitation also targets the liver and can lead to malfunction and the eventual failure of this organ. Each of the various fluids, vasoactive drugs, and pharmacologic substances used for resuscitation has its own distinct effect(s) on the liver, and the anesthetic agents used during surgical resuscitation also have an impact on hepatocytes. The aim of our study was to identify the specific effect of these substances on the liver. To this end, we conducted a literature search of MEDLINE for all types of articles published in English, with a focus on articles published in the last 12 years. Our search terms were "hemorrhagic shock," "liver," "resuscitation," "vasopressors," and "anesthesia." Experimental studies form the majority of articles found in bibliographic databases. The effect of a specific resuscitation agent on the liver is assessed mainly by measuring apoptotic pathway regulators and inflammation-induced indicators. Apart from a wide range of pharmacological substances, modifications of Ringer's Lactate, colloids, and pyruvate provide protection to the liver after hemorrhage and resuscitation. In this setting, it is of paramount importance that the treating physician recognize those agents that may attenuate liver injury and avoid using those which inflict additional damage.

Heme oxygenase 1 protects against hepatic hypoxia and injury from hemorrhage via regulation of cellular respiration

Heme oxygenase 1 (HO-1) is an important regulator of the cellular response to stress and inflammation. These investigations test the hypothesis that HO-1 overexpression protects against hemorrhage-induced hypoxia by regulating cellular respiration and oxygen availability. Male C57BL/6 mice or primary mouse hepatocytes were treated with adenoviral gene transfer of HO-1 (AdHO-1) or beta-galactosidase (AdLacZ). Mice were subjected to hemorrhagic shock and resuscitation or cannulation without hemorrhage. AdHO-1 prevented hemorrhagic shock/resuscitation-induced liver injury. In addition, AdHO-1 prevented hemorrhage-induced liver hypoxia and depletion of adenosine triphosphate. In vitro, HO-1 overexpression resulted in decreased cellular respiration under hypoxic conditions as determined by oxygen consumption and cytochrome c oxidase activity. This resulted in increased intracellular oxygen levels in the setting of low oxygen tensions. In conclusion, HO-1 overexpression protects the liver against hemorrhage-induced injury. This may be secondary to the ability of HO-1 to protect against bioenergetic failure via regulation of cellular respiration.

Systematic analysis of the salutary effect of estrogen on cardiac performance after trauma-hemorrhage

Although 17beta-estradiol (estrogen) and estrogen receptor (ER) agonist administration after trauma-hemorrhage improves cardiac function, it remains unknown what the optimal estrogen or ER agonist dosage is to elicit this beneficial effect. To study this, the dose-dependent effects of estrogen, propylpyrazole triol (ER-alpha agonist), and diarylpropionitrile (DPN; ER-beta agonist) on heart performance (+dP/dt) were determined in sham rats and in experimental animals at the time of maximal bleedout (MBO) or at 2 h after trauma-hemorrhage. The results showed that estrogen and DPN induced dose-dependent increases in the maximal rate of left ventricular pressure increase (+dP/dt) in all groups, whereas propylpyrazole triol was ineffective at all doses. The maximal dose and the 50% effective dose of DPN were approximately 100-fold lower than those of estrogen. The half-life of estrogen in plasma was approximately 25 min in sham and MBO groups. A positive correlation between the estrogen-induced increase in +dP/dt and survival in MBO rats were observed. These results collectively suggest that the salutary effects of estrogen on cardiac performance are dose-dependent and mediated via ER-beta.

Expression and subcellular localization of BNIP3 in hypoxic hepatocytes and liver stress

We have previously demonstrated that the Bcl-2/adenovirus EIB 19-kDa interacting protein 3 (BNIP3), a cell death-related member of the Bcl-2 family, is upregulated in vitro and in vivo in both experimental and clinical settings of redox stress and that nitric oxide (NO) downregulates its expression. In this study we sought to examine the expression and localization of BNIP3 in murine hepatocytes and in a murine model of hemorrhagic shock (HS) and ischemia-reperfusion (I/R). Freshly isolated mouse hepatocytes were exposed to 1% hypoxia for 6 h followed by reoxygenation for 18 h, and protein was isolated for Western blot analysis. Hepatocytes grown on coverslips were fixed for localization studies. Similarly, livers from surgically cannulated C57Bl/6 mice and from mice cannulated and subjected to 1-4 h of HS were processed for protein isolation and Western blot analysis. In hepatocytes, BNIP3 was expressed constitutively but was upregulated under hypoxic conditions, and this upregulation was countered by treatment with a NO donor. Surprisingly, BNIP3 was localized in the nucleus of normoxic hepatocytes, in the cytoplasm following hypoxia, and again in the nucleus following reoxygenation. Upregulation of BNIP3 partially required p38 MAPK activation. BNIP3 contributed to hypoxic injury in hepatocytes, since this injury was diminished by knockdown of BNIP3 mRNA. Hepatic BNIP3 was also upregulated in two different models of liver stress in vivo, suggesting that a multitude of inflammatory stresses can lead to the modulation of BNIP3. In turn, the upregulation of BNIP3 appears to be one mechanism of hepatocyte cell death and liver damage in these settings.

Cardiovascular homeostasis in hypotension associated with initial stages of severe acute pancreatitis

OBJECTIVES

To identify the mechanisms underlying hypotension during the early phase of severe acute pancreatitis (SAP) by analyzing whether an impaired response to vasoactive substances occurs in this pathological process.

METHODS

Experimental SAP was induced by infusing 5% sodium taurocholate through the main pancreatic duct in rats. Once mean arterial pressure (MAP) in animals with pancreatitis was reduced, different vasoactive substances and inhibitors were administered.

RESULTS

Administration of the nonspecific nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester caused a similar increase in MAP in rats with pancreatitis and control rats, whereas inducible nitric oxide synthase inhibition did not cause changes in MAP. Moreover, the hypertensive response to endothelin and angiotensin II was lower in pancreatitis. Inhibition of angiotensin II synthesis by the angiotensin-converting enzyme inhibitor perindopril in animals with pancreatitis caused severe hypotension, causing death in 40% of them. Finally, pressor hyporesponsiveness to angiotensin II in animals with pancreatitis was avoided by previous administration of perindopril and N omega-nitro-L-arginine methyl ester.

CONCLUSIONS

The SAP-induced hypotension is associated with a deficient pressor responsiveness to angiotensin II and endothelin-1. The renin-angiotensin system plays an important role in the control of MAP in animals with pancreatitis.

Circulating angiotensin II attenuates the sympathetic baroreflex by reducing the barosensitivity of medullary cardiovascular neurones in the rat

Chronic intravenous angiotensin II (Ang II) has been widely used to establish centrally mediated hypertension in experimental animals, and disruption of Ang II activity is a frontline treatment for hypertensive disease. However, the acute central actions of circulating Ang II are poorly understood. We examined the effects of intravenous pressor doses of Ang II on autonomic activity in anaesthetized rats under neuromuscular blockade, and compared baroinhibition evoked by Ang II pressor ramps to equipressor responses evoked by phenylephrine (PE). Baroinhibition of splanchnic sympathetic nerve activity was attenuated during Ang II trials compared with PE, and rats remained sensitive to electrical stimulation of the aortic depressor nerve at higher arterial pressures during Ang II trials. This was not due to a direct effect of Ang II on aortic nerve baroreceptors. In a separate series of experiments, we provide direct evidence that bulbospinal barosensitive neurones in the rostral ventrolateral medulla are differentially sensitive to pressure ramps evoked by Ang II or PE vasoconstriction. Nineteen out of 41 units were equally sensitive to increased arterial pressure evoked by Ang II or PE. In 17 of 41 units, barosensitivity was attenuated during Ang II trials, and in five of 41 cases units that had previously been barosensitive increased their firing rate during Ang II trials. These results show, for the first time, that circulating Ang II acutely modulates central cardiovascular control mechanisms. We suggest that this results from activation by Ang II of a central pathway originating at the circumventricular organs.

The role of RAGE in the pathogenesis of intestinal barrier dysfunction after hemorrhagic shock

The receptor for advanced glycation end products (RAGE) has been implicated in the pathogenesis of numerous conditions associated with excessive inflammation. To determine whether RAGE-dependent signaling is important in the development of intestinal barrier dysfunction after hemorrhagic shock and resuscitation (HS/R), C57Bl/6, rage(-/-), or congenic rage(+/+) mice were subjected to HS/R (mean arterial pressure of 25 mmHg for 3 h) or a sham procedure. Twenty-four hours later, bacterial translocation to mesenteric lymph nodes and ileal mucosal permeability to FITC-labeled dextran were assessed. Additionally, samples of ileum were obtained for immunofluorescence microscopy, and plasma was collected for measuring IL-6 and IL-10 levels. HS/R in C57Bl/6 mice was associated with increased bacterial translocation, ileal mucosal hyperpermeability, and high circulating levels of IL-6. All of these effects were prevented when C57Bl/6 mice were treated with recombinant human soluble RAGE (sRAGE; the extracellular ligand-binding domain of RAGE). HS/R induced bacterial translocation, ileal mucosal hyperpermeability, and high plasma IL-6 levels in rage(+/+) but not rage(-/-) mice. Circulating IL-10 levels were higher in rage(-/-) compared with rage(+/+) mice. These results suggest that activation of RAGE-dependent signaling is a key factor leading to gut mucosal barrier dysfunction after HS/R.

Inhibition of cardiac PGC-1alpha expression abolishes ERbeta agonist-mediated cardioprotection following trauma-hemorrhage

PGC-1alpha (peroxisome proliferator-activated receptor [PPARgamma] coactivator-1alpha) activates PPARalpha and mitochondrial transcription factor A (Tfam), which regulate proteins, fatty acid and ATP metabolism (i.e., FAT/CD36, MCAD, and COX I). Recently we found that the salutary effects of estradiol (E2) on cardiac function following trauma-hemorrhage (T-H) are mediated via estrogen receptor (ER)beta. In this study we tested the hypothesis that ERbeta-mediated cardioprotection is induced via up-regulation of PGC-1alpha through PPARalpha or Tfam-dependent pathway. Male rats underwent T-H and received ERalpha agonist propylpyrazole-triol (PPT), ERbeta agonist diarylpropionitrile (DPN), E2, or vehicle. Another group was treated with antisense PGC-1alpha oligonucleotides prior to administration of DPN. E2 and DPN treatments attenuated the decrease in cardiac mitochondrial ATP, abrogated the T-H-induced lipid accumulation, and normalized PGC-1alpha, PPARalpha, FAT/CD36, MCAD, Tfam, and COX I after T-H. In contrast, PPT administration did not abrogate lipid accumulation. Moreover, in PPT-treated animals mitochondrial ATP remained significantly lower than those observed in DPN- or E2-treated animals. Prior administration of antisense PGC-1alpha prevented DPN-mediated cardioprotection and increase in ATP levels and Tfam but not in PPARalpha following T-H. These findings suggest that the salutary effects of E2 on cardiac function following T-H are mediated via ERbeta up-regulation of PGC-1alpha through Tfam-dependent pathway.

Flutamide restores cardiac function after trauma-hemorrhage via an estrogen-dependent pathway through upregulation of PGC-1

Although previous studies have shown that flutamide improves cardiovascular function after trauma-hemorrhage, the mechanisms responsible for the salutary effect remain unknown. We hypothesized that flutamide mediates its beneficial effects via an estrogen-dependent pathway through upregulation of peroxisome proliferator-activated receptor-γ coactivator 1 (PGC-1). PGC-1, a key regulator of cardiac mitochondrial ATP production, induces mitochondrial DNA (mtDNA)-encoded genes such as cytochrome- c oxidase (COX) subunit I, II, and III (COX I, COX II, and COX III), which regulates mitochondrial oxidative phosphorylation. To test this hypothesis, male rats underwent trauma-hemorrhage (mean arterial pressure of 35–40 mmHg for ∼90 min) followed by resuscitation. At the onset of resuscitation, rats received vehicle, flutamide (25 mg/kg body wt), flutamide in combination with estrogen receptor (ER) antagonist ICI-182,780 (3 mg/kg body wt), or ICI-182,780 alone. Flutamide administration after trauma-hemorrhage restored the depressed cardiac function and increased cardiac testosterone, estrogen levels, and aromatase activity. These increases were accompanied by normalized cardiac ER-α and ER-β protein levels, PGC-1, and COX I mRNA expression, mitochondrial COX activity, and ATP contents. However, cardiac dihydrotestosterone, 5α-reductase II, androgen receptor protein levels, and mtDNA-encoded genes COX II and COX III were unaffected by flutamide treatment. The flutamide-mediated restoration of cardiac function, the increases in aromatase activity and estrogen levels, ER-α, ER-β, PGC-1, COX I, COX activity, and ATP contents were, however, abolished when ER antagonist ICI-182,780 was administrated along with flutamide. These findings suggest that the salutary effect of flutamide on cardiac function after trauma-hemorrhage is mediated via an estrogen-dependent pathway through upregulation of PGC-1.

Mechanism responsible for the salutary effects of flutamide on cardiac performance after trauma-hemorrhagic shock: Upregulation of cardiomyocyte estrogen receptors

BACKGROUND

Although flutamide (FTM), an androgen-receptor antagonist, normalizes the depressed immune and cardiac function in males after trauma hemorrhage (T-H), the mechanism responsible for its salutary effects remains unknown. We hypothesized that the salutary effects of FTM are mediated via upregulation of estrogen receptors (ERs).

METHODS

Male Sprague-Dawley rats underwent T-H (laparotomy and 90 minutes of hemorrhage (35-40 mm Hg) and then resuscitated with 4x the volume of shed blood in the form of Ringer's lactate). FTM (25 mg/kg) or vehicle (propanediol) was injected subcutaneously 30 minutes before the end of resuscitation. At 2 hours after T-H or sham operation, cardiac output, stroke volume, heart rate, mean arterial pressure, +/- dp/dt, and total peripheral resistance were measured (n = 6 rats per group). Immediately after the measurement of cardiac function, cardiomyocytes were isolated, RNA was extracted, and expression of ER-alpha, ER-beta, and androgen-receptor (AR) mRNA in cardiomyocytes was determined by quantitative real-time polymerase chain reaction. ER-alpha, ER-beta, and AR protein levels in cardiomyocytes were also measured by Western blot analysis.

RESULTS

The depressed cardiac output, stroke volume, and +/- dp/dt after T-H were significantly improved in the FTM-treated T-H group. Moreover, the decrease in expression of ER-alpha and ER-beta mRNA and protein in cardiomyocytes in the T-H group was prevented with FTM treatment after T-H. However, expression of cardiomyocytes AR mRNA and protein were not significantly different between the T-H or sham group with or without FTM treatment.

CONCLUSIONS

These findings collectively suggest that, in addition to blockade of androgen receptors, flutamide-mediated ER upregulation is likely to play a role in mediating the salutary effect of flutamide on cardiac function after trauma hemorrhage.

Angiotensin II blocks memory consolidation through an AT2 receptor-dependent mechanism

RATIONALE AND OBJECTIVES

Several studies suggest that the brain renin-angiotensin system is involved in memory consolidation. However, the participation of angiotensin II (AII) in this process is controversial. This is probably due to the fact that many of the studies carried out to elucidate this matter employed multitrial learning paradigms together with pretraining intracerebroventricular infusions, and therefore were unable to distinguish between consolidation and retrieval related events and lacked anatomical specificity. To circumvent this problem, we analyzed the role played in memory consolidation by AII using the hippocampal-dependent, one-trial, step-down inhibitory avoidance task (IA) in combination with stereotaxically localized intrahippocampal infusion of drugs.

METHODS AND RESULTS

Rats bilaterally implanted with infusion cannulae into the CA1 region of the dorsal hippocampus (CA1) were trained in IA and tested for memory retention 24 h later. We found that when infused into CA1 immediately or 30 min after training but not later, AII produced a dose-dependent amnesic effect without altering locomotor activity, exploratory behavior or anxiety state. The amnesic effect of AII was not mimicked by angiotensin IV (AIV) and was totally blocked by the AII-type 2 receptor (AT2) antagonist, PD123319, but not by the AII-type 1 receptor (AT1) antagonist, losartan. Importantly, when infused alone, neither PD123319 nor losartan produced any effect on memory retention.

CONCLUSIONS

Our data indicate that, when given into CA1, AII blocks memory formation through a mechanism involving activation of AT2 receptors; however, endogenous AII does not seem to participate in the consolidation of IA long-term memory.