Gender differences in small intestinal perfusion following trauma hemorrhage: the role of endothelin-1

The role of sex hormones in the intestinal injury after brain death using a surgical menopause model in rats

Among transplantable organs, the intestine is one of the most challenging organs to transplant. While there is considerable research on the effects of brain death (BD), little is known about the specific intestinal changes that occur, particularly in females. Here we investigated the role of female sex hormones in the BD-induced intestinal inflammation, using an ovariectomy (OVx) model for sex hormones depletion. Wistar rats (female) were divided into four experimental groups: Control non-OVx - non-manipulated; Control-OVx -ovariectomized; BD non-OVx - animals submitted to BD (6h); BD-OVx -ovariectomized animals submitted to BD. OVx was performed 10 days before BD induction. non-OVx groups were chosen during proestrus phase (heat period). Inflammatory mediators and white blood cell count were quantified in the blood. Intestine tissue was sampled for histopathological analysis, myeloperoxidase (MPO) activity, Evans blue dye extravasation assay and immunohistochemistry. Results show higher intestinal injury in BD-OVx than BD non-OVx animals, presenting reduced crypt depth and increased serum inflammatory mediators. Independently from the previous hormonal status, BD increased intestinal inflammation, with higher leukocyte infiltration, MPO activity, ICAM-1 expression, and higher serum MIP-1α. In summary, BD modulates intestinal inflammation by increasing leukocyte mobilization. Whereas OVx, and its consequences on the female hormonal profile, influences homeostasis and BD-induced inflammation, increasing inflammatory mediators and altering intestinal morphology.

Therapeutically Targeting Microvascular Leakage in Experimental Hemorrhagic SHOCK: A Systematic Review and Meta-Analysis

BACKGROUND

Microvascular leakage is proposed as main contributor to disturbed microcirculatory perfusion following hemorrhagic shock and fluid resuscitation, leading to organ dysfunction and unfavorable outcome. Currently, no drugs are available to reduce or prevent microvascular leakage in clinical practice. We therefore aimed to provide an overview of therapeutic agents targeting microvascular leakage following experimental hemorrhagic shock and fluid resuscitation.

METHODS

PubMed, EMBASE.com, and Cochrane Library were searched in January 2021 for preclinical studies of hemorrhagic shock using any therapeutic agent on top of standard fluid resuscitation. Primary outcome was vascular leakage, defined as edema, macromolecule extravasation, or glycocalyx degradation. Drugs were classified by targeting pathways and subgroup analyses were performed per organ.

RESULTS

Forty-five studies, published between 1973 and 2020, fulfilled eligibility criteria. The included studies tested 54 different therapeutics mainly in pulmonary and intestinal vascular beds. Most studies induced trauma besides hemorrhagic shock. Forty-four therapeutics (81%) were found effective to reduce microvascular leakage, edema formation, or glycocalyx degradation in at least one organ. Targeting oxidative stress and apoptosis was the predominantly effective strategy (SMD: -2.18, CI [-3.21, -1.16], P < 0.0001). Vasoactive agents were found noneffective in reducing microvascular leakage (SMD: -0.86, CI [-3.07, 1.36], P = 0.45).

CONCLUSION

Pharmacological modulation of pathways involved in cell metabolism, inflammation, endothelial barrier regulation, sex hormones and especially oxidative stress and apoptosis were effective in reducing microvascular leakage in experimental hemorrhagic shock with fluid resuscitation. Future studies should investigate whether targeting these pathways can restore microcirculatory perfusion and reduce organ injury following hemorrhagic shock.

SYSTEMATIC REVIEW REGISTRATION NUMBER

CRD42018095432.

Complement Initiation Varies by Sex in Intestinal Ischemia Reperfusion Injury

Intestinal ischemia reperfusion (IR)-induced tissue injury represents an acute inflammatory response with significant morbidity and mortality. The mechanism of IR-induced injury is not fully elucidated, but recent studies suggest a critical role for complement activation and for differences between sexes. To test the hypothesis that complement initiation differs by sex in intestinal IR, we performed intestinal IR on male and female WT C57B6L/, C1q-/-, MBL-/-, or properdin (P)-/- mice. Intestinal injury, C3b and C5a production and ex vivo secretions were analyzed. Initial studies demonstrated a difference in complement mRNA and protein in male and female WT mice. In response to IR, male C1q-, MBL- and P-deficient mice sustained less injury than male WT mice. In contrast, only female MBL-/- mice sustained significantly less injury than female wildtype mice. Importantly, wildtype, C1q-/- and P-/- female mice sustained significant less injury than the corresponding male mice. In addition, both C1q and MBL expression and deposition increased in WT male mice, while only elevated MBL expression and deposition occurred in WT female mice. These data suggested that males use both C1q and MBL pathways, while females tend to depend on lectin pathway during intestinal IR. Females produced significantly less serum C5a in MBL-/- and P-/- mice. Our findings suggested that complement activation plays a critical role in intestinal IR in a sex-dependent manner.

Eicosanoid production varies by sex in mesenteric ischemia reperfusion injury

Intestinal ischemia/reperfusion (I/R)-induced injury is an inflammatory response with significant morbidity and mortality. The early inflammatory response includes neutrophil infiltration. However, the majority of rodent studies utilize male mice despite a sexual dimorphism in intestinal I/R-related diseases. We hypothesized that sex may alter inflammation by changing neutrophil infiltration and eicosanoid production. To test this hypothesis, male and female C57Bl/6 mice were subjected to sham treatment or 30 min intestinal ischemia followed by a time course of reperfusion. We demonstrate that compared to male mice, females sustain significantly less intestinal I/R-induced tissue damage and produced significant LTB₄ concentrations. Male mice release PGE₂. Finally, treatment with a COX-2 specific inhibitor, NS-398, attenuated I/R-induced injury, total peroxidase level, and PGE₂ production in males, but not in similarly treated female mice. Thus, I/R-induced eicosanoid production and neutrophil infiltration varies between sexes suggesting that distinct therapeutic intervention may be needed in clinical ischemic diseases.

Therapeutic interventions to restore microcirculatory perfusion following experimental hemorrhagic shock and fluid resuscitation: A systematic review

Objective

Microcirculatory perfusion disturbances following hemorrhagic shock and fluid resuscitation contribute to multiple organ dysfunction and mortality. Standard fluid resuscitation is insufficient to restore microcirculatory perfusion; however, additional therapies are lacking. We conducted a systematic search to provide an overview of potential non‐fluid‐based therapeutic interventions to restore microcirculatory perfusion following hemorrhagic shock.

Methods

A structured search of PubMed, EMBASE, and Cochrane Library was performed in March 2020. Animal studies needed to report at least one parameter of microcirculatory flow (perfusion, red blood cell velocity, functional capillary density).

Results

The search identified 1269 records of which 48 fulfilled all eligibility criteria. In total, 62 drugs were tested of which 29 were able to restore microcirculatory perfusion. Particularly, complement inhibitors (75% of drugs tested successfully restored blood flow), endothelial barrier modulators (100% successful), antioxidants (66% successful), drugs targeting cell metabolism (83% successful), and sex hormones (75% successful) restored microcirculatory perfusion. Other drugs consisted of attenuation of inflammation (100% not successful), vasoactive agents (68% not successful), and steroid hormones (75% not successful).

Conclusion

Improving mitochondrial function, inhibition of complement inhibition, and reducing microvascular leakage via restoration of endothelial barrier function seem beneficial to restore microcirculatory perfusion following hemorrhagic shock and fluid resuscitation.

Modeling trauma in rats: similarities to humans and potential pitfalls to consider

Trauma is the leading cause of mortality in humans below the age of 40. Patients injured by accidents frequently suffer severe multiple trauma, which is life-threatening and leads to death in many cases. In multiply injured patients, thoracic trauma constitutes the third most common cause of mortality after abdominal injury and head trauma. Furthermore, 40-50% of all trauma-related deaths within the first 48 h after hospital admission result from uncontrolled hemorrhage. Physical trauma and hemorrhage are frequently associated with complex pathophysiological and immunological responses. To develop a greater understanding of the mechanisms of single and/or multiple trauma, reliable and reproducible animal models, fulfilling the ethical 3 R's criteria (Replacement, Reduction and Refinement), established by Russell and Burch in 'The Principles of Human Experimental Technique' (published 1959), are required. These should reflect both the complex pathophysiological and the immunological alterations induced by trauma, with the objective to translate the findings to the human situation, providing new clinical treatment approaches for patients affected by severe trauma. Small animal models are the most frequently used in trauma research. Rattus norvegicus was the first mammalian species domesticated for scientific research, dating back to 1830. To date, there exist numerous well-established procedures to mimic different forms of injury patterns in rats, animals that are uncomplicated in handling and housing. Nevertheless, there are some physiological and genetic differences between humans and rats, which should be carefully considered when rats are chosen as a model organism. The aim of this review is to illustrate the advantages as well as the disadvantages of rat models, which should be considered in trauma research when selecting an appropriate in vivo model. Being the most common and important models in trauma research, this review focuses on hemorrhagic shock, blunt chest trauma, bone fracture, skin and soft-tissue trauma, burns, traumatic brain injury and polytrauma.

The Role and Use of Estrogens Following Trauma

Several lines of evidence indicate that female sex is a protective factor in trauma and hemorrhage. In both clinical and experimental studies, proestrus females have been shown to have better chances of survival and reduced rates of posttraumatic sepsis. Estrogen receptors are expressed in a variety of tissues and exert genomic, as well as nongenomic effects. By improving cardiac, pulmonary, hepatic, and immune function, estrogens have been shown to prolong survival in animal models of hemorrhagic shock. Despite encouraging results from experimental studies, retrospective clinical studies have not clearly pointed to advantages of estrogens following trauma-hemorrhage, which may be due to insufficient study design. Therefore, this review aims to give an overview on the current evidence and emphasizes on the importance of further clinical investigation on estrogens following trauma.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

The influence of sex steroid hormones on the response to trauma and burn injury

Trauma and related sequelae result in disturbance of homeostatic mechanisms frequently leading to cellular dysfunction and ultimately organ and system failure. Regardless of the type and severity of injury, gender dimorphism in outcomes following trauma have been reported, with females having lower mortality than males, suggesting that sex steroid hormones (SSH) play an important role in the response of body systems to trauma. In addition, several clinical and experimental studies have demonstrated the effects of SSH on the clinical course and outcomes following injury. Animal studies have reported the ability of SSH to modulate immune, inflammatory, metabolic and organ responses following traumatic injury. This indicates that homeostatic mechanisms, via direct and indirect pathways, can be maintained by SSH at local and systemic levels and hence result in more favourable prognosis. Here, we discuss the role and mechanisms by which SSH modulates the response of the body to injury by maintaining various processes and organ functions. Such properties of sex hormones represent potential novel therapeutic strategies and further our understanding of current therapies used following injury such as oxandrolone in burn-injured patients.

Estradiol receptors agonists induced effects in rat intestinal microcirculation during sepsis

The steroid hormone estradiol is suggested to play a protective role in intestinal injury during systemic inflammation (sepsis). Our aim was to determine the effects of specific estradiol receptor (ER-α and ER-ß) agonists on the intestinal microcirculation during experimental sepsis. Male and sham ovariectomized female rats were subjected to sham colon ascendens stent peritonitis (CASP), and they were compared to male and ovariectomized female rats underwent CASP and either estradiol receptor α (ER-α) agonist propyl pyrazole triol (PPT), estradiol receptor ß (ER-ß) agonist diarylpropiolnitrile (DPN), or vehicle treatment. Intravital microscopy was performed, which is sufficiently sensitive to measure changes in the functional capillary density (FCD) as well as the major steps in leukocyte recruitment (rolling and adhesion). The leukocyte extravasations were also quantified by using histological paraffin sections of formalin fixed intestine. We found that either DPN (ER-β) or PPT (ER-α) significantly reduced (P<0.05) sepsis-induced leukocyte-endothelial interaction (rolling, adherent leukocytes and neutrophil extravasations) and improved the intestinal muscular FCD. [PPT: Female; Leukocyte rolling (n/min): V(3) 3.7±0.7 vs 0.8±0.2, Leukocyte adhesion(n/mm(2)): V(3) 131.3±22.6 vs 57.2±13.5, Neutrophil extravasations (n/10000 μm(2)): 3.1±0.7 vs 6 ±1. Male; Leukocyte adhesion (n/mm(2)): V(1) 154.8±19.2 vs 81.3±11.2, V(3) 115.5±23.1 vs 37.8±12]. [DPN: Female; neutrophil extravasations (n/10000 μm(2)) 3.8±0.6 vs 6 ±1. Male; Leukocyte adhesion (n/mm(2)) V(1) 154.8±19.2 vs 70±10.5, V(3) 115.5±23.1 vs 52.8±9.6].Those results suggest that the observed effects of estradiol receptors on different phases of leukocytes recruitment with the improvement of the functional capillary density could partially explain the previous demonstrated salutary effects of estradiol on the intestinal microcirculation during sepsis. The observed activity of this class of compounds could open up a new avenue of research into the potential treatment of sepsis.

Endothelin-1 is increased in cerebrospinal fluid and associated with unfavorable outcomes in children after severe traumatic brain injury

Severe pediatric traumatic brain injury (TBI) is associated with unfavorable outcomes secondary to injury from activation of the inflammatory cascade, the release of excitotoxic neurotransmitters, and changes in the reactivity of cerebral vessels, causing ischemia. Hypoperfusion of injured brain tissues after TBI is also associated with unfavorable outcomes. Therapeutic hypothermia is an investigational treatment strategy for use in patients with severe TBI that has shown differential effects on various cerebrospinal fluid (CSF) mediators in pediatric patients. Endothelin-1 (ET-1) is a powerful vasoconstrictor that exerts its effects on the cerebrovascular endothelium for sustained periods after TBI. The purpose of this study was to determine if CSF concentrations of ET-1 are increased after severe TBI in children, and if they are associated with demographics and outcomes that are affected by therapeutic hypothermia. This was an ancillary study to a prospective, randomized-controlled trial of early hypothermia in a tertiary care pediatric intensive care unit. Children (n = 34, age 3 months-15 years) suffering from severe TBI were randomized to hypothermia (n = 19) and normothermia (n = 15) as part of the efficacy study. Children undergoing diagnostic lumbar puncture (n = 11) to rule out infection were used as controls. Patients received either mild to moderate hypothermia (32-33°C) or normothermia as part of their treatment protocol. CSF was serially collected during the first 5 days after TBI. ET-1 concentrations were quantitated in patient and control CSF samples by a validated ELISA in duplicate with a limit of quantification of 0.195 pg/mL. CSF ET-1 concentrations were increased by two- to threefold in children after TBI compared to controls, and the increase was sustained for up to 5 days post-TBI. This relationship was not affected by hypothermia, and there were no differences in ET-1 response between children with inflicted and accidental TBI. Group-based trajectory analysis revealed two distinct groups with similar ET-1 levels over time. Univariate analysis showed a significant association between ET-1 levels and Glasgow Outcome Scale (GOS) scores, for which higher ET-1 levels over time were associated with unfavorable outcomes. ET-1 is increased in children with severe TBI and is associated with unfavorable outcomes. This increase in ET-1 may mediate the hypoperfusion or cerebrovascular dysfunction accompanying severe TBI in children. Importantly, hypothermia does not affect the brain's ET-1 response as measured in the CSF.

Proestrus female rats are more resistant to right ventricular pressure overload

Multiple studies of left ventricular dysfunction suggest that females may be more resistant to ischemia or endotoxemia. However, sex differences in right ventricular (RV) responses to pressure overload and/or endotoxemia have not been elucidated. We hypothesized that females would maintain better RV function during acute pressure overload (APO), endotoxemia, or a simultaneous insult from both processes. Age-matched male and proestrus female Sprague-Dawley rats were given an intraperitoneal injection of either phosphate buffered saline or LPS. Six hours after injection, hearts were removed by median sternotomy and isolated via Langendorff. End-diastolic pressures were sequentially elevated past physiologic levels by increasing the volume of a latex balloon that was inserted into the RV. Male RV function was depressed to a greater degree after APO injury compared with that in females (developed pressure: male, 44.97 mmHg vs. female, 58.23 mmHg). Interestingly though, at a physiologic end-diastolic pressure of 5 mmHg, endotoxic males and females maintained equivalent RV function. However, with concurrent endotoxic insult and APO, RV function was better maintained in males as compared with that in females (developed pressure: male, 59% of control versus female, 41% of control). Furthermore, tissue levels of IL-1 and IL-6, but not IL-10, were increased after endotoxin exposure but did not differ based on sex. Through this study, we have shown that sex differences exist in RV dysfunction, and that different cardiac insults diversely affect myocardial function. Understanding these differences may allow for the implementation of novel therapeutic treatment options that are designed to attenuate RV cardiovascular collapse.

Estrogen prevents intestinal inflammation after trauma-hemorrhage via downregulation of angiotensin II and angiotensin II subtype I receptor

Although angiotensin II (Ang II) plays a key role in development of organ ischemia-reperfusion injury, it remains unclear whether it is involved in development of intestinal injury following trauma-hemorrhage (T-H). Studies have shown that 17beta-estradiol (E2) administration following T-H improves small intestinal blood flow; however, it is unclear whether Ang II plays a role in this E2-mediated salutary effect. Male Sprague-Dawley rats underwent laparotomy and hemorrhagic shock (removal of 60% total blood volume, fluid resuscitation after 90 min). At onset of resuscitation, rats were treated with vehicle, E2, or E2 and estrogen receptor antagonist ICI 182,780 (ICI). A separate group of rats was treated with Ang II subtype I receptor (AT1R) antagonist losartan. At 24 h after T-H, plasma Ang II, IL-6, TNF-alpha, intercellular adhesion molecule (ICAM)-1, cytokine-induced neutrophil chemoattractant (CINC)-1 and CINC-3 levels, myeloperoxidase (MPO) activity, and AT1R expression were determined. T-H significantly increased plasma and intestinal Ang II, IL-6, TNF-alpha levels, intestinal ICAM-1, CINC-1, CINC-3 levels, MPO activity, and AT1R protein compared with shams. E2 treatment following T-H attenuated increased intestinal MPO activity, Ang II level, and AT1R protein expression. ICI administration abolished the salutary effects of E2. In contrast, losartan administration attenuated increased MPO activity without affecting Ang II and AT1R levels. Thus Ang II plays a role in producing small intestine inflammation following T-H, and the salutary effects of E2 on intestinal inflammation are mediated in part by Ang II and AT1R downregulation.

Organ blood flow and the central hemodynamic response are better preserved in female, as opposed to the male rats, after trauma-hemorrhagic shock

The objective of this study was to test the hypotheses that the better resistance of proestrus female than male rats to trauma-hemorrhagic shock (T/HS)-induced gut and other organ injury, and it is associated with better preservation of central hemodynamics and organ blood flow including blood flow to the intestine. Male and female proestrus rats were subjected to T/HS (laparotomy and 90 minutes of shock at a mean arterial blood pressure of 35-40 mm Hg) or trauma sham-shock after that cardiac index, systemic vascular resistance, and organ blood flow was measured 15 minutes before the end of the shock period and at 15 minutes, 60 minutes, and 180 minutes after volume resuscitation. The hemodynamic response to T/HS was better preserved during the shock period in the female than male rats and this was manifest as better maintenance of central hemodynamics (cardiac output and systemic vascular resistance) and intestinal as well as other organ microcirculatory blood flow. Cardiac output had returned toward normal at 15 minutes after volume resuscitation in both the male and female rats, however only in the female rats was there a consistent increase in organ blood flow after volume resuscitation. In contrast, in the male T/HS rats, the level of organ blood flow, especially to the splanchnic organs, remained similar to that observed during the shock period. These results indicate that the greater resistance of female than male rats to gut and other organ injury after T/HS is associated with better preservation of central hemodynamics and organ blood flow during the shock and postshock periods.

Mechanism of estrogen-mediated intestinal protection following trauma-hemorrhage: p38 MAPK-dependent upregulation of HO-1

p38 MAPK has been reported to regulate the inflammatory response in various cell types via extracellular stimuli. p38 MAPK activation also results in the induction of heme oxygenase (HO)-1, which exerts potent anti-inflammatory effects. Although studies have shown that 17beta-estradiol (E(2)) prevented organ dysfunction following trauma-hemorrhage, it remains unknown whether p38 MAPK/HO-1 plays any role in E(2)-mediated attenuation of intestinal injury under those conditions. To study this, male rats underwent trauma-hemorrhage (mean blood pressure approximately 40 mmHg for 90 min) followed by fluid resuscitation. At the onset of resuscitation, rats were treated with vehicle, E(2) (1 mg/kg body wt), the p38 MAPK inhibitor SB-203580 (2 mg/kg body wt) or E(2) plus SB-203580. Two hours thereafter, intestinal myeloperoxidase (MPO) activity and lactate, TNF-alpha, IL-6, ICAM-1, cytokine-induced neutrophil chemoattractant (CINC)-1, and macrophage inflammatory protein (MIP)-2 levels were measured. Intestinal p38 MAPK and HO-1 protein levels were also determined. Trauma-hemorrhage led to an increase in intestinal MPO activity and lactate, TNF-alpha, IL-6, ICAM-1, CINC-1, and MIP-2 levels. This was accompanied with a decrease in intestinal p38 MAPK activity and increase in HO-1 expression. Administration of E(2) normalized all the above parameters except HO-1, which was further increased following trauma-hemorrhage. Administration of SB-203580 with E(2) abolished the E(2)-mediated restoration of the above parameters as well as the increase in intestinal HO-1 expression following trauma-hemorrhage. These results suggest that the p38 MAPK/HO-1 pathway plays a critical role in mediating the salutary effects of E(2) on shock-induced intestinal injury.

Females exhibit relative resistance to depressive effects of tumor necrosis factor-alpha on the myocardium

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) plays a critical role in myocardial dysfunction following acute injury. It is unknown, however, if a gender-specific response to TNF infusion exists in isolated rat hearts. Elucidating such mechanisms is important to understanding the myocardial gender differences during acute injury. We hypothesize that females will exhibit a relative resistance to TNF-induced myocardial dysfunction compared to males and that menstrual cycle would influence the degree of female myocardial resistance to TNF-induced myocardial functional depression.

MATERIALS AND METHODS

Adult male, proestrus female, and metestrus/diestrus female hearts were subjected to 60 min of TNF infusion at 10,000 pg/mL.min via Langendorff. Myocardial contractile function (left ventricular developed pressure, and the positive/negative first derivative of pressure) was continuously recorded.

RESULTS

10,000 pg/mL.min of TNF markedly depressed myocardial function in males compared with other doses of TNF. Myocardial function was significantly decreased in males compared to females following TNF infusion. Additionally, both the proestrus and the metestrus/diestrus females exhibited equal resistance to TNF-induced myocardial dysfunction.

CONCLUSION

Our study shows that females exhibit a significantly greater degree of resistance to TNF-induced myocardial depression. Moreover, data from this study suggest that fluctuations in estrogen during the reproductive cycle may have little to no influence on TNF-induced myocardial depression.

Endothelin, sex and hypertension

The ETs (endothelins) comprise a family of three 21-amino-acid peptides (ET-1, ET-2 and ET-3) and 31-amino-acid ETs (ET-1(1-31), ET-2(1-31) and ET-3(1-31)). ET-1 is synthesized from a biologically inactive precursor, big ET-1, by ECEs (ET-converting enzymes). The actions of ET-1 are mediated through activation of the G-protein-coupled ET(A) and ET(B) receptors, which are found in a variety of cells in the cardiovascular and renal systems. ET-1 has potent vasoconstrictor, mitogenic, pro-inflammatory and antinatriuretic properties, which have been implicated in the pathophysiology of a number of cardiovascular diseases. Overexpression of ET-1 has been consistently described in salt-sensitive models of hypertension and in models of renal failure, and has been associated with disease progression. Sex differences are observed in many aspects of mammalian cardiovascular function and pathology. Hypertension, as well as other cardiovascular diseases, is more common in men than in women of similar age. In experimental models of hypertension, males develop an earlier and more severe form of hypertension than do females. Although the reasons for these differences are not well established, the effects of gonadal hormones on arterial, neural and renal mechanisms that control blood pressure are considered contributing factors. Sex differences in the ET-1 pathway, with males displaying higher ET-1 levels, greater ET-1-mediated vasoconstrictor and enhanced pressor responses in comparison with females, are addressed in the present review. Sex-associated differences in the number and function of ET(B) receptors appear to be particularly important in the specific characteristics of hypertension between females and males. Although the gonadal hormones modulate some of the differences in the ET pathway in the cardiovascular system, a better understanding of the exact mechanisms involved in sex-related differences in this peptidergic system is needed. With further insights into these differences, we may learn that men and women could require different antihypertensive regimens.

Metabolic modulators following trauma sepsis: Sex hormones

BACKGROUND

The development of metabolic perturbations following severe trauma/sepsis leading to decreased energy production, hyperglycemia, and lipolysis is often rapid. Gender is increasingly recognized as a major factor in the outcome of patients suffering from trauma/sepsis. Moreover, sex hormones influence energy, glucose, and lipid metabolism. Metabolic modulators, such as peroxisome proliferator-activated receptor-gamma coactivator-1 and peroxisome proliferator-activated receptor-alpha, which are required for mitochondrial energy production and fatty acid oxidation, are regulated by the estrogen receptor-beta and consequently contribute to cardioprotection following trauma hemorrhage. Additionally, sex steroids regulate inflammatory cytokines that cause hypermetabolism/catabolism via acute phase response, leading to increased morbidity and mortality.

MEASUREMENTS

This article examines the following: (1) the evidence for gender differences; (2) energy, glucose, and lipid metabolism and the acute phase protein response; (3) the mechanisms by which gender/sex hormones affect the metabolic modulators; and (4) the tissue-specific effect of sex hormone receptors and the effect of genomic and nongenomic pathways of sex hormones following trauma.

RESULTS AND CONCLUSIONS

The available information indicates that sex steroids not only modulate the immune/cardiovascular responses but also influence various metabolic processes following trauma. Thus, alteration or modulation of the prevailing hormone milieu at the time of injury appears to be a novel therapeutic adjunct for improving outcome after injury.

Mechanisms of direct peritoneal resuscitation-mediated splanchnic hyperperfusion following hemorrhagic shock

Conventional resuscitation (CR) from hemorrhagic shock causes a persistent and progressive splanchnic vasoconstriction and hypoperfusion despite hemodynamic restoration with intravenous fluid therapy. Adjunctive direct peritoneal resuscitation (DPR) with a clinical peritoneal dialysis solution instilled into the peritoneal cavity has been shown to restore splanchnic tissue perfusion, down-regulate the gut-derived exaggerated systemic inflammatory response, promote early fluid mobilization, and improve overall outcome. This study was conducted to define the molecular mechanisms of DPR-induced gut hyperperfusion after hemorrhagic shock. Male rats were bled to 50% baseline mean arterial pressure and resuscitated with the shed blood plus two volumes of saline (CR). In vivo videomicroscopy and Doppler velocimetry were used to assess terminal ileal microvascular diameters and blood flow. Direct peritoneal resuscitation animals received CR and topical application of a clinical glucose-based peritoneal dialysis solution (Delflex). Inhibitors, glibenclamide (K(+)ATP channels), N-monomethyl-L-arginine (L-NMMA) (nitric oxide synthase), 8-cyclopentyl-1,3-diprophylxanthine (DPCPX) (A1 adenosine receptor), tetrabutylammonium (K(+)Ca2+ channels), and mefenamic acid (cyclooxygenase) were topically applied (individually or in combination) with DPR according to protocol; BQ-123 (endothelin A receptor antagonist) and BQ-788 (endothelin B receptor antagonist) were used topically with CR to define the mechanism of post-CR vasoconstriction and hypoperfusion. Conventional resuscitation caused a persistent progressive intestinal vasoconstriction and hypoperfusion that can be abolished with endothelin antagonists. In contrast, adjunctive DPR caused an instantaneous sustained vasodilation and hyperperfusion. Glibenclamide or L-NMMA partially attenuated DPR-induced vasodilation, whereas the addition of DPCPX to the two inhibitors eliminated the dilation. Cyclooxygenase and K(+)Ca2+channels were not active in DPR-mediated microvascular effects. In conclusion, DPR improves splanchnic tissue perfusion by endothelium-dependent mechanisms mediated by activations of glibenclamide-sensitive K(+) channels (KATP), adenosine A1 receptor subtype activation, and nitric oxide release. Direct peritoneal resuscitation preserves endothelial dilatory functions, thereby overriding any endothelium-derived constrictor response triggered by hemorrhagic shock and CR.

Adrenomedullin and adrenomedullin binding protein-1 prevent metabolic acidosis after uncontrolled hemorrhage in rats

OBJECTIVE

Management of trauma victims with uncontrolled hemorrhage remains a major problem in combat casualty care at the far-forward battlefield setting. The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Decreased organ perfusion after hemorrhagic shock is associated with metabolic acidosis, in which the up-regulated endothelin-1 plays an important role. We have recently shown that vascular responsiveness to adrenomedullin (AM), a newly discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Down-regulation of AM binding protein (AMBP-1) appears to be responsible for this hyporesponsiveness. We therefore hypothesized that administration of AM/AMBP-1 would prevent metabolic acidosis after uncontrolled hemorrhage via down-regulation of endothelin-1.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats (275-325 g).

INTERVENTIONS

A rat model of uncontrolled hemorrhage with an extremely low volume of fluid resuscitation was used to mimic the combat situation.

MEASUREMENTS AND MAIN RESULTS

Both lumbar veins of male adult rats were isolated and severed at the junction to the vena cava. The abdomen was kept open but covered with a saline wet gauze for 45 mins and then closed in layers. The animals received 1 mL of normal saline (vehicle) with or without AM (12 microg/kg of body weight) and AMBP-1 (40 microg/kg of body weight) over 45 mins. Various variables were measured at 4 hrs after resuscitation. The bleed-out volumes in the vehicle group and the AM/ AMBP-1 treatment group were 6.78 +/- 0.19 and 6.81 +/- 0.25 mL/rat, respectively. The results indicate that AM/AMBP-1 administration prevented metabolic acidosis, mitigated organ injury, down-regulated preproendothelin-1 gene expression, and decreased plasma levels of endothelin-1 after hemorrhage.

CONCLUSIONS

AM/AMBP-1 may provide a novel approach for the treatment of uncontrolled hemorrhage. The beneficial effect of AM/AMBP-1 is associated with down-regulation of endothelin-1.

Does estrogen contribute to the hepatic regeneration following portal branch ligation in rats?

The aim of this study was to determine whether estrogen plays any role in the hepatic regeneration of nonligated lobe following portal branch ligation (PBL). Male rats were subjected to PBL on the left and middle lobes. Two and 7 days after PBL, the rats were killed and blood and liver samples were analyzed. Sham animals underwent only laparotomy. The serum estradiol levels were significantly elevated on day 2 following PBL and returned to normal levels on day 7. The expression of estrogen receptors (ER) in the liver evaluated by Western blotting did not show any change in the nonligated lobe compared with shams. Immunohistochemical study for ER showed a predominant ER expression in the hepatocyte nucleus in periportal area (zone 1), although there was no apparent difference in the amount and expression pattern between sham and PBL. However, chronic inhibition of ER by an ER antagonist (ICI 182,780) showed a significantly lower regeneration rate of the nonligated lobe compared with vehicle treatment. Liver regeneration-associated genes also were less activated in the ICI group. Moreover, portal venous flow, determined by fluorescent microsphere injection, was significantly lower in the ICI group compared with vehicle group. These changes correlated with the attenuated expression of endothelial nitric oxide synthase mRNA in both superior mesenteric arteries and veins. In conclusion, these results indicate that the estrogen's contribution on hepatic regeneration following PBL is at least partly mediated through maintaining mesenteric blood flow by mesenteric endothelial nitric oxide synthase upregulation rather than directly activating liver regeneration in the liver.

17β-Estradiol modulates vasoconstriction induced by endothelin-1 following trauma-hemorrhage

Although endothelin-1 (ET-1) induces vasoconstriction, it remains unknown whether 17β-estradiol (E2) treatment following trauma-hemorrhage alters these ET-1-induced vasoconstrictive effects. In addition, the role of the specific estrogen receptor (ER) subtypes (ER-α and ER-β) and the endothelium-localized downstream mechanisms of actions of E2 remain unclear. We hypothesized that E2 attenuates increased ET-1-induced vasoconstriction following trauma-hemorrhage via an ER-β-mediated pathway. To study this, aortic rings were isolated from male Sprague-Dawley rats following trauma-hemorrhage with or without E2 treatment, and alterations in tension were determined in vitro. Dose-response curves to ET-1 were determined, and the vasoactive properties of E2, propylpyrazole triol (PPT, ER-α agonist), and diarylpropionitrile (DPN, ER-β agonist) were determined. The results showed that trauma-hemorrhage significantly increased ET-1-induced vasoconstriction; however, administration of E2 normalized ET-1-induced vasoconstriction in trauma-hemorrhage vessels to the sham-operated control level. The ER-β agonist DPN counteracted ET-1-induced vasoconstriction, whereas the ER-α agonist PPT was ineffective. Moreover, the vasorelaxing effects of E2 were not observed in endothelium-denuded aortic rings or by pretreatment of the rings with a nitric oxide (NO) synthase inhibitor. Cyclooxygenase inhibition with indomethacin had no effect on the action of E2. Thus, E2 administration attenuates ET-1-induced vasoconstriction following trauma-hemorrhage via an ER-β-mediated pathway that is dependent on endothelium-derived NO synthesis.

Gonadal steroids in critical illness

Gonadal steroids are metabolized in target cells and then interact with specific receptors to exert genomic and nongenomic effects. Complex feedback loops that involve the immune-neuroendocrine axis, limbic system, and gonadal steroids play a vital role in the adaptation to critical illness. Preclinical studies demonstrate adverse physiological effects of androgens on the cardiovascular and immune systems despite its purported anabolic effects. Similar models also demonstrate salutary effects of estrogens on these systems. Thus, during the catabolic phases of acute and chronic critical illness, estrogen, and not androgen, therapy may prove to be a valuable intervention. However, during the post-critical illness recovery phase, when anabolism is critical, androgen therapy may still be useful and safe.