The influence of antibodies to TNF-alpha and IL-1beta on haemodynamic responses to the cytokines, and to lipopolysaccharide, in conscious rats

Sinus Tachycardia: a Multidisciplinary Expert Focused Review

Sinus tachycardia (ST) is ubiquitous, but its presence outside of normal physiological triggers in otherwise healthy individuals remains a commonly encountered phenomenon in medical practice. In many cases, ST can be readily explained by a current medical condition that precipitates an increase in the sinus rate, but ST at rest without physiological triggers may also represent a spectrum of normal. In other cases, ST may not have an easily explainable cause but may represent serious underlying pathology and can be associated with intolerable symptoms. The classification of ST, consideration of possible etiologies, as well as the decisions of when and how to intervene can be difficult. ST can be classified as secondary to a specific, usually treatable, medical condition (eg, pulmonary embolism, anemia, infection, or hyperthyroidism) or be related to several incompletely defined conditions (eg, inappropriate ST, postural tachycardia syndrome, mast cell disorder, or post-COVID syndrome). While cardiologists and cardiac electrophysiologists often evaluate patients with symptoms associated with persistent or paroxysmal ST, an optimal approach remains uncertain. Due to the many possible conditions associated with ST, and an overlap in medical specialists who see these patients, the inclusion of experts in different fields is essential for a more comprehensive understanding. This article is unique in that it was composed by international experts in Neurology, Psychology, Autonomic Medicine, Allergy and Immunology, Exercise Physiology, Pulmonology and Critical Care Medicine, Endocrinology, Cardiology, and Cardiac Electrophysiology in the hope that it will facilitate a more complete understanding and thereby result in the better care of patients with ST.

Gonadal hormone receptors underlie the resistance of female rats to inflammatory and cardiovascular complications of endotoxemia

The male gender is more vulnerable to immunological complications of sepsis. Here, we tested the hypotheses that female rats are protected against endotoxemia-evoked hypotension and cardiac autonomic dysfunction, and that gonadal hormone receptors account for such protection. Changes in blood pressure, heart rate, and cardiac sympathovagal balance caused by i.v. lipopolysaccharide (LPS) were determined. In male rats, LPS elevated serum TNFα together with falls in blood pressure and rises in heart rate. The spectral index of cardiac sympathovagal balance (low-frequency/high-frequency ratio, LF/HF) was reduced by LPS, suggesting an enhanced parasympathetic dominance. Remarkably, none of these LPS effects was evident in female rats. We also report that pretreatment of female rats with fulvestrant (nonselective estrogen receptor blocker), PHTPP (estrogen receptor β blocker), or mifepristone (progesterone receptor blocker) uncovered clear inflammatory (increased serum TNFα), hypotensive and tachycardic responses to LPS. However, these female rats, contrary to their male counterparts, exhibited increases in LF/HF ratio. On the other hand, LPS failed to modify inflammatory or cardiovascular states in rats pretreated with MPP (estrogen receptor α blocker). In females treated with formestane (aromatase inhibitor), LPS increased LF/HF ratio but had no effect on blood pressure. In male rats, the hypotensive and cardiac autonomic effects of LPS were (i) eliminated after treatment with estrogen, and (ii) intensified and inhibited, respectively, in flutamide (androgen receptor blocker)-pretreated rats. These findings highlight important roles for female gonadal hormones and functional estrogen receptor β and progesterone receptors in offsetting inflammatory and cardiovascular derangements caused by endotoxemia in female rats.

Oral Infections, Metabolic Inflammation, Genetics, and Cardiometabolic Diseases

Although several epidemiologic studies reported plausible and potentially causal associations between oral infections and cardiometabolic diseases (CMDs), controversy still lingers. This might be due to unrecognized confounding from metabolic inflammation and genetics, both of which alter the immune responses of the host. Low-grade inflammation termed metainflammation is the hallmark of obesity, insulin resistance, type 2 diabetes, and CMDs. According to the common soil theory, the continuum of obesity to CMDs is the same pathology at different time points, and early metainflammations, such as hyperglycemia and obesity, display many adverse cardiometabolic characteristics. Consequently, adipose tissue is now considered a dynamic endocrine organ that expresses many proinflammatory cytokines such as TNF-α, IL-6, plasminogen activator inhibitor 1, and IL-1β. In metainflammation, IL-1β and reactive oxygen species are generated, and IL-1β is a pivotal molecule in the pathogenesis of CMDs. Note that the same cytokines expressed in metainflammation are also reported in oral infections. In metabolic inflammation and oral infections, the innate immune system is activated through pattern recognition receptors-which include transmembrane receptors such as toll-like receptors (TLRs), cytosolic receptors such as nucleotide-binding oligomerization domain-like receptors, and multiprotein complexes called inflammasome. In general, TLR-2s are presumed to recognize lipoteichoic acid of Gram-positive microbes-and TLR-4s, lipopolysaccharide of Gram-negative microbes-while nucleotide-binding oligomerization domain-like receptors detect both Gram-positive and Gram-negative peptidoglycans on the bacterial cell walls. However, a high-fat diet activates TLR-2s, and obesity activates TLR-4s and induces spontaneous increases in serum lipopolysaccharide levels (metabolic endotoxemia). Moreover, genetics controls lipid-related transcriptome and the differentiation of monocyte and macrophages. Additionally, genetics influences CMDs, and this creates a confounding relationship among oral infections, metainflammation, and genetics. Therefore, future studies must elucidate whether oral infections can increase the risk of CMDs independent of the aforementioned confounding factors.

Susceptibility to ventilator induced lung injury is increased in senescent rats

Introduction

The principal mechanisms of ventilator induced lung injury (VILI) have been investigated in numerous animal studies. However, prospective data on the effect of old age on VILI are limited. Under the hypothesis that susceptibility to VILI is increased in old age, we investigated the pulmonary and extrapulmonary effects of mechanical ventilation with high tidal volume (VT) in old compared to young adult animals.

Interventions

Old (19.1 ± 3.0 months) and young adult (4.4 ± 1.3 months) male Wistar rats were anesthetized and mechanically ventilated (positive end-expiratory pressure 5 cmH2O, fraction of inspired oxygen 0.4, respiratory rate 40/minute) with a tidal volume (VT) of either 8, 16 or 24 ml/kg for four hours.

Respiratory and hemodynamic variables, including cardiac output, and markers of systemic inflammation were recorded throughout the ventilation period. Lung histology and wet-to-dry weight ratio, injury markers in lung lavage and respiratory system pressure-volume curves were assessed post mortem. Basic pulmonary characteristics were assessed in non-ventilated animals.

Results

Compared to young adult animals, high VT (24 ml/kg body weight) caused more lung injury in old animals as indicated by decreased oxygenation (arterial oxygen tension (PaO2): 208 ± 3 vs. 131 ± 20 mmHg; P <0.05), increased lung wet-to-dry-weight ratio (5.61 ± 0.29 vs. 7.52 ± 0.27; P <0.05), lung lavage protein (206 ± 52 mg/l vs. 1,432 ± 101; P <0.05) and cytokine (IL-6: 856 ± 448 vs. 3,283 ± 943 pg/ml; P <0.05) concentration. In addition, old animals ventilated with high VT had more systemic inflammation than young animals (IL-1β: 149 ± 44 vs. 272 ± 36 pg/ml; P <0.05 - young vs. old, respectively).

Conclusions

Ventilation with unphysiologically large tidal volumes is associated with more lung injury in old compared to young rats. Aggravated pulmonary and systemic inflammation is a key finding in old animals developing VILI.

The flow dependency of Tie2 expression in endotoxemia

RATIONALE

Tie2 is predominantly expressed by endothelial cells and is involved in vascular integrity control during sepsis. Changes in Tie2 expression during sepsis development may contribute to microvascular dysfunction. Understanding the kinetics and molecular basis of these changes may assist in the development of therapeutic intervention to counteract microvascular dysfunction.

OBJECTIVE

To investigate the molecular mechanisms underlying the changes in Tie2 expression upon lipopolysaccharide (LPS) challenge.

METHODS AND RESULTS

Studies were performed in LPS and pro-inflammatory cytokine challenged mice as well as in mice subjected to hemorrhagic shock, primary endothelial cells were used for in vitro experiments in static and flow conditions. Eight hours after LPS challenge, Tie2 mRNA loss was observed in all major organs, while loss of Tie2 protein was predominantly observed in lungs and kidneys, in the capillaries. A similar loss could be induced by secondary cytokines TNF-α and IL-1β. Ang2 protein administration did not affect Tie2 protein expression nor was Tie2 protein rescued in LPS-challenged Ang2-deficient mice, excluding a major role for Ang2 in Tie2 down regulation. In vitro, endothelial loss of Tie2 was observed upon lowering of shear stress, not upon LPS and TNF-α stimulation, suggesting that inflammation related haemodynamic changes play a major role in loss of Tie2 in vivo, as also hemorrhagic shock induced Tie2 mRNA loss. In vitro, this loss was partially counteracted by pre-incubation with a pharmacologically NF-кB inhibitor (BAY11-7082), an effect further substantiated in vivo by pre-treatment of mice with the NF-кB inhibitor prior to the inflammatory challenge.

CONCLUSIONS

Microvascular bed specific loss of Tie2 mRNA and protein in vivo upon LPS, TNFα, IL-1β challenge, as well as in response to hemorrhagic shock, is likely an indirect effect caused by a change in endothelial shear stress. This loss of Tie2 mRNA, but not Tie2 protein, induced by TNFα exposure was shown to be controlled by NF-кB signaling. Drugs aiming at restoring vascular integrity in sepsis could focus on preventing the Tie2 loss.

Low-dose dexamethasone prevents endotoxaemia-induced muscle protein loss and impairment of carbohydrate oxidation in rat skeletal muscle

We recently provided evidence suggesting a role for cytokine-mediated inhibition of Akt/Forkhead box O 1 (FOXO1) signalling in the induction of muscle atrophy and impairment of muscle carbohydrate oxidation during lipopolysaccharide (LPS)-induced endotoxaemia in rats. We hypothesized that a low-dose dexamethasone (Dex; anti-inflammatory agent) infusion during endotoxaemia would prevent the LPS-induced impairment of Akt/FOXO1 signalling, and therefore prevent the muscle atrophy and impairment of carbohydrate oxidation. Chronically instrumented Sprague-Dawley rats received a continuous intravenous infusion of LPS (15 microg kg(-1) h(-1)), Dex (12.5 microg kg(-1) h(-1)), Dex+LPS or saline for 24 h at 0.4 ml h(-1). LPS infusion caused haemodynamic changes consistent with a hyperdynamic circulation and induced increases in muscle tumour necrosis factor-alpha (TNF-alpha; 10-fold, P < 0.001), interleukin-6 (IL-6; 14-fold, P < 0.001) and metallothionein-1A (MT-1A; 187-fold, P < 0.001) mRNA expression. Dex co-administration abolished most of the haemodynamic effects of LPS and reduced the increase in muscle TNF-alpha, IL-6 and MT-1A by 51% (P < 0.01), 85% (P < 0.001) and 58% (P < 0.01), respectively. Dex infusion during endotoxaemia also prevented the LPS-induced 40% reduction in the muscle protein:DNA ratio and decrease in Akt phosphorylation, and partially prevented the reduction in FOXO1 phosphorylation. However, Dex did not prevent the LPS-mediated increase in muscle atrophy F-box (MAFbx) and muscle RING finger 1 (MuRF1) mRNA expression, but did significantly reduce the LPS-mediated increase in cathepsin-L mRNA expression and enzyme activity by 43% (P < 0.001) and 53% (P < 0.05), respectively. Furthermore, Dex suppressed LPS-induced pyruvate dehydrogenase kinase 4 (PDK4) mRNA upregulation by approximately 50% (P < 0.01), and prevented LPS-mediated muscle glycogen breakdown and lactate accumulation. Thus, low-dose Dex infusion during endotoxaemia prevented muscle atrophy and the impairment of carbohydrate oxidation, potentially through suppression of cytokine-mediated Akt/FOXO inhibition, and blunting of cathepsin-L-mediated lysosomal protein breakdown.

Social isolation modulates corticotropin-releasing factor type 2 receptor, urocortin 1 and urocortin 2 mRNAs expression in the cardiovascular system of prairie voles

The purpose of the present study was to examine the effect of social isolation stress on the expression of messengers ribonucleic acid (mRNAs) for corticotropin-releasing factor receptor type 2 (CRF2 receptor), urocortin 1 (Ucn 1) and urocortin 2 (Ucn 2) in the cardiovascular system of female and male prairie voles (Microtus ochrogaster). Isolation for 1 h (single isolation) or 1 h of isolation every day for 4 weeks (repeated isolation) was followed by a marked increase in plasma corticosterone level. However, continuous isolation for 4 weeks (chronic isolation) did not significantly affect plasma corticosterone level in female or male animals. A single period of isolation did not influence the expression of the CRF2 receptor, however, both repeated and chronic isolation significantly decreased CRF2 receptor mRNA in the ventricle and aorta of both sexes. Neither single nor chronic isolation significantly affected Ucn 1 mRNAs expression; however, repeated isolation increased Ucn 1 mRNA expression in the ventricles of female and male animals. Although, a single isolation produced no effect on cardiac Ucn 2 mRNA expression, both repeated and chronic isolation were followed by increased heart Ucn 2 mRNA expression in both sexes. We speculate that during repeated isolation Ucn 1 along with Ucn 2 are increased, which in turn down-regulates CRF2 receptor mRNA expression, and that Ucn 2 also may be one of factors responsible for the down-regulation of CRF2 receptor mRNA expression in cardiovascular system that is associated with chronic isolation.

Heart rate, lifespan, and mortality risk

An increasing body of scientific research and observational evidence indicates that resting heart rate (HR) is inversely related to the lifespan among homeothermic mammals and within individual species. In numerous human studies with patients stratified by resting HR, increased HR is universally associated with greater risk of death. The correlation between HR and maximum lifespan seems to be due to both basal metabolic rate and cardiovascular-related mortality risk. Both intrinsic and extrinsic factors are already postulated to determine how the biological clock works, through regulating and modulating the processes such as protein oxidation, free radical production, inflammation and telomere shortening. Given the remarkable correlation between HR and lifespan, resting HR should be seriously considered as another possible cap on maximum lifespan. Future research is needed to determine whether deliberate cardiac slowing, through methods like lifestyle modification, pharmacological intervention, or medical devices, can decelerate biological clock of aging, reduce cardiovascular mortality and increase maximum lifespan in humans in general.

Tumor necrosis factor-alpha induces renal vasoconstriction as well as natriuresis in mice

Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of hypertension and renal injury. However, the direct effects of TNF-α on renal hemodynamic and excretory function are not yet clearly defined. We examined the renal responses to infusion of TNF-α (0.33 ng·g⁻¹·min⁻¹) in anesthetized mice. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by PAH and inulin clearance. The urine was collected from a cannula inserted into the bladder. Following the 60-min control clearance period, TNF-α infusion was initiated and 15 min were given for stabilization followed by another 60-min clearance period. TNF-α alone (n = 7) caused decreases in RBF (7.9 ± 0.3 to 6.4 ± 0.3 ml·min⁻¹·g⁻¹) and GFR (1.04 ± 0.06 to 0.62 ± 0.08 ml·min⁻¹·g⁻¹) as well as increases in absolute (0.8 ± 0.3 to 1.4 ± 0.3 μmol·min⁻¹·g⁻¹) and fractional excretion of sodium (0.5 ± 0.2 to 1.5 ± 0.4%) without affecting arterial pressure. TNF-α also increased 8-isoprostane excretion (8.10 ± 1.09 to 11.13 ± 1.34 pg·min⁻¹·g⁻¹). Pretreatment with TNF-α blocker etanercept (5 mg/kg sc; 24 and 3 h before TNF-α infusion; n = 6) abolished these responses. However, TNF-α induced an increase in RBF and caused attenuation of the GFR reduction in mice pretreated with superoxide (O₂⁻) scavenger tempol (2 μg·g⁻¹·min⁻¹; n = 6). Pretreatment with nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (0.1 μg·g⁻¹·min⁻¹; n = 6) resulted in further enhancement in vasoconstriction while natriuresis remained unaffected in response to TNF-α. These data suggest that TNF-α induces renal vasoconstriction and hypofiltration via enhancing the activity of O₂⁻ and thus reducing the activity of NO. The natriuretic response to TNF-α is related to its direct effects on tubular sodium reabsorption.

Interleukin-1 and ischemic brain injury in the newborn: development of a small molecule inhibitor of IL-1 receptor

Inflammation participates in the genesis and progression of hypoxic-ischemic brain injury. Interleukin (IL)-1 is a major pro-inflammatory cytokine, which plays a dominant role in hypoxic-ischemic (and postinfectious) brain damage. Abundant evidence reveals the principal involvement of IL-1 over other pro-inflammatory cytokines. IL-1 interacts with the IL-1 receptor I (IL-1RI). The natural IL-1 receptor antagonist (IL-1ra) is a large 17.5-kDa peptide that competes with IL-1 for its binding site on IL-1RI. Recombinant IL-1ra (Kineret) is effective in human inflammatory conditions. However, a number of drawbacks of IL-1ra limit its broader use; these include injection site reactions [70%], broad immunosuppression, and high costs. We hereby report the characterization of a small (peptide) IL-1RI antagonist we developed, namely rytvela (termed 101.10), and its efficacy in models of (gut) inflammation and of newborn hypoxic-ischemic brain injury. Experiments reveal that 101.10 is selective for the IL-1RI and inhibits to a variable extent different effects induced by IL-1. 101.10 is effective in vivo (on systemic as well as oral administration) in established models of inflammation involving IL-1, notably in inflammatory bowel disease, and is superior to dexamethasone. In a rat pup model of hypoxic-ischemic brain injury (Rice-Vannucci model), where IL-1 and IL-1R expression is increased, 101.10 preserved microvascular density, parenchymal integrity, and brain mass. In conclusion, we hereby describe for the first time the discovery of a stable, potent, and effective specific IL-1RI small (peptide) antagonist, namely 101.10 (rytvela), which exhibits allosteric modulatory properties, and is effective in vivo in models of inflammation (known to involve IL-1) and in particular in hypoxic-ischemic newborn brain injury. 101.10 (and small alike compounds) may be suitable alternatives to IL-1ra.

Development of a novel noncompetitive antagonist of IL-1 receptor

IL-1 is a major proinflammatory cytokine which interacts with the IL-1 receptor I (IL-1RI) complex, composed of IL-1RI and IL-1R accessory protein subunits. Currently available strategies to counter pathological IL-1 signaling rely on a recombinant IL-1 receptor antagonist, which directly competes with IL-1 for its binding site. Presently, there are no small antagonists of the IL-1RI complex. Given this void, we derived 15 peptides from loops of IL-1R accessory protein, which are putative interactive sites with the IL-1RI subunit. In this study, we substantiate the merits of one of these peptides, rytvela (we termed "101.10"), as an inhibitor of IL-1R and describe its properties consistent with those of an allosteric negative modulator. 101.10 (IC(50) approximately 1 nM) blocked human thymocyte proliferation in vitro, and demonstrated robust in vivo effects in models of hyperthermia and inflammatory bowel disease as well as topically in contact dermatitis, superior to corticosteroids and IL-1ra; 101.10 did not bind to IL-1RI deficient cells and was ineffective in vivo in IL-1RI knockout mice. Importantly, characterization of 101.10, revealed noncompetitive antagonist actions and functional selectivity by blocking certain IL-1R pathways while not affecting others. Findings describe the discovery of a potent and specific small (peptide) antagonist of IL-1RI, with properties in line with an allosteric negative modulator.

Endotoxin-induced acute lung injury and organ dysfunction are attenuated by pentobarbital anaesthesia

1. Acute lung injury (ALI) as a result of sepsis is a major cause of mortality. Certain anaesthetic agents have been reported to suppress pro-inflammatory cytokines and inducible nitric oxide (NO) synthase (iNOS) activities. We investigated the effects of pentobarbital on ALI and organ functions after the administration of endotoxin. 2. Intravenous (i.v.) pentobarbital (20 or 40 mg/kg) was administered 5 min after lipopolysaccharide (LPS; 10 or 30 mg/kg via i.v. infusion). To avoid hypoxia and/or hypercapnia following anaesthesia, we installed a special chamber connected to a rodent ventilator to provide ventilation with 95% oxygen content and 5% nitrogen. The animal was kept at eucapnic conditions (arterial PCO2 at an average of 38 +/- 2 mmHg). 3. We monitored the arterial pressure (AP) and heart rate (HR). Acute lung injury was evaluated by lung weight changes, protein concentration in bronchoalveolar lavage, and Evans blue leakage. Plasma nitrate/nitrite, methyl guanidine and biochemical factors were determined. Pathological and immunofluorescent examinations were performed to observe the lung changes and to determine the activities of pro-inflammatory cytokines, nitrotyrosine and iNOS. 4. Lipopolysaccharide caused dose-dependent systemic hypotension with an increase in the extent of ALI. The lung pathology included oedema and inflammatory cell infiltration. Accompanying the ALI, LPS elevated plasma nitrate/nitrite, methyl guanidine, blood urea nitrogen, lactic dehydrogenase, creatinine phosphokinase, glutamic transaminase and amylase. The lung tissue content of tumour necrosis factor-alpha, interleukin-lbeta, iNOS and nitrotyrosine was increased following LPS administration. These changes were abrogated by pentobarbital anaesthesia. 5. Our results indicated that pentobarbital anaesthesia significantly augmented the LPS-induced systemic hypotension. However, it attenuated the LPS-induced ALI and organ dysfunctions. This agent also improved the survival rate following LPS at high and low doses. This mechanism may be related to the inhibitory effects on the increases in the production or activity of NO, free radicals, pro-inflammatory cytokines, nitrotyrosine and iNOS.

Modulation of corticotropin-releasing hormone type 2 receptor and urocortin 1 and urocortin 2 mRNA expression in the cardiovascular system of prairie voles following acute or chronic stress

The purpose of this study was to compare the effects of an acute stressor (restraint) versus a chronic stressor (social isolation) on the expression of mRNAs for corticotropin-releasing hormone receptor type 2 (CRH-R2) and urocortin 1 (Ucn 1) and urocortin 2 (Ucn 2) in the cardiovascular system of socially monogamous prairie voles of both sexes. Acute restraint for 1 h was followed by a marked increase in plasma corticosterone, and when the animals were re-paired for 1 day, the increment of corticosterone was normalized. However, following chronic social isolation for 4 weeks, plasma corticosterone did not differ significantly from the levels measured in animals living in pairs. Restraint or isolation significantly decreased CRH-R2 mRNA in ventricle, atria, and aorta; however, when these animals were re-paired for 1 day, the modulation of CRH-R2 mRNA was normalized in restraint but not in isolated animals. Restraint stress increased the Ucn 1 mRNA expression in the heart of female and male prairie voles, and when the animals were re-paired, the modulation of Ucn 1 mRNA expression was normalized. However, chronic isolation showed no effect on cardiac Ucn 1 mRNA expression. Although acute restraint stress produced no effect on the cardiac Ucn 2 mRNA expression, chronic isolation was followed by an increased heart Ucn 2 mRNA expression in both sexes. When the isolated animals were re-paired for 1 day, the cardiac Ucn 2 mRNA expression remained upregulated. The results of the present study reveal that acute restraint as well as social isolation can have significant consequences for the modulation of gene expression for the CRH-R2 and the urocortin peptides in cardiovascular tissue in female and male prairie voles.

Arginine vasopressin in advanced cardiovascular failure during the post-resuscitation phase after cardiac arrest

Arginine vasopressin (AVP) has been employed successfully during cardiopulmonary resuscitation, but there exist only few data about the effects of AVP infusion for cardiovascular failure during the post-cardiac arrest period. Cardiovascular failure is one of the main causes of death after successful resuscitation from cardiac arrest. Although the "post-resuscitation syndrome" has been described as a "sepsis-like" syndrome, there is little information about the haemodynamic response to AVP in advanced cardiovascular failure after cardiac arrest. In this retrospective study, haemodynamic and laboratory variables in 23 patients with cardiovascular failure unresponsive to standard haemodynamic therapy during the post-cardiac arrest period were obtained before, and 30 min, 1, 4, 12, 24, 48, and 72 h after initiation of a supplementary AVP infusion (4 IU/h). During the observation period, AVP significantly increased mean arterial blood pressure (58+/-14 to 75+/-19 mmHg, p < 0.001), and decreased noradrenaline (norepinephrine) (1.31+/-2.14 to 0.23+/-0.3 microg/kg/min, p = 0.03), adrenaline (epinephrine) (0.58+/-0.23 to 0.04+/-0.03 microg/kg/min, p = 0.001), and milrinone requirements (0.46+/-0.15 to 0.33+/-0.22 microg/kg/min, p < 0.001). Pulmonary capillary wedge pressure changed significantly (p < 0.001); an initial increase being followed by a decrease below baseline values. While arterial lactate concentrations (95+/-64 to 21+/-18 mg/dL, p < 0.001) and pH (7.27+/-0.14 to 7.4+/-0.14, p < 0.001) improved significantly, total bilirubin concentrations (1.12+/-0.95 to 3.04+/-3.79 mg/dL, p = 0.001) increased after AVP. There were no differences in the haemodynamic or laboratory response to AVP between survivors and non-survivors. In this study, advanced cardiovascular failure that was unresponsive to standard therapy could be reversed successfully with supplementary AVP infusion in >90% of patients surviving cardiac arrest.

Inducible Nitric Oxide Synthase Inhibition Potentiates Multiple Organ Dysfunction Induced by Endotoxin in Conscious Rats

This study was designed to investigate the effects of inducible nitric oxide synthase (iNOS) inhibition with S-methylisothiourea (SMT) and L-N-(1-iminoethyl)-lysine (L-Nil) on the endotoxemia induced by intravenous lipopolysaccharide (LPS, 10 mg/kg) in conscious rats. Arterial pressure (AP), heart rate (HR), WBC, platelets, plasma nitrite/nitrate, tumor necrosis factor alpha (TNF alpha), and biochemical factors were measured for 24 hours after LPS with or without iNOS inhibitors. RT-PCR was employed to determine the iNOS and endothelial NOS (eNOS) mRNA. Pathologic examinations of the liver and heart were performed. SMT and L-Nil improved the systemic hypotension and increased the HR after LPS. These agents attenuated the LPS-induced leukocytopenia and thrombocytopenia and the increase in nitrite/nitrate. However, iNOS inhibition aggravated the LPS-induced changes in TNF alpha, all biochemical factors, and the hepatic and cardiac tissue damage. The iNOS mRNA, but not the eNOS, was reduced. Our results in conscious rats indicate that iNOS inhibition enhances the organ dysfunction and tissue damage in sepsis. The discrepancy may be attributed to the method for evaluating the sepsis and the effects of anesthesia. Further investigation is required to ensure the effects of iNOS inhibition on sepsis before iNOS inhibitors can be applied in clinical cases with sepsis.

Involvement of CB1-receptors and beta-adrenoceptors in the regional hemodynamic responses to lipopolysaccharide infusion in conscious rats

A possible involvement of endocannabinoids in a chronic model of endotoxemia was assessed by measuring the regional (renal, mesenteric, hindquarters) hemodynamic responses to continuous 24-h LPS infusion (150 microg.kg(-1).h(-1)) in conscious, male Sprague-Dawley rats, in the absence or presence of the cannabinoid (CB1) receptor antagonist AM-251 (3 mg/kg). AM-251 inhibited the tachycardic and hindquarters vasodilator effects of LPS, but did not influence the other hemodynamic changes. In subsequent experiments, it was shown that the tachycardic and hindquarters vasodilator effects of LPS were also inhibited by the nonselective beta-adrenoceptor antagonist propranolol. In addition, the late (at 24 h) hindquarters vasodilator effects of LPS were inhibited by the beta2-adrenoceptor antagonist ICI-118551. Against the background of our previous work showing beta-adrenoceptor involvement in the cardiovascular effects of exogenous cannabinoids, we conclude that AM-251 may have been inhibiting endocannabinoid-modulated, sympathoadrenal-mediated activation of vasodilator beta-adrenoceptors in LPS-infused rats rather than suppressing a direct vasodilator action of endocannabinoids.

Lipopolysaccharide induces anandamide synthesis in macrophages via CD14/MAPK/phosphoinositide 3-kinase/NF-kappaB independently of platelet-activating factor

Macrophage-derived endocannabinoids have been implicated in endotoxin (lipopolysaccharide (LPS))-induced hypotension, but the endocannabinoid involved and the mechanism of its regulation by LPS are unknown. In RAW264.7 mouse macrophages, LPS (10 ng/ml) increases anandamide (AEA) levels >10-fold via CD14-, NF-kappaB-, and p44/42-dependent, platelet-activating factor-independent activation of the AEA biosynthetic enzymes, N-acyltransferase and phospholipase D. LPS also induces the AEA-degrading enzyme fatty acid amidohydrolase (FAAH), and inhibition of FAAH activity potentiates, whereas actinomycin D or cycloheximide blocks the LPS-induced increase in AEA levels and N-acyltransferase and phospholipase D activities. In contrast, cellular levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) are unaffected by LPS but increased by platelet-activating factor. LPS similarly induces AEA, but not 2-AG, in mouse peritoneal macrophages where basal AEA levels are higher, and the LPS-stimulated increase in AEA is potentiated in cells from FAAH-/- as compared with FAAH+/+ mice. Intravenous administration of 107 LPS-treated mouse macrophages to anesthetized rats elicits hypotension, which is much greater in response to FAAH-/- than FAAH+/+ cells and is susceptible to inhibition by SR141716, a cannabinoid CB1 receptor antagonist. We conclude that AEA and 2-AG synthesis are differentially regulated in macrophages, and AEA rather than 2-AG is a major contributor to LPS-induced hypotension.

Modulation of corticotropin-releasing hormone receptor type 2 mRNA expression by CRH deficiency or stress in the mouse heart

The actions of corticotropin-releasing hormone (CRH) and the related peptides are coordinated by two receptors, CRH receptor type 1 (CRH-R1) and CRH receptor type 2 (CRH-R2). In this study, we examined the effects of CRH deficiency and/or stress due to physically restraint or lipopolysaccharide (LPS) administration on expression of transcripts for CRH-R2 (CRH-R2 mRNA) as well as urocortin (UCN) mRNA in the atria and ventricle using female and male CRH-deficient (knockout, KO) mice. We show that restraint stress caused a significant increase in plasma corticosterone levels in female CRH KO mice, but LPS administration induced a significant increase in plasma corticosterone levels in both female and male CRH KO mice. CRH deficiency caused a robust decrease in basal levels of CRH-R2 mRNA and a significant increase of UCN mRNA expression in the atria and ventricle of female as well as male mice. Restraint stress markedly reduced CRH-R2 mRNA and increased UCN mRNA expression on atria as well as ventricle in both female and male wild-type (WT) mice. Following LPS injection to both female and male mice, CRH-R2 mRNA expression was decreased and UCN mRNA expression was increased in the atria and ventricle of both WT and CRH KO mice in each sex. We speculate that stress or lack of CRH may increase urocortin, which in turn down-regulates CRH-R2 mRNA expression in the heart. These data indicate: (1) that lack of CRH may decreases cardiac CRH-R2 mRNA expression in basal state, (2) that inhibitory effect of CRH deficiency on cardiac CRH-R2 mRNA expression in stress condition seems to be more closely linked to type of stressor than rise in plasma corticosterone level.

Down-regulation of corticotropin-releasing hormone receptor type 2beta mRNA expression in the rat cardiovascular system following food deprivation

The present study was conducted to assess the effect of nutritional stress induced by food deprivation on expression of messenger ribonucleic acid (mRNA) for corticotropin-releasing hormone receptor type 2beta (CRH-R2beta) in the rat cardiovascular system in the presence or absence of changes in circulating corticosterone. Food deprivation for 96 h caused a robust increase in plasma corticosterone levels and a significant decrease in CRH-R2beta mRNA expression in the rat heart. Starvation for 48 and 96 h decreased CRH-R2beta mRNA expression in the atria, ventricle as well as aorta of sham-adrenalectomized (sham) rats. Surprisingly, clamping plasma glucocorticoids at low levels by adrenalectomy with corticosterone pellet replacement (ADX+B) did not completely prevent starvation-induced decreases of CRH-R2beta mRNA expression in the rat cardiovascular system. Urocortin (Ucn) mRNA expression was increased significantly by food deprivation in the heart of sham as well as ADX+B rats. We speculate that food deprivation may increase urocortin, which in turn down-regulates CRH-R2beta mRNA expression in cardiovascular system. These data indicate that food deprivation despite the presence or absence of changes in circulating corticosterone may have an inhibitory effect on CRH-R2beta mRNA expression in the rat cardiovascular system.

Roles of central interleukin-1 on stress-induced-hypertension and footshock-induced-analgesia in rats

Central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors. Here we tested whether central IL-1 is involved in stress-induced hypertension or footshock (FS)-induced-analgesia. We observed that: (1) intracerebral ventricular injection of (ICV) IL-1beta induced pressor responses; (2) hypertension induced by IL-1beta was blocked by ICV an IL-1 antagonist, IL-1ra; (3) ICV IL-1ra attenuated the pressor response induced by FS but intravenous injection of IL-1ra did not significantly reduce this response; (4) the hypertensive response to conditioned fear stimuli was reversed by ICV IL-1ra; (5) FS-induced-analgesia was attenuated by ICV IL-1ra and this effect disappeared 15 min after ICV IL-1ra. These results suggest that both the pressor response to FS or conditioned fear stimuli and short lasting analgesia induced by FS are mediated by central IL-1.

Haemodynamic effects of the bacterial quorum sensing signal molecule, N-(3-oxododecanoyl)-L-homoserine lactone, in conscious, normal and endotoxaemic rats

N-acylhomoserine lactones (AHLs) are small, diffusible signalling molecules, employed by Gram-negative bacteria to coordinate gene expression with cell population density. Recent in vitro findings indicate that AHLs may function as virulence determinants per se, through modification of cytokine production by eukaryotic cells, and by stimulating the relaxation of blood vessels. In the present study, we assessed the influence of AHLs on cardiovascular function in conscious rats, and draw attention to the ability of the N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL), a signal molecule produced by P. aeruginosa, to cause marked bradycardia. This bradycardic effect was blocked by atropine and atenolol, and did not occur in vitro. Furthermore, modification of the acyl side chain length resulted in the loss of activity, whereas removal of the homoserine lactone ring, did not. The bradycardic effect of 3-oxo-C12-HSL was also observed in endotoxaemic animals, albeit attenuated. In normal rats, 3-oxo-C12-HSL caused initial mesenteric and hindquarters vasoconstriction, but only slight, and delayed signs of vasodilatation in the renal and mesenteric vascular beds. Furthermore, administration of 3-oxo-C12-HSL (pre-treatment or 2 h post-treatment) together with LPS, did not modify the established regional haemodynamic effects of the LPS, 6 h after the onset of its infusion. Our observations do not provide any clear evidence for an ability of 3-oxo-C12-HSL to modify the haemodynamic responses to LPS infusion. However, they are not inconsistent with the hypothesis that some of the cardiovascular sequelae of bacterial infection may be modulated by an influence of bacterial quorum sensing signalling molecules on the host.

Splenic denervation worsens lipopolysaccharide-induced hypotension, hemoconcentration, and hypovolemia

During lipopolysaccharide (LPS)-induced endotoxemia, increased intrasplenic fluid efflux contributes to a reduction in plasma volume. We hypothesized that splenic sympathetic nerve activity (SSNA), which increases during endotoxemia, limits intrasplenic fluid efflux. We reasoned that splenic denervation would exaggerate LPS-induced intrasplenic fluid efflux and worsen the hypotension, hemoconcentration, and hypovolemia. A nonlethal dose of LPS (150 microg x kg(-1) x h(-1) for 18 h) was infused into conscious male rats bearing transit time flow probes on the splenic artery and vein. Fluid efflux was estimated from the difference in splenic arterial inflow and venous outflow (A-V). LPS significantly increased the (A-V) flow differential (fluid efflux) in intact rats (saline -0.01 +/- 0.02 ml/min, n = 8 vs. LPS +0.21 +/- 0.06 ml/min, n = 8); this was exaggerated in splenic denervated rats (saline -0.03 +/- 0.01 ml/min, n = 7 vs. LPS +0.41 +/- 0.08 ml/min, n = 8). Splenic denervation also exacerbated the LPS-induced hypotension, hemoconcentration, and hypovolemia (peak fall in mean arterial pressure: denervated 19 +/- 3 mmHg, n = 10 vs. intact 12 +/- 1 mmHg, n = 8; peak rise in hematocrit: denervated 6.7 +/- 0.3%, n = 8 vs. intact 5.0 +/- 0.3%, n = 8; decrease in plasma volume at 90-min post-LPS infusion: denervated 1.08 +/- 0.15 ml/100 g body wt, n = 7 vs. intact 0.54 +/- 0.08 ml/100 g body wt, n = 8). The exaggerated LPS-induced hypovolemia associated with splenic denervation was mirrored in the rise in plasma renin activity (90 min post-LPS: denervated 11.5 +/- 0.8 ng x ml(-1) x h(-1), n = 9 vs. intact 6.6 +/- 0.7 ng x ml(-1) x h(-1), n = 8). These results are consistent with our proposal that SSNA normally limits LPS-induced intrasplenic fluid efflux.

iNOS gene expression modulates microvascular responsiveness in endotoxin-challenged mice

Septic shock is characterized by vasodilation and decreased responsiveness to vasoconstrictors. Recent studies suggest this results from nitric oxide (NO) overproduction after expression of the calcium-independent isoform of NO synthase (iNOS) in smooth muscle cells. However, direct evidence linking iNOS (NOS2) expression and decreased microvascular responsiveness after septic stimuli is lacking. In the present study, we determined the effect of bacterial lipopolysaccharide (LPS, 20 mg/kg, IP) on smooth muscle contraction and endothelial relaxation in mesenteric resistance arteries from wild-type and iNOS knockout mice. Four hours after challenge with LPS or saline in vivo, concentration-dependent responses to norepinephrine (NE) and acetylcholine (NE+ACh) were measured in cannulated, pressurized vessels ex vivo. In vessels from wild-type mice, NE-induced contraction was markedly impaired after LPS, and pretreatment with the iNOS inhibitor aminoguanidine (AG) partly restored the NE contraction. In contrast, NE contraction in microvessels from iNOS knockout mice was unaffected by LPS. ACh-induced relaxation was unaffected by LPS in vessels from either genotype. These data provide direct evidence that iNOS gene expression mediates the LPS-induced decrease in microvascular responsiveness to vasoconstrictors. Moreover, the observation that AG did not fully restore NE contraction after LPS, whereas iNOS gene deficiency did, suggests that iNOS expression plays a central role in the development of the NO-independent effect of LPS on microvascular responsiveness. Finally, our data indicate that LPS or iNOS expression has little effect on endothelium-dependent relaxation, and eNOS activity does not appear to play a role in the decreased smooth muscle responsiveness after LPS in this model. The full text of this article is available at http://www.circresaha.org.

Regulation of corticotropin-releasing factor receptor type 2 beta messenger ribonucleic acid in the rat cardiovascular system by urocortin, glucocorticoids, and cytokines

CRF receptor type 2 (CRF R2) messenger RNA (mRNA) expression in the rodent heart is modulated by exposure to both the bacterial endotoxin lipopolysaccharide (LPS) and glucocorticoids. In this study we examined the roles of glucocorticoids, cytokines, and CRF R2beta ligands in the regulation of CRF R2beta expression in the cardiovascular system both in vivo and in vitro. Using ribonuclease protection assays, we found that, in addition to the injection of LPS or corticosterone, physical restraint caused a decrease in CRF R2beta mRNA levels in the rat heart and aorta. Adrenalectomy with corticosterone replacement at constant levels partially blocked LPS-induced decreases in CRF R2beta mRNA expression in the heart. Thus, elevations of endogenous circulating corticosterone could contribute to the down-regulation of CRF R2beta mRNA expression in heart. To identify other putative modulating factors, we examined CRF R2beta expression in the aorta-derived A7R5 cell line. Incubation with CRF R2 ligands or dexamethasone reduced CRF R2beta mRNA levels. In addition, incubation with a variety of cytokines, proteins released during immune challenge, also reduced CRF R2beta mRNA expression. The multifactorial regulation of CRF R2beta mRNA expression in the cardiovascular system may serve to limit the inotropic and chronotropic effects of CRF R2 agonists such as urocortin during prolonged physical or immune challenge.

Regional haemodynamic responses to infusion of lipopolysaccharide in conscious rats: effects of pre- or post-treatment with glibenclamide

1. To determine the putative contribution of K(ATP)-channels to the haemodynamic sequelae of endotoxaemia, three experiments were carried out in different groups of conscious, chronically-instrumented, unrestrained, male Long Evans rats. 2. In the first experiment, pretreatment with the K(ATP)-channel antagonist, glibenclamide, abolished the initial hypotension, but not the renal vasodilatation caused by LPS infusion. Subsequently, however, in the presence of glibenclamide and LPS there was a significant increase in mean arterial blood pressure, and a bradycardia, in contrast to the fall in mean arterial blood pressure and the tachycardia seen in the presence of vehicle and LPS. The pressor and bradycardic changes in the presence of glibenclamide and LPS were accompanied by significant reductions in hindquarters flow and vascular conductance, and these were significantly greater than those seen in the presence of vehicle and LPS, or glibenclamide and saline. 3. Administration of glibenclamide 6 h after the onset of saline and LPS infusion, or 6 h after the onset of saline and LPS infusion in the presence of the AT(1)-receptor antagonist, losartan, and the ET(A)-, ET(B)- receptor antagonist, SB 209670, in the absence or presence of dexamethasone, caused a significant increase in mean arterial blood pressure and reductions in renal, mesenteric and hindquarters conductances, although the latter was the only vascular bed in which there was a reduction in flow. 4. The results are consistent with a contribution from K(ATP)-channels to the vasodilatation caused by LPS, particularly in the hindquarters vascular bed.

Influence of FR 167653, an inhibitor of TNF-alpha and IL-1, on the cardiovascular responses to chronic infusion of lipopolysaccharide in conscious rats

Conscious, male Long Evans rats (350-450 g) chronically instrumented for the measurement of regional haemodynamics, were infused with FR 167653, a dual inhibitor of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) synthesis (0.32 mg/kg/h) for 24 h, beginning 1 h before coinfusion of saline, or with saline for 24 h beginning 1 h before coinfusion of lipopolysaccharide (150 microg/kg/h), or with FR 167653 beginning 1 h before coinfusion of lipopolysaccharide. Animals infused with FR 167653 and saline showed progressive hindquarters vasoconstriction over the 24-h period, but this was not different from the change seen in animals (n = 3) infused with saline alone. However, plasma analysis at the end of the coinfusion of FR 167653 and saline showed substantial elevation in levels of creatine kinase, lactate dehydrogenase, and potassium, consistent with some tissue damage (heart, liver, or skeletal muscle, or a combination of these). Animals coinfused with saline and lipopolysaccharide showed biphasic decreases in mean arterial blood pressure accompanied by renal hyperaemic vasodilatation, and decreases followed by increases in mesenteric and hindquarters flows and vascular conductances. At the end of the infusion period, plasma analysis showed signs of renal dysfunction (elevated creatinine) and hepatic dysfunction (elevated alkaline phosphatase, gamma-glutamyl transferase, and alanine aminotransferase). In the presence of FR 167653, the hypotensive effects of lipopolysaccharide were abolished, but regional haemodynamics were unchanged, as were signs of organ dysfunction. One explanation of these observations is that FR 167653 causes a relative improvement in cardiac function during infusion of lipopolysaccharide, and this opposes the hypotensive effects of the latter, in spite of its persistent vasodilator effects.