Differentiated effects on splanchnic homeostasis by selective and non-selective endothelin receptor antagonism in porcine endotoxaemia

Cardiopulmonary bypass is associated with altered vascular reactivity of isolated pulmonary artery in a porcine model: therapeutic potential of inhaled tezosentan

OBJECTIVE

Whereas it is established that endothelin-1 elicits sustained deleterious effects on the cardiovascular system during cardiopulmonary bypass (CPB), presently it remains unknown whether the inhaled administration of the dual ETA and ETB antagonist tezosentan prevents the development of pulmonary endothelial dysfunction.

DESIGN

A prospective, randomized laboratory investigation.

SETTING

University research laboratory.

PARTICIPANTS

Landrace swine.

INTERVENTIONS

Three groups of animals underwent a 90-minute period of full bypass followed by a 60-minute period of reperfusion. Among treated groups, one received tezosentan through inhalation prior to CPB, whereas the other one received it intravenously at weaning from CPB; the third group remained untreated. Pulmonary vascular reactivity studies, realized on a total of 285 rings, were performed in all groups, including 1 sham.

MEASUREMENTS AND MAIN RESULTS

The contractility of pulmonary arteries to prostaglandin F2α and to the thromboxane A2 mimetic U46619 was preserved in animals submitted to CPB. By contrast, there were significant increases both in the maximal contraction to endothelin-1 and in the plasma levels of the peptide 60 minutes after reperfusion. Tezosentan administered by inhalation or intravenously did not prevent the development of pulmonary CPB-associated endothelial dysfunction. However, while hemodynamic disturbances were improved with both routes, the inhaled administration had a beneficial effect on oxygen parameters over intravenous administration.

CONCLUSIONS

Despite the blockade of the endothelin-1 pathway with tezosentan, the development of the pulmonary endothelial dysfunction associated with CPB still occurred. However, only the inhalation route had a significant impact on gas exchange during CPB.

Influence of specific endothelin-1 receptor blockers on hemodynamic parameters and antioxidant status of plasma in LPS-induced endotoxemia

BACKGROUND

The potent vasoconstrictor endothelin-1 has been implicated in the pathogenesis of plasma oxidative stress seen in sepsis. The selective endothelin receptor blockers BQ123 and BQ788 were used to investigate the importance of selective endothelin receptor blockage in modulating oxidative stress during endotoxemia.

METHODS

The study was performed on male Wistar rats (n = 6 per group) divided into groups: (1) saline, (2) lipopolysaccharide (LPS) (15 mg/kg)-saline, (3) BQ123 (0.5 mg/kg)-LPS, (4) BQ123 (1 mg/kg)-LPS, (5) BQ788 (3 mg/kg)-LPS. The endothelin receptor type A(ETA-R) or type B (ETB-R) antagonist was injected intravenously 30 min before LPS administration. Blood pressure was monitored and blood was taken before, 90 min and 300 min after saline or LPS administration.

RESULTS

Injection of LPS alone resulted in a decrease in mean arterial pressure (MAP) (p < 0.05), a decrease in ferric reducing ability of plasma (FRAP) value (p < 0.01) and a marked increase in plasma tumor necrosis factor α (TNF-α) and thiobarbituric acid reactive substances (TBARS) (p < 0.001, p < 0.001, respectively). Administration of BQ123 before LPS administration deteriorated MAP in a dose dependent way. Moreover, BQ123 (1 mg/kg) decreased plasma level of TBARS and TNF-α (p < 0.01 and p < 0.05, respectively) and increased FRAP value (p < 0.001). On the contrary, BQ788 prevented LPS-induced decrease in MAP(p < 0.001) and led to a significant reduction in plasma TBARS concentration (p < 0.01).

CONCLUSIONS

Our study showed that blockage of ETB-R during endotoxemia improved blood hemodynamics and decreased plasma lipid peroxidation. Blockage of ETA-R improved plasma antioxidant status and decreased lipid peroxidation and TNF-α production, but it deteriorated hemodynamic conditions.

Endothelin receptor A antagonism attenuates renal medullary blood flow impairment in endotoxemic pigs

Background

Endothelin-1 is a potent endogenous vasoconstrictor that contributes to renal microcirculatory impairment during endotoxemia and sepsis. Here we investigated if the renal circulatory and metabolic effects of endothelin during endotoxemia are mediated through activation of endothelin-A receptors.

Methods and Findings

A randomized experimental study was performed with anesthetized and mechanically ventilated pigs subjected to Escherichia coli endotoxin infusion for five hours. After two hours the animals were treated with the selective endothelin receptor type A antagonist TBC 3711 (2 mg⋅kg⁻¹, n = 8) or served as endotoxin-treated controls (n = 8). Renal artery blood flow, diuresis and creatinine clearance decreased in response to endotoxemia. Perfusion in the cortex, as measured by laser doppler flowmetry, was reduced in both groups, but TBC 3711 attenuated the decrease in the medulla (p = 0.002). Compared to control, TBC 3711 reduced renal oxygen extraction as well as cortical and medullary lactate/pyruvate ratios (p<0.05) measured by microdialysis. Furthermore, TBC 3711 attenuated the decline in renal cortical interstitial glucose levels (p = 0.02) and increased medullary pyruvate levels (p = 0.03). Decreased creatinine clearance and oliguria were present in both groups without any significant difference.

Conclusions

These results suggest that endothelin released during endotoxemia acts via endothelin A receptors to impair renal medullary blood flow causing ischemia. Reduced renal oxygen extraction and cortical levels of lactate by TBC 3711, without effects on cortical blood flow, further suggest additional metabolic effects of endothelin type A receptor activation in this model of endotoxin induced acute kidney injury.

Endothelin-mediated gut microcirculatory dysfunction during porcine endotoxaemia

BACKGROUND

The potent vasoconstrictor endothelin-1 has been implicated in the pathogenesis of the microcirculatory dysfunction seen in sepsis. The mixed endothelin receptor antagonist tezosentan and the selective endothelin A-receptor antagonist TBC3711 were used to investigate the importance of the different endothelin receptors in modulating splanchnic regional blood flow and microvascular blood flow in endotoxaemia.

METHODS

Eighteen anaesthetized pigs were i.v. infused with endotoxin (Escherichia coli lipopolysaccharide, serotype 0111:b4) for 300 min. After 120 min, six animals received tezosentan and six animals received TBC3711. Six animals served as endotoxin-treated controls. Laser Doppler flowmetry was used to measure microcirculatory blood flow in the liver and ileum. Superior mesenteric artery flow (SMA(FI)) and portal vein flow (PV(FI)) were measured with ultrasonic flow probes, and air tonometry was used to measure Pco₂ in the ileal mucosa.

RESULTS

TBC3711 did not improve splanchnic regional blood flow or splanchnic microvascular blood flow compared with endotoxin-treated controls. Tezosentan increased PV(FI) (P<0.05), but SMA(FI) was not improved compared with the other groups. In the tezosentan group, microvascular blood flow in the ileal mucosa (MCQ(muc)) improved and mucosal-arterial Pco₂ gap decreased (P<0.05 for both) compared with endotoxin-treated controls and the TBC3711 group.

CONCLUSIONS

Tezosentan improved MCQ(muc) without any concomitant increase in SMA(FI), implying a direct positive effect on the microcirculation. TBC3711 was not effective in improving regional splanchnic blood flow or splanchnic microvascular blood flow. Dual endothelin receptor antagonism was necessary to improve MCQ(muc), indicating a role for the endothelin B-receptor in mediating the microcirculatory failure in the ileal mucosa.

The role of endothelium and endogenous vasoactive substances in sepsis

Sepsis and septic shock are great challenges for the doctors who treat critically ill patients. A big part of the scientific community is performing researches about the pathophysiology and treatment of this clinical problem. The endothelium has a very significant role in the alterations that sepsis causes especially to the circulatory system. The disorders of the normal function of the endothelium include derangement of the vascular tone, increase of endothelium permeability, activation of the endothelial cells, production of various regulators and disorders of coagulation. Nitric oxide is the modulator that mediates the action of most vasodilators. The overproduction of nitric oxide during sepsis is possibly the most important cause of the vasopressor-resistant hypotension which characterizes septic shock. The levels of natriuretic peptides are also increased. These peptides act through several ways on the circulatory system both peripherally and directly on the myocardium. Endothelin, vasopressin, adrenomedullin and prostacyclin are vasoactive substances that have their own role in the regulation of the circulatory system during sepsis.

Inhaled tezosentan reduces pulmonary hypertension in endotoxin-induced lung injury

The vasoconstrictive and proinflammatory peptide endothelin 1 (ET-1) is highly involved in the pathogenesis of sepsis and associated lung injury. Systemic administration of ET-receptor antagonists has been beneficial in experimental pulmonary hypertension. We wanted to study the effects of inhaled tezosentan, a dual endothelin-receptor antagonist on endotoxin-induced pulmonary hypertension, deterioration of gas exchange, and edema formation. After 2 h of endotoxemia, 28 anesthetized, mechanically ventilated pigs were randomized to either inhaled tezosentan 0.5 mg x kg (TEZO(0.5), n = 7), 0.05 mg x kg (TEZO(0.05), n = 7), intravenous 0.5 mg x kg (TEZO(iv), n = 7), or control (n = 7). Cardiopulmonary hemodynamics and gas-exchange parameters were recorded as well as extravascular lung water and pulmonary capillary pressure. In addition, plasma levels of tezosentan and ET-1 were analyzed. The protocol lasted for 5 h. Endotoxin-induced pulmonary hypertension (mean pulmonary artery pressure) was efficiently reduced by all treatments (TEZO(0.5) 24 +/- 2, TEZO(0.05) 27 +/- 2, TEZO(iv) 26 +/- 1, and control 37 +/- 2 mmHg at 4 h). TEZO(0.5) and TEZO(iv) also reduced pulmonary capillary pressure. All treatments led to a modest reduction in extravascular lung water, whereas no effects were noted on oxygenation or systemic circulation. Despite similar effects on pulmonary hypertension systemic treatment resulted in significantly higher plasma levels of ET-1 (twofold) and tezosentan (10- to 100-fold). Inhalation of the dual ET-receptor antagonist tezosentan was feasible and efficiently counteracted endotoxin-induced pulmonary hypertension. These effects were obtained with only minor systemic uptake of tezosentan and without affecting circulating levels of plasma ET-1 as compared with intravenous administration.

LPS abolishes extrasplenic vasoconstriction to atrial natriuretic peptide: the role of NO and endothelin 1

Sepsis causes changes in vascular resistance and hypovolemia. Previous studies have demonstrated that the spleen regulates blood volume via atrial natiuretic peptide (ANP). We hypothesized that LPS alters extrasplenic responses to ANP via endothelial-dependent mechanisms and studied the role of NO and endothelin 1 (ET-1). Isolated extrasplenic arteries and veins (vessels in mesentery adjoining spleen) were obtained from male Wistar rats weighing 200 to 280 g (n = 102) and mounted on a pressure myograph to determine intraluminal diameter for 4 h. Isolated vessels constricted in response to the half-maximum response of ANP (veins, 30% +/- 1.7%; arteries, 34.5 +/- 1.7%; P < 0.05), and this was abolished by the NO donor S-nitroso-N-acetylpenicillamine (SNAP 75 microM). Arteries and veins incubated with LPS (50 microg mL(-1) for 4 h) were unresponsive to ANP, and constriction was not restored by the NOS inhibitor N omega-nitro-L-arginine methyl ester (L-NAME 100 microM). However, venular constriction returned in the presence of the ET-1 antagonist Bosentan, increasing from -1.5 +/- 1.2 (10 min) to -10 +/- 2.5% (4 h) with LPS + Bosentan (3 x 10(-6) M) compared with -2.3 +/- 1.2 and 0% with LPS alone. In conclusion, LPS abolished endothelial-dependent extrasplenic venular constriction to ANP partially due to increased ET-1, whereas NO seemed to modulate vascular responses to ANP.

Mixed endothelin receptor antagonism with tezosentan improves intestinal microcirculation in endotoxemic shock

BACKGROUND

Microcirculatory dysfunction is a common feature of sepsis. The potent vasoconstrictor endothelin (ET) is released in sepsis and endotoxemia, potentially contributing to sepsis-induced microcirculatory failure. In this study we tested the hypothesis that mixed ET receptor antagonism with tezosentan would improve splanchnic microcirculatory blood flow in acute porcine endotoxemia.

MATERIALS AND METHODS

Sixteen anesthetized and mechanically ventilated pigs received an infusion of endotoxin for 300 min. After 120 min eight pigs received a bolus dose of tezosentan 1 mg/kg followed by an infusion of tezosentan of 1 mg/kg/h throughout the experiment. Eight pigs served as endotoxin controls. Laser Doppler flowmetry was used to measure microcirculatory blood flow in the liver and in the ileal and colon mucosa. PCO(2) in the ileal mucosa was measured by air tonometry and portal vein flow by an ultrasonic flow probe.

RESULTS

Endotoxin administration induced a state of shock with impaired splanchnic microcirculatory blood flow. Microcirculation in the mucosa of the colon and ileum and mucosal-arterial PCO(2) gap were improved by tezosentan. Portal vein flow was increased, but hepatic microcirculatory blood flow was not significantly improved. Tezosentan preserved cardiac index and decreased pulmonary capillary wedge pressure compared to controls, without causing any differences in the heart rate or mean arterial blood pressure response. Tezosentan also distinctly improved pH and arterial lactate values.

CONCLUSIONS

The findings of this study indicate that ET is involved in the microcirculatory dysfunction seen in the ileal and colon mucosa in early endotoxemia. Moreover, this detrimental effect was counteracted by i.v. administration of the mixed ET receptor antagonist tezosentan.

Cardiac effects of endothelin receptor antagonism in endotoxemic pigs

Myocardial depression in sepsis is frequently encountered clinically and contributes to morbidity and mortality. Increased plasma levels of endothelin-1 (ET-1) have been described in septic shock, and previous reports have shown beneficial effects on cardiovascular performance and survival in septic models using ET receptor antagonists. The aim of the current study was to investigate specific cardiac effects of ET receptor antagonism in endotoxicosis. Sixteen domestic pigs were anesthetized and subjected to endotoxin for 5 h. Eight of these pigs were given tezosentan (dual ET receptor antagonist) after 3 h. Cardiac effects were evaluated using the left ventricular (LV) pressure-volume relationship. Endotoxin was not associated with any effects on parameters of LV contractile function [end-systolic elastance (Ees), preload recruitable stroke work (PRSW), powermax/end-diastolic volume (PWRmax/EDV) and dP/d tmax/end-diastolic volume (dP/d tmax/EDV)] but with impairments in isovolumic relaxation (time constant for pressure decay, tau) and mechanical efficiency. Tezosentan administration decreased Ees, PWRmax/EDV, and dP/d tmax/EDV, while improving tau and LV stiffness. Thus, dual ET receptor antagonism was associated with a decline in contractile function but, in contrast, improved diastolic function. Positive hemodynamic effects from ET receptor antagonism in acute endotoxemia may be due to changes in cardiac load and enhanced diastolic function rather than improved contractile function.

Tezosentan attenuates organ injury and mesenteric blood flow decrease in endotoxemia and cecal ligation and puncture

BACKGROUND

Decreased mesenteric blood flow and multiple organ injury due to free radicals are the consequences of septic shock. Since the blockade of endothelin receptors was reported to exert beneficial effects, we investigated the effects of tezosentan, a novel dual endothelin receptor antagonist, in two different experimental models of septic shock induced either by the injection of Escherichia coli endotoxin (ETX, 20 mg/kg, i.p.) or by cecal ligation and puncture (CLP).

STUDY DESIGN

Swiss albino mice received tezosentan (10 mg/kg, i.p.) or its solvent saline (0.9% NaCl, w/v) twice at 2 and 22 h after ETX or CLP. At 24 h, the animals were anesthetized and the mesenteric blood flow was monitored for 15 min by using perivascular ultrasonic Doppler flowmeter. Then the animals were exsanguinated, and spleen, liver, and kidneys were isolated accordingly for histopathological examination. Thiobarbituric acid reacting substances and glutathione and myeloperoxides activities were also determined in the liver.

RESULTS

In both ETX and CLP models, there was a decrease in mesenteric blood flow which was blocked by tezosentan. Similarly, tezosentan significantly attenuated the histopathological injury inflicted by both models. Although the glutathione levels were decreased and thiobarbituric acid reacting substances and myeloperoxidase activity were increased by ETX and CLP, tezosentan has failed to block these alterations in a consistent manner. However, a significant interaction between CLP and tezosentan with regard to myeloperoxidase activity and glutathione should be taken as partial evidence to explain the underlying mechanism of protection offered by tezosentan against liver injury.

CONCLUSIONS

Therefore, we concluded that tezosentan, by working via mechanisms mostly other than the blockade of free radical induced damage, is a useful treatment option for combating the deleterious effects of septic shock such as mesenteric ischemia as well as liver, spleen, and kidney injury.

Positive inotropic and negative lusitropic effects of endothelin receptor agonism in vivo

The endothelin (ET) system is involved in the regulation of myocardial function in health as well as in several diseases, such as congestive heart failure, myocardial infarction, and septic myocardial depression. Conflicting results have been reported regarding the acute contractile properties of ET-1. We therefore investigated the effects of intracoronary infusions of ET-1 and of the selective ETBreceptor-selective agonist sarafotoxin 6c with increasing doses in anesthetized pigs. Myocardial effects were measured through analysis of the left ventricular pressure-volume relationship. ET-1 elicited increases in the myocardial contractile status (end-systolic elastance value of 0.94 ± 0.11 to 1.48 ± 0.23 and preload recruitable stroke work value of 68.7 ± 4.7 to 83.4 ± 7.2) that appear to be mediated through ETAreceptors, whereas impairment in left ventricular isovolumic relaxation (τ = 41.5 ± 1.4 to 58.1 ± 5.0 and t1/2= 23.0 ± 0.7 to 30.9 ± 2.6, where τ is the time constant for pressure decay and t1/2is the half-time for pressure decay) was ETBreceptor dependent. In addition, intravenous administration of ET-1 impaired ventricular relaxation but had no effect on contractility. Intracoronary sarafotoxin 6c administration caused impairments in left ventricular relaxation (τ from 43.3 ± 1.8 to 54.4 ± 3.4) as well as coronary vasoconstriction. In conclusion, ET-1 elicits positive inotropic and negative lusitropic myocardial effects in a pig model, possibly resulting from ETAand ETBreceptor activation, respectively.

Differentiated and dose-related cardiovascular effects of a dual endothelin receptor antagonist in endotoxin shock

OBJECTIVE

To evaluate the effects of endothelin receptor antagonism on cardiac performance in endotoxin shock.

DESIGN

Prospective, experimental study.

SETTING

A university-affiliated research institution.

SUBJECTS

Domestic anesthetized landrace pigs.

INTERVENTIONS

Thirty-seven pigs were anesthetized and subjected to echocardiography, coronary sinus catheterization, and monitoring of central and regional hemodynamics in order to assess cardiac performance. All animals received endotoxin for 5 hrs. Twenty pigs served as endotoxin controls. Tezosentan, a dual endothelin-A and -B receptor antagonist, was administered during established endotoxemic shock. Seven pigs received an infusion of tezosentan of 1 mg x kg(-1) x hr(-1) (tezo1), and an additional ten pigs received a higher dose of 10 mg x kg(-1) x hr(-1) (tezo10).

MEASUREMENTS AND MAIN RESULTS

Endotoxemia evoked a state of shock with pulmonary hypertension and metabolic acidosis. A decrease in stroke volume and coronary perfusion pressure as well as an increase in troponin I was also noted. Tezosentan administration resulted in a significant increase in cardiac index, stroke volume index, left ventricular stroke work index, and left ventricular end-diastolic area index. Decreases in systemic and pulmonary vascular resistance indexes were also evident after intervention. This was achieved without changes in heart rate or systemic arterial or pulmonary artery occlusion pressures in tezo, animals compared with controls. In addition, metabolic variables were improved by tezosentan. These effects were sustained only in the tezo, group. In the higher dosage, tezosentan resulted in a deterioration of cardiac performance and 50% mortality rate. The endotoxin-induced increase in troponin I was attenuated in the tezo, group compared with controls.

CONCLUSIONS

In this porcine model of volume-resuscitated, endotoxemic shock, endothelin-receptor blockade with tezosentan improved cardiac performance. However, the effect was not sustained with higher doses of tezosentan, possibly due to reduced coronary perfusion pressure. These findings show differentiated, dose-dependent effects by dual endothelin receptor blockade on endotoxin-induced cardiovascular dysfunction.

Role of endothelin ETA receptors in sepsis-induced mortality, vascular leakage, and tissue injury in rats

The role of endothelin ETA receptors in sepsis-induced mortality and edema formation was evaluated with a selective antagonist ABT-627 [2-(4-methoxyphenyl)-4-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)amino carbonylmethyl)-pyrrolidine-3-carboxylic acid]. Sprague-Dawley rats received saline (control group), Escherichia coli endotoxin (10 mg/kg, sepsis group) or infusion of ABT-627 prior and immediately after saline and endotoxin injection. Mortality, edema formation (wet/dry ratios), and multiple tissue injury (indicated by serum concentrations of creatinine, urea, bilirubin, creatine kinase, lactate dehydrogenase, and aspartate aminotransferase) were monitored within 5 h. Endotoxin injection elicited 64% mortality, significantly augmented edema formation in liver, heart, lung, and kidney, and raised serum levels of tissue injury markers. Pretreatment with ABT-627 completely reversed endotoxin-induced mortality, significantly attenuated wet/dry ratios of the heart, liver, and kidney, but not lungs, and reduced serum levels of creatine kinase, creatinine, aspartate aminotransferase, and lactate dehydrogenase, but not that of urea and bilirubin. These results suggest that endothelin ETA receptors play a significant role in promoting mortality, edema formation (except in the lungs), and tissue injury in animals with severe sepsis.

Role of endothelins in septic, cardiogenic, and hemorrhagic shock

Shock is a condition where blood flow is inadequate for tissue needs. In all forms of shock, the concentrations of endothelins (ETs) are elevated, and they are especially high in septic shock. The rise in ETs plasma levels may initially have some positive homeostatic effects, for ETs can help restore normal vascular tone. However, high levels of ETs compromise the appropriate matching of flow to tissue needs and contribute to the pathophysiology of shock. Attempts at regulating the effects of ETs by the use of pharmacological blockers is made complicated by important interactions between the ETA and ETB receptors and potentially different effects on different tissues. We conclude that antagonism of ET receptors is unlikely to be helpful for cardiogenic or hemorrhagic shock. Furthermore, selective blockade is unlikely to be helpful. However, moderate doses of a mixed ET receptor antagonist may be of use for the management of septic patients.

Intestinal nitric oxide in the normal and endotoxemic pig

The gut is considered a central organ in the pathogenesis of sepsis and multiple organ failure, where several mediators, including endothelin (ET) and nitric oxide (NO), are involved. The aim of the current study was to characterize, by direct measurements, the intestinal NO production in the anesthetized pig during normal and endotoxemic conditions. In pigs subjected to endotoxin infusion, there was a progressive decrease in jejunal luminal NO levels, as well as portal venous blood flow and blood pressure. The ET- blocker 4-tert-butyl-N-[6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-2,2'-bipyrimidin-4-yl]-benzenesulfonamide (bosentan) completely reversed the reduction in portal venous blood flow without affecting intestinal NO levels. In control pigs, the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester dose-dependently decreased intestinal NO levels and mesenteric blood flow--effects that were reversed by L-arginine. We conclude that intestinal NO is a product of mucosal NO synthase activity, and is profoundly decreased during endotoxemia in the pig.

Endothelin A but not endothelin B receptor blockade reduces capillary permeability in severe experimental pancreatitis

INTRODUCTION

Microcirculatory disorders, in particular increased capillary permeability (CapPerm), contribute to the multiple organ dysfunction syndrome in severe acute pancreatitis (AP). Endothelin receptor antagonists (ET-RA) have been shown to stabilize capillary leakage and improve organ function in AP.

AIM

To find out which endothelin receptor subtype (ET-A or ET-B) mediates the changes in CapPerm.

METHODOLOGY

Severe AP was induced in rats by intraductal bile salt infusion and i.v. cerulein. Animals were randomized to receive (1) saline; (2) selective ET-A-RA (LU-135252; 30 mg/kg); (3) selective ET-B-RA (A-192621); (4) nonselective ET-RA (LU-135252; 120 mg/kg); or (5) combined ET-A/B-RA (30 mg/kg LU-135252 + A-192621). Capillary blood flow (CBF) and CapPerm in the pancreas and colon and leukocyte rolling in mesenteric venules were determined.

RESULTS

Selective ET-A-RA increased CBF and decreased CapPerm in the pancreas and colon by 90-147% and reduced leukocyte rolling in AP but had no effect in healthy controls. Selective ET-B-RA increased pancreatic CBF (2.3 +/- 0.03 versus 2.1 +/- 0.04 nL/min) and enhanced CapPerm in the pancreas and colon by 24-35% in healthy controls but had no effect in AP. Blockade of both receptors produced effects similar to but less pronounced than those of selective ET-A-RA.

CONCLUSIONS

Blockade of ET-A and ET-B receptors has different effects on CapPerm in healthy animals and those with AP. This may explain the inconclusive results reported with nonselective ET-RA. In severe AP, blockade of ET-A but not ET-B receptors reduces CapPerm.

Effects of levosimendan, a novel inotropic calcium-sensitizing drug, in experimental septic shock

OBJECTIVE

Levosimendan is a novel inodilator that improves cardiac contractility by sensitizing troponin C to calcium. This drug has proved to be effective in treating advanced congestive heart failure but has not been evaluated in septic settings. The purpose of the present study was to study the effects of this drug in a porcine model of endotoxemia.

DESIGN

Prospective experimental study.

SUBJECTS

Fourteen landrace pigs.

INTERVENTIONS

All animals were anesthetized and catheterized for measurement of central and pulmonary hemodynamics. Ultrasonic flow probes were placed around the renal artery and portal vein to measure blood flow. A tonometer was placed in the ileum to measure mucosal pH. Levosimendan was given to six animals as a bolus (200 microg x kg(-1)) followed by a continuous infusion (200 microg x kg(-1) x hr(-1)). Thirty minutes after onset of levosimendan treatment, all animals received endotoxin (20 microg x kg(-1) x hr(-1) for 3 hrs).

MEASUREMENTS AND MAIN RESULTS

At baseline, levosimendan induced a systemic vasodilation with a reduction in blood pressure and an increase in heart rate. A tendency to an increase in cardiac index did not reach statistical significance (p =.055). Cardiac index and systemic oxygen delivery were markedly improved in the levosimendan group during endotoxemia. Systemic vascular resistance and blood pressure were reduced in the levosimendan group. The latter parameter, however, was only different from the control group during the initial phase of endotoxin shock but not at the late, most pronounced phase of shock. Levosimendan also efficiently attenuated endotoxin-induced pulmonary hypertension. Portal venous blood flow and gut oxygen delivery were improved, but no concomitant reduction in endotoxin-induced intestinal mucosal acidosis was observed. Renal blood flow was unaffected, as was the endotoxin-induced increase in plasma endothelin-1-like immunoreactivity. These findings support previous reports of calcium desensitization as a potential component in septic myocardial depression. Furthermore, the vasodilatory properties of this drug were well tolerated in the current model of hypodynamic endotoxin shock, and they may have contributed to improved regional blood flow as seen in the gut as well as improved systemic perfusion by means of reduced biventricular afterload.

CONCLUSION

Pretreatment with levosimendan in pigs subjected to endotoxin shock improved cardiac output and systemic and gut oxygen delivery. In addition, pulmonary hypertension largely was attenuated without any adverse effects on gas exchange. These results are promising in several aspects, but the role of levosimendan in the treating circulatory failure in sepsis remains to be established.

Effects of the novel selective endothelin ET(A) receptor antagonist, SB 234551, on the cardiovascular responses to endotoxaemia in conscious rats

1. In conscious, freely moving, male, Long Evans rats, regional haemodynamic responses to exogenous endothelin-1 (ET-1; 25, 50 and 250 pmol kg(-1) i.v.) were assessed in the presence of vehicle, or the selective ET(A)-receptor antagonist, SB 234551. On the following day, the effects of SB 234551 on the haemodynamic responses to lipopolysaccharide (LPS) infusion (150 microg kg(-1) h(-1), i.v.) were determined. 2. When SB 234551 was given i.v. by primed infusion at a dose of 0.3 mg kg(-1) bolus, 0.3 mg kg(-1) h(-1) infusion, it caused selective inhibition of the vasoconstrictor effects of exogenous endothelin-1, whereas at a dose of 1 mg kg(-1), 1 mg kg(-1) h(-1), SB 234551 also inhibited some of the vasodilator effects of endothelin-1. 3. Infusion of LPS, in the presence of vehicle, caused a short-lived (1 - 2 h) hypotension, tachycardia, and vasodilatation in renal, superior mesenteric and hindquarters vascular beds. Thereafter, blood pressure, heart rate and mesenteric vascular conductance returned to baseline values, but renal vasodilatation persisted, and there was vasoconstriction in the hindquarters. 4. In the presence of SB 234551 (0.3 mg kg(-1), 0.3 mg kg(-1) h(-1)), the early (1 - 2 h) cardiovascular responses to LPS infusion were unaffected, but the subsequent recovery of mean arterial blood pressure was impaired, due to developing vasodilatation in the mesenteric and, to a lesser extent, hindquarters, vascular beds. SB 234551 had no effect on the renal haemodynamic responses to LPS infusion. 5. The results confirm an important, regionally-selective, vasoconstrictor role for endogenous endothelin in this model of endotoxaemia.

The endothelin system in septic and endotoxin shock

The view of the endothelium as a passive barrier has gradually changed as a number of endothelium-derived substances have been discovered. Substances like nitric oxide, prostaglandins and endothelins have potent and important properties, involving not only the circulation as such but also the response to stimuli like inflammation and trauma. The endothelin system, discovered in 1988, has not only strong vasoconstrictor properties, but also immunomodulating, endocrinological and neurological effects exerted through at least two types of receptors. Septic shock, a condition with high mortality, is associated with vast cardiovascular changes, organ dysfunction with microcirculatory disturbances and dysoxia. In the experimental setting, endotoxaemia resembles these changes and is, as well as septic shock, accompanied by a pronounced increase in plasma endothelin levels. The pathophysiology in septic and endotoxin shock remains to be fully elucidated, but several studies indicate that endothelial dysfunction is one contributing mechanism. Activation of the endothelin system is associated with several pathological conditions complicating septic shock, such as acute respiratory distress syndrome, cardiac dysfunction, splanchnic hypoperfusion and disseminated intravascular coagulation. Through the development of both selective and nonselective endothelin receptor antagonists, the endothelin system has been the object of a large number of studies during the last decade. This review highlights systematically the findings of previous studies in the area. It provides strong indications that the endothelin system, apart from being a marker of vascular injury, is directly involved in the pathophysiology of septic and endotoxin shock. Interventions with endothelin receptor antagonists during septic and endotoxin shock have so far only been done in animal studies but the results are interesting and promising.