Impaired microvascular vasoconstrictive responses to vasopressin in septic rats

Dysregulation of the renin-angiotensin system in septic shock: Mechanistic insights and application of angiotensin II in clinical management

Synergistic physiologic mechanisms involving the renin-angiotensin system (RAS), the sympathetic nervous system, and the arginine-vasopressin system play an integral role in blood pressure homeostasis. A subset of patients with sepsis experience septic shock with attendant circulatory, cellular, and metabolic abnormalities. Septic shock is associated with increased mortality because of an inadequacy to maintain mean arterial blood pressure (MAP) despite volume resuscitation and the use of vasopressors. Vasodilatory shock raises the dose of vasopressors required to maintain a MAP of > 65 mm Hg. The diminished response to endogenous angiotensin II in sepsis-induced vasoplegia may be related to the aberrant RAS activation that stimulates a proinflammatory beneficial antibacterial response, increasing the secretion of proinflammatory cytokines that downregulate AT-1 receptors expression. Moreover, excessive systemic upregulation of nitric oxide synthase, stimulation of prostaglandin synthesis, and activation of ATP-sensitive potassium channels followed by reduced vascular entry of calcium ions are putative mechanisms in the reduced responsiveness to vasopressors. However, intravenous angiotensin II in catecholamine-resistant septic shock patients showed substantial evidence of raising the MAP to target hemodynamic levels, thus allowing time to treat underlying conditions. Nevertheless, evidence of catecholamine-sparing effect by adding angiotensin II, aimed at increasing the therapeutic index of vasopressor therapy, does not show an attenuation of end-organ damage. The use of angiotensin II in septic shock has not been evaluated in patients who are not catecholamine resistant. This, in conjunction with an evolving definition of catecholamine resistance, provides an opportunity for further evaluation of exogenous angiotensin II in septic shock.

Pralidoxime improves the hemodynamics and survival of rats with peritonitis-induced sepsis

Several studies have suggested that sympathetic overstimulation causes deleterious effects in septic shock. A previous study suggested that pralidoxime exerted a pressor effect through a mechanism unrelated to the sympathetic nervous system; this effect was buffered by the vasodepressor action of pralidoxime mediated through sympathoinhibition. In this study, we explored the effects of pralidoxime on hemodynamics and survival in rats with peritonitis-induced sepsis. This study consisted of two sub-studies: survival and hemodynamic studies. In the survival study, 66 rats, which survived for 10 hours after cecal ligation and puncture (CLP), randomly received saline placebo, pralidoxime, or norepinephrine treatment and were monitored for up to 24 hours. In the hemodynamic study, 44 rats were randomly assigned to sham, CLP-saline placebo, CLP-pralidoxime, or CLP-norepinephrine groups, and hemodynamic measurements were performed using a conductance catheter placed in the left ventricle. In the survival study, 6 (27.2%), 15 (68.1%), and 5 (22.7%) animals survived the entire 24-hour monitoring period in the saline, pralidoxime, and norepinephrine groups, respectively (log-rank test P = 0.006). In the hemodynamic study, pralidoxime but not norepinephrine increased end-diastolic volume (P <0.001), stroke volume (P = 0.002), cardiac output (P = 0.003), mean arterial pressure (P = 0.041), and stroke work (P <0.001). The pressor effect of norepinephrine was short-lived, such that by 60 minutes after the initiation of norepinephrine infusion, it no longer had any significant effect on mean arterial pressure. In addition, norepinephrine significantly increased heart rate (P <0.001) and the ratio of arterial elastance to ventricular end-systolic elastance (P = 0.010), but pralidoxime did not. In conclusion, pralidoxime improved the hemodynamics and 24-hour survival rate in rats with peritonitis-induced sepsis, but norepinephrine did not.

SOFA Score, Hemodynamics and Body Temperature Allow Early Discrimination between Porcine Peritonitis-Induced Sepsis and Peritonitis-Induced Septic Shock

Porcine model of peritonitis-induced sepsis is a well-established clinically relevant model of human disease. Interindividual variability of the response often complicates the interpretation of findings. To better understand the biological basis of the disease variability, the progression of the disease was compared between animals with sepsis and septic shock. Peritonitis was induced by inoculation of autologous feces in fifteen anesthetized, mechanically ventilated and surgically instrumented pigs and continued for 24 h. Cardiovascular and biochemical parameters were collected at baseline (just before peritonitis induction), 12 h, 18 h and 24 h (end of the experiment) after induction of peritonitis. Analysis of multiple parameters revealed the earliest significant differences between sepsis and septic shock groups in the sequential organ failure assessment (SOFA) score, systemic vascular resistance, partial pressure of oxygen in mixed venous blood and body temperature. Other significant functional differences developed later in the course of the disease. The data indicate that SOFA score, hemodynamical parameters and body temperature discriminate early between sepsis and septic shock in a clinically relevant porcine model. Early pronounced alterations of these parameters may herald a progression of the disease toward irreversible septic shock.

The Management of Sepsis: A Practical Review

The incidence of the sepsis syndrome has increased dramatically in the last few decades. During this time we have gained new insights into the pathophysiologic mechanisms leading to organ dysfunction in sepsis and the importance of the host-bacterial interactions in mediating many of these processes. This knowledge has led to new therapeutic approaches and the investigation of a number of novel agents. An assessment of these approaches is presented to aid clinicians in the management of patients with severe sepsis. Criteria used to select studies included their relevance to the management of sepsis and their pertinence to clinicians. Appropriate antibiotic selection and volume resuscitation remain the cornerstone of treatment of septic patients. Hydroxyethyl starch solutions have theoretical advantages over crystalloids; there is, however, no data that the type of resuscitation fluid alters outcome. Vasoactive agents are required in patients who remain hemodynamically unstable or have evidence of tissue hypoxia after adequate volume resuscitation. Although dopamine is widely used, dobutamine and norepinephrine are our vasoactive agents of choice. Dopamine has no proven role in oliguric patients, with early dialysis recommended in patients with acute renal failure. The preferred method of renal replacement therapy remains to be determined. Blood products should be used cautiously in patients with disseminated intravascular coagulation. Therapeutic strategies that interfere with the immune system have not been proven to improve the outcome in unselected groups of patients. However, immunomodulation may prove to have a role in select subgroups of patients. Antibiotic therapy and intensive physiological support continues to be the main approach to the management of patients with severe sepsis. Despite the development of numerous novel therapeutic agents, these drugs have not been demonstrated to improve patient outcome.

Investigational vasopressin receptor modulators in the pipeline

The vasopressin system is complex and interacts with the central nervous, cardiovascular, renal, and hematological systems. Vasopressin plays an important role in the control of blood osmolarity and vascular tone, but is also involved in many other physiological events, which are mediated mainly via three types of vasopressin receptor: V1R, V2R, and V3R. V1R primarily mediate the vascular, and V2R the aquaretic, effects of vasopressin. Vasopressin may also interact with other receptors, like adrenergic and angiotensin-II receptors, or with distinct biological pathways, including those of nitric oxide and the K(ATP) channel. There are numerous clinical situations where vasopressin receptor modulators (agonists or antagonists) could be used. Currently, vasopressin and terlipressin are most commonly used to stimulate V1R in vasodilatory shock and cardiac arrest, while desmopressin, a synthetic analogue of vasopressin, acts on V2R; but new molecules are becoming available in the treatment of inappropriate antidiuretic hormone (ADH) secretion.

How to protect the heart in septic shock: a hypothesis on the pathophysiology and treatment of septic heart failure

Heart failure is a well-recognized manifestation of organ failure in sepsis and septic shock. The pathophysiology of septic heart failure is complex and currently believed to involve several mechanisms. So far, the contributory role of high plasma catecholamine levels has not been investigated. In this manuscript, we present a hypothesis suggesting that excessive catecholamine production and exogenous administration of catecholamines may relevantly contribute to the development of heart failure and cardiovascular collapse in patients suffering from septic shock. Substantially elevated plasma catecholamine levels were measured during critical illness and sepsis or septic shock. There is a growing body of clinical and experimental evidence demonstrating that high catecholamine plasma levels exert direct toxic effects on the heart. The pathophysiologic mechanisms involved in catecholamine-induced cardiomyocyte toxicity may involve a combination of inflammation, oxidative stress, and abnormal calcium handling resulting in myocardial stunning, apoptosis and necrosis. Clinical signs of catecholamine-induced heart failure can present with a wide range of symptoms reaching from subtle histological changes with preserved myocardial pump function to severe heart failure exhibiting a distinctive echocardiographic pattern which became known as "Takotsubo"-like cardiomyopathy or the left ventricular apical ballooning syndrome. In a medical intensive care unit patient population, presence of sepsis was the only variable associated with the development of left ventricular apical ballooning. Since several therapeutic interventions influence catecholamine plasma levels in septic shock patients, treatment strategies aiming at the reduction of endogenous or exogenous catecholamine exposure may protect the heart during septic shock and could facilitate patient survival.

Vasopressin attenuates TNF-mediated inflammation in the rat cremaster microcirculation

BACKGROUND

Our previous study in a swine polytrauma model suggested that equieffective systemic pressor doses of arginine vasopressin (AVP) versus phenylephrine (PE) have differential effects on the systemic and cerebral microcirculation. The purpose of this study was to directly observe the effects of AVP versus PE on inflammatory changes evoked by tumor necrosis factor alpha (TNF) in the skeletal muscle microcirculation.

METHODS

Seventy-five male rats (180-250 g) were anesthetized with isoforane, intubated and mechanically ventilated with 100% oxygen. The cremaster muscle microcirculation was prepared for intravital video microscopy while being suffused with a heated hetastarch-electrolyte solution. Fluorescein isothiocyanate-labeled albumin (100 mg/kg) was administered intravenously (i.v.) before one of five protocols. In series 1 (n = 20), either AVP (0.2 U/mL) or its vehicle was added to the suffusate for 10 minutes, washed out for 30 minutes, then TNF was suffused (5 ng/mL) for 30 minutes. In series 2 (n = 16), the protocol was similar, except AVP (0.2 U/mL) or an equieffective dose of PE (0.04 mg/mL) was administered i.v. (4.5 mL/h) for 15 minutes before, during, and 45 minutes after TNF suffusion. In series 3 (n = 12), the protocol was similar to series 2, except venous hemorrhage preceded i.v. AVP or PE. In series 4 (n = 15), the protocol was similar to series 3, except an AVP antagonist (vaprisol, 1 mg/kg i.v.) or its vehicle was administered after hemorrhage. In the control series (n = 13), inflammation was evaluated either with a different suffusate (lactated Ringers instead of hetastarch solution), different antigen (histamine instead of TNF), or hemorrhage with no antigen.

RESULTS

In series 1, the TNF-evoked increase in leukocyte infiltration (i.e., rolling), leukocyte activation (i.e., sticking), and macromolecular permeability (i.e., albumin extravasation) were attenuated with topical AVP versus vehicle (both p < 0.05), with no effect on venular blood flow (which determines sheer stress). In series 2, the TNF-evoked increase in infiltration, activation, and permeability were all attenuated, and arteriolar blood flow (which determines perfused capillary surface area and hydrostatic pressure) was reduced with i.v. AVP versus i.v. PE (all p < 0.05). In series 3, after hemorrhage to mean arterial pressure <50 mm Hg for 30 minutes, the TNF-evoked increase in infiltration and activation was attenuated, and arteriolar and venular blood flow were both reduced with i.v. AVP versus PE (all p < 0.05). In series 4, after hemorrhage, the TNF-evoked increase in leukocyte activation was potentiated with the vaprisol versus vehicle (p < 0.05) with no effect on arteriolar or venular blood flow. In series 5 (controls), suffusion with lactated Ringers' versus hetastarch solution more than doubled the TNF-evoked increase in activation (p < 0.05).

CONCLUSION

(1) AVP can attenuate TNF-evoked leukocyte infiltration, activation or permeability changes in the skeletal muscle microcirculation. (2) The mechanism is probably receptor mediated and does not entirely depend on sheer stress in venules or Starling forces in capillaries. (3) The magnitude of this anti-inflammatory effect is influenced by several conditions, including volume status, the colloid or crystalloid suffusion fluid, and is possibly specific to the antigenic stimulus (TNF vs. histamine).

Role of nuclear factor-kappaB-dependent induction of cytokines in the regulation of vasopressin V1A-receptors during cecal ligation and puncture-induced circulatory failure

OBJECTIVE

Here we characterize the impact of nuclear factor-kappaB and cytokines on cecal ligation and puncture-induced circulatory failure and regulation of vasopressin V1A-receptors during inflammation.

DESIGN

Prospective animal trial.

SETTING

Laboratory of the Department of Anesthesiology.

SUBJECTS

Male C57/BL6 mice.

INTERVENTIONS

The effects of cecal ligation and puncture on hemodynamic parameters and V1A-receptor expression were measured in cytokine knock-out mice, in mice with/without treatment with glucocorticoids or NF-kappaB-inhibitors, in mice pretreated with small interfering RNA silencing NF-kappaB and in mice treated with V1 receptor agonists. Furthermore, the effects of cytokines on V1A-receptor expression were determined.

MEASUREMENTS AND MAIN RESULTS

Cecal ligation and puncture resulted in a hyperdynamic circulatory failure with diminished blood pressor dose response to V1 receptor agonists and down-regulation of V1A-receptors. Dexamethasone inhibited proinflammatory cytokine production and attenuated cecal ligation and puncture-induced cardiovascular failure in parallel with attenuated down-regulation of V1A-receptor expression. Tumor necrosis factor-alpha, interleukin-1beta, interferon-gamma or interleukin-6 dose-dependently decreased V1A-receptor expression, whereas cecal ligation and puncture-induced down-regulation of V1A-receptors was not affected in cytokine knock-out mice. In contrast, inhibition of NF-kappaB strongly reduced induction of cytokines, prevented septic circulatory failure and down-regulation of V1A-receptor gene expression and improved survival of septic animals.

CONCLUSIONS

Our data demonstrate that down-regulation of V1A-receptor expression during sepsis may be due to proinflammatory cytokines. Our findings explain the failure of therapeutic strategies targeting single cytokines as well as the success of glucocorticoid therapy and define a critical role for NF-kappaB in the pathogenesis of septic shock.

Resuscitating the microcirculation in sepsis: the central role of nitric oxide, emerging concepts for novel therapies, and challenges for clinical trials

Microcirculatory dysfunction is a critical element of the pathogenesis of severe sepsis and septic shock. In this Bench-to-Bedside review, we present: 1) the central role of the microcirculation in the pathophysiology of sepsis; 2) new translational research techniques of in vivo video microscopy for assessment of microcirculatory flow in human subjects; 3) clinical investigations that reported associations between microcirculatory dysfunction and outcome in septic patients; 4) the potential role of novel agents to "rescue" the microcirculation in sepsis; 5) current challenges facing this emerging field of clinical investigation; and 6) a framework for the design of future clinical trials aimed to determine the impact of novel agents on microcirculatory flow and organ failure in patients with sepsis. We specifically focus this review on the central role and vital importance of the nitric oxide (NO) molecule in maintaining microcirculatory homeostasis and patency, especially when the microcirculation sustains an insult (as with sepsis). We also present the scientific rationale for clinical trials of exogenous NO administration to treat microcirculatory dysfunction and augment microcirculatory blood flow in early sepsis therapy.

Differential effects of vasopressin and norepinephrine on vascular reactivity in a long-term rodent model of sepsis

OBJECTIVE

There is escalating interest in the therapeutic use of vasopressin in septic shock. However, little attention has focused on mechanisms underlying its pressor hypersensitivity, which contrasts with the vascular hyporesponsiveness to catecholamines. We investigated whether a long-term rodent model of sepsis would produce changes in endogenous levels and pressor reactivity to exogenous norepinephrine and vasopressin comparable with those seen in septic patients.

DESIGN

In vivo and ex vivo animal study.

SETTING

University research laboratory.

SUBJECTS

Male adult Wistar rats.

INTERVENTIONS AND MEASUREMENTS

Fecal peritonitis was induced in conscious, fluid-resuscitated rats. Biochemical and hormonal profiles were measured at time points up to 48 hrs. Pressor responses to intravenous norepinephrine, vasopressin, and F-180, a selective V1 receptor agonist, were measured at 24 hrs. Contractile responses to these drugs were assessed in mesenteric arteries taken from animals at 24 hrs using wire myography. Comparisons were made against sham operation controls.

MAIN RESULTS

Septic rats became unwell and hypotensive, with a mortality of 64% at 48 hrs (0% in controls). Plasma norepinephrine levels were elevated in septic animals at 24 hrs (1968 +/- 490 vs. 492 +/- 90 pg/mL in controls, p = .003), whereas vasopressin levels were similar in the two groups (4.5 +/- 0.8 vs. 3.0 +/- 0.5 pg/mL, p = not significant). In vivo, the pressor response to norepinephrine was markedly reduced in the septic animals, but responses to vasopressin and F-180 were relatively preserved. In arteries from septic animals, norepinephrine contractions were decreased (efficacy as measured by maximum contractile response, Emax: 3.0 +/- 0.3 vs. 4.7 +/- 0.2 mN, p < .001). In contrast, the potency of vasopressin (expressed as the negative log of the concentration required to produce 50% of the maximum tension, pD2: 9.1 +/- 0.04 vs. 8.7 +/- 0.05, p < .001) and F-180 (pD2 8.2 +/- 0.04 vs. 7.6 +/- 0.02, p < .001) was enhanced (n > or = 6 for all groups).

CONCLUSIONS

This long-term animal model demonstrates changes in circulating vasoactive hormones similar to prolonged human sepsis, and decreased pressor sensitivity to norepinephrine. Ex vivo sensitivity to vasopressin agonists was heightened. This model is therefore appropriate for the further investigation of mechanisms underlying vasopressin hypersensitivity, which may include receptor or calcium-handling alterations within the vasculature.

Comparison of two dose regimens of arginine vasopressin in advanced vasodilatory shock

OBJECTIVE

To evaluate the effects of two arginine vasopressin (AVP) dose regimens (0.033 vs. 0.067 IU/min) on treatment efficacy, hemodynamic response, prevalence of adverse events, and changes in laboratory variables.

DESIGN

Retrospective, controlled study.

PATIENTS

A total of 78 patients with vasodilatory shock (mean norepinephrine dosage, 1.07 microg.kg-1.min-1; 95% confidence interval, 0.82-1.56 microg.kg-1.min-1).

INTERVENTIONS

Supplementary infusion of AVP at 0.033 (n = 39) and 0.067 IU/min (n = 39).

MEASUREMENTS AND MAIN RESULTS

Cardiocirculatory, laboratory, and clinical variables were evaluated and compared between groups before and at 0.5, 1, 4, 12, 24, 48, and 72 hrs after initiation of AVP. Treatment efficacy was assessed by the increase in mean arterial blood pressure and the extent of norepinephrine reduction during the first 24 hrs of AVP therapy. Standard tests and a mixed-effects model were used for statistical analysis. Although the relative increase in mean arterial pressure was comparable between groups (0.033 vs. 0.067 IU/min: 16.8 +/- 18.4 vs. 21.4 +/- 14.9 mm Hg, p = .24), norepinephrine could be reduced significantly more often in patients receiving 0.067 IU/min. AVP at 0.067 IU/min resulted in a higher mean arterial pressure (p < .001), lower central venous pressure (p = .001), lower mean pulmonary arterial pressure (p = .04), and lower norepinephrine requirements (p < .001) during the 72-hr observation period. Increases in liver enzymes occurred more often in patients treated with 0.033 IU/min (71.8% vs. 28.2%, p < .001). The prevalence of a decrease in cardiac index (69.2% vs. 53.8%, p = .24), decrease in platelet count (94.8% vs. 84.6%, p = .26), and increase in total bilirubin (48.7% vs. 71.8%, p = .06) was not significantly different between groups. Bilirubin levels (3.1 +/- 3.4 vs. 5.2 +/- 5.5 mg/dL, p = .04) and base deficit (-7.2 +/- 4.3 vs. -3.9 +/- 5.9 mmol/L, p = .005) were lower and arterial lactate concentrations higher (76 +/- 67 vs. 46 +/- 38 mg/dL, p < .001) in patients receiving 0.033 IU/min.

CONCLUSIONS

AVP dosages of 0.067 IU/min seem to be more effective to reverse cardiovascular failure in vasodilatory shock requiring high norepinephrine dosages than 0.033 IU/min.

Methylprednisolone reverses vasopressin hyporesponsiveness in ovine endotoxemia

Tachyphylaxis against catecholamines often complicates hemodynamic support in patients with septic shock. Recent experimental and clinical research suggests that the hemodynamic response to exogenous arginine vasopressin (AVP) infusion may also be blunted. The purpose of the present study was therefore to clarify whether the efficacy of a continuous AVP infusion (0.04 U x min(-1)) decreases over time in ovine endotoxemia. An additional objective was to determine whether the anticipated hyporesponsiveness can be counteracted by corticosteroids. Fourteen adult ewes (37 +/- 1 kg) were instrumented for chronic hemodynamic monitoring. All ewes received a continuous endotoxin infusion that contributed to a hypotensive-hyperdynamic circulation. After 16 h of endotoxemia, the sheep were randomized to receive either AVP (0.04 U x min(-1)) or the vehicle (normal saline; n = 7 each). After 6 h of AVP or placebo infusion, respectively, methylprednisolone (30 mg x kg(-1)) was injected. Arginine vasopressin infusion increased mean arterial pressure and systemic vascular resistance index at the expense of a reduced cardiac index (P < 0.05 each). Supraphysiologic AVP plasma levels in the treatment group (298 +/- 15 pg x mL(-1)) were associated with increased surrogate parameters of liver, mesenterial, and myocardial dysfunction. After 6 h of continuous AVP infusion, the vasopressor effect was significantly reduced. Interestingly, a bolus infusion of methylprednisolone (30 mg x kg(-1)) reestablished mean arterial pressure by increasing both cardiac index and systemic vascular resistance index. The present study demonstrates that in endotoxemia, (a) the vasopressor effect of AVP infusion may be reduced, (b) corticosteroids may potentially be useful to increase the efficacy of AVP infusion, and (c) even moderate AVP doses may potentially impair myocardial and hepatic function.

Vasopressin: mechanisms of action on the vasculature in health and in septic shock

BACKGROUND

Vasopressin is essential for cardiovascular homeostasis, acting via the kidney to regulate water resorption, on the vasculature to regulate smooth muscle tone, and as a central neurotransmitter, modulating brainstem autonomic function. Although it is released in response to stress or shock states, a relative deficiency of vasopressin has been found in prolonged vasodilatory shock, such as is seen in severe sepsis. In this circumstance, exogenous vasopressin has marked vasopressor effects, even at doses that would not affect blood pressure in healthy individuals. These two findings provide the rationale for the use of vasopressin in the treatment of septic shock. However, despite considerable research attention, the mechanisms for vasopressin deficiency and hypersensitivity in vasodilatory shock remain unclear.

OBJECTIVE

To summarize vasopressin's synthesis, physiologic roles, and regulation and then review the literature describing its vascular receptors and downstream signaling pathways. A discussion of potential mechanisms underlying vasopressin hypersensitivity in septic shock follows, with reference to relevant clinical, in vivo, and in vitro experimental evidence.

DATA SOURCE

Search of the PubMed database (keywords: vasopressin and receptors and/or sepsis or septic shock) for articles published in English before May 2006 and manual review of article bibliographies.

DATA SYNTHESIS AND CONCLUSIONS

The pathophysiologic mechanism underlying vasopressin hypersensitivity in septic shock is probably multifactorial. It is doubtful that this phenomenon is merely the consequence of replacing a deficiency. Changes in vascular receptors or their signaling and/or interactions between vasopressin, nitric oxide, and adenosine triphosphate-dependent potassium channels are likely to be relevant. Further translational research is required to improve our understanding and direct appropriate educated clinical use of vasopressin.

Vasopressin during cardiopulmonary resuscitation and different shock states: a review of the literature

Vasopressin administration may be a promising therapy in the management of various shock states. In laboratory models of cardiac arrest, vasopressin improved vital organ blood flow, cerebral oxygen delivery, the rate of return of spontaneous circulation, and neurological recovery compared with epinephrine (adrenaline). In a study of 1219 adult patients with cardiac arrest, the effects of vasopressin were similar to those of epinephrine in the management of ventricular fibrillation and pulseless electrical activity; however, vasopressin was superior to epinephrine in patients with asystole. Furthermore, vasopressin followed by epinephrine resulted in significantly higher rates of survival to hospital admission and hospital discharge. The current cardiopulmonary resuscitation guidelines recommend intravenous vasopressin 40 IU or epinephrine 1mg in adult patients refractory to electrical countershock. Several investigations have demonstrated that vasopressin can successfully stabilize hemodynamic variables in advanced vasodilatory shock. Use of vasopressin in vasodilatory shock should be guided by strict hemodynamic indications, such as hypotension despite norepinephrine (noradrenaline) dosages >0.5 mug/kg/min. Vasopressin must never be used as the sole vasopressor agent. In our institutional routine, a fixed vasopressin dosage of 0.067 IU/min (i.e. 100 IU/50 mL at 2 mL/h) is administered and mean arterial pressure is regulated by adjusting norepinephrine infusion. When norepinephrine dosages decrease to 0.2 microg/kg/min, vasopressin is withdrawn in small steps according to the response in mean arterial pressure. Vasopressin also improved short- and long-term survival in various porcine models of uncontrolled hemorrhagic shock. In the clinical setting, we observed positive effects of vasopressin in some patients with life-threatening hemorrhagic shock, which had no longer responded to adrenergic catecholamines and fluid resuscitation. Clinical employment of vasopressin during hemorrhagic shock is experimental at this point in time.

Hemodynamic management of septic shock

Septic shock is characterized by profound cardiovascular alterations, including hypovolemia, severe alterations in vascular tone, and myocardial depression. These effects can lead to tissue hypoperfusion, the persistence of which could contribute to multiple organ failure. In addition, regional blood flow alterations and microvascular blood flow alterations may coexist and persist even after whole body hemodynamic alterations are corrected. Early aggressive interventions to improve oxygen delivery have been shown to improve outcome, but ongoing hemodynamic support is often required. This review will examine the hemodynamic management of patients with septic shock.

Effects of vasopressin, norepinephrine, and l-arginine on intestinal microcirculation in endotoxemia*

OBJECTIVE

The effects of vasopressin, norepinephrine, and L-arginine alone or combined on intestinal microcirculation were evaluated in the septic mouse by intravital microscopy, with which we measured the erythrocyte flux and velocity in villus tip arterioles and the density of perfused villi.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Female BALB/c mice weighing between 18 and 21 g.

INTERVENTIONS

Anesthetized and ventilated mice received at t0 an intravenous injection of Escherichia coli endotoxin (2 mg/kg bolus intravenously), inducing after 1 hr (t60) a decrease in mean arterial blood pressure to 40-50 mm Hg associated with a significant decrease in erythrocyte flux and velocity in villus tip arterioles and in the density of perfused villi. The mice then received a randomly different treatment for endotoxin-induced shock. Treatments consisted in continuous intravenous infusion for 1 hr with either saline (control group), norepinephrine, vasopressin, L-arginine, vasopressin+L-arginine, or norepinephrine+L-arginine. The doses of vasopressors (used alone or combined with L-arginine) were titrated to restore mean arterial pressure to the baseline level.

MEASUREMENTS AND MAIN RESULTS

At the end of the treatment (t120), we observed in the control group further decreases in arteriolar flux and velocity and in the density of perfused villi. In the groups treated by a vasopressor alone, mean arterial pressure returned to baseline and there were no additional decreases in arteriolar flux and velocity or in the density of perfused villi. However, these latter three variables did not return to their preshock baseline values. Even though L-arginine did not restore mean arterial pressure, the infusion of L-arginine alone prevented the decrease in flux or erythrocyte velocity occurring between t60 and t120 and conserved to some extent the density of perfused villi compared with that in the control groups. In addition, we found that simultaneous administration of norepinephrine or vasopressin with L-arginine improved all microcirculation variables more efficiently than either vasopressor alone.

CONCLUSIONS

From these data, we conclude that a) restoring mean arterial pressure after 1 hr of endotoxemia was not sufficient to restore ad integrum intestinal mucosa microvascular perfusion; b) L-arginine could have a beneficial effect at the microcirculatory level, which was independent of mean arterial pressure; and c) administration of L-arginine combined with the maintenance of perfusion pressure by vasopressive drugs allowed a better preservation of intestinal microcirculation at an early stage of endotoxemia.

Decreased vasopressin responsiveness in vasodilatory septic shock-like conditions

OBJECTIVE

To determine the effect of vasodilatory septic shock-like conditions on vasoconstricting responses to vasopressin and norepinephrine in isolated resistance arteries.

DESIGN

Prospective, randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Male adult Sprague-Dawley rats.

INTERVENTIONS

Small mesenteric arteries (outside diameter, 50-150 microm) were cannulated and studied in vitro under physiologic conditions. A vasodilatory septic shock-like state was produced by treatment with the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), and the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Vasoconstricting concentration-response relationships were determined for norepinephrine and vasopressin before and after application of SNAP or SNAP+ IBMX. Synergism between low-dose vasopressin and norepinephrine and between low-dose norepinephrine and vasopressin was determined before and after SNAP or SNAP+IBMX.

MAIN RESULTS

Norepinephrine and vasopressin produced concentration-dependent contractions (half-maximal effective concentration [EC(50)] = 2.5 microM and 3.9 nM, respectively) that were significantly inhibited by 1 microM SNAP (EC(50) = 3.6 microM and 8.1 nM, respectively) or 100 microM SNAP + 10 microM IBMX (EC(50) = 10 microM and 8.2 nM, respectively). Low-dose vasopressin significantly increased the responsiveness to norepinephrine (EC50 = 0.5 microM) just as a low-dose norepinephrine significantly enhanced the vasopressin response (EC(50) = 2.3 nM). The synergistic effects of low-dose vasopressin and norepinephrine, or low-dose norepinephrine and vasopressin, were also significantly inhibited by 1 microM SNAP (EC(50) = 2.5 microM and 4.2 nM, respectively) or 100 microM SNAP + 10 microM IBMX (EC(50) = 9 microM and 8.4 nM, respectively).

CONCLUSIONS

Vasoconstriction produced by vasopressin or norepinephrine, and the synergistic vasoconstriction produced by the combinations, was inhibited in vasodilatory septic shock-like conditions. Thus, in addition to the well-described vasopressin deficiency in vasodilatory septic shock, these studies indicate that decreased vasopressin responsiveness further contributes to a state of relative vasopressin insufficiency in this condition.

Catecholamines and vasopressin during critical illness

In critical care medicine, catecholamines are most widely used to reverse circulatory dysfunction and thus to restore tissue perfusion. However, catecholamines not only influence systemic and regional hemodynamics, but also exert a variety of significant metabolic, endocrine, and immunologic effects. Arginine vasopressin is a vasomodulatory hormone with potency to restore vascular tone in vasodilatory hypotension. Although the evidence supporting the use of low doses of vasopressin or its analogs in vasodilatory shock is increasing, lack of data regarding mortality and morbidity prevent their implementation in critical care protocols.

Serum vasopressin concentrations in critically ill patients*

OBJECTIVE

To measure arginine vasopressin (AVP) serum concentrations in critically ill patients.

DESIGN

Prospective study.

SETTING

Twelve-bed general and surgical intensive care unit in a tertiary, university teaching hospital.

PATIENTS

Two-hundred-thirty-nine mixed critically ill patients and 70 healthy volunteers.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Demographic data, hemodynamic variables, vasopressor drug requirements, blood gases, AVP serum concentrations within 24 hrs after admission, multiple organ dysfunction score, and outcome were recorded. Twenty-four hours after admission, study patients had significantly higher AVP concentrations (11.9 +/- 20.6 pg/mL) than healthy controls (0.92 +/- 0.38 pg/mL; p < .001). Males had lower AVP concentrations than females (9.7 +/- 19.5 vs. 15.1 +/- 20.6 pg/mL; p = .014). Patients with hemodynamic dysfunction had higher AVP concentrations than patients without hemodynamic dysfunction (14.1 +/- 27.1 vs. 8.7 +/- 10.8 pg/mL; p = .042). Patients after cardiac surgery (n = 96) had significantly higher AVP concentrations when compared to patients admitted for other diagnoses (n = 143; p < .001). AVP concentrations were inversely correlated with length of stay in the intensive care unit (correlation coefficient, -0.222; p = .002). There was no correlation between serum AVP concentrations and the incidence of shock or specific hemodynamic parameters. Four (1.7%) of the 239 study patients met criteria for an absolute AVP deficiency (AVP, <0.83 pg/mL), and 32 (13.4%) met criteria for a relative AVP deficiency (AVP, <10 pg/mL, and mean arterial pressure, <70 mm Hg). In shock patients, relative AVP deficiency occurred in 22.2% (septic shock), 15.4% (postcardiotomy shock), and 10% (shock due to a severe systemic inflammatory response syndrome) (p = .316).

CONCLUSIONS

AVP serum concentrations 24 hrs after intensive care unit admission were significantly increased in this mixed critically ill patient population. The lack of a correlation between AVP serum concentrations and hemodynamic parameters suggests complex dysfunction of the vasopressinergic system in critical illness. Relative and absolute AVP deficiency may be infrequent entities during acute surgical critical illness, mostly remaining without significant effects on cardiovascular function.

Inhibition of prostaglandins does not reduce the cardiovascular changes during endotoxemia in rats

Vasodilatory prostanoids, such as prostacyclin and PGE2, and pro-inflammatory cytokines are known to play a central role in the pathogenesis of endotoxemia. This study was undertaken to elucidate whether indomethacin (INDO), a non-selective COX inhibitor, has protective effects against the cardiovascular alterations that occur during endotoxemia. Sprague-Dawley rats were injected intraperitoneally with 15 mg/kg lipopolysaccharide (LPS). LPS injection led to a prominent decrease in cardiac left ventricular end diastolic area (LVEDA) and increased LV fractional shortening (FS), as measured by echocardigraphy. LPS also led to a significant increase in plasma and myocardial TNF-alpha and IL-1beta levels, and elevated plasma and hypothalamic levels of PGE2. Neither the decrease in LVEDA and the increase in FS, nor the elevation in plasma and myocardial cytokine levels were altered by INDO (10 mg/kg). On the other hand, pretreatment with INDO significantly reduced the elevation in PGE2 and the hypothermia induced by LPS. Taken together, this study demonstrates that solely inhibiting the production of PGE2 is not sufficient to reduce the cardiovascular alteration seen in endotoxemia.

The microcirculation as a functional system

This review examines experimental evidence that the microvascular dysfunction that occurs early in sepsis is the critical first stage in tissue hypoxia and organ failure. A functional microvasculature maintains tissue oxygenation despite limitations on oxygen delivery from blood to tissue imposed by diffusion; the density of perfused (functional) capillaries is high enough to ensure appropriate diffusion distances, and arterioles regulate the distribution of oxygen within the organ precisely to where it is needed. Key components of this regulatory system are the endothelium, which communicates and integrates signals along the microvascular network, and the erythrocytes, which directly monitor and regulate oxygen delivery. During hypovolemic shock, a functional microvasculature responds to diminish the impact of a decrease in oxygen supply on tissue perfusion. However, within hours of the onset of sepsis, a dysfunctional microcirculation is, due to a loss of functional capillary density and impaired regulation of oxygen delivery, unable to maintain capillary oxygen saturation levels and prevent the rapid onset of tissue hypoxia despite adequate oxygen supply to the organ. The mechanism(s) responsible for this dysfunctional microvasculature must be understood in order to develop appropriate management strategies for sepsis.

Effects of Nimesulide, a Selective Cyclooxygenase-2 Inhibitor, on Cardiovascular Alterations in Endotoxemia

Prostanoids and cytokines are known to play a pivotal role in the mechanisms leading to endotoxin-induced cardiovascular failure. We investigated the effect of nimesulide (NIM), a selective cyclooxygenase-2 (COX-2) inhibitor, on the cardiovascular alterations occurring during endotoxemia, and on prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) levels in endotoxemic rats. NIM significantly reduced endotoxin-induced elevation of plasma and myocardial levels of TNF-alpha, but not those of IL-1beta. Searching for the mechanism underlying the anti-TNF-alpha effect of NIM, it was found that the drug reduced nuclear factor kappa B activation through diminished nuclear levels of p-65 accompanied by a protective effect against the cardiovascular alterations and mortality seen during endotoxemia. In addition, the inhibitory effect of NIM on endotoxin-induced elevation in plasma and hypothalamic levels of PGE2 was noteworthy, and this may suggest that the large amounts of PGE2 observed during endotoxemia are mainly produced via COX-2.

Systemic and renal macro- and microcirculatory responses to arginine vasopressin in endotoxic rabbits

OBJECTIVE

Arginine vasopressin is being used increasingly to treat vasodilatory hypotension, although little is known of its effects on regional perfusion. Arginine vasopressin hemodynamic effects in physiology are mainly mediated through the V1a receptor on blood vessels. To investigate this further, we studied the effect of arginine vasopressin on systemic and renal blood flow in anesthetized, ventilated rabbits given either intravenous saline or endotoxin, and the impact of blocking V1a receptors.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal research laboratory.

SUBJECTS

Male White New Zealand rabbits.

INTERVENTIONS

Measurement was made of mean arterial blood pressure, aortic and renal blood flow velocities (pulsed Doppler), and renal cortical and medullary flow (laser Doppler).

MEASUREMENTS AND MAIN RESULTS

In a first series of animals, incremental intravenous boluses of arginine vasopressin ranging from 1 to 1000 ng were administered 90 mins postendotoxin or saline. In control rabbits (n = 9), increasing doses of arginine vasopressin elevated mean arterial blood pressure but reduced both aortic and renal blood flow velocity and renal cortical flow (p <.05). In endotoxic animals (n = 6), arginine vasopressin produced a similar increase in mean arterial blood pressure although aortic flow was maintained while renal blood flow velocity increased, mostly in its diastolic component (p <.05). Pretreatment with the V1a receptor antagonist in a second series of animals blunted all the effects observed in both control (n = 5) and endotoxic (n = 6) animals, suggesting that arginine vasopressin acted mainly through V1a subtype in this early phase of sepsis.

CONCLUSIONS

Preservation of renal blood flow with arginine vasopressin during endotoxemia, in particular to the cortex, suggests it could be a promising agent for hemodynamic support during septic shock.

Arginine vasopressin and serum nitrite/nitrate concentrations in advanced vasodilatory shock

BACKGROUND

Arginine-vasopressin (AVP) can successfully stabilize hemodynamics in patients with advanced vasodilatory shock. It has been suggested that inhibition of cytokine-induced nitric oxide production may be an important mechanism underlying AVP-induced vasoconstriction. Therefore, serum concentrations of nitrite/nitrate (NOx), the stable metabolite of nitric oxide, were measured in patients suffering from advanced vasodilatory shock treated with either AVP in combination with norepinephrine (NE) or NE alone.

METHODS

This trial was a separate study arm of a previously published prospective, randomized, controlled study on the effects of AVP in advanced vasodilatory shock. Thirty-eight patients were prospectively randomized to receive a combined infusion of AVP (4 U h(-1)) and NE, or NE infusion alone. Serum NOx concentrations were measured at baseline, 24, and 48 h after randomization. The increase in mean arterial pressure during the first hour after study enrollment was documented in all patients.

RESULTS

No difference in NOx concentrations was found between groups throughout the study period. AVP patients demonstrated a significantly greater increase in mean arterial pressure than NE patients (22 +/- 10 vs. 5 +/- 9 mmHg; P < 0.001). The magnitude of pressure response to AVP was not correlated with NOx concentrations before start of AVP infusion (Pearson's correlation coefficient, -.009; P = 0.971).

CONCLUSION

Cardiovascular effects of AVP infusion in advanced vasodilatory shock are not mediated by a clinically relevant reduction in serum NOx concentrations. Therefore, hemodynamic improvement of patients in advanced vasodilatory shock during continuous infusion of AVP has to be attributed to other mechanisms than inhibition of nitric oxide synthase. In addition, the magnitude of pressure response to AVP is not correlated with baseline concentrations of NOx.

Arginine vasopressin compromises gut mucosal microcirculation in septic rats

OBJECTIVE

Arginine vasopressin (AVP) is increasingly used in the therapy of septic patients with hypotension. However, its effects on the microvascular networks have not been studied in detail. This study was designed to determine the effects of AVP infusion on the villus microcirculation of the septic rat ileum.

DESIGN

Prospective, placebo-controlled, randomized, single-blinded trial.

SETTING

University research laboratory.

SUBJECTS

Fifteen male Sprague-Dawley rats.

INTERVENTIONS

Twenty-four hours after cecal ligation and perforation to create sepsis (M1), rats (n = 8) received a continuous AVP infusion to increase mean arterial pressure by 20 mm Hg (M2) and 40 mm Hg (M3) from M1. In the control group (n = 7), an equivalent volume of normal saline was infused.

MEASUREMENTS AND MAIN RESULTS

Videomicroscopy was performed on 6-10 villi of ileum mucosa at M1 and was repeated at M2 and M3. Blood was drawn to determine plasma levels of AVP and interleukin-6. At M1, both study groups were hypotensive compared with preseptic data (mean arterial pressure, -25%). The increase in mean arterial pressure was linked to supraphysiologic AVP plasma levels and was accompanied by a decrease in mean mucosal blood flow by 76% at M2 and 81% at M3 (p <.001 vs. control). Red blood cell velocity fell by 45% and 47%, respectively (p <.05 vs. control). Whereas periods of arrested villus blood flow increased from 8.1 +/- 2.6 secs/min to 43.8 +/- 5.2 and 47 +/- 6.2 secs/min at M2 and M3 (p <.001), the diameter of terminal arterioles remained unchanged. In addition, AVP infusion further augmented the sepsis-associated increase in interleukin-6 levels (AVP, 905 +/- 160 vs. control, 638 +/- 55 pg/mL; p =.022).

CONCLUSIONS

This study provides evidence for severe abnormalities in gut mucosal blood flow after AVP infusion in septic rats, accompanied by an augmented inflammatory response to the septic injury. The effects of AVP on microvascular blood flow in this model may be related to AVP activities on larger arterioles (>40 microm), a concomitant reduction in cardiac output, or even both.

Effects of terlipressin on systemic and regional haemodynamics in catecholamine-treated hyperkinetic septic shock

OBJECTIVES

To determine the effects of an intravenous bolus dose of a vasopressin analogue, terlipressin (1 mg), on systemic haemodynamic parameters and gastric mucosal perfusion (GMP) in patients with catecholamine-treated septic shock using a gastric tonometry and laser-Doppler flowmetry technique.

DESIGN

Prospective open label study.

SETTINGS

Two multidisciplinary intensive care units.

PATIENTS

Fifteen patients with norepinephrine-treated septic shock.

INTERVENTIONS

Every patient with mean arterial pressure between 50 and 55 mmHg treated with high dose norepinephrine received an intravenous bolus dose of terlipressin as last resort therapy. A laser-Doppler probe and tonometer were introduced into the gastric lumen.

MEASUREMENTS AND MAIN RESULTS

Terlipressin produced a decrease in cardiac output ( p<0.05), a progressive increase in mean arterial pressure ( p<0.05) and in GMP, detected by laser-Doppler flowmetry ( p<0.05) over 30 min and sustained for at least 24 h. The ratio of GMP to systemic oxygen delivery increased after terlipressin bolus dose ( p<0.05). The gradient between gastric mucosal and arterial PCO(2) tended to be lower after terlipressin, and the difference was statistically significant ( p<0.05) after 8 h. Terlipressin administration significantly increased ( p<0.05) urine output compared to baseline and higher values were found at each set of measurement. The terlipressin-induced increase in urine output was associated with a significantly increased creatinine clearance ( p<0.05). Reduction of the high-dose norepinephrine was observed in all patients ( p<0.05).

CONCLUSIONS

Our findings showed that, in patients with norepinephrine-treated septic shock, terlipressin increased GMP, urine output and creatinine clearance by an increase in mean arterial pressure.

Inflammation-induced vasoconstrictor hyporeactivity is caused by oxidative stress

OBJECTIVES

We sought to determine the role of oxidative stress in the development of vascular dysfunction in inflammation.

BACKGROUND

Hyporeactivity to catecholamines and other vasoconstrictors is present in acute inflammation. Because oxidative stress plays a significant role in inflammation, impaired responsiveness may be overcome by anti-oxidants.

METHODS

In randomized, double-blind, cross-over studies, forearm blood flow (FBF) responses to norepinephrine (NE), angiotensin II (ANG II), and vasopressin (VP) were assessed before and 4 h after induction of systemic inflammation by low doses of Escherichia coli endotoxin (lipopolysaccharide [LPS], 20 IU/kg intravenously) or after placebo in healthy volunteers. Furthermore, the effect of intra-arterial vitamin C (24 mg/min) or placebo on NE-induced or ANG II-induced vasoconstriction was studied after LPS.

RESULTS

Administration of LPS caused systemic and forearm vasodilation, increased white blood cell count, elevated body temperature, and reduced vitamin C plasma concentrations. Lipopolysaccharide decreased the responses of FBF to NE by 59%, to ANG II by 25%, and to VP by 51% (n = 9, p < 0.05, all effects). Co-administration of vitamin C completely restored the response to NE and to ANG II, which was comparable to that observed under baseline conditions (n = 8).

CONCLUSIONS

E. coli-endotoxemia reduces FBF responsiveness to vasoconstrictors. The hyporeactivity can be corrected by high doses of vitamin C, suggesting that oxidative stress may represent an important target for inflammation-induced impaired vascular function.

Effect of vasopressin on sublingual microcirculation in a patient with distributive shock

OBJECTIVE

To assess the sublingual microcirculation in a patient during vasopressin administration for a distributive shock after cardiopulmonary bypass.

DESIGN AND SETTING

Case-report in the Department of Intensive Care of a university hospital.

PATIENT

A 53 year-old man developed severe distributive shock after cardiac transplant, requiring massive doses of vasopressor agents.

METHODS

Vasopressin administered twice at a dose of 0.02 U/min increased mean blood pressure and allowed partial weaning of other vasopressor drugs. Microcirculatory alterations were assessed by orthogonal polarization spectral technique: 50% and 60% of capillaries were perfused at baseline, and these proportions did not worsen when vasopressin was administered.

CONCLUSIONS

Despite its strong vasopressor effects vasopressin infusion did not worsen microcirculatory alterations in this patient with distributive shock following cardiac surgery.

Management of vasodilatory shock: defining the role of arginine vasopressin

The rationale for an arginine vasopressin (argipressin) infusion was put forward after it was discovered that patients in shock states might have an endogenous arginine vasopressin deficiency. Subsequently, several investigations impressively demonstrated that arginine vasopressin can successfully stabilise haemodynamics even in advanced vasodilatory shock. We report on physiological and pharmacological aspects of arginine vasopressin, and summarise current clinical knowledge on employing a continuous arginine vasopressin infusion in critically ill patients with catecholamine-resistant vasodilatory shock of different aetiologies. In view of presented experimental evidence and current clinical experience, a continuous arginine vasopressin infusion of approximately 2 to approximately 6 IU/h can be considered as a supplemental strategy to vasopressor catecholamines in order to preserve cardiocirculatory homeostasis in patients with advanced vasodilatory shock. Because data on adverse effects are still limited, arginine vasopressin should be reserved for patients in whom adequate haemodynamic stabilisation cannot be achieved with conventional vasopressor therapy or who have obvious adverse effects of catecholamines that result in further significant haemodynamic deterioration. For the same reasons, arginine vasopressin should not be used as a single, alternative vasopressor agent instead of catecholamine vasopressors. Future prospective studies will be necessary to define the exact role of arginine vasopressin in the therapy of vasodilatory shock.

Low-dose terlipressin improves systemic and splanchnic hemodynamics in fluid-challenged endotoxic rats

OBJECTIVE

Vasopressin has been used to treat arterial hypotension associated with hyperdynamic vasoplegic states, but detrimental effects on splanchnic circulation have been reported. We tested the effects of a low-dose vasopressin analogue, terlipressin (6 microg/kg), on systemic and splanchnic hemodynamics in fluid-challenged endotoxic rats (lipopolysaccharide, 30 mg/kg in 1 hr).

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

A total of 77 rats were divided into five groups: group C, control (17 rats); group E, LPS (18 rats); group EF, LPS plus fluid challenge (18 rats); group EFT, LPS plus fluid challenge plus terlipressin (18 rats); and group ET, LPS plus terlipressin (seven rats).

INTERVENTIONS

Rats were anesthetized, mechanically ventilated, and instrumented to measure heart rate, mean arterial pressure, and abdominal aortic and mesenteric vein indexed blood flows; ileal microcirculation was assessed by laser Doppler. After LPS infusion, rats experienced an endotoxic shock and were resuscitated after the allocation group. The fluid challenge was targeted to maintain mean arterial pressure of >90 mm Hg and aortic blood flow at baseline values.

MEASUREMENTS AND MAIN RESULTS

Terlipressin significantly (p <.05) increased mean arterial pressure without decreasing indexed aortic blood flow and heart rate in the fluid-challenged endotoxic rats (EFT) compared with EF rats and had detrimental effects in hypodynamic endotoxic rats (ET). Fluid challenge significantly (p <.05) increased mesenteric vein blood flow in both the EF and EFT groups, and terlipressin had no detrimental effect on mesenteric blood flow. Terlipressin significantly (p <.05) increased ileal microcirculation in fluid-challenged endotoxic rats (EF and EFT) but not in hypodynamic endotoxic rats (E and ET).

CONCLUSION

Low-dose terlipressin in fluid-challenged endotoxic rats improved systemic and splanchnic hemodynamics and improved the ileal microcirculation.

Cyclooxygenase-2 inhibition attenuates lipopolysaccharide-induced cardiovascular failure

The present study aimed to determine the relevance of cyclooxygenase-2 (COX-2)-derived prostanoids for the adverse effects of lipopolysaccharides (LPSs) on cardiovascular function. For this goal, male Sprague-Dawley rats received a single intravenous dose of LPS (10 mg/kg) and were treated with different cyclooxygenase inhibitors. Injection of LPS caused a marked decrease of systolic arterial pressure, from 128 to 79 mm Hg, and a concomitant increase of heart rate, from 380 to 530 minutes(-1). Both the decrease of systemic arterial pressure and the increase of heart rate induced by LPS were almost absent if the animals also received the COX-2 blocker rofecoxib (20 mg/kg), regardless whether the drug was given 1 hour before or 1 hour after LPS. Although plasma and organ levels of prostanoids were lowered by rofecoxib, the characteristic LPS-induced increases of NO synthase II and COX-2 gene expression, as well as of plasma and tissue nitrate/nitrite concentrations, were not affected by rofecoxib. Although rofecoxib treatment did also not change LPS-induced tissue cytokine concentrations, it markedly improved LPS-induced liver damage, as indicated by the decrease of transaminases. Moreover, the overall well-being of the LPS-injected animals improved on concomitant treatment with the COX-2 inhibitor. Taken together, our data suggest that COX-2-derived prostanoids are major mediators for the detrimental effects of LPS on cardiovascular and organ function.

Cytokine-mediated downregulation of vasopressin V(1A) receptors during acute endotoxemia in rats

The reduced pressure response to vasopressin during acute sepsis has directed our interest to the regulation of vasopressin V(1A) receptors. Rats were injected with lipopolysaccharide for induction of experimental gram-negative sepsis. V(1A) receptor gene expression was downregulated in the liver, lung, kidney, and heart during endotoxemia. Inasmuch as the concentrations of proinflammatory cytokines such as interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma were highly increased during sepsis, the influence of these cytokines on V(1A) receptor expression was investigated in primary cultures of hepatocytes and in the aortic vascular smooth muscle cell line A7r5. V(1A) receptor expression was downregulated by the cytokines in a nitric oxide-independent manner. Blood pressure dose-response studies after injection of endotoxin showed a diminished responsiveness to the selective V(1) receptor agonist Phe(2),Ile(3),Orn(8)-vasopressin. Our data show that sepsis causes a downregulation of V(1A) receptors and suggest that this effect is likely mediated by proinflammatory cytokines. We propose that this downregulation of V(1A) receptors contributes to the attenuated responsiveness of blood pressure in response to vasopressin and, therefore, contributes to the circulatory failure in septic shock.

Hemodynamic effects of terlipressin (a synthetic analog of vasopressin) in healthy and endotoxemic sheep

OBJECTIVE

Hypotension, vasodilation, and vasoplegia are characteristic signs of septic shock. The vasoconstrictive response to catecholamines typically is reduced. A decreased vasopressive effect of catecholamines can be observed in the late phase of hemorrhagic shock. Interestingly, an unaltered vasopressive response to vasopressin can be demonstrated in hemorrhagic shock. In this study, we investigated the vasoconstrictive response to an agonist of the vasopressin receptor, terlipressin, in healthy sheep as well as in ovine hyperdynamic endotoxemia.

DESIGN

Prospective controlled trial.

SETTING

University research laboratory.

SUBJECTS

Six female adult sheep.

INTERVENTIONS

Healthy sheep, instrumented for chronic study, received terlipressin (15 microg/kg) as a bolus; 30 mins later, norepinephrine was continuously given for 30 mins. Three hours later, a continuous infusion of endotoxin (Salmonella typhosa, 10 ng x kg(-1) x min(-1)) was started in the same sheep and given for the next 23 hrs. After 20 hrs of endotoxemia, terlipressin and norepinephrine were given as described previously.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters were measured before and 30 mins after application of terlipressin and after 30 mins of continuous infusion of norepinephrine. Terlipressin significantly increased systemic vascular resistance index in healthy and endotoxemic sheep (p <.05). The increase was higher in endotoxemic compared with healthy animals (p <.05). Only during endotoxemia, terlipressin increased pulmonary vascular resistance index. This was accompanied by a significant decrease in cardiac index, whereas mean pulmonary arterial pressure did not change after application of terlipressin. Additional treatment with norepinephrine did not further increase systemic vascular resistance index or pulmonary vascular resistance index.

CONCLUSIONS

Terlipressin reversed the hemodynamic changes in ovine endotoxemia. However, its pulmonary vasopressive effect might limit its therapeutic use in septic shock.

Downregulation of angiotensin II type 1 receptors during sepsis

Our study aimed to characterize the mechanisms underlying the attenuated cardiovascular responsiveness toward the renin-angiotensin system during sepsis. For this purpose, we determined the effects of experimental Gram-negative and Gram-positive sepsis in rats. We found that sepsis led to a ubiquitous upregulation of NO synthase isoform II expression and to pronounced hypotension. Despite increased plasma renin activity and plasma angiotensin (Ang) II levels, plasma aldosterone concentrations were normal, and the blood pressure response to exogenous Ang II was markedly diminished in septic rats. Mimicking the fall of blood pressure during sepsis by short-term infusion of the NO donor sodium nitroprusside in normal rats did not alter their blood pressure response to exogenous Ang II. Therefore, we considered the possibility of an altered expression of Ang II receptors during sepsis. It turned out that Ang II type 1 receptor expression was markedly downregulated in all organs of septic rats. Further in vitro studies with rat renal mesangial cells showed that NO and a combination of proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma) downregulated Ang II type 1 receptor expression in a synergistic fashion. In summary, our data suggest that sepsis causes a systemic downregulation of Ang II type 1 receptors that is likely mediated by proinflammatory cytokines and NO. We suggest that this downregulation of Ang II type 1 receptors is the main reason for the attenuated responsiveness of blood pressure and of aldosterone formation to Ang II and, therefore, contributes to the characteristic septic shock.

Effect of endotoxemia on hepatic portal and sinusoidal blood flow in rats

A decrease in liver blood flow leads to dysfunction of hepatocytes and Kupffer cells, with subsequent local and systemic liberation of proinflammatory mediators that may maintain systemic inflammatory response syndrome (SIRS) and may lead to multiple organ dysfunction syndrome (MODS). There is only limited knowledge on the hepatic micro- and macrocirculation during sepsis or endotoxemia. Therefore, the aim of our study was to investigate alterations in hepatic portal blood flow (PBF) and sinusoidal blood flow (SBF) during endotoxemia. In male Wistar rats endotoxemia was induced by continuous infusion of 2 mg/kg/h lipopolysaccharides from Escherichia coli 026:B6 immediately after baseline measurements (n = 8). The control group (n = 8) received an equivalent volume of Ringer's solution. Mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), PBF, and SBF were measured at baseline and 60 and 120 min after induction of endotoxemia. PBF was measured using an ultrasonic flow probe that was positioned around the portal vein. SBF was detected by in vivo videomicroscopy of the left liver lobe. In the LPS group MAP decreased, but CO remained at baseline values. During endotoxemia PBF decreased significantly from 23 +/- 3 to 15 +/- 4 mL/min (60 min) and 16 +/- 3 mL/min (120 min). SBF also significantly decreased to 68.5% (60 min) and 57.1% (120 min) of baseline value. Our results demonstrate that during early endotoxemia hepatic macro- and microcirculatory perfusion is significantly decreased despite unchanged CO. This early reduction of hepatic perfusion might be caused by an increased hepatic vessel resistance as a consequence of liberation of vasoconstrictive mediators or/and by a decrease in intestinal perfusion.

Microcirculatory dysfunction in sepsis: a pathogenetic basis for therapy?

Sepsis is a frequent complication of multiple organ dysfunction syndrome and remains a major problem of intensive care medicine. It is also a common factor in the final cause of death in hospital populations. Clinical observations, assisted by invasive monitoring techniques as well as pathological-anatomical studies, clearly indicate that microcirculatory dysfunction lies at the centre of sepsis pathogenesis. Numerous animal models, from rodents to primates, many of which employ bacteria or their toxins, especially endotoxins, have helped to shed light on the pathomechanisms leading to this dysregulation in the peripheral circulation. Among these are activation of humoral and cellular inflammatory mediator systems, with special emphasis on neutrophil-endothelial interactions, affecting endothelial barrier function and vasoregulation and ultimately leading to severely perturbed oxygen transport and utilization. In vitro studies have provided more insight into the molecular mechanisms involved in this microcirculatory dysfunction, although much more attention must be directed towards microvascular endothelial cells and the role of heterogeneity of response in various vascular beds. These experimental data must in turn be validated by comparing with the human in situ situation, both clinical and morphological. This review aims at a critical appraisal of the clinical and experimental evidence for sepsis-induced dysregulation of the microcirculation and how knowledge of the underlying cellular and molecular pathology could be used to make therapy more rational and effective. To date, therapeutic approaches, such as anti-cytokine and anti-oxidant regimens, which have been highly successful in experimental models, have failed to demonstrate clinical efficacy. Newer approaches, such as targeting the coagulation system, nitric oxide synthesis or intracellular signal transduction, are also discussed. The necessity to focus on the role of anti-inflammatory mediators, as well as the pathogenetic significance of important molecular groups, such as the heat shock proteins, which until now have been given scant attention, will be stressed.

Pathophysiological role of endothelins in pulmonary microcirculatory disorders due to intestinal ischemia and reperfusion

BACKGROUND

This study was conducted to investigate pulmonary microcirculatory disorders caused by intestinal ischemia reperfusion (IIR), and the pathophysiological roles of endothelin (ET) in acute lung injury (ALI).

METHODS

Male rats were pretreated with normal saline or a nonselective ET receptor antagonist (TAK-044) and subjected to IIR (60 min of intestinal ischemia and 180 min of reperfusion). The right upper lobe of the lung was examined by intravital confocal microscopy.

RESULTS

The size of arterioles and venules was not significantly reduced during IIR, but the functional capillary density (FCD) decreased significantly. TAK-044 improved the pulmonary microhemodynamics, inhibiting the accumulation of leukocytes, the pulmonary edema, and the decrease of FCD.

CONCLUSIONS

In the early stage of IIR, pulmonary microhemodynamics seemed more likely to be disturbed by the decrease of FCD, than by arteriolar or venular vasoconstriction. ETs decrease the FCD, promoting the interaction between leukocytes and pulmonary vessels.

The effects of vasopressin on endotoxin-induced attenuation of contractile responses in human gastroepiploic arteries in vitro

We studied the effects of vasopressin on contraction in normal and endotoxin-treated human gastroepiploic arterial rings in vitro. In this tissue, vasopressin (50-500 pg/mL) produced concentration-dependent, endothelium-independent contractions. Vasopressin also potentiated the contraction elicited by 1.0 micromol/L norepinephrine (NE) in both the presence and absence of endothelium. Endotoxin (10 microg/mL) attenuated the 1.0 micromol/L NE-induced contractions, and this attenuation was reversed by 300 micromol/L N(G)-nitro-L-arginine-methyl ester (L-NAME) and by 300 micromol/L N(G)-nitro-L-arginine (L-NoArg). After 12 h endotoxin treatment, the vasopressin-induced contraction was attenuated, and the enhancing effect of vasopressin was diminished. However, both before and after endotoxin, the enhancement produced by vasopressin was larger than the vasopressin-contraction itself. An antagonist of the vasopressin V1 receptor, 1.0 micromol/L beta-mercapto-[beta,beta-cyclopentamethylenpropionyl1,O-MeTyr2+ ++,Arg8]-vasopressin, and an antagonist of V1 + V2 receptor receptor, 1.0 micromol/L des-Gly9-[beta-mercapto-beta,beta-cyclopentamethylenepropionyl1 ,O-Et-Tyr2,Val,Arg8]-vasopressin, each diminished the vasopressin-induced enhancement of the NE contraction.

IMPLICATIONS

The results of our study suggest that, in addition to its direct vasoconstrictor effect, vasopressin strongly enhances the responses to norepinephrine through V1-receptor stimulation and that vasopressin could find a role in the management of endotoxin-induced vasodilation.