Local venous responses to endotoxin in humans

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

Replacement therapy with hydrocortisone in catecholamine-dependent septic shock

Septic shock is one of the leading causes of death in intensive care units world-wide. Scientists have made great improvements in understanding mechanisms of inflammation, and the sequence of activation of the various pro- and anti-inflammatory markers is now well known. In contrast, physicians have failed to improve survival from septic shock despite the development of specific targets at various points in the cytokine cascade considered to have a key role in host survival in sepsis. Corticosteroids were among the first anti-inflammatory drugs to be tested in large randomized controlled trials. These trials showed that patients with septic shock did not benefit from a short course of large doses of steroids. More recent findings highlighting the role of the integrity of the hypothalamic—pituitary—adrenal axis to respond appropriately to a septic insult, have led to a re-appraisal of the use of steroids in septic shock. Several randomized controlled trials have evaluated the efficacy of a replacement therapy with hydrocortisone in severe sepsis. These trials strongly suggest that this replacement therapy reduces the morbidity of septic shock and may favorably affect survival from septic shock.

[Interaction between hypnotic agents and the hypothalamic-pituitary-adrenocorticotropic axis during surgery]

During stress, the relationship between the central nervous system and the immune system is essential to maintain homeostasis. The main neuroendocrine system involved in this interaction is the hypothalamic-pituitary-adrenal axis (HPA), which via the synthesis of glucocorticoids will modulate the intensity of the inflammatory response. Anaesthetic agents could be interacting with the HPA axis during surgery. Although etomidate currently remains in the center of the discussions, it seems, at least experimentally, that most hypnotics have the capacity to modulate the synthesis of adrenal steroids. Nevertheless, with the large literature on this subject, etomidate seems to be the most deleterious hypnotic agent on the HPA axis function. Its use should be limited when HPA axis is already altered.

The role of vasoactive agents in the resuscitation of microvascular perfusion and tissue oxygenation in critically ill patients

Purpose

The clinical use of vasoactive drugs is not only intended to improve systemic hemodynamic variables, but ultimately to attenuate derangements in organ perfusion and oxygenation during shock. This review aims (1) to discuss basic physiology with respect to manipulating vascular tone and its effect on the microcirculation, and (2) to provide an overview of available clinical data on the relation between vasoactive drugs and organ perfusion, with specific attention paid to recent developments that have enabled direct in vivo observation of the microcirculation and concepts that have originated from it.

Methods

A MedLine search was conducted for clinical articles in the English language over the last 15 years pertainig to shock, sepsis, organ failure, or critically ill patients in combination with vasoactive drugs and specific variables of organ perfusion/oxygenation (e.g., tonometry, indocyanine clearance, laser Doppler, and sidestream dark field imaging).

Results

Eighty original papers evaluating the specific relationship between organ perfusion/oxygenation and the use of vasoactive drugs were identified and are discussed in light of physiological theory of vasomotor tone.

Conclusions

Solid clinical data in support of the idea that increasing blood pressure in shock improves microcirculatory perfusion/oxygenation seem to be lacking, and such a concept might not be in line with physiological theory of microcirculation as a low-pressure vascular compartment. In septic shock no beneficial effect on microcirculatory perfusion above a mean arterial pressure of 65 mmHg has been reported, but a wide range in inter-individual effect seems to exist. Whether improvement of microcirculatory perfusion is associated with better patient outcome remains to be elucidated.

Hydrocortisone effects on cardiovascular variability in septic shock: a spectral analysis approach

RATIONALE

Septic shock may be associated with a loss in cardiovascular variability and adrenal dysfunction.

OBJECTIVES

To investigate the relationship between cardiovascular autonomic modulation and adrenal function during sepsis.

MEASUREMENT AND MAIN RESULTS

Seventy-five volunteers with septic shock and six healthy volunteers were prospectively included in the study. Cardiovascular variability was assessed by spectral analysis of heart rate and diastolic blood pressure signals, which included computation of normalized low (LF(nu)) and high frequency (HF(nu)) components. Cardiovascular variability was investigated in patients and healthy volunteers immediately before and 1 hr after a single bolus of 50 mg of hydrocortisone (study phase I); in patients according to adrenal function (study phase II); and in patients with septic shock and adrenal insufficiency, before and 72 hrs after a treatment with 50 mg every 6 hrs of hydrocortisone and 50 microg daily of fludrocortisone or their placebos (study phase III). As compared to healthy volunteers, patients had decreased LF(nu)-HR (.16 +/- .05 vs. .23 +/- .07 p = .01) and LF(nu)-DBP (.18 +/- .11 vs. .28 +/- .02 p = .01) and, after hydrocortisone, they had a greater increase in LF(nu)-DBP (p = .01). As compared to patients with normal adrenal function, those with adrenal failure had decreased LF(nu)-HR (.1 +/- .01 vs. .2 +/- .15 p = .01) and LF(nu)-DBP (.008 +/- .01 vs. .14 +/- .22 p = .0003). In patients with adrenal failure, as compared to placebos, hydrocortisone plus fludrocortisone increased significantly LF(nu)-DBP (p = .02) and low frequency/high volume ratio (p = .009).

CONCLUSION

In septic shock, the loss in cardiovascular variability is more marked in patients with adrenal insufficiency and is partly restored by exogenous administration of corticosteroids.

A role for nitric oxide-mediated peroxynitrite formation in a model of endotoxin-induced shock

The aim of the present study was to assess the relative contributions of peroxynitrite formation following induction of nitric-oxide synthase (iNOS) in the pathophysiology of endotoxin-induced shock in the rat. To this end, we used a selective inhibitor of iNOS, N-(3-(aminomethyl)benzyl)acetamidine (1400W), and a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTTPs). Intravenous (i.v.) administration of Escherichia coli lipopolysaccharide (LPS; 4 mg/kg) elicited a time-dependent fall in mean arterial pressure as well as liver, renal, and pancreatic tissue damage. 1400W (3-10 mg/kg i.v.) administered 30 min before LPS delayed the development of hypotension but did not improve survival. On the other hand, FeTTPs administered (10-100 mg/kg i.v.) inhibited in a dose-dependent manner LPS-induced hypotension, tissue injury, and improved mortality rate. In separate experiments, rats were treated with LPS (4 mg/kg) or saline for control, and their aortas were isolated and placed in organ baths 2 h later. Tissues from LPS-treated rats had significant inhibition of contractile activity to phenylephrine as well as a significantly impaired relaxation response to acetylcholine. FeTPPs, when administered (100 mg/kg i.v.) 1 h before LPS, prevented the LPS-induced aortic contractile and endothelial dysfunction. These results demonstrate that nitric oxide-derived peroxynitrite formation plays an important role in this model of endotoxemia. Our results also suggest that use of an iNOS inhibitor in this setting has little beneficial effect in part because, in the presence of a failing eNOS system, some NO is needed to maintain adequate organ function.

Glucocorticoids in the treatment of severe sepsis and septic shock

PURPOSE OF REVIEW

Septic shock remains one of the leading causes of death in intensive care units. In recent years, there is general use of low to moderate doses of corticosteroids in the treatment of septic shock. However, there are wide variations in the practical modality of this treatment, mainly with regard to patients' selection, treatment's dose, timing, route of administration, duration, and weaning. This review provides opinion-based guidelines for the use of corticosteroids in severe sepsis and septic shock.

RECENT FINDINGS

A summary of the latest understanding of the mechanisms of action of corticosteroids and the most recent observations in the clinical and biologic responses to corticosteroids in severe sepsis and septic shock is presented.

SUMMARY

In septic shock, intravenous hydrocortisone should be started immediately after a 250 microg corticotropin test, at a dose of 200-300 mg per day. When adrenal insufficiency is confirmed, treatment should be continued at full doses for 7 days. Otherwise, hydrocortisone should be stopped. It is worth considering adding enteral fludrocortisone at a dose of 50 microg per day for 7 days. In severe sepsis, despite growing evidence to support the use of a moderate dose of corticosteroids, the efficacy and safety of this treatment needs to be assessed in a large-scale study.

The endothelium in intensive care

This article reviews the major role that the vascular endothelium plays in pathophysiological processes related to metabolism, vascular function, and blood coagulation. Normally an antithrombotic surface, inflammation activates endothelium to become a prothrombotic and pro-inflammatory interface that is critically involved in multi-organ failure in patients with severe systemic diseases including sepsis. Improving endothelial functions in sepsis is a major therapeutic challenge.

Practice parameters for hemodynamic support of sepsis in adult patients: 2004 update

OBJECTIVE

To provide the American College of Critical Care Medicine with updated guidelines for hemodynamic support of adult patients with sepsis.

DATA SOURCE

Publications relevant to hemodynamic support of septic patients were obtained from the medical literature, supplemented by the expertise and experience of members of an international task force convened from the membership of the Society of Critical Care Medicine.

STUDY SELECTION

Both human studies and relevant animal studies were considered.

DATA SYNTHESIS

The experts articles reviewed the literature and classified the strength of evidence of human studies according to study design and scientific value. Recommendations were drafted and graded levels based on an evidence-based rating system described in the text. The recommendations were debated, and the task force chairman modified the document until <10% of the experts disagreed with the recommendations.

CONCLUSIONS

An organized approach to the hemodynamic support of sepsis was formulated. The fundamental principle is that clinicians using hemodynamic therapies should define specific goals and end points, titrate therapies to those end points, and evaluate the results of their interventions on an ongoing basis by monitoring a combination of variables of global and regional perfusion. Using this approach, specific recommendations for fluid resuscitation, vasopressor therapy, and inotropic therapy of septic in adult patients were promulgated.

New approaches to the treatment of sepsis

The clinical spectrum of sepsis, severe sepsis, and septic shock is responsible for a growing number of deaths and excessive health care expenditures. Until recently, despite multiple clinical trials, no intervention provided a beneficial outcome in septic patients. Within the last 2 years, studies that involved drotrecogin alfa (activated), corticosteroid therapy, and early goal-directed therapy showed efficacy in those with severe sepsis and septic shock. These results have provided optimism for reducing sepsis-related mortality.

Rôle de la dysfonction endothéliale dans la mortalité liée au sepsis

During the past decade, a unifying hypothesis has been developed to explain the vascular changes that occur in septic shock on the basis of the effect of inflammatory mediators on the vascular endothelium. The vascular endothelium plays a central role in the control of microvascular flow, and it has been proposed that widespread vascular endothelial activation, dysfunction and eventually injury occur in septic shock, ultimately resulting in multiorgan failure. This has been characterised in various models of experimental septic shock. Now, direct and indirect evidence for endothelial cell alteration in humans during septic shock is emerging. The present review details recently published literature on this rapidly evolving topic.

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.

Clinical review: corticotherapy in sepsis

The use of glucocorticoids (corticotherapy) in severe sepsis is one of the main controversial issues in critical care medicine. These agents were commonly used to treat sepsis until the end of the 1980s, when several randomized trials casted serious doubt on any benefit from high-dose glucocorticoids. Later, important progress in our understanding of the role played by the hypothalamic–pituitary–adrenal axis in the response to sepsis, and of the mechanisms of action of glucocorticoids led us to reconsider their use in septic shock. The present review summarizes the basics of the physiological response of the hypothalamic–pituitary–adrenal axis to stress, including regulation of glucocorticoid synthesis, the cellular mechanisms of action of glucocorticoids, and how they influence metabolism, cardiovascular homeostasis and the immune system. The concepts of adrenal insufficiency and peripheral glucocorticoid resistance are developed, and the main experimental and clinical data that support the use of low-dose glucocorticoids in septic shock are discussed. Finally, we propose a decision tree for diagnosis of adrenal insufficiency and institution of cortisol replacement therapy.

Corticosteroids in sepsis: from bench to bedside?

The use of corticosteroids in patients with septic shock has been recently revisited and the use of low dose corticosteroids led to very promising results, particularly in patients with corticosteroid insufficiency. We review the different mechanisms that can account for their beneficial effects in patients. Glucocorticoids display a wide spectrum of anti-inflammatory properties that have been identified in in vitro and in vivo experimental models (e.g., inhibition of production of pro-inflammatory cytokines, free radicals, prostaglandins and inhibition of chemotaxis, and adhesion molecule expressions.) In addition, glucocorticoids have profound effects on the cardiovascular system (e.g., increasing mean blood pressure, increasing pressor sensitivity, and therefore decreasing the duration of use of catecholamines during septic shock.) Through these anti-inflammatory and cardiovascular effects, low doses of glucorticoids may improve septic shock survival.

Bench-to-bedside review: endothelial cell dysfunction in severe sepsis: a role in organ dysfunction?

During the past decade a unifying hypothesis has been developed to explain the vascular changes that occur in septic shock on the basis of the effect of inflammatory mediators on the vascular endothelium. The vascular endothelium plays a central role in the control of microvascular flow, and it has been proposed that widespread vascular endothelial activation, dysfunction and eventually injury occurs in septic shock, ultimately resulting in multiorgan failure. This has been characterized in various models of experimental septic shock. Now, direct and indirect evidence for endothelial cell alteration in humans during septic shock is emerging. The present review details recently published literature on this rapidly evolving topic.

The use of corticosteroids in severe sepsis and acute respiratory distress syndrome

During sepsis or acute respiratory distress syndrome, the hypothalamic pituitary adrenal axis is rapidly activated through a systemic pathway, i.e. by circulating pro-inflammatory cytokines and through the vagus nerve. Subsequently, the adrenal glands release cortisol, a hormone which will likely counteract the inflammatory process and restore cardiovascular homeostasis. Both experimental models and studies in humans suggest that inadequate hypothalamic pituitary adrenal axis response to stress accounts, at least partly, for the genesis of shock and organ dysfunction in sepsis and acute respiratory distress syndrome. Relative adrenal insufficiency and peripheral glucocorticoid resistance syndrome are the two main features of the inappropriate hormonal response and provide the grounds for cortisol replacement in these diseases. In practice, a high dose of corticosteroids (i.e. one to four boluses of 30 mg/kg of methylprednisolone, or equivalent) had no effects on survival in severe sepsis or acute respiratory distress syndrome. There are at least seven randomised controlled trials reporting the benefits and risks of low dose corticosteroids (i.e. 200 to 300 mg daily of hydrocortisone or equivalent) given for a prolonged period in severe sepsis or in the late phase of acute respiratory distress syndrome. These trials showed consistently that, in these patients, the use of low dose of corticosteroids alleviated inflammation, restored cardiovascular homeostasis, reduced organ dysfunction, improved survival and was safe. Further studies are ongoing to better identify the target population. In the meantime, cortisol replacement (i.e. 200 to 300 mg daily of hydrocortisone or equivalent) should be considered as standard care for these patients.

Endothelial cell dysfunction and coagulation

OBJECTIVES

a) To review endothelial properties and to establish how these unperturbed properties contribute to the maintenance of endothelium anticoagulant activity; b) to better understand the relative contributions of endothelial cells and monocytes in sepsis-induced altered coagulation.

DATA SOURCES

A summary of published literature from MEDLINE search files and other original articles and reviews published on endothelial cell and monocyte functions and modifications owing to sepsis.

DATA EXTRACTION AND SYNTHESIS

Unperturbed endothelial cells provide anticoagulant properties; exposure to inflammatory and/or septic stimuli can rapidly lead to procoagulant behavior. Sepsis alters endothelial cell surface and induces tissue factor synthesis at the endothelial and subendothelial levels. During endotoxemia, endothelial cells generate adhesion molecules that bind leukocytes and monocytes, increasing local procoagulant reactions. Tissue factor expression is also increased at the level of the monocyte; the relative importance of endothelial injury and monocyte activation in coagulation disorders was recently assessed. Endothelium protection before induction of septic shock was not associated with any reduction in monocyte tissue factor expression, suggesting that altered coagulation was present despite normal endothelial cell function. On the other hand, decreased monocyte tissue factor expression was associated with a marked reduction in endothelial injury, increased endothelium-derived relaxation, and improved survival rate in treated animals.

CONCLUSIONS

This review suggests that monocyte activation and tissue factor expression may be of paramount importance in sepsis-associated injuries and that coagulation activation may contribute to the endothelial cell injury observed during sepsis. Endothelial injury, in turn, exacerbates sepsis-induced coagulation abnormalities.

Corticosteroids for septic shock

OBJECTIVE

To gather the data to provide a rationale for using replacement therapy with hydrocortisone in septic shock patients.

DATA SOURCES

The Medline and the Cochrane Library databases.

STUDY SELECTION

Studies in animals and in humans were considered when significant data were available about the mechanisms of action of corticosteroids or about their use in severe sepsis.

DATA SUMMARY

Corticosteroids were the first anti-inflammatory drugs tested in septic patients. Randomized trials clearly showed that a short course of a large dose of anti-inflammatory steroids is ineffective and potentially harmful in patients with severe sepsis. Recent demonstrations of altered hypothalamic-pituitary-adrenal axis response to septic insult have led to a reappraisal of the use of steroids in septic shock. Randomized trials in catecholamine-dependent septic shock patients strongly suggest that replacement therapy with hydrocortisone may alleviate the symptoms of systemic inflammatory response, reduce the duration of shock, and favorably affect survival.

CONCLUSIONS

Current evidence that the therapeutic interest of replacement therapy with corticosteroids increases suggests that low doses of hydrocortisone should be offered to patients with catecholamine-dependent septic shock.

Vascular hyporesponsiveness of the renal circulation during endotoxemia in anesthetized pigs

OBJECTIVE

To compare the vascular reactivity of the renal circulation in control and septic conditions.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Anesthetized pigs (n = 17).

INTERVENTIONS

Ten pigs received a continuous intravenous infusion of endotoxin from Escherichia coli (160 ng x kg(-1) x hr(-1)) during 18 hrs, whereas seven control animals received a saline infusion. To test the vascular reactivity, norepinephrine (NE) (1 microg x kg(-1)), acetylcholine (10 microg x kg(-1)), and sodium nitroprusside (10 microg x kg(-1)) were intravenously injected for 20 secs and changes of mean arterial pressure and renal blood flow were observed during the 200 secs after the drug administration. To compare the evolution of the vascular reactivity over time, three tests were performed 5 hrs, 11 hrs, and 17 hrs after initial endotoxin or saline administration.

MEASUREMENTS AND MAIN RESULTS

Endotoxin infusion induced a hypotensive and hypokinetic syndrome with renal hypoperfusion. The mean arterial pressure increase after NE injection and the mean arterial pressure decrease after acetylcholine and nitroprusside were lower in endotoxin than in control pigs. In the renal circulation, the increase of resistance after NE injection and the decrease of renal resistance after acetylcholine and nitroprusside injections were lower in endotoxin than in control pigs.

CONCLUSIONS

This study shows a hyporesponsiveness of the renal circulation to vasoactive agents during endotoxemia. Vasoconstriction to NE, endothelium-dependent as well as endothelium-independent relaxations are altered during endotoxemia but not abolished, and despite the continuous infusion of endotoxin for 18 hrs, no recovery was observed over time.

[Endothelial dysfunction in patients with acute coronary syndrome]

Increased vasoconstriction, activation of platelet vessel wall interaction and invasion of monocytes into the subintima as well as vascular smooth muscle cell proliferation play a fundamental role in the pathogenesis of coronary artery disease. Acute coronary syndromes such as myocardial infarction and unstable angina pectoris are characterized by plaque rupture or erosion, activation of platelets and the coagulation system and vasoconstriction. Endothelial dysfunction may be one of the underlying mechanisms linking coronary artery disease and acute coronary syndromes. Both of these are often temporarily limited. Therefore, "non-invasive examination" of endothelial function by venous occlusion plethysmography or high resolution ultrasound might be useful for monitoring high-risk patients.

A quantitative analysis of the microvascular sequestration of malaria parasites in the human brain

Microvascular sequestration was assessed in the brains of 50 Thai and Vietnamese patients who died from severe malaria (Plasmodium falciparum, 49; P. vivax, 1). Malaria parasites were sequestered in 46 cases; in 3 intravascular malaria pigment but no parasites were evident; and in the P. vivax case there was no sequestration. Cerebrovascular endothelial expression of the putative cytoadherence receptors ICAM-1, VCAM-1, E-selectin, and chondroitin sulfate and also HLA class II was increased. The median (range) ratio of cerebral to peripheral blood parasitemia was 40 (1.8 to 1500). Within the same brain different vessels had discrete but different populations of parasites, indicating that the adhesion characteristics of cerebrovascular endothelium change asynchronously during malaria and also that significant recirculation of parasitized erythrocytes following sequestration is unlikely. The median (range) ratio of schizonts to trophozoites (0.15:1; 0.0 to 11.7) was significantly lower than predicted from the parasite life cycle (P < 0.001). Antimalarial treatment arrests development at the trophozoite stages which remain sequestered in the brain. There were significantly more ring form parasites (age < 26 hours) in the cerebral microvasculature (median range: 19%; 0-90%) than expected from free mixing of these cells in the systemic circulation (median range ring parasitemia: 1.8%; 0-36.2%). All developmental stages of P. falciparum are sequestered in the brain in severe malaria.

Effects of adrenaline or endotoxin tolerance states on mesenteric blood flow in endotoxaemia

BACKGROUND

Endotoxic shock is associated with release of catecholamines as well as decreased mesenteric vascular perfusion, which is thought to cause remote organ injury. Adrenaline tolerance was reported to decrease mortality in endotoxic shock and have cross-tolerance with endotoxin tolerance. Our aim was to investigate the effect of these two tolerance conditions on the lipopolysaccharide (LPS)-induced decrease in mesenteric blood flow (MBF).

METHODS

Adrenaline tolerance was developed by injecting 0.03 mg/kg adrenaline to Swiss-albino mice, gradually increasing the dose to 2 mg/kg over 5 days. Endotoxin tolerance was developed by injecting saline for 4 days and LPS 1 mg/kg at the fifth day. Control animals were injected with saline for 5 days. At 72 h after completion of injections, half of the animals in each group were challenged with saline and the other half with 20 mg/kg LPS, at 0 h. Mesenteric blood flow was measured at 4 and 24 h.

RESULTS

Neither endotoxin nor adrenaline tolerance prevented an LPS-induced decrease in MBF.

CONCLUSION

A low dose of LPS prior to a higher dose does not prevent an LPS-induced decrease in MBF and may actually prime for a decrease. Also, catecholamines are not primary mediators of LPS-induced decreases in MBF.

Invasive hemodynamics and force-frequency relationships in open- versus closed-chest mice

We compared hemodynamics, ventricular function, and force-frequency relationships in six open-chest and six closed-chest anesthetized mice (FVB/N strain). Left ventricular (LV) pressure was measured with a 1.8- or 1.4-Fr Millar catheter placed via the right carotid artery and the LV apex in the closed- and open-chest state, respectively. Pacing was performed with electrodes placed either directly on atrial appendages (open chest) or with a 1-Fr bipolar catheter via the jugular vein (closed chest). Closed-chest animals had greater spontaneous heart rate (267 +/- 106 vs. 147 +/- 27 beats/min), LV systolic (81 +/- 14 vs. 48 +/- 9 mmHg) and diastolic pressures (11.2 +/- 4.8 vs. 5.6 +/- 2.4 mmHg), and maximal rise (+ dP/dtmax: 6,208 +/- 2,519 vs. 3,682 +/- 671 mmHg/s) and fall in pressure development (-dP/dtmax: -6,094 +/- 2,386 vs. -3,001 +/- 399 mmHg/s). LV systolic pressure (98 +/- 18 vs. 52 +/- 11 mmHg), + dP/dtmax (9,240 +/- 2,459 vs. 5,777 +/- 2,473 mmHg/s), and -dP/dtmax (-8,375 +/- 2,551 vs. -3,753 +/- 1,170 mmHg/s) were significantly higher when animals were matched at a heart rate of 420 beats/min in closed-chest vs. open-chest animals. Biphasic force-frequency relationships were seen in all animals, but the critical heart rate was greater in the closed- than open-chest animals (432 +/- 42 vs. 318 +/- 42 beats/min). We conclude that 1) there are significant differences between invasive indexes of systolic and diastolic function between the closed- and open-chest preparations, 2) there is a biphasic force-frequency relationship in the anesthetized mouse, and 3) dP/dtmax can be used to assess the cardiovascular phenotype.