LY171883 preserves mesenteric perfusion in porcine endotoxic shock

Gastrointestinal dysfunction following cardiac surgery

Cardiac surgery is associated with a low incidence of GI complications, but with a disproportionate mortality. A number of risk factors have become established which identify patients at risk. CPB is associated with profound reductions in mucosal blood flow. Mesenteric perfusion is altered by primary endothelial dysfunction, which may further be exacerbated by the use of vasoconstrictors during CPB; inflammatory mediators can 'prime' the mesenteric vasculature. Cardiac surgery with or without CPB is associated with increased tissue oxygen demands, particularly by the splanchnic bed. The disparity in general and regional oxygen supply and demand results in the development of mucosal hypoxia and this cannot be attributed to CPB alone. This injury is measurable by reductions in both absorptive and barrier functions of the gut. Protection may be conferred by modulating the perfusion protocol during bypass and pharmacological interventions which modify the inflammatory response to surgery.

TNF-alpha release in monocytes after exposure to calcium hydroxide treated Escherichia coli LPS

Lipopolysaccharide (LPS), a cell wall component of Gram negative anaerobic bacteria, has been implicated in the pathogenesis of periapical disease resulting from infected root canals. Calcium hydroxide [Ca(OH)2] has been shown to be an effective medicament in such infections, reducing the microbial titre within the canal. It has been proposed that the therapeutic effect of Ca(OH)2 may also be the result of direct inactivation of LPS. The aim of this study was to investigate whether the toxic potential of an Escherichia coli LPS could be reduced or eliminated by Ca(OH)2. Four concentrations of E. coli LPS ranging from 1-1000 ng/ml sterile water were incubated in duplicate either with 25 mg Ca(OH)2 or sterile water alone. Controls consisted of Ca(OH)2 without LPS or sterile water only. Monocytes were collected from peripheral blood by centrifuging through a gradient and plated to a specific density. Adherent monocytes were incubated for 4 days at 37 degrees C with 5% CO2 in M199 medium with 10% autologous serum. The different LPS solutions were added to the wells on day 5. After 4 h the supernatants were collected and quantitatively assayed for TNF-alpha using a commercial ELISA kit. Statistical analysis was performed with ANOVA. Results indicated that Ca(OH)2 is able to eliminate the ability of an E. coli LPS to stimulate TNF-alpha production in peripheral blood monocytes (P < 0.0001).

Hemodynamic and metabolic effects of vasopressin blockade in endotoxin shock

BACKGROUND

Arginine vasopressin V1 receptor antagonist (AVPRA) was administered to investigate the influence of vasopressin blockade on hemodynamics and metabolism during endotoxin shock.

METHODS

Anesthetized rats were divided into four groups: control (0.9% saline solution, n = 5), drug control (AVPRA, n = 5), endotoxin (endotoxin, 5 mg/kg, n = 10), and pretreatment (AVPRA and endotoxin, n = 10). Hemodynamics and oxygen transport were evaluated for 2 hours. Terminal arterial and portal venous concentrations of endotoxin, pyruvate, lactate, and ketone bodies were determined.

RESULTS

The endotoxin group maintained blood pressure levels similar to those of control animals. AVPRA pretreatment decreased vascular resistance and resulted in lower blood pressure than endotoxin alone. Endotoxin decreased oxygen consumption and the oxygen extraction ratio and increased arterial lactate concentration and the lactate/pyruvate ratio. Endotoxin also decreased arterial ketone body concentration and markedly decreased ketone body availability in the mesenteric circulation. AVPRA pretreatment improved oxygen consumption, oxygen extraction ratio, and ketone body availability; arterial lactate concentration, lactate/pyruvate ratio, and arterial ketone body concentration were not affected. Pretreatment with AVPRA also decreased arterial and portal venous concentrations of endotoxin.

CONCLUSIONS

Vasopressin receptor blockade during endotoxemia resulted in lower blood pressure than endotoxin alone. Vasopressin receptor blockade also maintained oxygen extraction ratio and ketone body availability in the mesenteric circulation. Vasopressin may play a key role in the response to endotoxemia.

The gastric tonometer. A valuable monitor of splanchnic perfusion?

Minimally invasive assessment of the adequacy of perfusion of the gastrointestinal tract has become clinically feasible with the availability of the gastric tonometer. This modified nasogastric tube permits calculation of the pH of the gut mucosal cells; a low tissue pH may indicate tissue hypoxia due to regional hypoperfusion. Such regional hypoperfusion is often undetected by other monitors and, if it occurs intra-operatively, may result in a poor outcome following major surgery. In critical illness, the splanchnic area seems to be particularly vulnerable to hypoperfusion and such a regional oxygen deficit is implicated in the causation of organ dysfunction/failure. Recent studies have begun to define the circumstances in which splanchnic tissue acidosis develops and several therapies have been proposed to reverse the regional oxygen deficit. This review seeks to clarify whether or not the tonometer is a valuable addition to our current monitoring aids.

Mediators and vascular effects in response to endotoxin

Recent experimental findings indicate that endotoxin (i.e. lipopolysaccharide) interacts with specific membrane receptors localized to mononuclear phagocytic cells and neutrophils. Binding of endotoxin to these cells, together with endotoxin-induced activation of host vascular endothelium, initiates a series of signal transduction events that culminate in release of numerous biochemical mediators. The latter include cytokines, platelet-activating factor, thromboxane A2, prostaglandins, leukotrienes, nitric oxide, proteases, toxic O2 radicals, and vasoactive amines. These mediators orchestrate complex biological interactions and amplification signals that lead to cardiopulmonary dysfunction and multi-organ failure within 4-6 h of experimental infusion of endotoxin into animals. The pathophysiological changes include decreased cardiac output, systemic hypotension, decreased blood flow and O2 delivery to tissues, intense pulmonary vasoconstriction and hypertension, bronchoconstriction, increased permeability, pulmonary oedema, ventilation-to-perfusion inequalities, hypoxaemia, and haemoconcentration. Metabolic alterations include increased blood lactate and pyruvate, metabolic acidosis, hyperkalaemia and hypoglycaemia. Potential therapeutic modalities for treatment of endotoxaemia/septic shock include specific antagonists directed against lipopolysaccharide, cytokine, and platelet-activating factor receptors, monoclonal antibodies directed against cytokines and lipid A/core polysaccharides of endotoxin, antiproteases, and agents that block release of toxic O2 and arachidonic acid metabolites.

Hemodynamic changes and gut barrier function in sequential hemorrhagic and endotoxic shock

Multisystem organ failure (MSOF) is the major cause of late death following trauma. The gut is hypothesized to be the source of an ongoing systemic inflammatory response that drives MSOF. It has also been suggested that while a single physiologic insult might not reliably cause MSOF, the addition of a delayed second stress will. This is known as the "two-hit" theory. The purpose of this study was to investigate the two-hit theory by observing the hemodynamic and bacteriologic response to a second stress in a subacute pig model of hemorrhagic and endotoxic shock. Swine (n = 18, 30-40 kg) were fed an antibiotic-free diet for 14 days. During instrumentation and experimentation on days 1 and 3, all animals were anesthetized (ketamine, isofluorane). On day 1, all animals had placement of central venous and arterial catheters, a portal venous catheter, and superior mesenteric artery flow probe. Group E (n = 6) underwent instrumentation on day 1, then infusion of endotoxin (25 mcg/kg E. coli lipopolysaccharide) on day 3. Group HE (n = 7) underwent instrumentation then hemorrhagic shock (mean arterial pressure = 40 mm Hg for 4 hours) on day 1, then infusion of endotoxin on day 3. Group H (n = 5) were instrumented and hemorrhaged on day 1, and underwent anesthesia only on Day 3. Between periods of anesthesia the animals were allowed food and water ad lib and systemic blood was sampled for culture every 12 hours. On day 5, the animals were euthanized prior to organ sampling for bacterial culture. One animal from group HE died during endotoxic shock on day 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipopolysaccharide epitope specificity and binding cross reactivity of the human IgM anti-lipid A monoclonal antibody SdJ5-1.17.15

The binding properties and specificity of the SdJ5-1.17.15 (SdJ5) human IgM monoclonal antibody (mAb), prepared against S. minnesota R595 heat killed whole organisms, were assessed by dot blot assay in vitro. In that assay, lipopolysaccharide (LPS) related antigens, immobilized on nitrocellulose membrane, were reacted with the test and control human IgM antibodies. Results indicated that SdJ5 mAb reacted specifically with lipid A, a component of LPS, from a variety of bacterial species, but not with the whole LPS molecule. The inability of the mAb to react with whole LPS in dot blot assay was attributed to the possible effect of the solid phase on epitope exposure or structure. This hypothesis was tested by inhibition studies which indicated that liquid phase adsorption with LPS abolished or greatly reduced the specific recognition of solid phase lipid A by the mAb. These results indicated that LPS-associated antigens were recognized by the SdJ5 anti-lipid A mAb in liquid, but not solid, phase. In an attempt to identify the SdJ5-specific epitope on lipid A, the pattern of reactivities of different lipid A analogues with the mAb were examined by dot blot assay. Results indicated that a combination of the fatty acid side chains and the phosphate groups of lipid A (both groups being implicated as important for sepsis mediation) were either directly involved in the epitope structure or affected the exposure of epitope in solid phase. Because SdJ5 recognizes an LPS epitope on lipid A closely associated with endotoxin activity, this mAb could potentially be a useful therapeutic agent against septic shock.

Multiple Organ Failure Syndrome—Part I: Epidemiology, Prognosis, and Pathophysiology

The multiple organ failure syndrome (MOFS) is the leading cause of death in intensive care units. Although sepsis is an important cause of MOFS, it is clear that MOFS can occur in the absence of infection. The pathophysiology of MOFS is complex and multifactorial and includes derangements in oxygen delivery and consumption, the release of inflammatory and vasoactive mediators capable of inflicting tissue damage, and alterations in the barrier function of the intestinal mucosa. Although advances have been made in our understanding of MOFS, treatment remains nonspecific and largely supportive. Early and aggressive restoration of tissue perfusion, adequate treatment of infection, timely nutritional support, and support of individual failed organs remain the mainstay of therapy. Therapeutic agents directed against the various mediators associated with the pathophysiology of MOFS may prove useful in the future.

Leukotriene C4 induces mesenteric hypoperfusion and intestinal intramural acidosis in pigs

We examined the effect of intravenous infusion of graded doses of authentic leukotriene (LT) C4 on several physiological variables in pentobarbital-anesthetized immature swine. Mesenteric blood flow (Qsma) was measured using an ultrasonic flow probe and ileal intramucosal hydrogen ion concentration ([H+]I) was estimated tonometrically. Three groups were studied. Pigs in Group I (n = 6) were infused beginning at t = 0 min with increasing doses (0.03-1.0 microgram/kg-min) of LTC4, each dose being administered for 10 min. Pigs in Group II (n = 6) were infused with LTC4 as above, but were pre- and post-treated with a specific sulfidopeptide LT receptor antagonist, LY203647 (30 mg/kg bolus and then 10 mg/kg-hr) beginning at t = -20 min. Pigs in Group III (n = 4) received only normal saline (5 ml/kg-h). Infusing LTC4 significantly decreased Qsma and mesenteric oxygen uptake and significantly increased ileal [H+]I. These changes were prevented by LY203647. These data support the idea that sulfido-peptide LT are capable of causing mesenteric ischemia and that this phenomenon can be blocked by LY203647.