Sepsis is a major clinical challenge that is associated with encephalopathy and multi-organ dysfunction. Current therapeutic interventions are relatively ineffective and the development of novel treatments is hampered by the lack of a well-characterised animal model. Therefore, the behavioural, metabolic, physiological and histological changes resulting from 'through and through' caecal ligation and puncture (CLP) in the rat were investigated to determine its suitability as an animal model of human sepsis. CLP resulted in bacteraemia, characterised by the presence of multiple enteric species within 18-20 h. Locomotor activity was reduced within 4 h of CLP and this reduction increased with time. Pyrexia was evident 4-5 h after CLP and was followed by hypothermia beginning 17 h after intervention. CLP resulted in reduced white blood cell and platelet counts and an increased neutrophil: lymphocyte ratio within 18-20 h. It also resulted in decreased blood glucose, but not lactate levels. CLP caused histopathological changes in the cerebral cortex, liver, lungs and vascular system indicative of multi-organ dysfunction. Therefore, CLP in the rat mimics the cardinal clinical features of human sepsis and the subsequent development of multi-organ dysfunction. It appears to be the best available animal model currently available, in which to investigate the underlying pathophysiology of sepsis and identify therapeutic targets.

Objective: to compare diafiltered 6% pentastarch (Pentafraction-PDP, MWn 120000 and MWw 280000) and native pentastarch (Pentaspan-PSP, MWn 63000 and MWw 264000 dalton) in a porcine model of faecal peritonitis.Design: Randomised prospective study in 12 adolescent pigs.Interventions: Prior to infection the study solution was infused to increase Qt by 25%. Thereafter adjustments in infusion rate were made (up to 1 l/h) in an attempt to maintain Qt at 25% above baseline values.Measurements and results: Animals were sacrificed at 8h. Tissue was excised from the right lobe of liver and from the right lung and fixed for later electron microscopy and digital morphometric analysis. Patent sinusoidal lumen was significantly greater in group PDP compared to PSP (11.3%±2.3% of liver tissue versus 4.8%±1.1%,p<0.05) and this was accounted for by a significantly lower proportion of sinusoidal lumen occluded with white cells (2.1%±0.6% versus 6.6%±1.9%,p<0.05). Similarly, patent capillary represented a significantly higher proportion of lung tissue for group PDP versus PSP (26.2%±1.9% versus 18.5%±2.7%,p<0.05). The arithmetic mean alveolar capillary barrier thickness was significantly greater in group PSP than in group PDP (4.3±03 μm versus 2.5±03 μm,p<0.01).Conclusions: The molecular weight profile of Pentafraction was associated with less structural organ damage including less tissue oedema and less white cell occlusion.

Objective:To investigate the effects of adrenergic agents on the cerebral response to sepsis. Design:Prospective, randomized, controlled, experimental animal study. Setting:Medical school research laboratories. Subjects:Twenty-eight middle white pigs (25–30 kg). Interventions:Pigs were anesthetized, mechanically ventilated, and randomly assigned to one of the following groups: cecal peritonitis (n = 5), cecal peritonitis with dopexamine (n = 5), cecal peritonitis with dopexamine and the &bgr;2-adrenergic receptor antagonist ICI 118,551 (n = 4), cecal peritonitis with methoxamine (n = 5), cecal peritonitis with dopexamine and methoxamine (n = 4), and sham-operated (n = 5). Sham-operated pigs were killed after laparotomy, and pigs with cecal peritonitis were killed 8 hrs after its induction. Samples of frontal cerebral cortex were taken immediately after death, processed for light and electron microscopy, and then subjected to morphometric analysis. Measurements and Main Results:There was significantly more (p < .0005) cerebral perimicrovessel edema in pigs with cecal peritonitis (80.2 &mgr;m2 ± 5.3 sem) than in sham-operated pigs (26.2 &mgr;m2 ± 2.7 sem) and significantly less (p < .0005) perimicrovessel edema in dopexamine-treated pigs with cecal peritonitis (39.8 &mgr;m2 ± 5.5 sem) than in pigs with cecal peritonitis alone (80.2 &mgr;m2 ± 5.3 sem). There was no significant difference between the amount of perimicrovessel edema in pigs with cecal peritonitis treated with dopexamine plus ICI118,551 and pigs with cecal peritonitis alone. The mean cerebral microvessel endothelial cell cross-sectional area in methoxamine-treated pigs with cecal peritonitis (26.3 &mgr;m2 ± 2.6 sem) was significantly greater than that in pigs with cecal peritonitis alone (16.3 &mgr;m2 ± 2.1 sem, p = .008) or in sham-operated pigs (12.3 &mgr;m2 ± 1.3 sem, p = .0005). Conclusions:Dopexamine protects against cerebral edema formation in sepsis by stimulation of &bgr;2-adrenergic receptors, whereas the &agr;1 adrenoceptor agonist methoxamine induces cerebral microvessel endothelial cell swelling.

The tight junction protein occludin 'glues' normal, adjacent brain microvessel endothelial cells together. Malignant brain tumours cause cerebral oedema because they have leaky endothelial tight junctions, which allow plasma fluid to enter the brain from the microvessel lumen. In order to identify molecular abnormalities in tumour endothelial tight junctions, we investigated occludin expression in microvessels from adult human non-neoplastic brain tissue using immunohistochemistry and immunoblotting, The proportions of microvessels immunolabelling for occludin were >2/3 in 5/5 non-neoplastic brain tissue samples, >1/3 in 5/5 low grade (Daumas-Duport I or II) astrocytomas and <1/3 in 5/5 high grade (III or IV) astrocytomas and 6/6 metastatic adenocarcinomas. Six non-neoplastic brain tissue immunoblots gave a 55-kDa occludin band, three low-grade astrocytomas gave 55-kDa and 60-kDa bands, 13 high-grade astrocytomas gave 60-kDa or no band and four adenocarcinomas did not give an occludin band. Expression of 55-kDa occludin inversely correlated with the presence of contrast enhancement on computed tomograms (P<0.001). Electron microscopy showed open endothelial tight junctions in 0/2 non-neoplastic human brain specimens and 2/2 high-grade astrocytomas. We suggest that loss of 55-kDa occludin expression in human brain tumours may contribute to endothelial tight junction opening. Characterizing the molecular pathology of brain endothelial tight junctions may facilitate the design of novel drugs against cerebral oedema.

Objectives: Encephalopathy is a common complication of sepsis. This review describes the different pathologic mechanisms that may be involved in its etiology.Data Sources: The studies described here were derived from the database PubMed (http:\\www.nlm.nih.gov) and from references identified in the bibliographies of pertinent articles and books. The citations are largely confined to English language articles between 1966 and 1998. Older publications were used if they were of historical significance.Study Selection: All investigations in which any aspect of septic encephalopathy was reported were included. This selection encompasses clinical, animal, and in vitro cell culture work.Data Extraction: The literature cited was published in peer-reviewed clinical or basic science journals or in books.Data Synthesis: Contradictions between the results of published studies are discussed.Conclusions: The most immediate and serious complication of septic encephalopathy is impaired consciousness, for which the patient may require ventilation. The etiology of septic encephalopathy involves reduced cerebral blood flow and oxygen extraction by the brain, cerebral edema, and disruption of the blood-brain barrier that may arise from the action of inflammatory mediators on the cerebrovascular endothelium, abnormal neurotransmitter composition of the reticular activating system, impaired astrocyte function, and neuronal degeneration. Currently, there is no treatment.

Encephalopathy is a common complication of sepsis. However, little is known about the morphological changes that occur in the brain during sepsis. Faecal peritonitis was induced in pigs that were killed 8 h later and frontal cortex samples were taken immediately after death. The tissue was investigated using light and electron microscopy and compared with frontal cortex samples taken from sham-operated controls. Septic pigs had 49.5% more perimicrovessel oedema than sham pigs. However, the tight junctions between cerebral microvessel endothelial cells appeared morphologically intact in both septic and sham pigs. Sepsis also resulted in neuronal injury, disruption of astrocytic end-feet and swollen, rounded erythrocytes. These morphological changes may be sufficient to underlie the clinical features seen in septic encephalopathy.

The systemic inflammatory response syndrome (SIRS) with end-organ failure has a high mortality rate that has successfully defied all attempts to intervene with a therapeutic agent. Most of the pharmaceutical agents employed have been targeted at blocking one of the many inflammatory mediators in the cascade between tissue injury and the cellular response (Fig. 1).

Objective: To compare the effectiveness of two hydroxyethyl starch solutions of different molecular weight ranges for volume maintenance in a porcine model of fecal peritonitis.Design: Randomized prospective trial.Setting: Laboratory investigation.Subjects: Adolescent female pigs weighting approximately 30 kg.Interventions: We compared diafiltered 6% pentastarch with 6% high molecular weight hetastarch for volume maintenance in a porcine model of fecal peritonitis. The number average molecular weight of pentastarch is higher than hetastarch, although the weight average molecular weight is lower, i.e., a narrow range of medium weight molecules. The infusion rate of each agent was adjusted to maintain baseline arterial Hct for less-than-or-equal-to 7 hr after instrumentation and induction of fecal peritonitis.Main Outcome Measurements: The volume of fluid required to maintain arterial Hct was compared along with comparisons of hemodynamic and histologic responses associated with the two agents.Results: Significantly less pentastarch was required to prevent hemoconcentration than hetastarch (109 +/- 22.8 vs. 150 +/- 10.3 mL/kg; p < .05) while hemodynamics, colloid osmotic pressure, and oxygen transport responses were similar. Capillary patency was greater (21.99 +/- 3.68 vs. 10.09 +/- 1.17%; p < .05) and mean alveolar capillary barrier thickness was less (2.36 +/- 0.13 vs. 3.06 +/- 0.17-mu-m; p < .05) with pentastarch than with hetastarch, as judged by electron microscopy.Conclusions: These data suggest that pentastarch is better retained in the circulation in capillary leak syndromes compared with hetastarch.

We studied the effects of two catecholamines with differing receptor profiles on hepatic blood flow and hepatic structure in a porcine model of faecal peritonitis. We treated animals with dopexamine (group Dp) or dobutamine (group Db) and fluid, or fluid alone as a control, to achieve a 2.5% increase in Qt from baseline values. After the induction of faecal peritonitis the increased Qt was maintained throughout the 8 h study period by adjustment of the fluid infusion rate. The dose of catecholamines remained constant. Hepatic blood flow was correspondingly maintained at above baseline values throughout the study. Post-mortem liver biopsy specimens were analysed from experimental animals and t sham animals who had not been instrumented or infected. In experimental animals there was a reduction in sinusoidal patency between sham and group Dp (76% of total sinusoid vs 51%,p<0.05) and group Dp and control (51% vs 33%,p<0.05) or groups Dp and Db (51% vs 34%,p<0,05) animals. This was accounted for by an increase in sinusoidal leukocytes and endothelial swelling. In addition to the changes noted above there was marked hepatocellular destruction in group Db. We conclude that maintenance of organ blood flow does not guarantee structural integrity in the sepsis syndrome and hepatocellular damage was greater in group Db than group Dp or control.