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Meningococcal infection is a major infective cause of death in children and young people. Central to the underlying pathophysiological disturbances that occur in the course of invasive disease is a profound alteration in endothelial function giving rise to capillary leak, which is associated with high morbidity and mortality. The endothelium has an important role in maintaining the balance between intraluminal contents and the surrounding interstitial tissues. The key tenet in this thesis is that there is an increase in endothelial permeability in meningococcal disease, leading to hypovolaemia and tissue oedema. A central component of the capillary leak is the movement of colloidal proteins across the capillary wall. Albumin, a negatively charged protein, is the most important colloidal protein and is the protein predominantly involved. The hypothesis in this thesis is that albumin movement across the capillary wall relates to loss of negative charge on the endothelial surface (i.e. loss of electrostatic repulsion). As albumin moves out of the circulation, fluid and electrolyte movement occurs into interstitial tissues due to alteration in the osmotic forces that normally retain fluid within the vascular space, so contributing to capillary leak. The biochemical features of commercially available human, bovine and rabbit albumins were found to comprise a monomer, dimer and trimer. Rabbit serum albumin (fatty acid form), (RSA FFA) was labelled with a fluorescent marker Texas Red (TR), making the protein slightly negatively charged but otherwise unaltered biochemically. The TR labelled protein was made slightly more positive by methylation. Again the only difference from RSA was in charge. The clearances of these 2 protein probes were studied in healthy rabbits, with methylated albumin cleared faster from the circulation. In ventilated animals, the clearances of all the components of the labelled albumin were faster than in healthy animals, nonetheless the methylated albumin was still cleared faster. In ventilated shocked animals (by meningococcal lipopolysaccharide), there was no difference in the clearances of the 2 monomers, supporting the hypothesis. The dimers and trimers were handled differently to the monomers throughout. This work contributes to the idea that electrostatic forces have a role in shock.

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Bacterial sepsis and septic shock are major causes ofdeath in the critically ill. The majority ofthese deaths are due to the development ofmyocardial contractile dysfunction. The pathophysiology ofthis phenomenon is incompletely understood,. with previous work focussing on the influence ofcirculating inflammatory mediators ofnon-cardiac origin. Despite the recognised importance ofthese factors in contrit>uting to myocardial dysfunction, how the heart itselfresponds to bacterial pathogens directly has not been fully elucidated. The aims ofthis study were, first, to characterise the functional changes induced in isolated cardiac myocytes by whole bacteria. With the recent identification ofToll-like receptors (TLR)s (pattern recognition receptors (PRR)s) within the cardiac compartment, the second aim was to examine their roles in any changes seen. Finally, the role ofkey inflammatory mediators was examined. A novel method ofevaluating how Gram positive Staphylococcus aureus (S. aureus) or Gram negative Escherichia coli (E. call) directly modified 'populations' ofcardiac rat and mouse myocytes is described. Bacteria not' only decreased the propot:tion ofviable rod-shaped cells, they also decreased the proportion ofcells able to contract to electrical stimulation. S. aureus was found to have more pronounced effects than E. coli. In separate experiments, extracellular oxidants mimicked the effects ofbacteria on cardiac myocytes. The effects ofS. aureus and E. coli were mediated by TLR2ffLR6 and TLR4 respectively. Although no role for nitric oxide was found in bacteria-induced changes in myocyte function, the adverse effects ofS. aureus were partly prevented by specific cyclo-oygenase-2 inhibitors. However, the central hormone mediating the effects of bacteria (and oxidants) was found to be endothelin-l (ET-l), acting on ETA receptors. Caspase activation, without leading to apoptosis, was also implicated in mediating the phenotype changes induced by bacteria. Finally, cardiac myocytes ofthe noncontracting phenotype showed a reduced myofilament sensitivity to calcium, explaining the functional changes seen. Although the data are limited, a similar phenomenon was seen in failing human myocytes.

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No description available.