Cytochemical demonstration of sites of hydrogen peroxide generation and increased vascular permeability in isolated pig hearts after ischaemia and reperfusion

Isolated pig hearts, subsequently perfused with pig or human blood, were prepared for the cytochemical demonstration of sites of hydrogen peroxide generation and increased vascular permeability. Oxidant stress was associated with ultrastructural changes commonly seen following myocardial reperfusion. In addition, the precipitation of cerium perhydroxide following perfusion with physiological saline containing cerium chloride suggested the vascular endothelium and leukocytes as sources of oxidants. This was associated with rapid penetration of horseradish peroxidase through the intercellular clefts of the vascular endothelium into the interstitial space, suggesting increased vascular leakiness at these sites. The rapid penetration of horseradish peroxidase was observed at all monitored periods of reperfusion with pig or human blood. This indicates that the increased permeability occurred during the ischaemic period and continued during reperfusion. Morphological damage was greatest in pig hearts reperfused with whole human blood and this was attenuated if the blood was preabsorbed to remove antibodies prior to reperfusion. We conclude that oxidant stress was initiated during ischaemia and continued during reperfusion in this model.

Hyperacute lung rejection in a pig-to-human transplant model: the role of anti-pig antibody and complement

BACKGROUND

The physiology of hyperacute rejection of pig lung by human blood and the role of antispecies antibody and complement in this phenomenon have not previously been characterized.

METHODS

Human blood was perfused through an ex vivo pig heart-lung preparation. In the treatment groups, blood was either unmodified or modified to deplete alternative pathway complement (heat treatment), anti-pig antibody, or both. Control experiments were performed with unmodified and heat-treated pig blood. Physiologic parameters, organ survival, and immunohistology were the primary outcome measures assessed.

RESULTS

Pig lung was consistently damaged by human blood within 45 min (median 20 min), as evidenced by elevated pulmonary vascular resistance and parenchymal injury. Immunohistologic studies of perfused lungs showed prominent deposition of IgM and classical pathway component, C4, and weaker deposition of alternative pathway component, properdin. Heat treatment did not impede the rise in pulmonary vascular resistance or significantly prolong survival. Depletion of anti-pig antibody prolonged survival (median 90 min) and attenuated the rise in pulmonary vascular resistance. Antibody absorption, combined with heat treatment of plasma, prevented the elevation in pulmonary vascular resistance and yielded median graft survival (210 min) similar to pig blood perfusion (approximately 240 min).

CONCLUSIONS

These results show that elevated pulmonary vascular resistance and pulmonary parenchymal injury are mediated at least in part by antispecies antibody and heat-sensitive pathways. They are consistent with the hypothesis that complement activation contributes significantly to acute lung damage in the pig-to-human species combination.

Free radicals in anaesthesia and intensive care

This review aims to outline the nature and origin of free radicals, or oxidants, in biological systems and to summarise their involvement in diseases of interest to anaesthetists, with particular reference to reperfusion injury (of the gut, brain, myocardium and transplanted organs), shock/trauma, inflammation/sepsis and halothane hepatitis. In-vitro and animal studies examining the role of free radicals and antioxidants in the pathophysiology and treatment of these conditions are presented. Some of the evidence from clinical studies supporting the use of antioxidant therapy in patients is also presented.

New horizons in ICU sedation: exploring non-sedative effects of ICU sedation

Sedative drugs are widely used in intensive care, primarily in ventilated patients. The common actions and side-effects of these agents are widely recognised. However, recent evidence suggests that opiates and other sedative agents that are used in this situation also have important, but not widely appreciated, effects on metabolism, physiological signalling and disease mechanisms. Some of these effects are an extension of their expected therapeutic actions; these are being elucidated as the biological consequences of stress, and its suppression is now being clarified. An example is the central effects of benzodiazepines and opioids on metabolism and immune function. In other instances these drugs have important peripheral actions, with immunomodulatory or metabolic roles. Furthermore, some drugs may modify disease processes--an example being the antioxidant effect of propofol. Finally, basic cellular mechanisms, such as immediate early gene expression and transcription factor activation, may involve processes that may be susceptible to modification by sedative agents. Such secondary effects of sedative agents need to be investigated for three reasons. First, they provide explanations for some phenomena observed during their use. Second, some of the undesirable side-effects may be avoided by judicious use of drugs in certain clinical situations. Finally, there is the prospect that we may be able to harness some actions for novel therapeutic purposes.