The potential role of platelet-activating factor in shock and ischemia

Inhibition of phospholipase A(2) as a therapeutic target

The hydrolysis of cell membrane phospholipids by phospholipase A(2) (PLA(2)) leads to the production of numerous lipid mediators of diverse pathological conditions, mainly inflammatory diseases. These include lysophospholipids and their derivatives, and arachidonic acid and its derivatives (the eicosanoids). Both these groups of mediators are produced predominantly by the secretory PLA(2)s (sPLA(2)s) which hydrolyze the phospholipids of the cell surface membrane. Protection of cell membrane from these 'inflammatory enzymes' can therefore be used for the treatment of inflammatory processes. A prototype of cell-impermeable PLA(2) inhibitors, which protect the cell membrane from different sPLA(2)s without affecting vital phospholipid metabolism, is presented and discussed in the present review.

Acute respiratory failure in pregnancy. An analysis of 19 cases

We studied 19 peripartum patients with acute respiratory failure associated with pregnancy. Although it is an uncommon event, noncardiogenic pulmonary edema is the most common cause of respiratory failure in the peripartum period. This acute lung injury syndrome was observed to be associated with a variety of complications of pregnancy including premature labor, the use of tocolytics, infection, hypertension, leukoagglutinin reactions, aspiration, abruptio placentae, and amniotic fluid embolism. From 1989 through 1992 there were 10,852 deliveries and 19 patients with noncardiogenic pulmonary edema at our institution. Analyzing these cases has led us to favor the hypothesis that the respiratory failure associated with the various complications of pregnancy primarily represents the fatal and nonfatal cases of amniotic fluid embolism that Steiner and Lushbaugh initially believed undoubtedly to exist. Moreover, we suggest, as have others, that the nonspecific symptom complex of inflammation, coagulopathy, and cardiopulmonary failure represents the release of soluble mediators into the maternal circulation. It is not clear what the predominant mediator is, but we have focused on platelet activating factor. It is also not established whether the mediator(s) is of amniotic fluid origin or a result of maternal anaphylactoid-type of response to a fetal or amnioplacental antigen. In conclusion, monitoring maternal oxygenation either directly or indirectly by oximetry should be considered routinely in the peripartum period, especially in complicated pregnancies, to detect at an early stage "asymptomatic" or preclinical cases of noncardiogenic pulmonary edema, in hopes of then modifying management to prevent their progression.

The pathogenesis of septic shock

A new age of treating patients with septic shock is rapidly approaching. A multidrug approach will likely be used to interrupt the systemic inflammatory response to infection, with use of new immune and inflammatory modulating therapies. In this article are reviewed the advances made in understanding the cellular events that cause septic shock. Critical care nurses need to update themselves on this new information to provide optimal care that patients with septic shock demand. Symptoms of septic shock, its hemodynamic characteristics, and the actions of principal inflammatory mediators that cause vasodilation and capillary leak are discussed.

Platelet-activating factor antagonism enhances the liver's recovery from warm ischemia in situ

Hepatic outcome after ischemia is compromised by anoxic injury and by release of oxygen free radicals or other pathological mediators at reperfusion. The platelet-activating factor (PAF) is an endogenous lipid-mediator which plays a key role in catalysing various pro-inflammatory processes. In this study the possible influence of platelet-activating factor antagonism was investigated on the integrity of the vascular endothelium, on free radical-mediated peroxidation and on post-ischemic functional outcome of the liver in the rat. Animals under pentobarbital anesthesia were subjected to 60 min of ischemia of the left and median liver lobes followed by 30 min of reperfusion in vivo. Pre-ischemic injection of the platelet-activating factor antagonist BN 52021 resulted in a significant reduction of endothelial enzyme loss into the plasma (purine nucleoside phosphorylase 56.2 vs. 83.1 U/l), and lowered hepatic lipid peroxidation (malondialdehyde 830 vs 932 nmol/g), leading to a significant improvement of postischemic bile flow and higher tissue levels of ATP. This suggests that the platelet-activating factor may play an important role in hepatic ischemia-reperfusion injury and that PAF antagonists like BN 52021 may be useful for clinical treatment.

Effects of a platelet activating factor antagonist on oedema formation following burns

Deep dermal burns covering 30 per cent of the total body surface area were prepared by immersing the backs of rabbits in hot water at 80 degrees C for 20 s, to determine whether platelet activating factor (PAF) was involved in the onset of oedema following burns and to evaluate the effect of TCV-309, a potent PAF antagonist. The PAF antagonist, which was infused soon after the burn, blocked oedema formation in the wound and significantly (P < 0.001) inhibited PAF increase (P < 0.05) in the damaged tissue in a dose-dependent manner. This was confirmed by immunohistochemistry. In contrast, the superoxide dismutase content in the group treated with a high dose of TCV-309 was significantly (P < 0.01) higher than that of the control group. These findings suggest that administration of large doses of a PAF antagonist immediately after injury prevents oedema of burn wounds and the subsequent onset of burn shock by suppressing PAF and superoxide radical formation.