FMLP Causes Eicosanoid-dependent Vasoconstriction and Edema in Lungs from Endotoxin-primed Rats

Abstract

Recruitment of inflammatory cells to the lung capillaries has been proposed as an important step in the sequence of events that lead to acute lung injury. Frequently, in the clinical setting, bacteremia and sepsis syndrome precede the acute lung failure and endotoxin priming may represent a comparable paradigm, useful for experimental pursuit. Following addition of the chemotactic tripeptide FMLP (10(-9) to 10(-6) M) to the cell-free, salt solution perfusate of isolated rat lungs, only a small degree of vasoconstriction was observed. However, in lungs isolated from rats that received 2 mg/kg intraperitoneal Salmonella enteritidis endotoxin 2 h before lung perfusion, FMLP dose dependently caused a large, transient pulmonary pressor response, edema formation, and release of large amounts of thromboxane and leukotriene B4. Since in vitro priming with endotoxin, direct vascular injury by neutrophil elastase, nor direct stimulation with FMLP of pulmonary artery rings from endotoxin-pretreated rats, mimicked the effects of in vivo endotoxin priming, we conclude that the presence of inflammatory cells in the lung capillaries accounted for the large amount of eicosanoids produced by the lungs after FMLP stimulation. In fact, by retrograde lavage of the lung circulation with a collagenase solution, previously adherent cell clumps were mobilized and identified. These cell clumps, composed of red blood cells, neutrophils, and platelets, were not seen in the vascular lavage sediment obtained from unprimed control lungs. Indomethacin, a thromboxane antagonist, AA861, a 5-lipoxygenase inhibitor, and WEB 2086, a platelet-activating factor (PAF) antagonist, reduced the thromboxane synthesis and release after FMLP (10(-7) M) in in vivo endotoxin-primed lungs. None of the inhibitors employed exclusively inhibited only one particular eicosanoid mediator but rather affected the release of several mediators, suggesting a close link between the different synthetic arachidonic acid pathways. An inhibitor of phospholipase C (2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate), NCDC, but not an inhibitor of phospholipase D (Wortmannin) or of protein kinase C (staurosporine) inhibited the FMLP-stimulated pulmonary pressure rise and eicosanoid release in endotoxin-primed lungs in vivo. Our data suggest that eicosanoids (in particular thromboxane) released from cells trapped in the lung circulation, but not from constitutive lung cells, contribute to vasoconstriction and edema formation caused by the chemoattractant FMLP in endotoxin-primed lungs.

Eicosanoid Transcellular Biosynthesis: From Cell-Cell Interactions to in Vivo Tissue Responses

“…Evidence for the direct interaction of these same cell types was also obtained in isolated rat lung preparations (Voelkel et al, 1992) when animals were injected with Salmonella enteritidis endotoxin (2 mg/kg i.p.). Lungs were perfused with buffer in an antegrade, recirculating mode and then challenged with fMLP (100 nM).…”

“…When endotoxin-treated, isolated lungs were perfused in a retrograde fashion, cell clumps that contained a core of neutrophils and platelets surrounded by a layer of red blood cells were collected in the perfusate, suggesting that adhesion of these cells took place after endotoxin treatment of the animal and these clumps became lodged in the pulmonary capillary network. These cell aggregates were felt to be responsible for the production of eicosanoids by transcellular biosynthetic mechanisms (Voelkel et al, 1992).…”

Formation of sulphidopeptide‐leukotrienes by cell‐cell interaction causes coronary vasoconstriction in isolated, cell‐perfused heart of rabbit

“…Most in vitro studies of transcellular biosynthesis have used cells isolated from blood or cultured endothelial cells as a reflection of what might happen in pathological situations such as in inflammatory reactions or in cardiovascular diseases where cell-cell interactions constitute an important part of this process (Lucchesi & Mullane, 1986). Fewer studies have addressed situations using blood cell-organ interactions (Voelkel et al, 1992), where it seems logical to assume that such reactions do exist in disease. Adhesive reactions between blood and vascular wall cells, mediated by the selectins (Johnston et al, 1990) or the integrins (Hynes, 1987), are likely to play an active role for the 'anchoring' of circulating cells that may allow more efficient reactive substrate uptake between adjacent cells rather than via the extracellular matrix or fluid phase.…”

Epoxyeicosatrienoates are the dominant eicosanoids in human lungs upon microbial challenge

“…Previous investigations performed with non-human lungs of different species under various pathophysiological conditions, including challenge with A23187, ECH and fMLP [2,3,5,8,9,18,19,31,[35][36][37][38][39][40][41][42], revealed the generation of individual eicosanoids/eicosanoid groups (TXA 2 , PGI 2 , LTs or HETEs), paralleled by pressor response and increased endothelial permeability. Intriguingly, challenge of human lungs with A23187 elicited the generation of all main LOX-and CYPmediated eicosanoids dominated by the CYP-mediated EETs and paralleled by lung injury [10].…”