Reactive Nitrogen Species Inhibit Alveolar Epithelial Fluid Transport After Hemorrhagic Shock in Rats

Abstract

Our recent experimental work demonstrated that a neutrophil-dependent inflammatory response in the lung prevented the normal up-regulation of alveolar fluid clearance by catecholamines following hemorrhagic shock. In this study, we tested the hypothesis that the release of NO within the airspaces of the lung was responsible for the shock-mediated failure of the alveolar epithelium to respond to catecholamines in rats. Hemorrhagic shock was associated with an inducible NO synthase (iNOS)-dependent increase in the lung production of NO and a failure of the alveolar epithelium to up-regulate vectorial fluid transport in response to β-adrenergic agonists. Inhibition of iNOS restored the normal catecholamine-mediated up-regulation of alveolar liquid clearance. Airspace instillation of dibutyryl cAMP, a stable analog of cAMP, restored the normal fluid transport capacity of the alveolar epithelium after prolonged hemorrhagic shock, whereas direct stimulation of adenyl cyclase by forskolin had no effect. Pretreatment with pyrrolidine dithiocarbamate or sulfasalazine attenuated the iNOS-dependent production of NO in the lung and restored the normal up-regulation of alveolar fluid clearance by catecholamines after prolonged hemorrhagic shock. Based on in vitro studies with an alveolar epithelial cell line, A549 cells, the effect of sulfasalazine appeared to be mediated in part by inhibition of NF-κB activation, and the protective effect was mediated by the inhibition of IκBα protein degradation. In summary, these results provide the first in vivo evidence that NO, released within the airspaces of the lung probably secondary to the NF-κB-dependent activation of iNOS, is a major proximal inflammatory mediator that limits the rate of alveolar epithelial transport after prolonged hemorrhagic shock by directly impairing the function of membrane proteins involved in the β-adrenergic receptor-cAMP signaling pathway in alveolar epithelium.

Selected Contribution: Mechanisms that may stimulate the resolution of alveolar edema in the transplanted human lung

“…By contrast, the four donors who received high doses of dopamine, out of the dopaminergic range, had very low rates of alveolar fluid clearance. In this group, the high doses of dopamine may have been a marker of circulatory shock, a condition that has been associated with impaired alveolar fluid clearance in both animal models (24,27) and humans (40). Although the overall severity of pulmonary edema was low in the donor lungs, the degree of edema was lowest in donors who had received higher doses of diuretics.…”

Inhibition of Lung Fluid Clearance and Epithelial Na+ Channels by Chlorine, Hypochlorous Acid, and Chloramines

“…Reabsorption of isotonic fluid was inhibited during prolonged hemorrhagic shock. Instillation of aminoguanidine, an inhibitor of inducible nitric-oxide synthase, restored fluid reabsorption to normal levels (73). Mycoplasma infection resulted in a significant decrease of both Na ϩ -dependent alveolar fluid clearance in BALB/c mice and inhibition of amiloridesensitive Na ϩ currents across alveolar type II cells isolated from these mice.…”

Allogeneic human mesenchymal stem cells for treatment of E. coli endotoxin-induced acute lung injury in the ex vivo perfused human lung

“…To further test potential mechanisms of benefit of MSCs on alveolar fluid transport, we exposed primary cultures of human alveolar epithelial type II cells grown on a Transwell plate with an air-liquid interface to cytomix (33), a mixture of the most biologically active cytokines in ALI pulmonary edema fluid (34). Cytomix reduced vectorial fluid transport across epithelial type II cells by 70% over 24 h, an effect that was not associated with an increase in apoptosis or necrosis of the type II cells, as previously measured by flow cytometry (33).…”