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1 Institute of Anatomy and Cell Biology, 2 Department of Internal Medicine, and 3 Department of Pathology, Justus-Liebig-University Giessen, 35385 Giessen, Germany
Enhanced prostanoid generation has been
implicated in vascular abnormalities occurring during endotoxemia and
sepsis, and the lung is particularly prone to such events. Prostanoids
are generated from arachidonic acid (AA) via cyclooxygenase (COX)-1 or
-2, both isoenzymes recently demonstrated to be expressed in different
lung cell types. Upregulation of COX may underlie the phenomenon that
endotoxin [lipopolysaccharide (LPS)]-exposed lungs show
markedly enhanced vasoconstrictor responses to secondarily applied
stimuli (priming). Isolated rat lungs were perfused with a
physiological salt buffer solution in the absence and presence of 1.5%
rat plasma and exposed to different concentrations of LPS (1,000 or
10,000 ng/ml) during a 2-h priming period. No change in
physiological variables was noted during this period, although enhanced
baseline liberation of both thromboxane (Tx) A2 and
PGI2 as well as of tumor necrosis factor (TNF)-
was
evident compared with that in control lungs in the absence of LPS. LPS
priming caused a significant elevation in AA-induced pulmonary arterial pressure, ventilation pressure, and lung weight gain. Concomitant increased levels of TxA2 were found in the buffer
perfusate. All changes were largely suppressed by three selective,
structurally unrelated COX-2 inhibitors (NS-398, DUP-697, and SC-236)
in both buffer- and buffer-plasma-perfused lungs. Anti-TNF-
neutralizing antibodies were ineffective under conditions of buffer
perfusion. In the presence of plasma components, manyfold augmented
TNF-
generation was noted, and anti-TNF-
antibodies significantly suppressed the increase in ventilation pressure but not in the vascular
pressor response and lung edema formation. We conclude that the
propensity of LPS-primed lungs to respond with enhanced vasoconstriction, edema formation, and bronchoconstriction to a
secondarily applied stimulus proceeds nearly exclusively via COX-2 and
increased Tx formation, with TNF-
generation being involved in the
change in bronchomotor reactivity in the presence of plasma
constituents. In context with recent immunohistological investigations,
LPS-induced upregulation of the COX-2-thromboxane synthase axis in
vascular and bronchial smooth muscle cells is suggested to underlie
these events.
lipopolysaccharide; isolated perfused rat lung; tumor necrosis factor; selective cyclooxygenase-2 inhibition
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