Lipocortin 1 mediates the inhibition by dexamethasone of the induction by endotoxin of nitric oxide synthase in the rat.
Administration of Escherichia coli lipopolysaccharide (LPS; 10 mg/kg i.v.) to male Wistar rats caused within 240 min (i) a sustained fall (approximately 30 mmHg) in mean arterial blood pressure, (ii) a reduction (> 75%) in the pressor responses to norepinephrine (1 microgram/kg i.v.), and (iii) an induction of nitric oxide synthase (iNOS) as measured in the lung. Dexamethasone (1 mg/kg i.p. at 2 h prior to LPS) attenuated the hypotension and the vascular hyporeactivity to norepinephrine and reduced (by approximately 77%) the expression of iNOS in the lung. These effects of dexamethasone were prevented by pretreatment of LPS-treated rats with a neutralizing antiserum to lipocortin 1 (anti-LC1; 60 mg/kg s.c. at 24 h prior to LPS) but not by a control nonimmune sheep serum. Stimulation of J774.2 macrophages with LPS (1 microgram/ml for 24 h) caused the expression of iNOS and cyclooxygenase 2 (COX-2) protein and significantly increased nitrite generation; this was prevented by dexamethasone (0.1 microM at 1 h prior to LPS), which also increased cell surface lipocortin 1. Pretreatment of J774.2 cells with anti-LC1 (1:60 dilution at 4 h prior to LPS) also abolished the inhibitory effect of dexamethasone on iNOS expression and nitrite accumulation but not that on COX-2 expression. A lipocortin 1 fragment (residues 1-188 of human lipocortin 1; 20 micrograms/ml at 1 h prior to LPS) also blocked iNOS in J774.2 macrophages activated by LPS (approximately 78% inhibition), and this too was prevented by anti-LC1. We conclude that the extracellular release of endogenous lipocortin 1 (i) mediates the inhibition by dexamethasone of the expression of iNOS, but not of COX-2, and (ii) contributes substantially to the beneficial actions of dexamethasone in rats with endotoxic shock.
Wu
C C
CC
Department of Vascular Biology, William Harvey Research Institute, St. Bartholomew's Hospital Medical College, London, United Kingdom.
Croxtall
J D
JD
Perretti
M
M
Bryant
C E
CE
Thiemermann
C
C
Flower
R J
RJ
Vane
J R
JR
D000594:Amino Acid Oxidoreductases / Q000096:biosynthesis*; D000818:Animals; D017305:Annexin A1 / Q000096:biosynthesis* / Q000276:immunology; D000906:Antibodies / Q000494:pharmacology; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology* / Q000627:therapeutic use; D004731:Endotoxins / Q000494:pharmacology; D007022:Hypotension / Q000188:drug therapy / Q000378:metabolism; D008264:Macrophages / Q000201:enzymology / Q000502:physiology*; D008297:Male; D019001:Nitric Oxide Synthase; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012772:Shock, Septic / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*
D017305:Annexin A1; D000906:Antibodies; D004731:Endotoxins; D003907:Dexamethasone; D019001:Nitric Oxide Synthase; D011451:Prostaglandin-Endoperoxide Synthases; D000594:Amino Acid Oxidoreductases