Time-dependent aggravation or attenuation of lipopolysaccharide-induced gastric injury by nitric oxide synthase inhibition.
BACKGROUND
This study was conducted to test the hypothesis that nonselective nitric oxide synthase (NOS) inhibitors have different effects on lipopolysaccharide (LPS)-induced gastric injury depending upon whether they are given concurrently with LPS or after LPS at a time point that inducible NOS is up-regulated.


METHODS
Female Sprague-Dawley rats received intraperitoneal (IP) LPS (20 mg/kg) for 3 h. Western immunoblot was used to determine iNOS, eNOS, and nNOS immunoreactivity after 3 h. In an additional set of experiments, we assessed the time dependent effects of nitric oxide synthase inhibition by giving rats LPS (20 mg/kg, IP) concurrently with Nitro-l-arginine methyl ester (l-NAME; 2-5 mg/kg, SC) or l-N(G)-(1-iminoethyl) lysine (l-NIL; 10 mg/kg, IP) for 5 h or LPS and delayed administration of l-NAME or l-NIL 3 h following LPS injection in identical doses. For these NOS inhibition experiments microscopic and macroscopic injury was assessed by a blinded observer using previously published scoring systems. Injury studies were conducted by exposing the stomach to 3 ml of 5 mM acidified taurocholate for 5 minutes in an anesthetized prep.


RESULTS
A 3-h treatment with LPS (20 mg/kg IP) significantly increased iNOS protein immunoreactivity (Western immunoblot) but not eNOS or nNOS. N(G)-l-NAME (2-5 mg/kg SC) dose dependently aggravated macroscopic (computerized planimetry) and morphological gastric injury caused by the intraluminal bile irritant 5 mm acidified taurocholate for 10 min when given concurrently with LPS, an effect reversed by l- but not D-arginine (300 mg/kg). In contrast, delayed administration of l-NAME (3 h after LPS) dose dependently attenuated the ability of LPS to exacerbate gastric injury from bile. Both concurrent and delayed administration of the selective iNOS inhibitor, l-NIL (10 mg/kg IP) attenuated the effects of LPS.


CONCLUSIONS
These data indicate that during endotoxemia, the stomach is rendered more susceptible to damage from luminal irritants such as bile, a frequent occurrence in septic patients with a gastrointestinal ileus. In this setting, iNOS has a pathologic role while the constitutive NOS isoforms play gastroprotective roles.
Suliburk
James W
JW
Department of Surgery, University of Texas Medical School at Houston, Houston, Texas 77026, USA.
Helmer
Kenneth S
KS
Kennison
Sasha D
SD
Mercer
David W
DW
Robinson
Emily K
EK
D000818:Animals; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005750:Gastric Juice / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008239:Lysine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012772:Shock, Septic / Q000188:drug therapy* / Q000378:metabolism; D013270:Stomach / Q000201:enzymology; D013272:Stomach Diseases / Q000188:drug therapy* / Q000378:metabolism; D013997:Time Factors
D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; C090663:N(6)-(1-iminoethyl)lysine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496318:Nos2 protein, rat; D008239:Lysine; D019331:NG-Nitroarginine Methyl Ester