nitroarginine and Uveitis--Anterior

The authors previously reported that in vitro treatment with N(G)-nitro L-arginine (L-NNA), an inhibitor of nitric oxide synthase (NOS), reduces aqueous humor (AH) protein and cellular infiltration in endotoxin-induced uveitis in the rat eye. The objective of the current study was to determine the role(s) of respective major forms (constitutive and inducible) of NOS by comparing the effects of relatively selective inhibitors of these NOS isozymes.. N(G)-nitro L-arginine (L-NNA), a relatively selective inhibitor for constitutive NOS (c-NOS), and N-iminoethyl L-ornithine (L-NIO), a more selective inhibitor for inducible NOS (i-NOS), were administered in vivo. Male Lewis rats were footpad injected with bacterial lipopolysaccharide (LPS, 200 microgram) and were injected intraperitoneally at 0 hours, 6 hours, or both, after LPS injection with 10 mg of NIO, NNA, or saline as a control. Nitric oxide synthase activity in the ocular tissue and AH protein and cell content were determined at various times after treatment with LPS.. After in vivo treatment, L-NIO was found to be a more potent inhibitor than L-NNA for ocular i-NOS (87% versus 43% inhibition), and L-NNA was more potent than L-NIO for ocular c-NOS (81% versus 39%). Two injections of L-NNA, one at time 0 and one 6 hours after LPS injection, inhibited the AH protein increase by 71%, but L-NIO did so by only 30%. L-NNA inhibited cellular infiltration by 86%, whereas L-NIO had no significant effect on cellular infiltration. A significant inhibition of cellular infiltration and AH protein increase also was observed with a single injection of 10 mg of L-NNA but not of L-NIO when the inhibitors were given simultaneously with LPS. Thus, reduction of uveitis symptoms correlates with the inhibition of c-NOS.. The constitutive form of NOS in ocular tissue, presumably in vascular endothelial cells, appears to play a critical role at the onset of the development of endotoxin-induced uveitis.

Topics: Animals; Aqueous Humor; Arginine; Cell Count; Disease Models, Animal; Endothelium, Vascular; Enzyme Inhibitors; Isoenzymes; Lipopolysaccharides; Male; Nitric Oxide Synthase; Nitroarginine; Ornithine; Phagocytes; Rats; Rats, Inbred Lew; Salmonella; Uveitis, Anterior

To evaluate the role of nitric oxide synthase (NOS) in endotoxin-induced uveitis (EIU).. EIU was caused in Lewis rats by injecting lipopolysaccharide (LPS) into the foot pad, and the effects of an NOS inhibitor, NG-nitro L-arginine (NA), was comparatively studied by the simultaneous administration of NA and LPS. Total NOS and inducible NOS (iNOS) activities were differentially assayed in the anterior segment of the eye in EIU with and without NA treatment. The effects of NA on EIU were also evaluated by clinical manifestation, histology, and protein concentration in the aqueous humor.. In untreated rats, there was no significant iNOS activity. With the EIU model, iNOS activity showed a marked increase in the anterior segment of the eye, reaching a maximum 9 hours after LPS injection (10,850 +/- 1,650 cpm/mg protein, mean +/- SEM). NA reduced the iNOS activity 9 hours after injection to 2,400 +/- 90 cpm/mg protein (P < 0.001). Aqueous humor protein concentration in the EIU model was 10.6 +/- 0.75 mg/ml, and the cell number was 216 +/- 12 cells/microliters. NA significantly reduced these factors to 4.25 +/- 0.48 mg/microliters for the protein concentration (P < 0.0005) and 25 +/- 6 cells/ml for the cell number (P < 0.0005). Histologic studies showed less prominent infiltration of polymorphonuclear cells in the anterior uvea than for conventional EIU.. Induction of iNOS may play a key role in the pathogenesis of EIU. Because inhibition of iNOS activity reduced the inflammatory response, suppression of NO formation may inhibit the development of EIU.

Topics: Amino Acid Oxidoreductases; Animals; Anterior Eye Segment; Aqueous Humor; Arginine; Bacterial Toxins; Disease Models, Animal; Endotoxins; Enterotoxins; Enzyme Induction; Eye Proteins; Leukocyte Count; Male; Neutrophils; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Inbred Lew; Salmonella; Uveitis, Anterior