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Nitric oxide: a mediator of endotoxin-induced middle ear effusions
Abstract:
Using a rat model, the authors investigated the role of nitric oxide (NO) in endotoxin-induced middle ear effusion (MEE). After the eustachian tube was obstructed, the middle ear was transtympanically injected with 35 microL of either 1 mg/mL lipopolysaccharide (LPS) or LPS and 1 mmol/L N-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase. Over the next 6 hours, the fluid within the middle ear was collected every 2 hours, and the quantity of albumin in the fluid, an index of vascular leakage, was determined using enzyme-linked immunosorbent assay. L-NAME significantly reduced LPS-induced vascular extravasation into the middle ear. Inoculation of the ear with L-arginine, the substrate for NO synthase, reversed the effects of L-NAME. These results indicate that NO is a mediator of LPS-induced MEE. Therefore, inhibition of NO synthase may represent a novel approach to the treatment of otitis media with effusion.
Insights
Nitric oxide (NO) plays a key role in endotoxin-induced middle ear effusion (MEE). Inhibiting NO synthase reduced vascular leakage, suggesting a potential treatment for otitis media with effusion.
Area of Science:
- Otolaryngology
- Immunology
- Pharmacology
Background:
- Otitis media with effusion (OME) is a common condition.
- The role of nitric oxide (NO) in endotoxin-induced middle ear effusion (MEE) is not fully understood.
Purpose of the Study:
- To investigate the role of NO in LPS-induced MEE in a rat model.
- To evaluate the potential of NO synthase inhibition as a treatment for OME.
Main Methods:
- Rats underwent eustachian tube obstruction.
- Middle ears were injected with lipopolysaccharide (LPS) with or without N-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor.
- Middle ear fluid was collected, and albumin levels (indicating vascular leakage) were measured via ELISA.
Main Results:
- L-NAME significantly reduced LPS-induced vascular extravasation into the middle ear.
- L-arginine administration reversed the inhibitory effects of L-NAME.
- NO was identified as a mediator of LPS-induced MEE.
Conclusions:
- Nitric oxide (NO) mediates endotoxin-induced middle ear effusion.
- Inhibition of NO synthase may offer a novel therapeutic strategy for otitis media with effusion.