An immunohistochemical study of inducible nitric oxide synthase in the ratmiddle ear, with reference to tympanosclerosis

Tympanoscelerosis and myringosclerosis are well-known sequelae after acute and chronic otitis media and are also often seen after treatment of secreto ry otitis media with ventilation tubes. The sometimes cause serious hearing disability, There is no successful treatment for these conditions. There m ight be reactors triggering an immunological or autoimmune chain reaction, which leads to tympanosclerosis. intervention with thr aim of abolishing th is type of response might be possible if an interruption of the chain react ion can be found. Nitric oxide is a radical molecule with the ability to ki ll pathogens and is produced by the enzyme nitric oxide synthase. Expressio n of inducible nitric oxide synthase (iNOS) was analysed immunohistochemica lly in a rat model of acute otitis media. In pars sacrificed at days 3 and 6 after inoculation, iNOS was also strongly expressed in the middle ear muc ose and in the tympanic membrane as well as in the inner ear. In control sp ecimens as well as in infected ones. iNOS was expressed in the tissue of th e external ear canal. In rats sacrificed at day 10 and after 3 months, iNOS was expressed at the same locations, although less frequently. These data indicate that iNOS expression is induced during acute otitis media and sugg est that nitric oxide may be important in the host defence against ear infe ctions.