The effect of N-Nitro L-Arginine Methyl Ester on the development process of experimentally induced myringosclerosis in rat tympanic membrane

Myringosclerosis is a pathology characterized with hyalin degeneration of collagenous structure and calcification in the lamina propria of tympanic membrane that may occur after myringotomy or ventilation tube insertion for the treatment of otitis media with effusion. Healing of the perforation and development of myringosclerosis were completely explained in the experimental studies in which tympanic membrane damage was created with myringotomy. Recently it has been shown that the hyperoxic condition developing after a myringotomy because of the increased O2 concentration in the middle ear to the environmental level caused production of oxygen derived free radicals inducing tissue damage. Myringosclerosis is the result of healing process with fibrosis and calcification seen after tissue damage.Clarification of the development of myringosclerosis is important to improve effective treatment regimens against myringosclerosis formation. A lot of antioxidants and antiinflammatory drugs have been tested in an effort to prevent myringosclerosis in the previous studies.N-Nitro L-Arginine Methyl Ester (L-NAME) is a widely-used substance which has proven antiinflammatory, antioxidant and antifibrotic effects, shown in different studies. Although the positive effects of L-NAME were shown in wound healing process of different tissues, there has been no study examining the effects of L-NAME in the healing of tympanic membrane perforation. In this study, the effects of L-NAME which had been used topically and intraperitoneally were investigated for tympanic membrane healing and development of myringosclerosis.Twenty Wistar rats were used in our study. Rats with healthy tympanic membranes proven with otomicroscopic examination underwent bilateral myringotomies and were divided randomly into four groups, each including five rats.The first group received no treatment. In the second group, 10 microliter saline soaked gelfoams were applied on the perforation of both tympanic membranes three times: immediately after myringotomy, in the12th hour and the 24th hour. In the third group, 10 microliter (100 mg/ml) L-NAME soaked gelfoams were applied on the perforation of both tympanic membranes three times: immediately after myringotomy, in the 12th hour and 24th hour. In the fourth group, 10 mg/kg (5 mg/ml) L-NAME was injected intraperitoneally three times: immediately after myringotomy, in the12th hour and 24th hour.After a fourteen-day healing period, rats were sacrificed following otomicroscopic evaluation for myringosclerosis and tympanic membranes were removed for histopathologic examination. Sections stained with Hematoxylin-Eosin and Von Gieson were examined under light microscopy. While inflammation and myringosclerosis were scored, the thickness of tympanic membranes was also measured.The present study showed that both topical and intraperitoneal applications of L-NAME supressed inflammation, reduced fibroblastic proliferation and prevented formation of myringosclerosis in contrast to untreated and only saline applied group.Key words: N-Nitro L-Arginine Methyl Ester, Myringosclerosis, Nitric oxide, Tympanic membrane, Myringotomy