Expression of Nitric Oxide Synthase in Primary and Recurrent Pterygium

Purpose: The aim of this study was to investigate the expression of different nitric oxide synthases (NOSs) in primary and recurrent pterygia and to investigate the probable role of any nitric oxide synthase on pterygium recurrence. Materials and Method: Specimens of 40 primary pterygia and 10 recurrent pterygia excised during pterygium surgery were included in the study. Also, 15 normal conjunctiva of medial limbus obtained from patients free of pterygia and removed during other ophthalmologic surgeries formed the control group. Specimens were stained with hematoxylin and eosin for general histological and morphologic evaluation. The distribution of n-NOS, e-NOS and i-NOS were analyzed using indirect immunoperoxidase staining. Results: Histological evaluation of specimens revealed that the epithelium in primary and recurrent pterygia groups was thicker compared to that in the control group. Immunohistochemical analysis revealed that in both primary pterygium and control groups, immunoreactivity was positive for all NOSs in both epithelium and connective tissue. For recurrent pterygium group, NOS immunoreactivity could be detected moderately for n-NOS in the epithelium and weakly for e-NOS in both epithelium and connective tissue. However, in recurrent pterygium samples, i-NOS immunoreactivity was lacking in both epithelium and connective tissue. Discussion: These data are the first to demonstrate that NOS expression may differ between primary and recurrent pterygia. Meanwhile, continuous expression of n-NOS with suppression of i-NOS and e-NOS may be an important step in the recurrence process of pterygia.