Distribution of epidermal growth factor in rat ocular and periocular tissues

Using a sensitive radioimmunoassay (RIA) specific for rat epidermal growth factor (rEGF), we investigated the presence of rEGF in a variety of rat ocular and periocular tissues. Immunoreactive rEGF (IR-rEGF) was present in tear fluids (25.5 +/- 5.8 ng/ml), exorbital lacrimal gland (6.73 ng/g wet weight), intraorbital lacrimal gland (2.80 ng/g wet weight), Harderian gland (1.90 ng/g wet weight), and conjunctiva (0.16 ng/g wet weight). EGF was not detectable in aqueous humor, cornea, iris and ciliary body, lens, or the posterior part of the globe (retina, choroid, and vitreous body). Gel exclusion chromatography and reverse-phase high-performance liquid chromatography revealed that IR-rEGF in the above ocular fluids and tissues was indistinguishable from standard rEGF. Using enzyme-linked immunohistochemistry, rEGF was demonstrated to be localized in the duct epithelial cells of lacrimal glands. These findings reveal that EGF is preferentially localized in the ocular surface and lacrimal apparatus.