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P Steven, M Föge, R Mentlein, AB Thale, BN Tillmann, FP Paulsen; Tear Fluid Components Are Absorbed by the Epithelium of the Rabbit Nasolacrimal Duct . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3018.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: An animal experiment was carried out to determine whether absorption of components of tear fluid occurs in normal nasolacrimal ducts. Methods: The nasolacrimal systems of five different vertebrates were investigated using light microscopy to find a species with a nasolacrimal system comparable to that of humans for use in the absorption experiments. 3H-cortisol was dropped into the eyes of female rabbits. After 21, 43 or 146 min. the rabbits were killed, the blood collected and the nasolacrimal systems were prepared and embedded for histological examination. Serum was obtained from the clotted blood and radioactivity was counted. Furthermore, autoradiographs of rabbit nasolacrimal ducts were prepared. Results: Histology revealed the lacrimal systems of rabbits to be most closely comparable to that of humans. It revealed a double layered, stratified epithelium and a lamina propria, composed of two strata: (1) loose connective tissue containing elastic fibers and lymphatic cells as well as (2) a rich venous plexus comparable to a cavernous body. Rabbits were chosen for the absorption experiments. Uptake of radioactivity into the serum was high and increased with time. After 21 min. maximal incorporation of the applied radioactivity into the blood was 7.1%, after 43 min. 12.4%, and after 146 min. 15.5%. Transport of radioactivity was visualized in autoradiographs of rabbit nasolacrimal systems. Conclusion: In rabbits 3H-cortisol is incorporated from the nasolacrimal ducts into the blood. Based on the comparable morphology of rabbits and humans, it is suggested that absorption also takes place in humans. The normally constant absorption of tear fluid components into the blood vessels of the surrounding cavernous body connected to the blood vessels of the eye, i.e. the ocular surface, could be a feedback signal for tear fluid production, which comes to a halt when tear components are not absorbed. Future investigations in the nasolacrimal passage are needed in order to understand the physiological function of absorption of tear fluid components in the nasolacrimal ducts fully, especially under pathological conditions, i.e. in dry eye. Supported by the Deutsche Forschungsgemeinschaft (German Research Foundation) - program grants Pa 738/1-2 and Pa 738/1-3. CR. NONE.
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