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J.E. Schechter, M.E. Pidgeon, K.A. Kopp, Y.–W. Wang, C. Ding; Distribution and Functional Significance of Aquaporin–5 Within the Lacrimal Gland of Pregnant Rabbits . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1929.
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Our recent work has demonstrated that pregnancy is associated with decreased production of lacrimal fluid. Aquaporin–5 (AQP5) is a water channel protein that is localized within the lacrimal gland, and which influences water permeability across the plasma membranes of glandular epithelial cells. The goal of this study was to determine if alterations in the expression of AQP5 may be a factor in the decreased production of lacrimal fluid in pregnancy.
Non–pregnant and term pregnant New Zealand White rabbits were used in this study. Lacrimal fluid was collected by direct cannulation of the main lacrimal duct, 10–15 min for basal rate, and 3 x 10 min each after iv pilocarpine injection. At necropsy inferior lacrimal glands were collected and frozen for subsequent immunostaining of AQP5.
The acinar cells of both non–pregnant and pregnant rabbits stained intensely positive for AQP5. Immunostaining revealed a mosaic pattern with some lobules containing well defined clusters of immunopositive acini juxtaposed against acini with minimal or no immunopositivity. Immunopositivity for AQP5 was minimal or absent from ductal epithelial cells in non–pregnant rabbits but was strongly immunopositive in the apical membranes and cytoplasm of larger inter– and interlobar ducts in pregnant animals. Pilocarpine was able to elicit a strong response in fluid production both in non–pregnant and pregnant animals.
These results suggest that water transport across the plasma membranes of lacrimal acinar cells is variable or cyclical within a given lobule, and no differences in AQP5 localization could be detected between the lacrimal acinar cells of non–pregnant versus pregnant animals. However, the expression and distribution of AQP5 within ductal epithelial cells of pregnant animals suggests that water transport may occur from lumen to the periductal vasculature, resulting in the observed diminished fluid production characteristic of pregnancy.
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